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BODHAINE, B.A., L.A. Barrie, R.C. SCHNELL, G.E. Shaw, and J.K. McKie. Symposium on the tropospheric chemistry of the Antarctic Region. Tellus 44B:250-251 (1992).

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BODHAINE, B.A. The U.S. aerosol monitoring program in Antarctica. Proceedings, 4th Workshop Italian Research on Antarctic Atmosphere, Porano, Italy, October 21-23, 1991. Italian Physical Society, Bologna, Italy, 15-25 (1992).

The Climate Monitoring and Diagnostics Laboratory (CMDL) of the National Oceanic and Atmospheric Administration (NOAA) operates an atmospheric monitoring observatory at Amundsen-Scott Station, South Pole. Long-term measurements of carbon dioxide, ozone, aerosols, and other background pollutants are obtained to understand their possible effects on the earth's climate. The aerosol measurement program consists of the continuous measurement of condensation nucleus (CN) concentration and aerosol scattering extinction coefficient (s_sp). A nearly continuous record of CN measurements from 1974 to the present, and s_sp measurements from 1979 to the present, has been acquired. The CN data show an annual cycle with a maximum exceeding 100 cm^-3 in the austral summer and a minimum of about 10 cm^-3 in the winter. The s_sp data show an annual cycle markedly different from that of CN, with a maximum in the late winter, a secondary maximum in summer, and a minimum in May. Angstrom exponents calculated from the multiwavelength s_sp data show a strong annual cycle suggesting larger particles in the winter than in the summer. The Symposium on the Tropospheric Chemistry of the Antarctic Region was held during June 3-6, 1991, in Boulder, Colorado. In conjunction with this meeting, a workshop was held to assess the state of Antarctic research and to provide recommendations for future research.

BODHAINE, B.A., and J.M. HARRIS. Aerosol measurements at the South Pole during 1987. NOAA DR ERL CMDL-9 120 pp. (1992).

The Climate Monitoring and Diagnostics Laboratory (CMDL) of the National Oceanic and Atmospheric Administration (NOAA) operates an atmospheric monitoring observatory at Amundsen-Scott Station, South Pole. The aerosol measurement program consists of the continuous measurement of condensation nuclei (CN) concentration and aerosol scattering extinction coefficient (s_sp). During 1987, a special aerosol experiment was conducted that included filter samples for subsequent analysis by the proton induced x-ray emission (PIXE) technique, diffusion battery measurements for size information in the sub-0.1 mm size range, and aerosol absorption measurements using an aethalomter. Surface and upper air meteorological data were also available. The purpose of this report is to present all of the aerosol data obtained during 1987.

BODHAINE, B.A., J.M. HARRIS, J.A. OGREN, and D.J. HOFMANN. Aerosol optical properties at Mauna Loa Observatory: Long-range transport from Kuwait? Geophysical Research Letters 19(6): 581-584 (1992).

Aerosol light absorption has been measured continuously at Mauna Loa Observatory, Hawaii (MLO), since April 1990. During the spring of 1991, after oil wells were fired in Kuwait, there was speculation among scientists concerning long-range transport of smoke particles and its possible effect on global climate. The MLO light absorption record from April 1990 to June 1991 shows low values in the 0.1 ´ 10^-7 m^-1 range in the summer of 1990, and an increased baseline level of about 2-4 ´ 10^-7 m^-1 with numerous superimposed events in the 5-10 ´ 10^-7 m^-1 under range in the spring of 1991. These levels correspond to black carbon (BC) concentrations of 1-10, 20-40, and 50-100 ng m^-3, respectively, under the assumption that BC is the dominant light absorbing species and has a specific absorption of 10 m² g^-1. Large-scale 500-hPa trajectories calculated backwards from MLO sometimes show direct transport paths from China and Kuwait to Hawaii that coincide with the back carbon events. Those measurements set an upper limit on the possible contribution of Kuwait black carbon to the background troposphere near MLO during long periods of rapid transport. The aerosol observed at MLO is expected to cause a net cooling of the atmosphere.

Bradley, R.S., F.T. Keimig, and H.F. DIAZ. Climatology of surface-based inversions in the North American Arctic. Journal of Geophysical Research 97(D14):15,699-15,712 (1992).

