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Abstract

Austin, J., D.J. HOFMANN, N. Butchart, and S.J. OLTMANS. Mid stratospheric ozone minima in polar regions. Geophysical Research Letters 22(18):2489-2492 (1995).

Recent springtime measurements of ozone vertical profiles in polar regions have revealed local ozone depressions of about 25% at altitudes near 30 km. Similar features are also identified in three-dimensional photochemical model results. The modeled ozone depressions are local and Temporary, often associated with stratospheric warming events which transport air from low latitudes, altering its photochemical history. The feature may be a component of the climatology of the region, but occurs less frequently in the model, possibly because of the long-standing problem of the underprediction of upper stratospheric ozone.

BAKWIN, P.S., P.P. TANS, W. Ussler, III, and E. Quesnell. Measurements of carbon dioxide on a very tall tower. Tellus 47B:535-549 (1995).

We present a continuous, 2-year long record of carbon dioxide (CO) mixing ratio at three altitudes up to 496 m above the ground on a television transmitter tower in the southeastern United States. The data show strong diurnal and seasonal variations, and large vertical gradients. The diurnal cycles are modulated by surface uptake and release by vegetation and soils, emissions from fossil fuel combustion, and by the diurnal development of the planetary boundary layer. Gradients of 1-2 ppm between 496 m and 51 m are typically observed during summertime afternoons, due to vigorous photosynthetic uptake. With increasing altitude the magnitude of the diurnal cycle is damped, and daily average mixing ratios decrease, caused by coincident changes in the sign and magnitude of the surface flux, and changes in vertical stability of the boundary layer over the course of the day. Measurements at 496 m give an approximate measure (within a few tenths of a ppm) of the afternoon mean mixing ratio in the convective boundary layer. Vertical gradients between 51 m and 496 m are typically close to zero, and monthly mean mixing ratios increase slowly between November and April, indicating that biological activity is minimal during this period. The amplitude of the seasonal cycle of CO₂ is larger at the tower site than at marine boundary layer and mountaintop sites which are at nearly the same latitude, because of the proximity of the tower site to terrestrial sources and sinks. Comparison of our continental tower data with data from "background" sites should provide a strong constraint for regional and global models of terrestrial CO fluxes. We also present data from weekly flask samples taken from the 496 m level and which have been analyzed for methane (CH₄), carbon monoxide (CO), and the stable isotopes of carbon in CO (¹³C). The flask data provide further information about the processes that drive observed changes in CO mixing ratios at the tower.

BERGIN, M.H., C.I. Davidson, J.E. Dibb, J.L. Jaffrezo, H.D. Kuhns, and S.N. Pandis. A simple model to estimate atmospheric concentrations of aerosol chemical species based on snow core chemistry at Summit, Greenland. Geophysical Research Letters 22(24):3517-3520 (1995).

A simple model is presented to estimate atmospheric concentrations of chemical species that exist primarily as aerosols based on snow core/ice core chemistry at Summit, Greenland. The model considers the processes of snow, fog, and dry deposition. The deposition parameters for each of the processes are estimated for SO₄^2- and CA²⁺ and are based on experiments conducted during the 1993 and 1994 summer field seasons. The seasonal mean atmospheric concentrations are estimated based on the deposition parameters and snow cores obtained during the field seasons. The ratios of the estimated seasonal mean airborne concentration divided by the measured mean concentration (C_a,est/C_a,meas) for SO₄^2- over the 1993 and 1994 field seasons are 0.85 and 0.95, respectively. The C_a,est/C_a,meas ratios for CA²⁺ are 0.45 and 0.90 for the 1993 and 1994 field seasons. The uncertainties in the estimated atmospheric concentrations range from 30% to 40% and are due to variability in the input parameters. The model estimates the seasonal mean atmospheric SO₄^2- and CA²⁺ concentrations to within 15% and 55%, respectively. Although the model is not directly applied to ice cores, the application of the model to ice core chemical signals is briefly discussed.

BERGIN, M.H., J.-L. Jaffrezo, C.I. Davidson, J.E. Dibb, S.N Pandis, R. Hillamo, W. Maenhaut, H.D. Kuhns, and T. Makela. The contributions of snow, fog, and dry deposition to the summer flux of anions and cations at Summit, Greenland. Journal of Geophysical Research 100(D8):16,275-16,288 (1995).

Experiments were performed during the period May-July of 1993 at Summit, Greenland. Aerosol mass size distributions as well as daily average concentrations of several anionic and cationic species were measured. Dry deposition velocities for SO₄^2- were estimated using surrogate surfaces (symmetric airfoils) as well as impactor data. Real-time concentrations of particles greater than 0.5 mm and greater than 0.01 mm were measured. Snow and fog samples from nearly all of the events occurring during the field season were collected. Filter sampler results indicate that SO₄^2- is the dominant aerosol anion species, with Na⁺, NH₄⁺, and CA²⁺ being the dominant cations. Impactor results indicate that MSA and SO₄^2- have similar mass size distributions. Furthermore, MSA and SO₄^2- have mass in both the accumulation and coarse modes. A limited number of samples for NH₄⁺ indicate that it exists in the accumulation mode. Na, K, Mg, and Ca exist primarily in the coarse mode. Dry deposition velocities estimated from impactor samples and a theory for dry deposition to snow range from 0.017 cm/s ± 0.011 cm/s for NH₄⁺ to 0.110 cm/s ± 0.021 cm/s for Ca. SO₄^2- dry deposition velocity estimates using airfoils are in the range 0.023 cm/s to 0.062 cm/s, as much as 60% greater than values calculated using the airborne size distribution data. The rough agreement between the airfoil and impactor-estimated dry deposition velocities suggests that the airfoils may be used to approximate the dry deposition to the snow surface. Laser particle counter (LPC) results show that particles >0.5 mm in diameter efficiently serve as nuclei to form fog droplets. Condensation nuclei (CN) measurements indicate that particles 0.5 mm are not as greatly affected by fog. Furthermore, impactor measurements suggest that from 50% to 80% of the aerosol SO₄^2- serves as nuclei for fog droplets. Snow deposition is the dominant mechanism transporting chemicals to the ice sheet. For NO₃^-, a species that apparently exists primarily in the gas phase as HNO₃(g), 93% of the seasonal inventory (mass of a deposited chemical species per unit area during the season) is due to snow deposition, which suggests efficient scavenging of HNO₃(g) by snowflakes. The contribution of snow deposition to the seasonal inventories of aerosols ranges from 45% for MSA to 76% for ₄⁺. The contribution of fog to the seasonal inventories ranges from 13% for NA+ and CA²⁺ to 26% and 32 % for SO₄^2- and MSA. The dry deposition contribution to the seasonal inventories of the aerosol species is as low as 5% for NH₄⁺ and as high as 23% for MSA. The seasonal inventory estimations do not take into consideration the spatial variability caused by blowing and drifting snow. Overall, results indicate that snow deposition of chemical species is the dominant flux mechanism during the summer at Summit and that all three deposition processes should be considered when estimating atmospheric concentrations based on ice core chemical signals.

Bertman, S.B., J.M. Roberts, D.D. Parrish, M.P. Buhr, P.D. Goldan, W.C. Kuster, F.C. Fehsenfeld, S.A. MONTZKA, and H. Westberg. Evolution of alkyl nitrates with air mass age. Journal of Geophysical Research 100(D11):22,805-22,813 (1995).

Alkyl nitrates (RONO₂) and alkanes (RH) were measured at Scotia, Pennsylvania, in 1988 and at the Kinterbish Wildlife Area, Alabama, in 1992. A simple kinetic analysis was developed to relate the two species' concentrations based on the analytical solution of two sequential first-order reactions using OH chemistry, RONO₂ photolysis, and assuming peroxy radicals (ROO) + NO as the source of RONO₂. The analysis predicts an increase in RONO₂/RH ratio with time. The C₄ and C₅ secondary alkyl nitrate/alkane ratios vary in a manner consistent with ROO + NO chemistry as their only source and photolysis and OH reaction as their only sinks. Comparison of ambient measurements of these compounds with predictions indicate that measured air masses experienced photochemical processing times consistent with alkyl nitrate evolution times between 0.1 and 5 days. The relationships of ethyl nitrate, n-propyl nitrate and 2-propyl nitrate ratios to their parent alkanes all indicate additional sources of RONO₂, probably of a photochemical nature. Decomposition of larger alkoxy radicals are discussed as one possible source of smaller ROO radicals.

BODHAINE, B.A. Aerosol absorption measurements at Barrow, Mauna Loa, and the South Pole. Journal of Geophysical Research 100(D5):8967-8975 (1995).

