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BAKWIN, P.S., D.F. HURST, P.P. TANS, and J.W. ELKINS. Anthropogenic sources of halocarbons, sulfur hexafluoride, carbon monoxide, and methane in the southeastern United States. Journal of Geophysical Research 102(D13):15,915-15,925 (1997).

Mixing ratios of several radiatively active and ozone depleting trace gases were measured at 1-hour intervals from December 1994 to August 1996 at 496 m above the ground on a communications tower in eastern North Carolina. The time series show variability on a range of timescales, most apparently diurnal cycles, pollution episodes with synoptic time scale, seasonal cycles, and long-term trends. We focus on the pollution episodes and analyze the time series to reveal relationships between species in polluted air. These relationships are used to determine relative sources of the constituents on a regional scale. Using tetrachloroethene (C₂Cl₄) as a reference compound and assuming that the tower site is representative of the whole continent with respect to emissions ratios, we estimate source strengths of the other species for North America. For methyl chloroform (CH₃CCl₃) our emissions estimate is in excellent accord with an estimate from industrial production figures, giving confidence in our methods and assumptions. For carbon monoxide (CO) our estimate also agrees very well with an independent estimate of North American sources based on national inventories. Sources of chlorofluorocarbons 11, 12, and 113 are much lower than expected from global emissions inventories, a finding that may indicate that the ratio of North American to global emissions of these compounds has dropped dramatically since the mid-1980s, as was indeed the case for CH₃CCl₃, or that emissions of these compounds have decreased more rapidly in recent years than industry estimates, or most likely both. We also estimate the North American source of sulfur hexafluoride (SF₆).

BARNES, J.E., and D.J. HOFMANN. Lidar measurements of stratospheric aerosol over Mauna Loa Observatory. Geophysical Research Letters 24(15):1923-1926 (1997).

Dual-wavelength aerosol lidar backscatter measurements at Mauna Loa Observatory are used to monitor and characterize the 15-30 km stratospheric aerosol layer. The decay of aerosol loading following the El Chichón, Mexico (17ºN) and Pinatubo, Philippine Islands (15ºN) volcanic eruptions of 1982 and 1991, respectively, depends on the phase of the quasi-biennial oscillation (QBO) in tropical stratospheric winds. Averaged over a 3-year period, these effects are removed and an exponential decay with a characteristic (e^-1). Decay time of about 1 year is observed for both eruptions. By the end of 1996, about 5 ½ years after the Pinatubo eruption, stratospheric aerosol levels at Mauna Loa had decayed to pre-eruption levels, approximately matching the lowest aerosol levels seen here in the past 17 years (about 6 ´ 10^-5 sr^-1 at 694 nm integrated between 15.8 and 33 km). However, this background stratospheric aerosol level at Mauna Loa may depend on the QBO, being slightly lower during the westerly phase. Analyses of aerosol backscatter, Backscatter wavelength dependence, and trajectories provide evidence for a minor injection of aerosol from the Rabaul eruption in Papaua, New Guinea (4ºS) in September of 1994.

Bird, J.C., S.R. Pal, A.I. Carswell, D.P. Donovan, G.L. Manney, J.M. HARRIS, and O. Uchino. Observations of ozone structures in the Arctic polar vortex. Journal of Geophysical Research 102(D9):10,785-10,800 (1997).

Lidar and balloon measurements at the new observatory, AStrO (80.05°N, 86.42°W), near Eureka, in the Canadian Arctic, have revealed laminations inside the ozone layer both inside and outside the polar vortex. These observations have been conducted by the lidar group of the Institute for Space and Terrestrial Science during February-March 1993 and the winters of 1993-1994 and 1994-1995. Observations of the vortex edge region were obtained as it passed over Eureka, revealing ozone profiles rich in structure. This paper discusses the observed ozone structures and their relationship to vortex filaments, the vortex edge structure, low-ozone pockets, motion of the vortex edge region in the ozone profiles, and observed temperatures. Complementing the observations are back trajectories, potential vorticity maps, and Lagrangian domain-filling potential vorticity trajectories. The relations of magnitude and thickness of the laminations to their positions relative to the vortex are revealed by presenting data as a function of potential vorticity. Mechanisms for the formation and transport of the laminae are discussed, as well as their role as a possible exchange mechanism of air masses across the polar vortex boundary. From observations of the laminations and their relation to potential vorticity, it is suggested that motion of the vortex, sometimes associated with warmings, is involved in the formation of laminations, which are subsequently advected as filamentary structures.

Bishop, J.K., W.B. Rossow, and E.G. DUTTON. Surface solar irradiance from the International Satellite Cloud Climatology Project 1983-1991. Journal of Geophysical Research 102(D6):6883-6910 (1997).

An 8-year (July 1983 through June 1991) time series of daily and monthly mean surface solar irradiance has been produced for the globe using data from the International Satellite Cloud Climatology Project (ISCCP) and a revised Bishop and Rossow [1991] algorithm. We present a detailed validation analysis of the ISCCP solar irradiance fields with contemporaneous surface observations at buoys, at remote islands, and from the Global Energy Balance Archives (GEBA) [Ohmura et al., 1991]. The validation is hampered to some degree by the scale difference between the 280 km ISCCP product and the single-point measurements, some of which are affected by orographic clouds and other local meteorological effects. Our analysis suggests criteria for siting of island or coastal monitoring locations to minimize such biases. Particularly, eastward or poleward facing oceanic exposures are to be avoided. In addition, we suggest that deep sea buoys should be investigated for validation of oceanic surface fluxes. At open-ocean, clean-air sites, the ISCCP product is shown to be good to within 10 W m^-2 in the monthly mean. The high-frequency (daily) systematics of solar irradiance variability at the open-ocean sites are also well duplicated by the ISCCP product. An identifiable error in the revised solar irradiance product is the neglect of spatially and temporally varying aerosol extinction. This error, when translated into an equivalent aerosol extinction coefficient, can be as large as 0.6 in known polluted and mineral dust-affected regions. We cannot determine additional satellite sensor calibration errors beyond those already corrected in the ISCCP processing. This uniquely long data set has been publicly available since 1994 at the National Center for Atmospheric Research. The data documents significant differences in solar fluxes received by the major oceans as well as significant flux variability on seasonal to interannual timescales.