The annual cycle of surface-based inversions at nine Arctic weather stations is examined, based on a 20-year set of daily 1200 UT significant level radiosonde data. All stations are at or near the coast. Inversions in winter months are primarily the result of strongly negative net radiation at the surface, whereas in summer, inversions more commonly result from near-surface cooling of warm air masses. Inversion frequency is at a maximum in winter (generally >70% of days) when inversions range from 400 to 850 m in thickness. Inversion thickness and strength (temperature change across the inversion) are strongly related to surface temperature. Inversions may involve temperature changes of >30C in <1 km, with gradients of >6C 100 m-1 during periods of extreme warm air advection aloft. Midwinter inversions commonly persist for 2-4 days, but may remain undisturbed for several weeks, affecting lower tropospheric chemistry.

BUTLER, J.H., J.W. ELKINS, B.D. HALL, S.O. CUMMINGS, and S.A. MONTZKA. A decrease in the growth rates of atmospheric halon concentrations. Nature 359:403-405 (1992).

Halons H-1301 (CBrF3) and H-1211 (CBrClF2) have been introduced into the atmosphere, mainly through use in fire extinguishers, for almost three decades. Although each is now present in the troposphere at a concentration of only 2 parts per 1012, these gases have long atmospheric lifetimes (65-77 yr for H1301 and 11-16 yr for H-1211) and carry significant amounts of bromine to the stratosphere, where it can destroy ozone catalytically. For this reason, the halons have high ozone depletion potentials. The manufacture of both gases is to be discontinued globally by the year 2000, according to the Montreal Protocol, and perhaps sooner, as a result of unilateral action by users, manufacturers and producing countries. Here we present a six-year record of tropospheric halon mixing ratios which shows that the growth rates of H-1301 and H-1211 have already begun to decrease substantially. This recent decrease in growth rates is consistent with industry emission estimates (although these have greater uncertainties), and supports current appraisals of atmospheric lifetimes. Our results suggest that, even though these halons are relatively long-lived species, their atmospheric mixing ratios may stabilize or begin to decrease within the next few years.

Cantrell, C.A., J.A. Lind, R.E. Shetter, J.G. Calvert, P.D. Goldan, W. Kuster, F.C. Fehsenfeld, S.A. MONTZKA, D.D. Parish, E.J. Williams, M.P. Buhr, H.H. Westberg, G. Allwine, and R. Martin. Peroxy radicals in the ROSE experiment: Measurement and theory. Journal of Geophysical Research 97(D18):20,671-20,686 (1992).

The concentration of the HO₂-RO₂ species measured during July 11, 1990, in the ROSE (Rural Oxidants in the Southern Environment) study in Alabama are compared to those expected from theory from calculations based upon detailed hourly measurements of a variety of trace gases including the hydrocarbons, NO, NO₂, carbonyl compounds, CO, PAN (peroxyacetylnitrate) and calculated jO3 values. The measurements are also compared with the [HO₂] + [RO₂] as estimated from deviations from the NO₂ + hv (+O₂) NO + O₃ photostationary state. Within the error of the measurements all of the data appear to be in reasonable accord.

DELUISI, J.J., K. Dehne, R. Vogt, T. Konzelmann, and A. Ohmura. First results of the baseline surface radiation network (BSRN) broadband infrared radiometer intercomparison at Fire II. IRS '92 S. Keevallik and O. K�rner (eds.). Deepak, Hampton, VA, 559-564 (1992).

An intercomparison of seventeen broadband radiometers was conducted in parallel with the FIRE II field experiment at Coffeyville, Kansas, November 13 -December 7, 1991. The objective of this experiment was to determine the best method for measuring broadband irradiance by intercomparing instruments of different construction and by comparing measurements with the results of the SPECTRE. This paper describes preliminary results derived from a subset of the instruments participating in the intercomparison.

DIAZ, H.F., and G.N. KILADIS. Atmospheric teleconnections associated with the extreme phases of the Southern Oscillation. ,I>El Ni�o: Historical and Paleoclimatic Aspects of the Southern Oscillation H.G. Diaz and V. Markgraf (eds.). University Press, Cambridge, 7-28 (1992).

An overview is presented of the principal climatic characteristics associated with the development of warm and cold phases of the ocean-atmospheric phenomenon known as El Ni�o/Southern Oscillation (ENSO), and of the most salient large-scale teleconnection features related to those extremes. Besides giving the reader some appreciation of the typical climatic patterns in different parts of the globe during the extreme ENSO phases, we have made an effort to illustrate some of the event-to-event variability inherent in various climatic indices associated with this phenomenon. ENSO is not a stationary system; there are substantial differences between events that are reflected in a variety of ENSO indices. It is shown that even for a particular set of ENSO measures, the association among such indices may vary with time. It is important to keep this in mind when analyzing long-term associations with individual proxy variables of ENSO activity, such as tropical coral or glacier varves.