Aerosol absorption (s_ap) has been measured continuously using aethalometers at Barrow, Alaska (1986 to present); Mauna Loa, Hawaii (1990 to present); and South Pole, Antarctica (1987-1990). These three stations are part of a network of baseline monitoring stations operated by the Climate Monitoring and Diagnosis Laboratory (CMDL) of the National Oceanic and Atmospheric Administration (NOAA). Condensation nucleus (CN) concentration and multiwavelength aerosol scattering (s_sp) have also been measured continuously for many years at these stations. Aethalometer measurements are usually reported in terms of atmospheric black carbon aerosol (BC) concentration using the calibration suggested by the manufacturer. Here we deduce the in situ s_ap (550 nm) from aethalometer measurements by assuming that the aerosol absorption on the aethalometer filter is enhanced by a factor of 1.9 over that in the atmosphere. This is consistent with using 19 m² g^-1 for the specific absorption of BC on the aethalometer filter and 10 m² g^-1 for the in situ specific absorption of BC in the atmosphere (the ratio of the two specific absorptions is 1.9). Although these values of specific absorption may vary significantly for different environments, the ratio might be expected to be relatively constant. The single-scattering albedo, defined by w = s_sp /(s_sp + s_ap), has been estimated from the simultaneous measurements of s_ap and s_sp. Furthermore, assuming a 1/l dependence for s_ap in the 450 to 700-nm wavelength region, multiwavelength s sp measurements allow the estimation of the wavelength dependence of w . Each station shows a considerable annual cycle in s_ap, s_sp, and w . The maximum in the Barrow annual cycle is caused primarily by the springtime Arctic haze phenomenon; the maximum in the Mauna Loa annual cycle is caused by the springtime Asian dust transport; and the maximum in the South Pole annual cycle is caused by late winter transport from southern midlatitudes. It was found that annual mean values are s_ap = 4.1 ´ 10^-7 m^-1 (» 41 ng m^-3 BC) and w = 0.96 for Barrow; s_ap, = 5.8 ´ 10-8 m^-1 (» 5.8 ng m^-3 BC) and w = 0.97 for Mauna Loa; and s_ap = 6.5 ´ 10^-9 m^-1 (» 0.65 ng m^-3 BC) and w = 0.97 for South Pole. It was also found that the wavelength dependence of w may be important at Barrow and South Pole, but not important at Mauna Loa.

BODHAINE, B.A., and E.G. DUTTON. Reply to Jaffe et al., 1995. Geophysical Research Letters 22:741-742 (1995).

No abstract

BODHAINE, B.A., and E.G. DUTTON. Reply [Comment on "A long term decrease in arctic haze at Barrow, Alaska"]; by B.A. Bodhaine and E.G. Dutton. Geophysical Research Letters 22(6):741-742 (1995).

No abstract.

Buhr, M., D. Parrish, J. Elliot, J. Holloway, J. Carpenter, P. Goldan, W. Kuster, M. Trainer, S. MONTZKA, S. McKeen, and F. Fehsenfeld. Evaluation of ozone precursor source types using principal component analysis of ambient air measurements in rural Alabama. Journal of Geophysical Research 100(D11):22,853-22,860 (1995).

The sources of photochemical precursors for ozone, primarily NO_x (NO + NO₂) and reduced carbon (CO and hydrocarbons), were evaluated using principal component analysis (PCA) of concurrent measurements of [NO_x], [NO_y] (total reactive oxidized nitrogen species), [CO], [SO₂], [C₃H₈], [C₆H₆], and [O₃] collected at a rural Alabama field site during the summers of 1990 and 1992. Two separate data matrices were analyzed, including a low measurement frequency matrix that included all of the variables and a high measurement frequency matrix that included all of the variables except for the hydrocarbons. The results of the PCA indicated that the major sources of NO_y in the region are (1) coal-fired power plants and (2) biomass burning and/or paper mills. The identifications are based on the [CO]/[NO_y] and [SO₂]/[NO_y] emission ratios derived from the measurements in comparison with the expected emission ratios that are based upon the National Acid Precipitation Assessment Program (NAPAP) emission inventory and upon laboratory experiments. The results indicated that the NAPAP inventory, integrated over the southeastern region of the United States, may overestimate the current [SO₂]/[NO_y] emission ratio from coal-fired power plants and may underestimate the [CO]/[NO_y] emission ratio from paper mills. The results also suggest that biomass burning in the southeastern United States may be an important component in the NO_y inventory, both as a point source associated with paper mills and as a seasonally dependent area source. The variation of [O₃] observed at the site was primarily related to the variation of [NO_y].

BUTLER, J.H. Methyl bromide under scrutiny. Nature 376:469-470 (1995).

No abstract.

Cess, R.D., M.H. Zhang, P. Minnis, L. Corsetti, E.G. DUTTON, B.W. Forgan, D.P. Garber, W.L. Gates, J.J. Hack, E.F. Harrison, X. Jing, J.T. Kiehl, C.N. Long, J.-J. Morcrette, G.L. Potter, V. Ramanathan, B. Subasilar, C.H. Whitlock, D.F. Young, and Y. Zhou. Absorption of solar radiation by clouds: Observations versus models. Science 267:496-499 (1995).

There has been a long history of unexplained anomalous absorption of solar radiation by clouds. Collocated satellite and surface measurements of solar radiation at five geographically diverse locations showed significant solar absorption by clouds, resulting in about 25 watts per square meter more global-mean absorption by the cloudy atmosphere than predicted by theoretical models. It has often been suggested that tropospheric aerosols could increase cloud absorption. But the aerosols are temporally and spatially heterogeneous, whereas the observed cloud absorption is remarkably invariant with respect to season and location. Although its physical cause in unknown, enhanced cloud absorption substantially alters our understanding of the atmosphere's energy budget.

Ciais, P., R.J. Francey, P.P. TANS, J.W.C. White, and M. TROLIER. An analytical error estimate for the ocean and land uptake of CO₂ using ¹³C observations in the atmosphere. NOAA TM ERL CMDL-8 13 pp. (1995).

The quantity and quality of atmospheric data pertaining to the global carbon cycle have improved to an extent that more realistic error estimates can now be attempted for regional sources and sinks of CO₂ derived from such data. Enting et al. [1995] describe a Bayesian synthesis methodology for a 3-D atmospheric transport model. Recently, Ciais et al. [1995] deconvoluted the ocean and land uptake using CO₂ mixing ratio and ¹³C observations in the atmosphere in a 2-D inverse model of atmospheric transport. In their work, more attention was given to the description of the method than to a precise estimate of errors. A coarse estimate was provided by sensitivity tests of the model using drastic alterations of the important parameters. We present here a detailed error analysis of the land and ocean fluxes inferred by Ciais et al. [1995]. Because the analytic expression for the fluxes is known explicitly, it is possible to use an analytical propagation of errors. In this manner, we quantify the main uncertainties associated with the three principle parameters of the model: the discrimination against ¹³C by plant photosynthesis and the ocean and land isotopic disequilibria. This requires a physical, and thus partly subjective, estimate of the uncertainty of each of the three parameters. We also re-evaluate the "bootstrap" error associated with the longitudinal structure of data, which consist of flask samples from the Climate Monitoring and Diagnostics Laboratory (CMDL) global air sampling network, supplemented at high southern latitudes with Commonwealth Scientific and Industrial Research Organization/Global Atmospheric Sampling Laboratory (CSIRO/GASLAB) measurements [Francey et al., 1994]. This is done by propagating the errors associated with the CO₂ and ¹³CO₂ sources separately, which have been inferred by a bootstrap analysis. The error propagation includes their covariance, accounting for the very strong correlation between the sources of CO₂ and ¹³CO₂.

Ciais, P., P.P. TANS, M. TROLIER, J.W.C. White, and R.J. Francey. A large Northern Hemisphere terrestrial CO₂ sink indicated by ¹³C/¹²C of atmospheric CO₂. Science 269:1098-1102 (1995).

Measurements of the concentrations and ¹³C/¹² isotope ratios of atmospheric CO₂ can be used to quantify the net removal of CO₂ from the atmosphere by the oceans and terrestrial plants. Using a global network of 43 sites sampled weekly, the latitudinal and temporal patterns of the two carbon sinks are revealed. A strong terrestrial biospheric sink existed in the temperate latitudes of the Northern Hemisphere in 1992 and 1993, the magnitude of which is roughly half that of the global fossil fuel burning emissions for those years. From these atmospheric measurements, we strongly argue for the existence of this sink; the challenge now is to identify those processes which would cause the terrestrial biosphere to absorb CO₂ in such large quantities.

Ciais, P., P.P. TANS, J.W.C. White, M. TROLIER, R.J. Francey, J.A. Berry, D.R. Randall, P.J. Sellers, J.G. Collatz, and D.S. Schimel. Partitioning of ocean and land uptake of CO as inferred by ¹³C measurements from the NOAA Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network. Journal of Geophysical Research 100(D3):5051-5070 (1995).