BODHAINE, B.A., D.J. HOFMANN, E.G. DUTTON, R.L. McKenzie, P.V. Johnston, M. Kotkamp, R.C. SCHNELL, J.E. BARNES, and S.C. RYAN. Ultraviolet spectroradiometer measurements at Mauna Loa Observatory. In IRS’96: Current Problems in Atmospheric Radiation, W.L. Smith and K. Stamnes (eds.), pp. 841-844, Deepak, Hampton, VA (1997).

A scanning UV spectroradiometer was installed at Mauna Loa Observatory (MLO), Hawaii, in July 1995. This instrument, built around a commercially available double monochromator, is interfaced with a PC to provide automatic control and data acquisition. The spectral range sampled by the instrument is 290-450 nm, and the bandpass is about 1 nm. The UV irradiances measured at MLO are much more intense than at low altitude midlatitude locations. For example, at a solar zenith angle (SZA) of 45°, the erythermal UV sometimes exceeded 21 mW cm^-2. The larger irradiances are primarily due to the higher altitude at MLO (3.4 km). UV irradiance is strongly correlated (inversely) with total column ozone measurements at MLO, with higher correlations at shorter wavelengths. The radiative amplification factor (RAF) for erythema at MLO is about 1.4 at SZA 45°.

BODHAINE, B.A., E.G. DUTTON, D.J. HOFMANN, R.L. McKenzie, and P.V. Johnston. UV measurements at Mauna Loa: July 1995 to July 1996. Journal of Geophysical Research, 102(D15):19,265-19,273 (1997).

A UV spectroradiometer was installed at Mauna Loa Observatory (MLO), Hawaii, in July 1995. This instrument, based on a commercially available double monochromator, uses a diffuser mounted as a horizontal receptor inside a quartz dome and views the whole sky. The instrument scans over the 290-450 nm spectral range with a band pass of about 1 nm for each 5° of solar zenith angle (SZA). The UV irradiances measured at MLO are much more intense than at low-altitude midlatitude locations. For observations at SZA 45° the erythemally weighted UV irradiances can exceed 21 mW cm^-2, which is approximately 15-20% greater than that seen at Lauder, New Zealand, for similar ozone amounts. The difference is primarily due to the higher altitude at MLO (3.4 km). For overhead Sun conditions at MLO the largest value of erythemal UV was 51.3 ± 3.1 mW cm^-2, which to our knowledge is the highest recorded anywhere on the Earth's surface. UV irradiance is strongly correlated (inversely) with Dobson spectrophotometer total ozone measurements at MLO, with higher correlations at shorter wavelengths. The radiative amplification factor (RAF) for erythema at MLO is about 1.33 ± 0.2 at SZA 45°.

Darlington, J.P.E.C., P.R. Zimmerman, J. Greenberg, C. Westberg, and P. BAKWIN. Production of metabolic gases by nests of the termite Macrotermes jeanneli in Kenya. Journal of Tropical Ecology 13:491-510 (1997).

Nests of a fungus-growing termite Macrotermes jeanneli discharge all their metabolic gases through a single outlet to the atmosphere. This made it possible to measure the production of metabolic gases, and the rates of water loss, for intact nests in the field. Rates of production of carbon dioxide and methane from isolated nest components (different termite castes and intact fungus combs) were measured. Using previously published nest population data and fungus comb weights in relation to nest size, the expected gas production rates for intact nests were calculated. These estimates were compared with direct observations of the gaseous outflow from intact nests. The rates were in reasonable agreement, but some nests emitted excess carbon dioxide, probably produced by respiration of tree roots and non-termite soil organisms. Large nests may have a total gas outflow of 100,000 to 40,000 1 d^-1 including 800 to 1500 1 d^-1 of CO₂ and 0.5 to 1.3 1 d^-1 of CH₄. Nests lose water at the rate of up to 13 1 d^-1 gross, but allowing for ambient humidity the net water loss was up to about 5 1 d^-1. Some of this is metabolic water, but the larger proportion comes from the soil. Area-based estimates of gas production were made for this and two other species of Macrotermes, but they are not accurate because the field distribution and mound density are not adequately known.

DLUGOKENCKY, E.J., K.A. MASARIE, P.P. TANS, T.J. CONWAY, and X. Xiong. Is the amplitude of the methane seasonal cycle changing? Atmospheric Environment 31(1):21-26 (1997).

Twelve years of atmospheric CH₄ data from a globally distributed set of sampling sites ranging in latitude from 82°N to 90°S are analyzed to determine if a statistically significant trend in the peak-to-peak seasonal cycle amplitude exists. Two analysis methods are used. Agreement between amplitude trends determined by the two methods is reasonable. Trends in amplitude determined from sampling sites of similar latitude are not consistent, except in the high southern latitudes, so we focus on the latitude zone 30-90°S, where CH₄ destruction is the primary factor determining the seasonal cycle amplitude. In this high southern hemisphere latitude zone, the trend in seasonal cycle amplitude is not statistically different from zero. Statistical uncertainties in the peak-to-peak seasonal cycle amplitude suggest that the observations are consistent with the change in the amplitude expected due to the increasing burden of atmospheric CH₄, but not with an increase in the globally averaged OH concentration.

DUTTON, E.G., Radiative forcing of El Chichon and Pinatubo eruptions as determined from observations and radiative transfer calculations. IRS’96: Current Problems in Atmospheric Radiation, W.L. Smith and K. Stamnes (eds.), pp. 367-370, Deepak, Hampton, Virginia (1997).

Surface-based observations of irradiance perturbations and the optical properties necessary to compute those perturbations were obtained after the eruptions of both El Chichon and Mt. Pinatubo. Close agreement between the irradiance observations and computations is demonstrated. The maximum global seasonal mean radiative forcing (solar and IR) was computed to be –4.7 W m^-2 after the eruption of Pinatubo and only 2.1 W m^-2 after El Chichon. The temporal and spatial variation in the computed radiative forcing is used in a simple thermal mass model to estimate the evolution of global and hemispheric mean tropospheric cooling.

Emmons, L.K., M.A. Carroll, D.A. Hauglustaine, G.P. Grasseur, C. Atherton, J. Penner, S. Sillman, H. Levy II, F. Rohrer, W.M.F. Wauben, P.F.J. Van Velthoven, Y. Wang, D. Jacob, P. BAKWIN, R. Dickerson, B. Doddridge, C. Gerbig, R. Honrath, G. Hubler, D. Jaffe, Y. Kondo, J.W. Munger, A. Torres, and A. Voltz-Thomas. Climatologies of No_x and No_y: A comparison of data and models. Atmospheric Environment 31(12):1851-1904 (1997).