DIAZ, H.F., and R.S. PULWARTY. A comparison of Southern Oscillation and El Ni�o signals in the tropics. In El Ni�o: Historical and Paleoclimatic Aspects of the Southern Oscillation H.G. Diaz and V. Markgraf (eds.). University Press, Cambridge, 175-192 (1992).

A contingency table and spectral analysis of the El Ni�o and Nile River flood event records compiled by W. Quinn and colleages is performed. The purpose of this study is to assess and compare the long-term variance charateristics of these two measures of the El Ni�o/Southern Oscillation (ENSO) phenomenon. Several other modern indices of ENSO are also examined, such as sea-surface temperature in the upwelling regions of the eastern equatorial Pacific, the Tahiti-Darwin sea-level pressure index, and rainfall in the normally dry areas of the central equatorial Pacific. Consistent with previous studies of long-term variations in El Ni�o development in relation to the occurrence of SOI-negative episodes, it was found that the relative timing of these two manifestations of the ENSO system have varied in relation to one another over the past century. Another important feature of changes in the El Ni�o system is the fact that the spectral signature of El Ni�o event data shows a concentration of variance within relatively narrow bands at both short and long time scales. Relatively rapid transitions have occurred in the frequency of occurrence of El Ni�o events since the mid-16th century. A comparison of the El Ni�o and Nile River flood event record shows strong similarities, but also some differences. Over the common period 1821 to 1941, one difference noted is that return intervals for Nile flood deficit (all categories) are longer than those of moderate and stronger El Ni�o events. For the two strongest event categories, the first half of the common record has very nearly the same return period, whereas for the second half, the return interval for strong and very strong El Ni�os has been about twice as long as that for severe (categories 3 and 4) Nile flood deficits. Nevertheless, as a measure of the long-term variability of the greater ENSO system, the Nile flood intensity record compared by Quinn (this volume) represents a very useful contribution to ENSO studies.

DIAZ, H.F., K. WOLTER, and S.D. WOODRUFF (eds.). Proceedings, International COADS Workshop Boulder, CO, January 13-15, 1992. NOAA ERL Climate Research Division, Boulder, 390 pp. (1992).

This volume constitutes the proceedings of an international workshop held January 13-15, 1992, in Boulder, Colorado. The workshop was organized to provide a forum for user feedback and evaluation of the Comprehensive Ocean-Atmosphere Data Set (COADS), and to help guide future development of the data set. COADS was assembled in the U.S. and is the most complete historical record of surface marine weather observations now available. The data set, composed primarily of worldwide international ship observations, presently covers the period 1854-1991, and therefore represents a critical resource for studies of long-term climate change. A compilation of scientific papers and technical material presented or contributed to the workshop is provided. A summary of the most salient finds presented at the workshop is given, together with a synthesis of key recommendations made to assist in updating and improving the data set.

DUTTON, E.G. A coherence between the QBO and the amplitude of the Mauna Loa atmospheric transmission annual cycle. International Journal of Climatology 12:383-396 (1992).

The transmission of direct solar radiation through the atmosphere above Mauna Loa, Hawaii, is shown to have a quasi-biennial cyclic component that is coherent with the well-known tropical stratospheric quasi-biennial oscillation (QBO). The QBO-related signal in the 32-year transmission record is manifested as an oscillation in the amplitude of the annual cycle. The transmission annual cycle is known to be caused by seasonal transport of Asian continental dust to and over the island of Hawaii. Variations in water vapor and ozone are eliminated as possible influences in the transmission-QBO relationship, leaving aerosols as the source of the oscillation. The ultimate cause for the quasi-biennial signal in the transmission record is unknown. Small but cyclic modifications to the tropospheric energy budget occur as a result of the transmission variations. The magnitude of the energy budget variations are less than those typically expected to have a significant climatic impact.

DUTTON, E.G., and J.R. Christy. Solar radiative forcing at selected locations and evidence for global lower tropospheric cooling following the eruptions of El Chichon and Pinatubo. Geophysical Research Letters 19(23):2313-2316 (1992).

As a result of the eruption of Mt. Pinatubo (June 1991), direct solar radiation was observed to decrease by as much as 25-30% at four remote locations widely distributed in latitude. The average total aerosol optical depth for the first 10 months after the Pinatubo eruption at those sites is 1.7 times greater than that observed following the 1982 eruption of El Chichon. Monthly-mean clear-sky total solar irradiance at Mauna Loa, Hawaii, decreased by a much as 5% and averaged 2.4% and 2.7% in the first 10 months after the El Chichon and the Pinatubo eruptions, respectively. By September 1992 the global and northern hemispheric lower tropospheric temperatures had decreased by 0.5C and 0.7C, respectively compared to pre-Pinatubo levels. The temperature record examined consists of globally uniform observations from satellite microwave sounding units.