Using ¹³C measurements in atmospheric CO₂ from a cooperative global air sampling network, we determined the partitioning of the net uptake of CO₂ between ocean and land as a function of latitude and time. The majority of ¹³C measurements were made at the Institute of Arctic and Alpine Research (INSTAAR) of the University of Colorado. The network included 40 sites in 1992 and constitutes the most extensive data set available. We perform an inverse deconvolution of both CO₂ and ¹³C observations, using a two-dimensional model of atmospheric transport. New features of the method include a detailed calculation of the isotopic disequilibrium of the terrestrial biosphere from global runs of the CENTURY soil model. Also, the discrimination against ¹³C by plant photosynthesis, as a function of Using d ¹³C measurements in atmospheric CO₂ from a cooperative global air sampling network, we determined the partitioning of the net uptake of CO₂ between ocean and land as a function of latitude and time. The majority of d ¹³C measurements were made at the Institute of Arctic and Alpine Research (INSTAAR) of the University of Colorado. The network included 40 sites in 1992 and constitutes the most extensive data set available. We perform an inverse deconvolution of both CO₂ and d ¹³C observations, using a two-dimensional model of atmospheric transport. New features of the method include a detailed calculation of the isotopic disequilibrium of the terrestrial biosphere from global runs of the CENTURY soil model. Also, the discrimination against ¹³C by plant photosynthesis, as a function of latitude and time, is calculated from global runs of the SiB biosphere model. Uncertainty due to the longitudinal structure of the data, which is not represented by the model, is studied through a bootstrap analysis by adding and omitting measurement sites. The resulting error estimates for our inferred sources and sinks are of the order of 1 GTC (1 GTC = 10¹⁵ gC). Such error bars do not reflect potential systematic errors arising from our estimates of the isotopic disequilibria between the atmosphere and the oceans and biosphere, which are estimated in a separate sensitivity analysis. With respect to global totals for 1992 we found that 3.1 GTC of carbon dissolved into the ocean and that 1.5 GTC were sequestered by land ecosystems. Northern hemisphere ocean gyres north of 15�N absorbed 2.7 GTC. The equatorial oceans between 10�S and 10�N were a net source to the atmosphere of 0.9 GTC. We obtained a sink of 1.6 GTC in southern ocean gyres south of 20�S, although the deconvolution is poorly constrained by sparse data coverage at high southern latitudes. The seasonal uptake of CO₂ in northern gyres appears to be correlated with a bloom of phytoplankton in surface waters. On land, northern temperate and boreal ecosystems between 35�N and 65�N were found to be a major sink of CO₂ in 1992, as large as 3.5 GTC. Northern tropical ecosystems (equator-30�N) appear to be a net source to the atmosphere of 2 GTC which could reflect biomass burning. A small sink, 0.3 GTC, was inferred for southern tropical ecosystems (30�S-equator).

Crill, P.M., J.H. BUTLER, D.J. Cooper, and P.C. NOVELLI. Standard analytical methods for measuring trace gases in the environment. Biogenic Trace Gases: Measuring Emissions from Soil and Water, Methods in Ecology P.A. Matson and R.C. Harriss (eds.), University Press, Cambridge, U.K., 164-205 (1995).

No abstract.

DLUGOKENCKY, E.J., L.P. Steele, P.M. LANG, and K.A. MASARIE. Atmospheric methane at Mauna Loa and Barrow observatories: Presentation and analysis of in situ measurements. Journal of Geophysical Research 100(D11):23,103-23,113 (1995).

In situ methane (CH₄) measurement techniques and data from the NOAA Climate Monitoring and Diagnostics Laboratory observatories at Mauna Loa, Hawaii, and Barrow, Alaska, are presented. For Mauna Loa, the data span the time period April 1987 to April 1994. At Barrow the measurements cover the period January 1986 to January 1994. Sixty air samples per day were measured with a fully automated gas chromatograph using flame ionization detection. Details of the experimental methods and procedures are given. Data are presented and assessed over various timescales. The average peak to peak seasonal cycle amplitudes obtained from four harmonics fitted to the detrended data were 25.1 ppb at Mauna Loa and 47.2 ppb at Barrow. When the seasonal cycle amplitude during each calendar year was determined as the difference between the maximum and minimum value from a smooth curve fitted to the data, the average amplitudes were (30.6 4.2) ppb at Mauna Loa and (57.5 11.4) ppb at Barrow. A discrepancy exists between these two methods due to the temporal variability in the positions of the seasonal maxima. The average trend at Mauna Loa was 9.7 ppb yr^-1, but this trend was observed to decrease at a rate of 1.5 ppb yr^-2. For Barrow the average trend was 8.5 ppb yr^-1, and the rate of decrease in the trend was 2.1 ppb yr^-2. At Mauna Loa, a diurnal cycle was sometimes observed with an amplitude of up to 10 ppb when averaged over 1 month.

DUTTON, E.G., and S.K. Cox. Tropospheric radiative forcing from El Chichon and Mt. Pinatubo: Theory and observations. Colorado State University Atmospheric Science Paper No. 586, 217 pp. (1995).

The possibility of volcanic effects on global and regional climate variables has had a long history of speculation, correlative study, and proposed physical mechanisms. The potential for widespread surface cooling following the extensive spreading of long-lived stratospheric aerosols following major volcanic eruptions is based on the partial blocking of solar radiation incident at the top of the troposphere. Relatively simple physical mechanisms oppose this potential for cooling: dominant forward solar scattering and absorption of outgoing infrared radiation by the aerosols. More complex considerations are the spatial and temporal variations of the distributed aerosol and its optical and physical properties; potential for water/ice cloud modification by the volcanic particles; surface albedo, water vapor, and cloud feedbacks to a temperature change; the role of the oceans in a large-scale radiatively forced temperature variation; possible circulation modifications; and other forced and random variations in climate. In the current work, rigorous radiative transfer calculations relative to a subset of the above considerations are carried out and compared to observational data to examine deterministic volcanic effects on climate. Specifically, zonally resolved volcanic radiative forcing at the tropopause, and other levels, is computed from the best available information on the spatial and temporal distribution of volcanic aerosols from two recent eruptions, El Chichon (Mexico, 1982) and Mt. Pinatubo (Philippines, 1991). Accuracy of the radiative calculations is partially verified with surface- and satellite-based irradiance observations. Maximum global seasonal-mean radiative forcings of -4.5 and -2.2 W m^-2 are calculated following the Mt. Pinatubo and El Chichon eruptions, respectively. Within hemisphere irradiance gradient anomalies of up to 16% at the tropopause are calculated for the second N. Hemisphere summer following the eruptions. The computed radiative forcing is applied to a simple hemispheric tropospheric temperature change model, assuming constant cloudiness and surface albedo, in an effort to explain observed global temperature records (NOAA Microwave Sounding Unit) following the two eruptions. Excellent agreement is seen between explained (modeled) and observed global and hemispheric temperature changes after the Mt. Pinatubo eruption, but not following that of El Chichon. Details of this work and some discussion of the results are given. A simple parameterization of the radiative forcing calculations is given that may prove useful in higher spatial and temporal resolution investigations.

ENDRES, D. GPS-derived time baffles NOAA researcher. Ocean Navigator 66:22-24 (1995).

No abstract.

Fan, E.-M., M.L. Goulden, J.W. Munger, B.C. Daube, P.S. BAKWIN, S.C. Wofsy, J.S. Amthor, D.R. Fitzjarrald, K.E. Moore, and T.R. Moore. Environmental controls on the photosynthesis and respiration of a boreal lichen woodland: a growing season of whole-ecosystem exchange measurements by eddy correlation. Oecologia 102:443-452 (1995).

Measurements of net ecosystem CO₂ exchange by eddy correlation, incident photosynthetically active photon flux density (PPFD), soil temperature, air temperature, and air humidity were made in a black spruce (Picea mariana) boreal woodland near Schefferville, Quebec, Canada, from June through August 1990. Nighttime respiration was between 0.5 and 1.5 kg C ha-1 h^-1, increasing with temperature. Net uptake of carbon during the day peaked at 3 kg C ha^-1 h^-1, and the daily net uptake over the experiment was 12 kg C ha^-1 day^-1. Photosynthesis dropped substantially at leaf-to-air vapor pressure deficit (VPD) greater than 7 mb, presumably as a result of stomatal closure. The response of ecosystem photosynthesis to incident PPFD was markedly non-linear, with an abrupt saturation at 600 mol m^-2 s^-1. This sharp saturation reflected the geometry of the spruce canopy (isolated conical crowns), the frequently overcast conditions, and an increase in VPD coincident with high radiation. The ecosystem light-use efficiency increased markedly during overcast periods as a result of a more even distribution of light across the forest surface. A mechanistic model of forest photosynthesis, parameterized with observations of leaf density and nitrogen content from a nearby stand, provided accurate predictions of forest photosynthesis. The observations and model results indicated that ecosystem carbon balance at the site is highly sensitive to temperature and relatively insensitive to cloudiness.