Climatologies of tropospheric NO_x (NO + NO₂) and No_y (total reactive nitrogen: NO_x + NO₃+ 2 x ₂O₅ + HNO₂ + HNO₃ + HNO₄ + ClONO₂ + PAN peroxyacetylnitrate) + other organic nitrates) have been compiled from data previously published and, in most cases, publicly archived. Emphasis has been on non-urban measurements, including rural and remote ground sites, as well as aircraft data. Although the distribution of data is sparse, a compilation in this manner can begin to provide an understanding of the spatial and temporal distributions of these reactive nitrogen species. The cleanest measurements in the boundary layer are in Alaska, northern Canada, and the eastern Pacific, with median NO mixing ratios below 10 pptv, NO_x below 50 pptv, and No_y below 300 pptv. The highest NO values (greater than 1 ppbv) were found in eastern North America and Europe, with correspondingly high No_y (~5 ppbv). A significantly narrower range of concentrations is seen in the free troposphere, particularly at 3-6 km, with NO typically about 10 pptv in the boreal summer. NO increases with altitude to ~100 pptv at 9-12 km, whereas No_y does not show a trend with altitude, but varies between 100 and 1000 pptv. Decreasing mixing ratios eastward of the Asian and North American continents are seen in all three species at all altitudes. Model-generated climatologies of NO_x and No_y from six chemical transport models are also presented and are compared with observations in the boundary layer and the middle troposphere for summer and winter. These comparisons test our understanding of the chemical and transport processes responsible for these species distributions. Although the model results show differences between them, and disagreement with observations, none are systematically different for all seasons and altitudes. Some of the differences between the observations and model results may likely be attributed to the specific meteorological conditions at the time that measurements were made differing from the model meteorology, which is either climatological flow from GCMs or actual meteorology for an arbitrary year. Differences in emission inventories, and convection and washout schemes in the models will also affect the calculated NO_x and NO₆ distributions.

GELLER, L.W., J.W. ELKINS, J.M. LOBERT, A.D. CLARKE, D.F. HURST, J.H. BUTLER and R.C. MYERS. Tropospheric SF₆: Observed latitudinal distribution and trends, derived emissions, and interhemispheric exchange time. Geophysical Research Letters 24(6):675-678 (1997).

Sulfur hexafluoride (SF₆), an anthropogenically produced compound that is a potent greenhouse gas, has been measured in a number of NOAA CMDL air sampling programs. These include high resolution latitudinal profiles over the Atlantic and Pacific oceans, weekly flask samples from seven remote, globally distributed sites, hourly in situ measurements in rural North Carolina, and a series of archived air samples from Niwot Ridge, Colorado. The observed increase in atmospheric mixing ratio is consistent with an overall quadratic growth rate, at 6.9 ± 0.2% yr^-1 (0.24 ± 0.01 ppt yr^-1) for early 1996. From these data we derive an early 1996 emission rate of 5.9 ± 0.2 Gg SF6 yr^-1 and an interhemispheric exchange time of 1.3 ± 0.1 years.

Hanson, A.D.A., A.V. Polissar, and R.C. SCHNELL. Airborne aerosol and black carbon measurements over the East Siberian Sea, Spring 1992. Atmospheric Research 44:153-165 (1997).

In April 1992 we performed measurements of Arctic aerosol properties from an aircraft flying over the East Siberian Sea from Cherskiy (69°N, 161°E) to Bennett Island (76.5°N, 149°E). Eight round-trip flights were made over this 1000 kilometer path, with each flight incorporating several profiling descents from approximately 4.2 km altitude to the surface. On a 10-second time base were recorded measurements of aerosol black carbon BC), condensation nuclei (CN), air temperature and absolute barometric pressure, from which altitude was deduced. Some profiles showed considerable vertical structure with numerous temperature inversions and stratified aerosol layers. Peak BC and CN concentrations exceeded 1000 ng m^-3 and 1000 cm^-3 respectively. Occasionally, extremely clean air was found in some layers. Other descents showed stable temperature profiles, with aerosol BC and CN distributed throughout the lower 4 km of the atmosphere. In most cases, the surface temperature-inversion layer contained high concentrations of aerosol species. We conclude that the atmosphere in this remote area is strongly affected by anthropogenic emissions from distant source regions, and that the meteorological and aerosol concentration profile structures were similar to those regularly observed in the western sectors of the Arctic in springtime.

HARRIS, J.M. and S.J. OLTMANS. Variations in tropospheric ozone related to transport at American Samoa. Journal of Geophysical Research 102(D7):8781-8791 (1997).

Ten years of isentropic trajectories were summarized using cluster analysis to describe flow patterns for American Samoa. The trajectories were then paired with surface ozone data to determine the dependence of surface ozone on transport. The two main transport regimes affecting surface ozone are trade wind transport, where trajectories show flow bringing ozone from the east in the tropical marine boundary layer, and midlatitude transport, where trajectories show strong westerly flow at higher elevations of southern midlatitudes, followed by descent with anticyclonic curvature. These two transport regimes yield ozone from distinctly different origins, having different mixing ratios. The seasonally changing frequency of transport type is shown to be partly responsible for the seasonal cycle and changes in variability of Samoa surface ozone. On average, 45% of winter ozone variation can be explained by differences in transport type. This strong relationship was absent, however, during 1991 probably because of UV blocking by aerosols from the eruption of Mt. Pinatubo. Reduced total column ozone during winter 1992 may have contributed to this season having the lowest surface ozone levels of the study period.

Harris, N.R.P., G. Ancellet, L. Bishop, D.J HOFMANN, J.B. Kerr, R.D. McPeters, M. Prendez, W.J. Randel, J. Staehelin, B.H. Subbaraya, A. Volz-Thomas, J. Zawodny, and C.S. Zerefos. Trends in stratospheric and free tropospheric ozone. Journal of Geophysical Research 102(D1):1571-1590 (1997).