Facchini, M.C., S. Fuzzi, M. Kessel, W. Wobrock, W. Jaeschke, B.G. Arends, J.J. M�ls, A. Berner, I. Solly, C. Kruisz, G. Reischl, S. Pahl, A. Hallberg, J.A. OGREN, H. Fierlinger-Oberlinninger, A. Marzorati, and D. Schell. The chemistry of sulfur and nitrogen species in a fog systema multiphase approach. Tellus 44B:505-521 (1992).

Concentration and phase distribution of sulfur and nitrogen species during a particular fog episode in the Po Valley are experimentally described in this paper. Chemical measurements were carried out simultaneously at different heights within the fog layer, up to 50 m. Microphysical and meteorological parameters necessary for the description of the fog multiphase system were also concurrently measured as a function of height. The fog cycle (formation, evolution, dissipation) is described in terms of the total acidity of a unit volume of air containing gas species, interstitial aerosol particles and fog droplets. The fog system was not closed and input of acidic and basic components was observed during fog evolution. The driving force which determines the acidity of the fog multiphase atmospheric system was found to be the presence of NH₃ and its partitioning among the different phases. A strong decrease of fog water pH (from 5.6 down to 2.8) was observed during fog evolution and was attributed to a HNO₃ input to the system. These acidic and basic inputs are described in terms of a titration/back-titration process of the fog system. The SO₂ oxidation process in fog water was found to be of minor importance in determining the concentration within the fog system, due to both low SO₂ concentration and limited oxidant availability during the experiment.

FERGUSON, E.E., J.M. Van Doren, A.A. Viggiano, R.A. Morris, J.F. Paulson, J.D. Stewart, L.S. Sunderlin, and P.B. Armentrout. Internal and translational energy effect on the charge-transfer reaction of CO₂⁺ with O₂. International Journal of Mass Spectrometry and Ion Processes 117:261-282 (1992).

We have investigated the reaction of CO₂⁺ with O₂ over a range of kinetic energies with a guided ion beam apparatus and over a range of temperatures and kinetic energies with a variable-temperature selected-ion flow drift tube. The rate constants decrease with increasing kinetic energy at low energy and increase at higher energy. Below about 10cV, reaction proceeds by charge transfer only. Above 10cV, O+ and CO+ product ions are observed in addition to the charge-transfer channel. At low energy, i.e. below 0.1cV, the rate constants at a particular center-of-mass kinetic energy, <KE_cm>, do not depend on the temperature of the buffer gas. This indicates that energy in rotations and in the bending vibrational modes does not play a major role in determining reactivity. Above 0.1 eV, the rate constants at a particular <KE_cm> do depend on temperature, such that the higher the buffer gas temperature the larger the rate constants. Analysis of the data suggests that the enhancement observed with temperature is primarily due to excitation of the CO₂⁺ stretching vibrational mode. The analysis indicates that excitation of the CO₂⁺ stretching modes increases the rate constant by approximately an order of magnitude. Excitation of bending vibrations may also enhance the efficiency of charge transfer above 0.2eV. Translational energy causes a small increase in the charge-transfer rate constant above 0.3cV.

Foster, J.L., J.W. Winchester, and E.G. DUTTON. The date of snow disappearance on the Arctic tundra as determined from satellite, meteorological station and radiometric in situ observations. IEEE Transactions on Geoscience and Remote Sensing 30(4):793-798 (1992).

In this study satellite-derived snow cover maps for sites in Alaska, Canada, Scandinavia, and Siberia were employed to assess the date when snow disappeared on the Arctic tundra and to determine if the snow has been melting earlier in the spring in more recent years. Results show that for three of the four sites there has been a tendency toward earlier snowmelt during the 1980's. In Alaska, the satellite-derived date of snowmelt was compared to the date of snowmelt as observed at the Barrow meteorological station and a site near Barrow where radiometric in situ measurements were made for the last 5 years. The three data sources complement each other even though the satellite site is located 150 km from Barrow. One mechanism which could cause a trend toward earlier snowmelt in Alaska is the deposition of soot and particulates on the snow surface as a result of Arctic haze.

Friedman, I., G.I. Smith, J.D. Gleason, A. Warden, and J. HARRIS. Stable isotope composition of waters in Southeastern California 1. Modern precipitation. Journal of Geophysical Research 97(D5):5795-5812 (1992).