Ferrare, R.A., T.J. McGee, D. Whiteman, J. Burris, M. Owens, J. Butler, R.A. Barnes, F. Schmidlin, W. KOMHYR, P.H. Wang, M.P. McCormick, and A.J. Miller. Lidar measurements of stratospheric temperature during STOIC. Journal of Geophysical Research 100(D5):9303-9312 (1995).

Measurements of stratospheric temperature and density were acquired by the NASA/GSFC lidar during the Stratospheric Ozone Intercomparison Campaign (STOIC) experiment at the Jet Propulsion Laboratory Table Mountain Facility (TMF) (34.4°N, 117.7° W) in July and August 1989. Lidar temperatures, obtained on 21 nights preceding and during this experiment, are compared with temperatures derived by radiosondes, datasondes, Stratospheric Aerosol and Gas Experiment (SAGE II) satellite experiment, and National Meteorological Center (NMC) analyses. Radiosondes were flown from the TMF site as well as from San Nicholas Island (33.2°N, 119.5°W) located about 225 km southwest of TMF. Datasondes were deployed from Super-Loki rockets also launched at San Nicholas Island. SAGE II satellite temperature measurements were made within 1000 km of the Table Mountain site. NMC temperature analyses derived from the NOAA satellite measurements were interpolated to coincide in space and time with the lidar measurements. The lidar temperatures, which were derived for altitudes between 30 and 65 km, were within 2-3 K of the temperatures measured by the other sensors in the altitude range 30-45 km. Between 30 and 35 km, lidar temperatures were about 2 K cooler than those obtained from the datasondes and the NMC analyses, but were about 1-2 K warmer than those obtained from the radiosonde. These differences may be due to the time difference between the measurements as well as possible nonnegligible aerosol scattering near 30 km. Near and above the stratopause the temperature differences increased to 3-8 K. Lidar temperature profiles also show small-scale variations possible caused by wave activity.

Goldan, P.D., W. C. Kuster, F.C. Fehsenfeld, S.A. MONTZKA. Hydrocarbon measurements in the southeastern United States: The Rural Oxidants in the Southern Environment (ROSE) Program 1990. Journal of Geophysical Research 100(D12):25,945-25,963 (1995).

An automated gas chromatographic system was employed at a rural site in western central Alabama to measure atmospheric hydrocarbons and oxygenated hydrocarbons (oxy-hydrocarbons) on an hourly basis from June 8 to July 19, 1990. The location, which was a designated site for the Southern Oxidant Study (SOS), was instrumented for a wide variety of measurements allowing the hydrocarbon and oxy-hydrocarbon measurements to be interpreted both in terms of meteorological data and as part of a large suite of gas phase measurements. Although the site is situated in a Loblolly pine plantation, isoprene was observed to be the dominant hydrocarbon during the daytime with afternoon maxima of about 7 parts per billion by volume (ppbv). Decrease of isoprene after sunset was too rapid to be accounted for solely on the basis of gas phase chemistry. During the nighttime, -pinene and -pinene were the dominant hydrocarbons of natural origin. The ratio of -pinene to -pinene showed a well-defined diurnal pattern, decreasing by more than 30% during the night; a decrease that could be understood on the basis of local gas phase chemistry. Oxy-hydrocarbons, dominated by methanol and acetone, were the most abundant compounds observed. On a carbon atom basis, the oxy-hydrocarbons contributed about 46% of the measured atmospheric burden during the daytime and about 40% at night. The similarity of the observed diurnal methanol variation to that of isoprene and subsequent measurements [McDonald and Fall, 1993] indicate that much of the observed methanol was of local biogenic origin. Correlation of acetone with methanol suggests that it, also, has a significant biogenic source. In spite of the site's rural location, anthropogenic hydrocarbons constituted, on a carbon atom basis, about 21% of the hydrocarbon burden measured during the daytime and about 55% at night. Significant diurnal variations of the anthropogenic hydrocarbons, with increases at night, appeared to be driven by the frequent formation of a shallow nocturnal boundary layer.

Helas, G., J. LOBERT, D. Sch�rffe, L. Schafer, J. Goldammer, J. Baudet, B. Ahoua, A.-L. Ajavon, J.-P. Lacaux, R. Delmas, and M.O. Andreae. Ozone production due to emissions from vegetation burning. Journal of Atmospheric Chemistry 22:163-174 (1995).

Ozone has been observed in elevated concentrations by satellites over areas previously believed to be "background". There is meteorological evidence, that these ozone "plumes" found over the Atlantic Ocean originate from vegetation fires on the African continent. In a previous study (DECAFE-88), we have investigated ozone and assumed precursor compounds over African tropical forest regions. Our measurements revealed large photosmog layers at altitudes from 1.5 to 4 km. Both chemical and meteorological evidence point to savanna fires up to several thousand km upwind as sources. Here we describe ozone mixing ratios observed over western Africa and compare ozone production ratios from different field measurement campaigns related to vegetation burning. We find that air masses containing photosmog "ingredients" require several days to develop their oxidation potential, similar to what is known from air polluted by emissions from fossil fuel burning. Finally, we estimate the global ozone production due to vegetation fires and conclude that this source is comparable in strength to the stratospheric input.

HOFMANN, D., P. Bonasoni, M. DeMaziere, F. Evangelisti, G. Giovanelli, A. Goldman, F. Goutail, J. Harder, R. Jakoubek, P. Johnston, J. Kerr, W. A. Matthews, T. McElroy, R. McKenzie, G. Mount, U. Platt, J.-P. Pommereau, A. Sarkissian, P. Simon, S. Solomon, J. Stutz, A. Thomas, M. VanRoozendael, and E. Wu. Intercomparison of UV/visible spectrometers for measurements of stratospheric NO₂ for the Network for the Detection of Stratospheric Change. Journal of Geophysical Research 100(D8):16,765-16,791 (1995).

During the period May 12-23, 1992, seven groups from seven countries met in Lauder, New Zealand, to intercompare their remote sensing instruments for the measurement of atmospheric column NO₂ from the surface. The purpose of the intercomparison was to determine the degree of intercomparability and to qualify instruments for use in the Network for the Detection of Stratospheric Change (NDSC). Three of the instruments which took part in the intercomparison are slated for deployment at primary NDSC sites. All instruments were successful in obtaining slant column NO₂ amounts at sunrise and sunset on most of the 12 days of the intercomparison. The group as a whole was able to make measurements of the 90 solar zenith angle slant path NO₂ column amount that agreed to about 10% most of the time; however, the sensitivity of the individual measurements varied considerably. Part of the sensitivity problem for these measurements is the result of instrumentation, and part is related to the data analysis algorithms used. All groups learned a great deal from the intercomparison and improved their results considerably as a result of this exercise.

HOFMANN, D.J., S.J. OLTMANS, B.J. JOHNSON, J.A. LATHROP, J.M. HARRIS, and H. VÖMEL. Recovery of ozone in the lower stratosphere at the South Pole during the spring of 1994. Geophysical Research Letters 22(18):2493-2496 (1995).

During 1994, springtime Antarctic ozone measured at the south pole did not reach the record lows recorded during the 1993 ozone hole period when a value of 91 5 DU was observed. A low value of 102 DU was recorded on October 5, 1994, but such values were not sustained as in 1993. The recovery of total ozone in 1994 was mainly the result of moderation of ozone destruction in the 10-14 km region, probably related to diminishing stratospheric aerosol from the Pinatubo eruption, and may have also been partially related to disturbance of the vortex earlier than normal. As in 1993, ozone profiles at the minimum showed nearly complete destruction of ozone between 15 and 20 km in 1994. In this region, the rate of decline of ozone in September was at least as fast or somewhat faster than in 1992 and 1993 indicating continuing saturation of the ozone destroying chemistry, which is expected as stratospheric chlorine amounts continue to rise. As in 1993, ozone was again observed to be reduced in the 22-24 km region, suggesting that the ozone hole has now probably extended to a region unaffected prior to 1992.

Jaffe, D., T. Iversen, and G. Shaw. Comment on a �A long term decrease in arctic haze at Barrow, Alaska� by B.A. BODHAINE and E.G. DUTTON. Geophysical Research Letters 22(6):739-740 (1995).

In �Long Term Decrease in Arctic Haze at Barrow, Alaska� Bodhaine and Dutton present data which they believe demonstrates a decrease in the occurrence of pollutant aerosols in the arctic during spring. They account for this result by claiming substantial SO₂ emission reductions in the Former Soviet Union (FSU). We do not agree with their conclusions. Our interpretation is based on a number of factors which are discussed in detail below: emissions of SO₂ in Europe; transport of pollutants to Barrow, the statistical analysis of the data presented, volcanic effects on the data set, and the large, unexplained, year-to-year variability (much larger than the reported trends).