Current understanding of the long-term ozone trends is described. Of particular concern is an assessment of the quality of the available measurements, both ground and satellite based. Trends in total ozone have been calculated for the ground-based network and the combined data set from the solar backscatter ultraviolet (SBUV) instruments on Nimbus 7 and NOAA 11. At midlatitudes in the northern hemisphere the trends from 1979 to 1994 are significantly negative in all seasons and are larger in winter/spring (up to 7%/decade) than in summer/fall (about 3%/decade). Trends in the southern midlatitudes are also significantly negative in all seasons (3 to 6%/decade), but there is a smaller seasonal variation. In the tropics, trends are slightly negative and at the edge of being significant at the 95% confidence level: these tropical trends are sensitive to the low ozone amounts observed near the end of the record and allowance must also be made for the suspected drift in the satellite calibration. The bulk of the midlatitude loss in the ozone column has taken place at altitudes between 15 and 25 km. There is disagreement on the magnitude of the reduction, with the SAGE I/II record showing trends as large as -20± 8%/decade at 16-17 km and the ozonesondes indicating an average trend of -7± 3%/decade in the northern hemisphere. (All uncertainties given in this paper are two standard errors or 95% confidence limits unless stated otherwise). Recent ozone measurements are described for both Antarctica and the rest of the globe. The sulphate aerosol resulting from the eruption of Mount Pinatubo in 1991 and dynamic phenomena seem to have affected ozone levels, particularly at northern midlatitudes and in the Antarctic vortex. However, the record low values observed were partly caused by the long-term trends and the effect on the calculated trends was less than 1.5%/decade.

HOFMANN, D.J., S.J. OLTMANS, J.M. HARRIS, B.J. JOHNSON, and J.A. LATHROP. Ten years of ozonesonde measurements at the south pole: Implications for recovery of springtime Antarctic ozone. Journal of Geophysical Research 102(D7):8931-8943 (1997).

Ten years of ozonesonde data at the South Pole are used to investigate trends and search for indicators that can be used to detect Antarctic ozone recovery in the future. These data indicate that there have been no systematic winter temperature trends at altitudes of 7- 25 km and thus no expected changes in stratospheric cloud particle surface area, which would affect heterogeneous chemistry. Springtime ozone depletion has been very severe since about 1992, with near-total loss of ozone in the 14- to 18-km region, but has lessened somewhat in 1994 and 1995, probably because of the decay of the sulfate aerosol from the Mount Pinatubo eruption which was present at 10-16 km. Sulfate aerosol particles from the Pinatubo eruption resulted in new ozone depletion in 1992 and 1993 in the 10- to 12-km region where it is too warm for polar stratospheric clouds (PSCs) to form. The volcanic aerosol also augmented depletion related to PSCs at 12-16 km. Although ozone depletion was not as severe in 1995 as in 1993, the depleted region remained intact longer than ever, with record low values throughout December in 1995. Since about 1992, a pseudo-equilibrium seems to have been reached in which springtime ozone depletion, as measured by the total column or the ozone in the 12- to 20-km main stratospheric cloud region, has remained relatively constant. Independent of volcanic aerosol, ozone depletion has extended into the upper altitudes at 22-24 km since about 1992. There is some indication that ozone depletion has also worsened at the bottom of the depletion region at 12-14 km. Extensions of the ozone hole in the vertical dimension are believed to be the result of increases in man-made halogens and not due to changes in particle surface area or dynamics. A quasi-biennial component in the ozone destruction rate in September, especially above 18 km, is believed to be related to variations in the transport of halogen-bearing molecules to the polar region. A number of indicators for recovery of the ozone hole have been identified. They include an end to springtime ozone depletion at 22-24 km, a 12- to 20-km mid-September column ozone loss rate of less than 3 Dobson Units (DU) per day, and a 12- to 20-km ozone column value of more than 70 DU on September 15. It is estimated that if the Montreal protocol and its amendments, banning and/or limiting substances that deplete the ozone layer, is adhered to, recovery of the Antarctic ozone hole may be conclusively detected from the aforementioned changes in the vertical profile of ozone as early as the year 2008. Future volcanic eruptions would affect ozone at 10-16 km, making detection more difficult, but indicators such as depletion in the 22- to 24-km region will be immune to these effects.

HURST, D.F., P.S. BAKWIN, R.C. MYERS, and J.W. ELKINS. Behavior of trace gas mixing ratios on a very tall tower in North Carolina. Journal of Geophysical Research 102(D7):8825-8835 (1997).

We present a 15-month record of mixing ratios of CO, CH₄, N₂O, and eight halogenated gases (CCl₃F, CCl₂F₂, CCl₂FCClF₂, CH₃CCl₃, CCl₄, CHCl₃, C₂Cl₄, and SF₆) at a rural site in eastern North Carolina. The data result from hourly gas chromatographic analyses of air sampled at three heights on a 610-m-tall telecommunications tower during November 1994 through January 1996. At night, most of these gases were more abundant near the ground (51 m) than aloft (496 m) because of the buildup of local and regional surface emissions in the shallow nocturnal stable layer. The abundance and variability of trace gases at this continental site were generally higher than those at similar latitude remote locations. Mixing ratios of most gases were well correlated in polluted air masses occasionally advected to the tower. Frequent, strong enhancements in CHCl₃ at the lower sampling level(s) indicate a local point source(s) of this gas that is not associated with combustion. Temporal trends of regional background mixing ratios at this continental site are, for the most part, in good agreement with recent trends of remote background mixing ratios in the northern hemisphere.

Kahl, J.D.W., D.A. Martinez, H. Kuhns, C.I. Davidson, J.-L. Jaffrezo, and J.M. HARRIS. Air mass trajectories to Summit, Greenland: A 44-year climatology and some episodic events. Journal of Geophysical Research 102(C12):26,861-26,875 (1997).

The seasonal variation in atmospheric transport patterns to Summit, Greenland, is examined using a 44-year record of daily, 10-day, isobaric back trajectories at the 500-hPa level. Over 24,000 modeled trajectories are aggregated into distinct patterns using cluster analysis. Ten-day trajectories reaching Summit are longest during winter, with 67% extending upwind (westward) as far back as Asia or Europe. Trajectories are shortest during summer, with 46% having 10-day origins over North America. During all seasons a small percentage (3-7%) of trajectories originate in west Asia/Europe and follow a meridional path over the Arctic Ocean before approaching Summit from the northwest. Trajectories at the 700-hPa level tend to be shorter than at 500 hPa, with many of the 700-hPa trajectories from North America tracking over the North Atlantic and approaching Summit from the south. The long-range transport climatology for Summit is similar to a year-round climatology prepared for Dye 3, located 900 km to the south [Davidson et al., 1993b]. an analysis of several aerosol species measured at Summit during summer 1994 reveals examples of the usefulness and also the limitations of using long-range air trajectories to interpret chemical data.