Jaffe, D.A., R.E. Honrath, D. Furness, T.J. CONWAY, E. DLUGOKENCKY, and L.P. Steele. A determination of the CH₄, NO_x, and CO₂ emissions from the Prudoe Bay, Alaska oil development. Journal of Atmospheric Chemistry 20:213-227 (1995).

In this paper we quantify the CH₄, CO₂, and NO_x emissions during routine operations at a major oil and gas production facility, Prudhoe Bay, Alaska, using the concentrations of combustion by products measured at the NOAA-CMDL observatory at Barrow, Alaska and fuel consumption data from Prudhoe Bay. During the 1989 and 1990 measurement campaigns, 10 periods (called "events") were unambiguously identified where surface winds carry the Prudhoe Bay emissions to Barrow (approximately 300 km). The events ranged in duration from 8-48 h and bring ambient air masses containing substantially elevated concentrations of CH₄, CO₂, and NO_y to Barrow. Using the slope of the observed CH₄ vs. CO₂ concentrations during the events and the CO₂ emissions based on reported fuel consumption data, we calculate annual CH₄ emissions of (24 ± 8) ´ 10³ metric tons from the facility. In a similar manner, the annual NO_x emissions are calculated to be (12 ± 4) ´ 10³ metric tons, which is in agreement with an independently determined value. The calculated CH₄ emissions represent the amount released during routine operations including leakage. However this quantity would not include CH₄ released during non-routine operations, such as from venting or gas flaring.

Karl, T.R., V.E. Derr, D.R. Easterling, C.K. Folland, D.J. HOFMANN, S. Levitus, N. Nicholls, D.E. Parker, and G.W. Withee. Critical issues for long-term climate monitoring. Climatic Change 31:185-21 (1995).

Even after extensive re-working of past data, in many instances we are incapable of resolving important aspects concerning climate change and variability. Virtually every monitoring system and data set requires better data quality, continuity, and homogeneity if we expect to conclusively answer questions of interest to both scientists and policy-makers. This is a result of the fact that long-term meteorological data, (both satellite and conventional) both now and in the past, are and have been collected primarily for weather prediction, and only in some cases, to describe the current climate. Long-term climate monitoring, capable of resolving decade-to-century scale changes in climate, requires different strategies of operation. Furthermore, the continued degradation of conventional surface-based observing systems in many countries (both developed and developing) is an ominous sign with respect to sustaining present capabilities into the future. Satellite-based observing platforms alone will not, and cannot, provide all the necessary measurements. Moreover, it is clear that for satellite measurements to be useful in long-term climate monitoring much wiser implementation and monitoring practices must be undertaken to avoid problems of data inhomogeneity that currently plague space-based measurements. Continued investment in data analyses to minimize time-varying biases and other data quality problems from historical data are essential if we are to adequately understand climate change, but they will never replace foresight with respect to ongoing and planned observing systems required for climate monitoring. Fortunately, serious planning for a Global Climate Observing System (GCOS) is now underway that provides an opportunity to rectify the current crisis.

KOMHYR, W.D., R.A. Barnes, G.B. Brothers, J.A. LATHROP, and D.P. Opperman. Electrochemical concentration cell ozonesonde performance evaluation during STOIC 1989. Journal of Geophysical Research 100(D5):9273-9282 (1995).

Electrochemical concentration cell (ECC) ozonesondes flown by NOAA and NASA Wallops Flight Facility (WFF) personnel during the Stratospheric Ozone Intercomparison Campaign (STOIC) conducted at the Jet Propulsion Laboratory's Table Mountain Facility, Wrightwood, California, July 21 to August 1, 1989, exhibited highly similar ozone measurement precisions and accuracies even though considerably different methods were used by the two research groups in preparing the instruments for use and in calibrating the instruments. The Table Mountain data as well as data obtained in the past showed the precisions to range from about 3 to 12% in the troposphere, remain relatively constant at 3% in the stratosphere to 10 mbar, then decrease to about 10% at 4-mbar pressure altitude. Corresponding ozone measurement accuracies for individual ozonesonde soundings were estimated to be about 6% near the ground, decrease to -7 to 17% in the high troposphere where ozone concentrations are low, increase to about 5% in the low stratosphere and remain so to an altitude of about 10 mbar (~32 km), then decrease to -14 to 6% at 4 mbar (~38 km) where ozone concentrations are again low. Stratospheric ozone measurements were also made during STOIC with ground-based lidars and a microwave radiometer that will be used for ozone measurements in the future at sites of the Network for the Detection of Stratospheric Change (NDSC). The ECC ozonesonde observations provided useful comparison data for evaluating the performance of the lidar and microwave instruments.

KOMHYR, W.D., B.J. Connor, I.S. McDermid, T.J. McGee, A.D. Parrish, and J.J. Margitan. Comparison of STOIC 1989 ground-based lidar, microwave spectrometer, and Dobson spectrophotometer Umkehr ozone profiles with ozone profiles from balloon-borne electrochemical concentration cell ozonesondes. Journal of Geophysical Research 100(D5):9273-9282 (1995).

Ground-based measurements of stratospheric ozone using a Jet Propulsion Laboratory (JPL) lidar, a NASA Goddard Space Flight Center (GSFC) lidar, a Millitech Corporation/NASA Langley Research Center (Millitech/LaRC) microwave spectrometer, and a NOAA Dobson ozone spectrophotometer were compared with in situ measurements made quasi-simultaneously with balloon-borne electrochemical concentration cell (ECC) ozonesondes during 10 days of the Stratospheric Ozone Intercomparison Campaign (STOIC). The campaign was conducted at Table Mountain Observatory, California, during the summer of 1989. ECC ozonesondes were flown by NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) personnel as well as by personnel from the NASA Wallops Island Flight Facility (WFF). Within the altitude range of 20-32 km, ozone measurement precisions were estimated to be 0.6 to 1.2% for the JPL lidar, 0.7% for the GSFC lidar, 4% for the microwave spectrometer, and 3% for the NOAA ECC ozonesonde instruments. These precisions decreased in the 32 to 38.6-km altitude range to 1.3, 1.5, and 3% to 10% for the JPL lidar, GSFC lidar, and the ECC sondes, respectively, but remained at 4% for the microwave instrument. Ozone measurement accuracies in the 20 to 32 km altitude range were estimated to be 1.2 to 2.4% for the JPL lidar, 1.4% for the GSFC lidar, 6% for the microwave radiometer, and 5% for the ECC ozonesondes. The accuracies decreased in the 32 to 38.6-km altitude range to 2.6, 3.0, 7, and 1 4% to -4 10% for the JPL lidar, the GSFC lidar, the microwave spectrometer, and the ECC ozonesondes, respectively. While accuracy estimates for the ECC sondes were obtained by combining random and estimated bias errors, the accuracies for the lidar instruments were obtained by doubling the measurement precision figures, with the assumption that such doubling accounts for systematic errors. Within the altitude range of 20-36 km the mean ozone profiles produced by the JPL, GSFC, and the Millitech/LaRC groups did not differ from the mean ECC sonde ozone profile by more than about 2, 4, and 5%, respectively. Six morning Dobson instrument Umkehr observations yielded mean ozone amounts in layers 3 and 5-7 that agreed with comparison ECC ozonesonde data to within 4%. In layer 4 the difference was 7.8%. (Less favorable comparison data were obtained for six afternoon Umkehr observations made in highly polluted near-surface air.) This good agreement in overall results obtained lends credence to the reliability of the ozone measurements made at Table Mountain Observatory during STOIC 1989.

LOBERT, J.M., J.H. BUTLER, T.J. BARING, S.M. MONTZKA, R.C. MYERS, and J.W. ELKINS. OAXTC 92 Ocean/Atmosphere Exchange of Trace Compounds 1992: Oceanic measurements of HCFC-22, CFC-11, CFC-12, CFC-113, CH₃CCl₃, CCl₄, and N₂O in the marine air and surface waters of the west Pacific Ocean (August 3-October 21, 1992). NOAA TM ERL CMDL-9 43 pp. (1995).