Key, J.R., Y. Liu, and R.S. STONE. Development and evaluation of surface shortwave flux parameterizations for use in sea-ice models. Annals of Glaciology 25:33-37 (1997).

The surface radiation budget of the polar regions strongly influences ice growth and melt. Thermodynamic sea-ice models therefore require accurate yet computationally efficient methods of computing radiative fluxes. In this paper a new parameterization of the downwelling shortwave radiation flux at the Arctic surface is developed and compared to a variety of existing schemes. Parameterized fluxes are compared to in situ measurements using data for one year at Barrow, Alaska. Our results show that the new parameterization can estimate the downwelling shortwave flux with mean and root mean square errors of 1 and 5%, respectively, for clear conditions and 5 and 20% for cloudy conditions. The new parameterization offers a unified approach to estimating downwelling shortwave fluxes under clear and cloudy conditions, and is more accurate than existing schemes.

Kley, D., H.G.J. Smit, H. VÖMEL, H. Grassl, V. Ramanathan, P.J. Crutzen, S. Williams, J. Meywerk, and S. J. OLTMANS. Tropospheric water-vapor and ozone cross-sections in a zonal plane over the central equatorial Pacific Ocean. Quarterly Journal of the Royal Meteorological Society 123:2009-2040 (1997).

No abstract.

KOMHYR, W.D., G.C. Reinsel, R.D. EVANS, D.M. QUINCY, R.D. Grass, and R.K. Leonard. Total Ozone Trends at Sixteen NOAA/CMDL and Cooperative Dobson Spectrophotometer Observatories During 1979-1996. Geophysical Research Letters 24(24):3225-3228. (1997).

Ozone trends, derived from 1979-1996 Dobson spectrophotometer total ozone data obtained at five U.S. mainland midlatitude stations, averaged -3.4, -4.9, -2.6, -1.9, and -3.3%/decade for winter, spring, summer, and autumn months, and on an annual basis, respectively. At the lower latitude stations of Mauna Loa and Samoa, corresponding-period annual ozone trends were -0.4 and -1.3%/decade, respectively, while at Huancayo, Peru, the 1979-1991 annual trend was -.9%/decade. A linear trend approximation to ozone changes that occurred since 1978 during austral daylight times at Amundsen-Scott (South Pole) station, Antarctica, yielded a value of -12%/decade. By combining 1979-1996 annual trend data for three U.S. mainland stations with trends for the sites derived from 1963-1978 data, it is estimated that the ozone decrease at U.S. midlatitudes through 1996, relative to ozone present in the mid-1960s, was -6.7%. Similar analyses incorporating South Pole data obtained since 1963 yielded an ozone change at South Pole (daylight observations) through 1996 of approximately -25%. South Pole October total ozone values in 1996 were lower than mid-1960s October ozone values by a factor of two. Trend data are also presented for several shorter record period stations, including the foreign cooperative stations of Haute Provence, France; Lauder, New Zealand; and Perth, Australia.

Le Garrec, J.L., V. Lepage, B.R. Rowe, E.E. FERGUSON. The temperature dependence of the rate constant for O⁺ + NO NO⁺ + O from 23 to 3000 K. Chemical Physics Letters 270:66-70 (1997).

The rate constant, k, for the charge transfer reaction O⁺ + NO --> NO⁺ + O, known to be slow at 300 K (8 10^-13 cm³ s^-1) and to increase with relative kinetic energy (or temperature, T) to 2 10^-10 cm³s^-1 at 3000 K, has been measured down to 23 K. The results show that k also increases at low T (3.2 10-11 cm³s^-1 at 23 K) which is interpreted as being due to the formation of a long-lived complex in which electronic state curve crossings occur.

Levy, H. II, P.S. Kasibhatla, W.J. Moxim, A.A. Klonecki, A.I. Hirsch, S.J. OLTMANS, W.L. Chameides. The global impact of human activity on tropospheric ozone. Geophysical Research Letters 24(7):791-794 (1997).

Within a conceptual framework of stratospheric injection, CO-CH₄ background tropospheric chemistry, parameterized pollution production in the continental boundary layer and surface deposition, we use an 11 level GCTM to simulate global distributions of present and pre-industrial tropospheric O₃. The chemistry is driven by previously simulated present and pre-industrial NO_x fields, while prescribed fields CH₄ and H₂O are held constant. An evaluation with measurements from 12 surface sites, 21 ozonesonde sites, and 1 aircraft campaign finds agreement with 25% for 73% of the observations while identifying systematic errors in the wintertime high-latitude Northern Hemisphere (NH), the Southern Hemisphere (SH) tropics during biomass burning, and the remote SH. We predict that human activity has increased the annual integral of tropospheric ozone by 39% with 3/4's of that increase in the free troposphere, though the boundary layer [BL] annual integral has increased by 66%. The two largest components of the global O₃ budget are stratospheric injection at 695 TgO₃/yr, and loss through dry deposition, which increases from 459 TgO₃/yr to a present level of 825 TgO₃/yr. While tropospheric chemistry's net contribution is relatively small, changing from a pre-industrial destruction of -236 TgO₃/yr to a present production of +128 TgO₃/yr, it is a balance between two much larger terms, -558 TgO₃/yr of destruction in the background troposphere and +686 TgO₃/yr of production in the polluted boundary layer. Human impact on O₃ predominates in the summertime extratropical NH and in the tropics during their biomass burning seasons [increases of 50%-100% or more]. Conversely, there has been little increase in most of the upper troposphere [<20%], where ozone's influence on tropospheric climate is strongest.

LOBERT, J.M., S.A. YVON-LEWIS, J.H. BUTLER, S.A. MONTZKA, and R.C. MYERS. Undersaturation of CH₃Br in the Southern Ocean. Geophysical Research Letters 24(2):171-172 (1997).

Dry mole fractions of methyl bromide (CH₃Br) in marine boundary layer air and in air equilibrated with surface water were measured in the Southern Ocean. Saturation anomalies were consistently negative at -36 ± 7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH₃Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at -21 (-11 to -32) Gg y^-1.