CFC-11 (CCl₃F), CFC-12 (CCl2F2), CFC-113 (CCl2FCC1F2), methyl chloroform (CH₃CCl₃), carbon tetrachloride (CCl4), nitrous oxide (N₂O) and HCFC-22 (CHCIF₂) were measured in the air and surface waters of the Pacific Ocean between 55°N and 22°S during the later summer and early fall of 1992. Atmospheric measurements of all gases agreed well with results from NOAA fixed stations at similar latitudes. CFC-11, CFC-12, and CFC-113, which have long atmospheric lifetimes and are essentially inert in seawater, responded mainly to physical processes in the air and water. The first two gases were supersaturated by 2-6% at higher, northern latitudes, reflecting the effects of radiative warming. Their saturation anomalies declined southward through the tropics and ultimately became slightly negative in the southern hemisphere. HCFC-22 showed signs of small losses in the tropics and subtropics, a sink that may account for 2% of the losses of this gas from the atmosphere. CH₃CCl₃ showed a similar pattern, with only a tropical sink, which is consistent with hydrolysis and, together with data from an earlier expedition, implies that about 6% of atmospheric CH₃CCl₃ is lost to the ocean. The net saturation anomaly for CCl4 was virtually negative everywhere and only slightly dependent upon latitude. This would be expected for a sink that was not particularly temperature dependent and it is consistent with evidence from deepwater profiles that indicate a sink at depth. Fluxes calculated from CCl4 saturation anomalies indicate that 15-35% of atmospheric CCl4 is lost to the ocean. N₂O surface water data indicated weak equatorial upwelling. Saturation anomalies ranged from 1-6%, which would be consistent with a small source in the W. Pacific.

LOBERT, J.M., J.H. BUTLER, S.A. MONTZKA, L.S. GELLER, R.C. MYERS, and J.W. ELKINS. A net sink for atmospheric CH₃Br in the East Pacific Ocean. Science 267:1002-1005 (1995).

Surface waters along a cruise track in the East Pacific Ocean were undersaturated in methyl bromide (CH₃Br) in most areas except for coastal and upwelling regions, with saturation anomalies ranging from +100 percent in coastal waters to -50 percent in open ocean areas, representing a regionally weighted mean of -16 (-13 to -20) percent. The partial lifetime of atmospheric CH₃Br with respect to calculated oceanic degradation along this cruise track is 3.0 (2.9 to 3.6) years. The global, mean dry mole fraction of CH3Br in the atmosphere was 9.8 0.6 parts per trillion, with an interhemi-spheric ratio of 1.31 0.08. These data indicate that ~8 percent (0.2 parts per trillion) of the observed interhemispheric difference in atmospheric CH₃Br could be attributed to an uneven global distribution of oceanic sources and sinks.

Margitan, J.J., R.A. Barnes, G.B. Brothers, J. Butler, J. Burris, B.J. Connor, R.A. Ferrare, J.B. Kerr, W.D. KOMHYR, M.P. McCormick, I.S. McDermid, C.T. McElroy, T.J. McGee, A.J. MIller, M. Owens, A.D. Parrish, C.L. Parsons, A.L. Torres, J.J. Tsou, T.D. Walsh, and D. Whiteman. Stratospheric ozone intercomparison campaign (STOIC) 1989: Overview. Journal of Geophysical Research 100(D5):9193-9207 (1995).

The NASA Upper Atmosphere Research Program organized a Stratospheric Ozone Intercomparison Campaign (STOIC) held in July-August 1989 at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL). The primary instruments participating in this campaign were several that had been developed by NASA for the Network for the Detection of Stratospheric Change: the JPL ozone lidar at TMF, the Goddard Space Flight Center trailer-mounted ozone lidar which was moved to TMF for this comparison, and the Millitech/LaRC microwave radiometer. To assess the performance of these new instruments, a validation/intercomparison campaign was undertaken using established techniques: balloon ozonesondes launched by personnel from the Wallops Flight Facility and from NOAA Geophysical Monitoring for Climate Change (GMCC) (now Climate Monitoring and Diagnostics Laboratory), a NOAA GMCC Dobson spectrophotometer, and a Brewer spectrometer from the Atmospheric Environment Service of Canada, both being used for column as well as Umkehr profile retrievals. All of these instruments were located at TMF and measurements were made as close together in time as possible to minimize atmospheric variability as a factor in the comparisons. Daytime rocket measurements of ozone were made by Wallops Flight Facility personnel using ROCOZ-A instruments launched from San Nicholas Island. The entire campaign was conducted as a blind intercomparison, with the investigators not seeing each others data until all data had been submitted to a referee and archived at the end of a 2-week period (July 20 to August 2, 1989). Satellite data were also obtained from the Stratospheric Aerosol and Gas Experiment (SAGE II) aboard the Earth Radiation Budget Satellite and the total ozone mapping spectrometer (TOMS) aboard Nimbus 7. An examination of the data has found excellent agreement among the techniques, especially in the 20- to 40-km range. As expected, there was little atmospheric variability during the intercomparison, allowing for detailed statistical comparisons at a high level of precision. This overview paper will summarize the campaign and provide a "road map" to subsequent papers in this issue by the individual instrument teams which will present more detailed analysis of the data and conclusions.

MASARIE, K.A., and P.P. TANS. Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record. Journal of Geophysical Research 100(D6):11,593-11,610 (1995).

Atmospheric transport models are used to constrain sources and sinks of carbon dioxide by requiring that the modeled spatial and temporal concentration patterns are consistent with the observations. Serious obstacles to this approach are the sparsity of sampling sites and the lack of temporal continuity among observations at different locations. A procedure is presented that attempts to extend the knowledge gained during a limited period of measurements beyond the period itself resulting in records containing measurement data and extrapolated and interpolated values. From limited measurements we can define trace gas climatologies that describe average seasonal cycles, trends, and changes in trends at individual sampling sites. A comparison of the site climatologies with a reference defined over a much longer period of time constitutes the framework used in the development of the data extension procedure. Two extension methods are described. The benchmark trend method uses a deseasonalized long-term trend from a single site as a reference to individual site climatologies. The latitude reference method utilizes measurements from many sites in constructing a reference to the climatologies. Both methods are evaluated and the advantages and limitations of each are discussed. Data extension is not based on any atmospheric models but entirely on the data themselves. The methods described here are relatively straightforward and reproducible and result in extended records that are model independent. The cooperative air sampling network maintained by the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory in Boulder, Colorado, provides a test bed for the development of the data extension method; we intend to integrate and extend CO₂ measurement records from other laboratories providing a globally consistent atmospheric CO₂ database to the modeling community.

MONTZKA, S.A., M. Trainer, W.M. Angevine, and F.C. Fehsenfeld. Measurements of 3-methyl furan, methyl vinyl ketone, and methacrolein at a rural forested site in the southeastern United States. Journal of Geophysical Research 100(D6):11,393-11,401 (1995).

Three oxygenated hydrocarbons were measured in ambient air above a rural forested site in western Alabama. Mixing ratios of methyl vinyl ketone (MVK), methacrolein (MACR), and 3-methyl furan were determined during a 3-week period in the summer of 1992. While the mean mixing ratio for methyl vinyl ketone was determined to be 740 parts per 1012 (ppt), the mean mixing ratio for methacrolein was 480 ppt. The results for methyl vinyl ketone and methacrolein are compared to previously reported measurements from this same location during the summer of 1990. Although isoprene levels were lower by ~50% in 1992, mixing ratios of the carbonyls were reduced by only ~25%. These differences are discussed in light of the changes that had occurred in the forest canopy in the time elapsed between the two measurement campaigns. Despite the differences observed during the 2 years, a consistent diurnal variability is observed for methyl vinyl ketone, relative to methacrolein, during both years. In addition to a weak correlation observed between the carbonyls and temperature, levels of MVK and MACR in air sampled from just above the forest canopy are influenced by the depth of the mixed layer. A third oxidation product of isoprene, 3-methyl furan, was identified and measured in ambient air. Mean daytime mixing ratios were estimated at 60 ppt. Nighttime levels were lower, averaging 40 ppt. Mixing ratios of 3-methyl furan were highly correlated with isoprene (R2 - 0.82), and during the day, were typically ~2% of levels measured for isoprene.

Moody, J.L., S.J. OLTMANS, H. Levy II, and J.T. Merrill. Transport climatology of tropospheric ozone: Bermuda, 1988-1991. Journal of Geophysical Research 100(D4):7179-7194 (1995).

We determined the major transport patterns for Bermuda and quantified the degree to which they influenced variability in ozone concentrations by applying cluster analysis to isentropic trajectories from September 1988, through September 1991. Concentration distributions of ozone associated with these transport patterns were significantly different. The highest concentrations of ozone in each season were associated with transport off the North American continent; the lowest concentrations were during low-level maritime transport around the Bermuda high. Using the vertical component of the isentropic trajectories, we also showed that the most extreme concentrations of ozone occurred with rapidly descending air from midtropospheric levels. This pattern was most pronounced in April and May when more than 50% of the O₃ variability was related to transport differences. We conclude that this relatively remote marine site, which normally experienced low maritime ozone levels (~30 part per billion by volume (ppbv)), periodically entrained dry, ozone-rich (~55 ppbv) midtropospheric air in association with strong subsidence in high pressure behind spring low-pressure systems. Although the ultimate source of these midtroposphere, midlatitude, elevated-ozone concentrations is still being investigated, the synoptic meteorology associated with these transport patterns supports a significant contribution from the upper troposphere and lower stratosphere.

NOVELLI, P.C., and R.M. ROSSON (eds.). Report of the meeting of experts on carbon monoxide, Boulder, Colorado, February 1994. WMO Report 98 Geneva, Switzerland, 78 pp. (1995).

No abstract.

NOVELLI, P.C., T.J. CONWAY, E.J. DLUGOKENCY, and P.P. TANS. Recent changes in atmospheric carbon dioxide, methane and carbon monoxide, and the implications of these changes on global climate processes. World Meteorological Bulletin 44:32-37 (1995).

No abstract.

OGREN, J.A. A systematic approach to in situ observations of aerosol properties. Aerosol Forcing of Climate R.J. Charlson and J. Heintzenberg (eds.). Wiley & Sons, New York, 215-226 (1995).

Much is known about individual properties of the atmospheric aerosol, such as its bulk chemical composition and size distribution, and these properties have been studied in diverse locations; however, little emphasis has been placed on systematically determining the aerosol parameters that are most needed by the models used to evaluate the climate forcing by aerosol particles. The purpose of this paper is to describe the synthesis that is needed for integrating models and measurements, and the extent to which the available data satisfy this need. The ultimate goal of such a synthesis is the development and validation of methods for assessing the magnitude, mechanisms, and uncertainties of aerosol forcing of climate.

OLTMANS, S.J., and D.J. HOFMANN. Increase in lower-stratospheric water vapor at a mid-latitude Northern Hemisphere site from 1981 to 1994. Nature 374:146-149 (1995).

Water vapor in the atmosphere is the key trace gas controlling weather and climate, and plays a central role in atmospheric chemistry, influencing the heterogeneous chemical reactions that destroy stratospheric ozone. Although in the upper troposphere and lower stratosphere the radiative and chemical effects of water vapor are large, there are few measurements of water-vapor concentration and its long-term variation in this region. Here we present a set of water-vapor profiles for altitudes from 9 to 27 km, obtained at Boulder, Colorado, during 1981-1994, which show a significant increase in water-vapor concentration in the lower stratosphere over this time. The increase is larger, at least below about 25-25 km, than might be expected from the stratospheric oxidation of increasing concentrations of atmospheric methane. The additional increase in water vapor may be linked to other climate variations, such as the observed global temperatures rise in recent decades.

Parungo, F., Y. Kim, C. Zhu, J. HARRIS, R. SCHNELL, X. Li, D. Yang, X. Fang, M. Zhou, Z. Chen, and K. Park. Asian dust storms and their effcts on radiation and climate, Part I, STC Technical Report 2906, 56 pp., Science and Technology Corporation, Hampton, VA (1995).

No abstract.

Prospero, J.M., R. Schmitt, E. Cuevas, D.L. Savoie, W.C. Graustein, K.K. Turekian, A. Volz-Thomas, A. Diaz, S.J. OLTMANS, H. Levy II. Temporal variability of summer-time ozone and aerosols in the free troposphere over the eastern North Atlantic. Geophysical Research Letters 22(21):2925-2928 (1995).

In the free troposphere over Tenerife in the summer, O₃ concentrations are anti-correlated with major pollutant aerosols (nss-SO₄⁼ and NO₃^-) and with ²¹⁰Pb, a tracer for boundary layer sources. In contrast, O₃ is highly correlated with ⁷Be, a product of cosmic ray interactions in the upper troposphere and stratosphere. This suggests that natural O₃ sources (i.e., the stratosphere) might be playing an important role. Nonetheless our results do not preclude the possibility that substantial amounts of pollution-related O₃ could be transported in the free troposphere. However, to be consistent with our results, the transport mechanisms would have to incorporate efficient processes for the removal of pollutant aerosol species and ²¹⁰Pb.

Reagan, J., K. Thome, B. Herman, R. STONE, J. DE LUISI, and J. SNIDER. A comparison of columnar water vapor retrievals obtained with near-IR solar radiometer and microwave radiometer measurements. Journal of Applied Meteorology 34:1384-1391 (1995).

A simple two-channel solar radiometer and analysis technique have been developed for sensing atmospheric water vapor via differential solar transmission measurements in and adjacent to the 940-nm water vapor absorption band. A prototype solar radiometer developed for the National Oceanic and Atmospheric Administration NOAA)/Environmental Research Laboratory underwent trial measurements near Boulder, Colorado, and during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment Phase II cirrus intensive field observation program (Coffeyville, Kansas). These measurements provided the convenient opportunity to compare solar radiometer water vapor retrievals with those obtained using NOAA microwave radiometers. The solar radiometer and microwave radiometer retrievals were found to agree to within 0.1 cm most of the time and to within 0.05 cm the majority of the time, yielding a percent difference in the retrievals generally within 10%. Radiosonde soundings, when available, were also found to generally agree with the microwave and solar radiometer retrievals within 0.1 cm.

RYAN, S. Quiescent outgassing of Mauna Loa Volcano 1958-1994. Mauna Loa Revealed: Structure, Composition, History, and Hazards. Geophysical Monograph 92, J.M. Rhodes and J.P. Lockwood (eds.). American Geophysical Union, Washington, D.C., 95-115 (1995).

A continuous 37 year record of the quiescent CO₂ outgassing of Mauna Loa volcano was derived from atmospheric measurements made 6 km downslope of the summit caldera at Mauna Loa Observatory. The volcanic plume is sometimes trapped in the temperature inversion near the ground at night and transported downslope to the observatory. The amount of volcanic CO₂ was greatest shortly after the 1975 and 1984 eruptions and then decreased exponentially with decay constants of 6.5 and 1.6 years respectively. Between 1959 and 1973 the decay constant was 6.1 years. The total reservoir mass of CO₂ during each of the three quiescent periods was similar and estimated to be between 2 ´ 10⁸ kg and 5 ´ 10⁸ kg (0.2 Mt to 0.5 Mt). The 1975 eruption may have been receded by a small increase in CO₂ emissions. A similar increase has occurred since early 1993. Condensation nuclei (CN), presumably consisting of sulfate aerosol, were measured in the volcanic plume throughout the 1974 to 1994 record. The post-1975 period had consistently high levels of CN. Between 1977 and 1980, light-scattering aerosols were detected, coincident with a period of visible fuming at the summit. CN levels after the 1984 eruption were greatly reduced. Two brief periods of low CN emissions during this time correlate with temporary halts or reductions in the rate of summit expansion. These temporary reversals in the inflation of the mountain did not affect the steady exponential decline of the CO₂ emissions rate. Upper limits were set on the amounts of H₂O, O₃, CH₄, SO₂, aerosol carbon, radon, CO, and H₂ present in the plume at various periods between 1974 and 1993. The ratio of SO₂ to CO₂ was less than 1.8 ´ 10^-3 between 1988 and 1992.

Schmidt, E.O., R.F. Arduini, B.A. Wielicki, R.S. STONE, and S.-C. Tsay. Considerations for modeling thin cirrus effects via brightness temperature differences. Journal of Applied Meteorology 34(2):447-459 (1995).

Brightness temperature difference (BTD) values are calculated for selected Geostationary Operational Environmental Satellite (GOES-6) channels (3.9, 12.7 mm) and Advanced Very High Resolution Radiometer channels (3.7, 12.0 mm). Daytime and nighttime discrimination of particle size information is possible given the infrared cloud extinction optical depth and the BTD value. BTD values are presented and compared for cirrus clouds composed of equivalent ice spheres (volume, surface area) versus randomly oriented hexagonal ice crystals. The effect of the hexagonal ice crystals is to increase the magnitude of the BTD values calculated relative to equivalent ice sphere (volume, surface area) BTDs. Equivalent spheres (volume or surface area) do not do a very good job of modeling hexagonal ice crystal effects on BTDs; however, the use of composite spheres improves the simulation and offers interesting prospects. Careful consideration of the number of Legendre polynomial coefficients used to fit the scattering phase functions is crucial to realistic modeling of cirrus BTDs. Surface and view-angle effects are incorporated to provide more realistic simulation.

TANS, P.P., and P.S. BAKWIN. Climate change and carbon dioxide forever. Ambio 24:376-378 (1995).

We review current understanding of the long-term increase of carbon dioxide (CO₂) in the atmosphere from burning fossil fuels. At equilibrium with the oceans, which will take centuries to achieve because of the slow turnover of the oceans, the atmosphere will hold about 3-4 times as much CO₂ as in pre-industrial times, once all estimated conventional fossil fuel reserves have been burned. For the atmosphere to return to pre-industrial CO₂ levels will require enhanced mineral weathering, which will take many millennia. The terrestrial biosphere (vegetation and soils) could remove at most about one third of the CO₂ emitted if all fossil-fuel reserves are burned. Because of the extremely long-term nature of the CO₂ problem, we present a case that enough is known already for society to start taking steps toward decreasing CO₂ emissions. We also outline a research agenda for the carbon cycle. The importance to society of any serious attempt to curb CO₂ emissions makes it imperative that our knowledge of the carbon cycle is very firm; it should be based on several truly independent lines of evidence.