Mc INNES, L., D. Covert, and B. Baker. The number of sea-salt, sulfate, and carbonaceous particles in the marine atmosphere: EM measurements consistent with the ambient size distribution. Tellus 49B:300-313 (1997)

To evaluate the number of sea-salt, sulfate, and carbonaceous particles associated with the fine and coarse mode aerosol in the marine boundary layer and from the marine/continental interface, the elemental composition of individual aerosol particles was determined with EM. Samples were collected from the Pacific marine boundary layer during a research cruise along 140°W from the southern to northern hemisphere, and from a coastal station in NW Washington. Consistently, the most dominant aerosol types found were ammonium sulfate and acidic sulfate comprising 52 to 96% of the total number at a median diameter of 0.14 mm. Sea-salt particles were 4 to 13% of the total number, with modes at 0.2 and 0.6 mm. Carbonaceous particles, mostly as organic compounds, made up the remainder of the submicrometer aerosol at a few % to as much as 31% of the total number for continentally influenced periods. Silica-rich minerals and potassium and calcium salts were observed during such periods, representing a measurable, but small fraction of the total number. Sea-salt particles were 86 to 100% of the number of supermicrometer particles with a mass median diameter of 1.5 mm. A less abundant, and variable fraction of mineral particles made up the remainder of the coarse aerosol number concentration identified primarily as aluminosilicates, mass median diameter of 0.9 mm. Very little soot was observed in either the coarse or fine mode. Particle number concentrations were consistently low and airmass trajectories suggest the air originated over the open ocean for the majority of the sampling periods. Overall, normalized EM distributions agreed fairly well with in-situ measurements of the aerosol size distribution.

Parungo, F., R. SCHNELLl, A. YOSHINAGA, L. PAJO, Y. Kim, C. Zhu, J. HARRIS, B. BODHAINE, X. Li, D. Yang, X. Fang, Z. He, P. Yan, X. Yu, M. Zhou, Z. Chen, F. Qian, K. Park, J. Nam, Y. Iwasaka, and S. Kwon, Asian dust storms and their effects on radiation and climate, Part IV, STC Tech. Report. 3134, 124 pp., Science and Technology Corporation, Hampton, VA, 1997.

No abstract.

Petrov, K.P., S. Waltman, E.J. DLUGOKENCKY, M. Arbore, M.M. Fejer, F.K. Tittel, and L.W. Hollberg. Precise measurement of methane in air using diode-pumped 3.4-mm difference-frequency generation in PPLN. Applied Physics 64:567-572 (1997).

Fast, accurate measurement of the methane mixing ratio in natural air samples using a compact solid-state 3.4-mm difference-frequency spectrometer is reported. The spectrometer employed bulk periodically poled lithium niobate (PPLN) pumped by a solitary diode laser at 808 nm and a diode-pumped monolithic ring Nd:YAG laser at 1064 nm, and a 300 cm³ volume multi-pass absorption cell with an 18-m path length. The methane mixing ratio was determined by comparing the direct optical absorption measured in the sample with that measured in a reference gas at 100 torr and room temperature. Relative accuracy of better than 1 ppb (parts in 10⁹, by mole fraction) was achieved in measurements of natural air that contained 1700-1900 ppb methane. The typical measurement time for each sample was 60 seconds. The accuracy was limited by residual interference fringes in the multi-pass cell that resulted from scattering. Without the use of reference samples, the relative accuracy was 20 ppb; it was limited by the long-term reproducibility of the spectroscopic baseline, which was affected by drift in the optical alignment coupled to changes in the ambient temperature. This work demonstrates the use of diode-pumped difference-frequency generation (DFG) in PPLN in a high-precision infrared spectrometer. Compact, room-temperature solid-state gas sensors can be built based on this technology, for accurate real-time measurements of trace gases in the 3-5 mm spectroscopic region.

RYAN, S.C. The wind field around Mauna Loa derived from surface and balloon observations. Journal of Geophysical Research 102(D9):10,711-10,725 (1997).

The mountain wind field in the vicinity of Mauna Loa Observatory is derived by comparing vertical profiles of wind, ozone, and water vapor in the free troposphere to measurements made at the observatory. The wind field near the surface is described by two components: a radiation wind caused by the diurnal heating and cooling of the mountain slope, and a barrier wind caused by the free tropospheric wind flowing around the mountain barrier. The radiation wind is the primary factor in transporting air from different source altitudes in the free-troposphere to the observatory at 3400 m. At midday, air typically arrives from near the top of the marine boundary layer at 2500 m. After midnight, the average source altitude is 3400 m. The barrier wind field consists of a windward stagnation point, strong cross-slope and downslope flow in the flanks, and moderate downslope flow in the leeward sectors. The barrier wind field is effective at disrupting the surface temperature inversion and the radiation wind at night. A simple model is presented which relates the average properties and statistical variation of these winds to the vertical transport of air from the free troposphere to the observatory by the mountain wind field.

STONE, R.S. Variations in western Arctic temperatures in response to cloud radiative and synoptic-scale influences. Journal of Geophysical Research 102(D18):21,769-21,776 (1997).

The analysis focuses on Barrow, Alaska, a site that is sensitive to changing conditions because it is located near cryospheric boundaries and is influenced by both extratropical and Arctic synoptic activity. Surface and upper air meteorological data for a 31-year period (1965-1995) are used to evaluate temperature variations as they relate to dynamical and radiative processes. Both annual and monthly analyses indicate a tendency toward warming overall. However, the annual warming is not monotonic over time and varies seasonally. Comparisons of temperature time series from four sites along the Siberian-Alaskan coastline show that Barrow is a representative site to evaluate climate change in the western Arctic coastal zone. Regionally, the warming is dominated by significant temperature increases during winter and spring, but cooling is indicated for autumn. These results are not entirely consistent with model predictions of a more uniform high-latitude warming during the cold season in response to increasing concentrations of greenhouse gases in the atmosphere. Rather, the observed changes are attributed to well-known natural processes that affect regional cloud distributions in response to changing circulation patterns. Coincident daily and hourly meteorological and radiation data are also used to demonstrate empirically how clouds modulate Arctic temperatures.

Tuck, A.F., D. Baumgardner, KR. Chan, J.E. Dye, J.W. ELKINS, S.J. Hovde, K.K. Kelly, M. Loewenstein, J.J. Margitan, R.D. May, J.R. Podolske, M.H. Proffitt, K.H. Rosenlof, W.L. Smith, C.R. Webster, and J.C. Wilson. The Brewer-Dobson circulation in the light of high altitude in situ aircraft observations. Quarterly Journal of the Royal Meteorological Society 123(537):1-69 (1997).

Fast response in situ measurements of a suite of chemical species made from the NASA ER2 high altitude aircraft, between 60°N and 70°S at potential temperatures up to 530 K from March to November 1994 at longitudes 115°W to 150°E, are considered for the view they offer of the Brewer-Dobson circulation in the lower stratosphere and upper troposphere. In the southern hemisphere, where most of the flight occurred, comparisons are made with measurements taken in August/September 1987 at longitudes 120°W to 60°W to examine temporal and longitudinal differences. Interpretations made suggest conceptual modifications to the simple construct of advection in a two-dimensional long-term mean.

VOLK, C.M., J.W. ELKINS, D.W. Fahey, G.S. DUTTON, J.M. Gilligan, M. Loewenstein, J.R. Podolske, K.R. Chan, and M.R. Gunson. Evaluation of source gas lifetimes from stratospheric observations. Journal of Geophysical Research 102(D21):25,543-25,564 (1997).

Simultaneous in situ measurements of the long-lived trace species N₂O, CH₄, CFC-12, CFC-113, CFC-11, CCl₄, CH₃CCl₃, H-1211, and SF₆ were made in the lower stratosphere and upper troposphere on board the NASA ER-2 high-altitude aircraft during the 1994 campaign Airborne Southern Hemisphere Ozone Experiment/ Measurements for Assessing the Effects of Stratospheric Aircraft. The observed extratropical tracer abundances exhibit compact mutual correlations that show little interhemispheric difference or seasonal variability except at higher altitudes in southern hemisphere spring. The environmental impact of the measured source gases depends, among other factors, on the rate at which they release ozone-depleting chemicals in the stratosphere, that is, on their stratospheric lifetimes. We calculate the mean age of the air from the SF₆ measurements and show how stratospheric lifetimes of the other species may be derived semiempirically from their observed gradients with respect to mean age at the extratropical tropopause. We also derive independent stratospheric lifetimes using the CFC-11 lifetime and the slopes of the tracer’s correlations with CFC-11. In both cases, we correct for the influence of tropospheric growth on stratospheric tracer gradients using the observed mean age of the air, time series of observed tropospheric abundances, and model-derived estimates of the width of the stratospheric age spectrum. Lifetime results from the two methods are consistent with each other. Our best estimates for stratospheric lifetimes are 122 ± 24 years for N₂O, 93 ± 18 years for CH₄, 87 ± 17 years for CFC-12, 100 ± 32 years for CFC-113, 32 ± 6 years for CCl₄, 34 ± 7 years for CH₃CCl₃, and 24 ± 6 years for H-1211. Most of these estimates are significantly smaller than currently recommended lifetimes, which are based largely on photochemical model calculations. Because the derived stratospheric lifetimes are identical to atmospheric lifetimes for most of the species considered, the shorter lifetimes would imply a faster recovery of the ozone layer following the phaseout of industrial halocarbons than currently predicted.

VÖMEL, H., M. Rummukainen, R. Kivi, J. Karhu, T. Turunen, E. Kyro, J. Rosen, N. Kjome, and S.J. OLTMANS. Dehydration and sedimentation of ice particles in the Arctic stratospheric vortex. Geophysical Research Letters 24(7): 795-798 (1997).

Balloon borne frost-point hygrometers and backscatter sondes were launched at Sodankyla, Finland, in January and February of 1996. These instruments measure water vapor and the backscatter ratio of light due to polar stratospheric clouds in the Arctic stratospheric vortex. Here we report the results of a hygrometer sonde and a backscatter sonde launched within 3.5 hours of each other on January 22/23. Together these soundings show a strong loss of water vapor due to the formation of ice clouds as a result of record cold temperatures in the Arctic stratosphere. The separation of the upper edge of the layer showing water vapor loss and the upper edge of the PSC layer indicates sedimentation of the ice particle layer, possibly leading to a permanent dehydration in the upper part of the layer exhibiting water vapor loss.

Vong, R.J., B.M. Baker, F.J. Brechtel, R.T. Collier, J.M. HARRIS, A.S. Kowalski, N.C. McDonald, and L.M. McINNES. Ionic and trace element composition of cloud water collected on the Olympic Peninsula of Washington State. Atmospheric Environment 31(13):1991-2001 (1997).

Field measurements of the chemical composition of boundary-layer clouds that formed in clean, marine air are presented as a background reference point for comparison to cloud water composition in more polluted regions. An impaction-based sampler was used to simultaneously collect cloud water on two stages, where the ratio of droplet diameter was ~1.1 for the two droplet size fractions. Analysis revealed that large droplets were more concentrated than smaller cloud droplets by a factor of 1.5 for sea-salt-derived species. Cloud water concentrations of ionic species were generally five times greater the concentrations of the same ions in rain water. Aqueous-phase solute concentrations in cloud varied over two orders of magnitude but generally were quite low, correlated to each other and to aerosol (CN) concentration, but negatively correlated to LWC. Air-equivalent solute concentrations were calculated, allowing the detection of the influence of air-mass trajectory on cloud-water composition. A multivariate statistical analysis of the cloud water data suggested sea salt, biogenic, crustal, and anthropogenic emission source contributions; the last two sources existed only for continental air-mass trajectories. Coastal and oceanic trajectories were selected for the purpose of estimating a northern hemisphere, midlatitude, marine, background cloud water composition of 8 neq m^-3 non-sea salt SO₄^2- and 4 neq m^-3 NO₃^-.

Waugh, D.W., T.M. Hall, W.J. Randel, P.J. Rasch, B.A. Boville, K.A. Boering, S.C. Wofsy, B.C., Daube, J.W. ELKINS, D.W. Fahey, G.S. DUTTON, C.M. VOLK, and P.F. Vohralik. Three-dimensional simulations of long-lived tracers using winds from MACCM2. Journal of Geophysical Research 102(D17): 21,493-21,513 (1997).