THONING, K.W., T.J. CONWAY, N. ZHANG, and D. KITZIS. Analysis system for measurement of CO₂ mixing ratios in flask air samples. Journal of Atmospheric and Oceanic Technology 12(6): 1349-1356 (1995).

A system for measuring the concentration of CO₂ in flask air samples from the NOAA/CMDL worldwide flask sampling network is described. Up to 180 samples per day can be analyzed using a nondispersive infrared CO₂ analyzer. All data acquisition and instrument control operations are handled by a Hewlett-Packard Series 300 desktop computer. A noncontaminating diaphragm pump transfers the sample from the flask to the NDIR CO₂ analyzer. Tests conducted using flasks filled from tanks of dry air showed either no systematic offsets or a small offset of about 0.1 ppm. The precision of the analysis system is estimated to be better than 0.1 ppm.

Tuck, A.F., C.R. Webster, R.D. May, D.C. Scott, S.J. Hovde, J.W. ELKINS, and K.R. Chan. Time and temperature dependences of fractional HC1 abundances from airborne data in the southern hemisphere during 1994. Faraday Discuss 100:389-410 (1995).

Measurements of HCl and CH₄ taken by the aircraft laser infrared absorption spectrometer (ALIAS) on the ER-2 high-altitude research aircraft during the southern hemisphere winter of 1994 have been used to examine the abundance of HCl as a fraction of total inorganic chlorine. The fractional abundance of HC1 shows a threshold behavior as a function of temperature history; on a 10-day timescale, the abundance dropped sharply in those air parcels experiencing a temperature <195K, but little or no change was seen in parcels which stayed warmer than this temperature. The behavior mirrors well the temperature behavior calculated for the transformation of HCl into reactive forms (Cl₂, HOCl) from laboratory studies of sulfate aerosols and polar stratospheric clouds. During the course of the winter, the fractional abundance of HC1 outside the vortex decreased from its values in late May by about a third, while inside it dropped to near zero by early August. Some recovery was evident in October. Examples of the peel-off of low-HC1 air equatorward of the wind maximum were evident in early June. Meteorological trajectories are used to show, in a case study of a flight in early August, that air parcels which experienced temperatures of <195K, and as a result had low fractional HC1 abundances, did so largely poleward of the maximum in the polar night jet stream. Encountering temperatures of <195K during the previous 10 days was a necessary and sufficient condition for the transformation of HC1 into reactive forms by heterogeneous reactions. The trajectories further showed that air arriving from sub-tropical latitudes had higher fractional HC1 abundances than the air in the middle latitudes, and much higher fractions than the air at high latitudes. The resulting picture is one in which the fractional abundance of HC1 in air at midlatitudes was the result of mixing of air from sub-tropical latitudes with air mainly from poleward of the jet stream core which has experienced temperatures <195K. The sensitivity of the fractional abundance of HC1 to the assumption that no HC1 enters the stratosphere via the tropical tropopause is examined in the light of an observed profile near the equator with a volume fraction of 0.4 ppb HC1, zero C1O and tropospheric mixing ratios of CFCs at the tropical tropopause.

VÖMEL, H., D.J. HOFMANN, S.J. OLTMANS, and J.M. HARRIS. Evidence for midwinter chemical ozone destruction over Antarctica. Geophysical Research Letters 22(17):2381-2384 (1995).

Two ozone profiles on June 15 and June 19, obtained over McMurdo, Antarctica, showed a strong depletion in stratospheric ozone, and a simultaneous profile of water vapor on June 19 showed the first clear signs of dehydration. The observation of Polar Stratospheric Clouds (PSCs) beginning with the first sounding showing ozone depletion, the indication of rehydration layers, which could be a sign for recent dehydration, and trajectory calculations indicate that the observed low ozone was not the result of transport from lower latitudes. During this time the vortex was strongly distorted, transporting PSC processed air well into sunlit latitudes where photochemical ozone destruction may have occurred. The correlation of ozone depletion and dehydration indicates that water ice PSCs provided the dominant surface for chlorine activation. An analysis of the time when the observed air masses could have formed type II PSCs for the first time limits the time scale for the observed ozone destruction to about 4 days.

VÖMEL, H., S.J. OLTMANS, D.J. HOFMANN, T. Deshler, and J.M. Rosen. The evolution of the dehydration in the Antarctic stratospheric vortex. Journal of Geophysical Research 100(D7):13,919-13,926 (1995).

In 1994 an intensive program of balloon-borne frost point measurements was performed at McMurdo, Antarctica. During this program a total of 19 frost point soundings was obtained between February 7 and October 5, which cover a wide range of undisturbed through strongly dehydrated situations. Together with several soundings from South Pole station between 1990 and 1994, they give a comprehensive picture of the general development of the dehydration in the Antarctic stratospheric vortex. The period of dehydration typically starts around the middle of June, and a rapid formation of large particles leads to a fast dehydration of the vortex. The evaporation of falling particles leads to rehydration layers, which have significantly higher water vapor concentrations than the undisturbed stratosphere. Through the formation of these rehydration layers in the early stages of the dehydration we can estimate a particle fall speed of 1/3 km/d and thus a mean particle size of 4 m. Ice saturation was observed over McMurdo in only two cases and only well after the onset of the dehydration. From the inspection of synoptic maps it then follows that a small cold region inside the vortex seems to be sufficient to dehydrate the entire vortex. Above 20 km the dehydration is completed by the end of July. From the descent of the upper dehydration edge we can estimate a mean descent rate inside the vortex of 1.5 km/month. In McMurdo we observed occasional penetration of the vortex edge in cases where the vortex edge was close to McMurdo, however, these cases seem to have little effect on the bulk of the vortex. A sounding from November 3, 1990, at South Pole shows that the dehydration may persist into November and indicates that there is no significant transport into the vortex throughout winter and early spring.

VÖMEL, H., S.J. OLTMANS, D. Kley, and P.J. Crutzen. New evidence for the stratospheric dehydration mechanism in the equatorial Pacific. Geophysical Research Letters 22(21):3235-3238 (1995).

Water vapor profile measurements obtained in the western and central Pacific during the Central Equatorial Pacific Experiment (CEPEX) show a strong connection between the water vapor content near the tropopause and areas of deep convection. We show that air ascending within deep convective towers can be dried to mixing ratios below 1 part per million by volume (ppmv), which is much lower than the average mixing ratio observed in the stratosphere. A sharp increase of water vapor mixing ratio above the tropopause is an indication of the evaporation of ice particles at the top of deep convective cells. A mixed layer of up to around 1 km thickness above the tropopause in the regions of deep convection is indicated by the vertical profiles of ozone, water vapor, and potential temperature. Furthermore, a local maximum was observed at 20 km, which is an indication for the seasonal cycle of the tropopause temperature.

Woodbridge, E.L., J.W. ELKINS, D.W. Fahey, L.E. Heidt, S. Solomon, T.J. BARING, T.M. GILPIN, W.H. Pollock, S.M. Schauffler, E.L. Atlas, M. Lowenstein, J.R. Podolske, C.R. Webster, R.D. May, J.M. Gilligan, S.A. MONTZKA, K.A. Boering, and R.J. Salawitch. Estimates of total organic and inorganic chlorine in the lower stratosphere from in situ and flask measurements during AASE II. Journal of Geophysical Research 100(D2):3057-3064 (1995).

Aircraft sampling has provided extensive in situ and flask measurements of organic chlorine species in the lower stratosphere. The recent Airborne Arctic Stratospheric Expedition II (AASE II) included two independent measurements of organic chlorine species using whole air sample and real-time techniques. From the whole air sample measurements we derive directly the burden of total organic chlorine (CCl_y) in the lower stratosphere. From the more limited real-time measurements we estimate the CCl_y burden using mixing ratios and growth rates of the principal CCl_y species in the troposphere in conjunction with results from a two-dimensional photochemical model. Since stratospheric chlorine is tropospheric in origin and tropospheric mixing ratios are increasing, it is necessary to establish the average age of a stratospheric air parcel to assess its total chlorine (ClTotal) abundance. Total inorganic chlorine (Cl_y) in the parcel is then estimated by the simple difference, Cl_y = Cl_Total - CCl_y. The consistency of the results from these two quite different techniques suggests that we can determine the CCl_y and Cl_y in the lower stratosphere with confidence. Such estimates of organic and inorganic chlorine are crucial in evaluating the photochemistry controlling chlorine partitioning and hence ozone loss processes in the lower stratosphere.

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