Three-dimensional simulations of the stratospheric constituents CH₄, N₂O, O₃, SF₆, and CO₂ over annual cycle have been performed using a semi-Lagrangian chemical transport model [Rasch and Williamson, 1990; Rasch et al., 1994] driven by archived wind data from the Middle Atmosphere version of the National Center for Atmospheric Research Community Climate Model version 2 (MACCM2) general circulation model. The constituents undergo chemical production and loss at rates calculated by two-dimensional photochemical models. We compare these "off-line" simulations of CH₄ and N₂O with "on-line" simulations in which the trace constituent distributions are computed interactively within the MACCM2 general circulation model and find good agreement even when daily averaged wind data and no subgrid scale parameterized mixing are used in the off-line simulations. We also compare the model simulations to satellite, aircraft, and balloon measurements. In most regions and seasons, the zonally averaged model CH₄, N₂O, and O₃ field agree well with observations. Notable discrepancies are (1) a lack of a "double peak" structure in the zonally averaged mixing ratios of model CH₄ and N₂O at equinox, (2) an overall underestimate of CH₄ and N₂O in the upper stratosphere, and (3) an underestimate of the height of the mixing ratio peak in O₃, particularly at high latitudes. We find good agreement between modeled CO₂ and SF₆ and recent aircraft observations in the lower stratosphere, and balloon measurements in the lower and middle stratosphere. From the SF₆ distribution we determine the mean age of air in the model stratosphere, with values as old as 10 years in the wintertime polar upper stratosphere. In addition, we simulate the annual cycle of CO₂, a stringent test of model transport, which supplements the mean age. We obtain good agreement with aircraft measurements in phase and magnitude at the tropical tropopause, and the vertical profiles of CO₂ are similar to those observed. However, the amplitude of the cycle attenuates too rapidly with height in the model stratosphere, suggesting the influence of midlatitude air and/or the vertical diffusion are too large in the model tropics.

Waugh, D.W., R.A. Plumb, J.W. ELKINS, D.W. Fahey, K.A. Boering, G.S. DUTTON, C.M. VOLK, E. Keim, R.-S. Gao, B.C. Daube, S.C. Wofsy, M. Loewenstein, J.R. Podolske, K.R. Chan, M.H. Proffitt, K.K. Kelly, P.A. Newman, and L.R. Lait. Mixing of polar vortex air into middle latitudes as revealed by tracer-tracer scatterplots. Journal of Geophysical Research 102(D11):13,119-13,134 (1997).

The occurrence of mixing of polar vortex air with midlatitude air is investigated by examining the scatter plots of in situ measurements of long-lived tracers from the NASA ER-2 aircraft during the Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE, April, May 1993; northern hemisphere) and the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA, March-October 1994; southern hemisphere) campaigns. The tracer-trace scatter plots from SPADE form correlation curves which differ from those measured during previous aircraft campaigns (Airborne Antarctic Ozone Experiment (AAOE), Airborne Arctic Stratospheric Experiments I (AASE I) and II (AASE II). It is argued that these anomalous linear correlation curves are "mixing lines" resulting from the recent mixing of polar vortex air into the middle latitude environment. Further support for this mixing scenario is provided by contour advection calculations and calculations with a simple one-dimensional strain-diffusion model. The scatter plots from the midwinter deployments of ASHOE/MAESA are consistent with those from previous midwinter measurements (i.e., no mixing lines), but the spring CO₂:N₂O scatter plots form altitude-dependent mixing lines which indicate that air from the vortex edge region (but not from the inner vortex) is mixing with midlatitude air during this period. These results suggest that at altitudes above about 16 km the mixing of polar vortex air into middle latitudes varies with season: in northern and southern midwinter this mixing rarely occurs, in southern spring mixing of vortex-edge air occurs, and after the vortex breakup mixing of inner vortex air occurs.

YVON-LEWIS, S.A., and J.H. BUTLER. The potential effect of oceanic biological degradation on the lifetime of atmospheric CH₃Br. Geophysical Research Letters 24(10):1227-1230 (1997).

We use a global, coupled, ocean-atmosphere box model to examine the potential effect that biological degradation and its distribution can have on the lifetime of atmospheric CH₃Br. The results of this study show that both the value of the oceanic degradation rate constant and its geographic distribution are important in determining the calculated atmospheric lifetime. The best estimate of the partial lifetime of atmospheric CH₃Br with respect to oceanic loss now comes to 1.8-1.9 y with a full possible range of 1.1-3.9 y, which, together with other, non-oceanic losses, yields a total atmospheric lifetime of 0.7 y (0.6-0.9 y). A subsequent revision of the budget for atmospheric CH₃Br indicates that estimated sinks of CH₃Br today exceed estimated sources by about 70 Gg y^-1.

ZHAO, C.L., P.S. BAKWIN, and P.P. TANS. A design for unattended monitoring of carbon dioxide on a very tall tower. Journal of Atmospheric and Oceanic Technology 14:1139-1145 (1997).

Unattended measurements of carbon dioxide (CO₂) mixing ratio at three altitudes up to 496 m above the surface on a television transmitter tower in the southeastern United States have been made for a period of 4 yr. This report describes the design of the automatic tower measuring system in detail. A nondispersive infrared (NDIR) analyzer is used to measure the CO₂ concentration continuously. Real-time control and data collection uses a PC 486 running under the multitasking operating system QNX. The CO₂ data show strong diurnal and seasonal variations, and large vertical gradients. A comparison of this study’s continental tower data with data from "background" sites should provide a strong constraint for regional and global models of terrestrial CO₂ fluxes.

ZHAO, C.L. and P.S. BAKWIN. Data acquisition and control system for measurements of carbon dioxide on WITN tower. NOAA Technical Memorandum ERL CMDL 13 NOAA Environmental Research Laboratories, Boulder, CO, 24 pp. (1997).

The design of an automatic tower measuring system mounted on a television transmitter tower in the southeastern United States is described in detail. We use NDIR Li-Cor 6251 analyzers for unattended, continuous measurements of carbon dioxide (CO₂) mixing ratio at three altitudes up to 496 m above the surface. Real-time control and data collection uses a 486 PC running under the multi-tasking operating system QNX. The CO₂ data show strong diurnal and seasonal variations and large vertical gradients. Comparison of our continental tower data with data from "background" sites should provide a strong constraint for regional and global models of terrestrial CO₂ fluxes.

ZHAO, C.L., P.P. TANS, and K.W. THONING. A high precision manometric system for absolute calibrations of CO₂ in dry air. Journal of Geophysical Research 102(D5):5885-5894 (1997).

A high-precision manometric system has been developed for absolute calibrations of CO₂-in-air mixture gas. This report describes the principle of the calibration method and evaluates the performance of the manometric apparatus. The test results show that the reproducibility of the manometric system for calibrating CO₂-in-air gas mixtures is within 0.1 mol mol^-1 in the atmospheric CO₂ concentration range of 300 to 400 mol mol^-1. Preliminary measurements indicate that the agreement with the absolute World Meteorological Organization mole fraction scale, widely used for atmospheric CO₂ monitoring, is also within 0.1 mol mol^-1 in that same range.

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