Over a 7-year period from April 1982 to April 1989, integrated samples of rain and snow were collected at 32 sites by oil-sealed storage gage stations in (and adjoining) the southeast California desert; station elevations ranged from �65 m to 2280 m, and the collection network covered an area measuring about 400 km in each dimension. Deuterium (dD) analysis of 406 samples shows that the average dD of summer precipitation was �56 per mil (�), whereas winter values averaged �78�, averaged annual values were close to �69� because most of the area is in a winter-dominated precipitation regime. We found no correlation between wetness or dryness of a season and the dD of its precipitation. The d¹⁸ O versus dD plots show that rain samples define a line of slope 6.5, less than the 8 of the Meteoric Water Line, whereas snow samples define a line of slope 9.2. These differences in slope are the result of isotopic fractionation which occurred during evaporation of raindrops but not during sublimation of snow. Trajectory plots of 68 of the major storm events show that all of the winter storms originated in the Pacific, and passed over high mountains before reaching our collection stations. However, 21 of the 30 summer storms had trajectories that originated either over the Gulf of Mexico or the subtropical Pacific and traveled either west or north to reach our stations without traversing high mountains. The difference in dD between winter and summer precipitation is due to different air flow patterns during those seasons.

Fuzzi, S., C. Facchini, G. Orsi, J.A. Lind, W. Wobrock, M. Kesel, R. Maser, W. Jaeschke, B.G. Arends, A. Berner, I. Solly, C. Kruisz, G. Reischl, U. Kaminski, P. Winkler, J.A. OGREN, A. Hallberg, H. Fierlinger-Oberlinninger, H. Puxbaum, A. Marzorati, H.-C. Hansson, A. Wiedensohler, I.B. Svenningsson, B.G. Martinsson, d. Schell, and H.W. Georgii. The Po Valley fog experiment 1989: An overview. Tellus 44B:448-468 (1992).

An outline is presented here of the Po Valley Fog Experiment 1989, carried out within the EUROTRAC-GCE project. This experiment is a joint effort by several European research groups from five countries. The physical and chemical behavior of the fog multiphase system was studied experimentally following the temporal evolution of the relevant chemical species in the different phases (gas, droplet, interstitial aerosol) and the evolution of micrometeorological and microphysical conditions, from the pre-fog situation through the whole fog evolution, to the post-fog period. Some general results, useful for describing the general features of the fog system, are presented here, while specific scientific questions on the different processes taking place within the system itself will be addressed in other companion papers of this same issue.

GILLETTE, D.A., B.A. BODHAINE, and D. Mackinnon. Transport and deposition of desert dust in the Kafirnigan River Valley (Tadzhikistan) from Shaartuz to Esanbay: Measurements and a simple model. Atmospheric Environment 27A(16):2545-2552 (1993).

A model of deposition and transport was constructed for the Kafirnigan Valley, in Soviet Central Asia. Data, consisting of deposition measurements at Shaartuz, atmospheric columnar mass, aerosol concentrations, wind speed, optical scattering, and movement of soil, were collected for the dust storms of 16 and 20 September 1989. Results from the model were compared with measurements of total atmospheric columnar mass loading for the dust storm of 16 September. Although sensitivity of the model to dust layer height does not recommend the model for general use, the model has some merit in predicting transport and deposition for dust contained in a river valley.

Hallberg, A., J.A. OGREN, K.J. Noone, J. Heintzenberg, A. Berner, I. Solly, C. Kruisz, G. Reeischl, S. Fuzzi, C. Facchini, H.-C. Hansson, A. Wiedensohler, and I.B. Svenningsson. Phase partitioning for different aerosol species in fog. Tellus 44B:545-555 (1992).

Simultaneous measurements of several non-volatile species in unscavenged aerosol particles and in fog droplets have revealed differences in partitioning for different chemical species. The average scavenged fraction of sulfate was 18% and the corresponding fraction of elemental carbon was only 6%. This suggests that the aerosol was externally mixed, and that the chemical mixture of the aerosol as a function of size is important in the context of nucleation scavenging. The measurements obtained could not distinguish between the two primary hypotheses for explaining the observed differences, (a) that the particles had the same size distribution and their chemical composition was the controlling factor, and (b) that the elemental carbon was associated with smaller particles than the sulfate, so that the difference in scavenging efficiency was controlled by the size distribution of the particles.

HARRIS, J.M. An analysis of 5-day midtropospheric flow patterns for the South Pole: 1985-1989. Tellus 44B:409-421 (1992).

An analysis of 5-day midtropospheric flow patterns for the South Pole during 1985-1989 is presented. Cluster analysis was used to summarize trajectories by year and by month. The results indicate that flow from the east was most often anticyclonic and light, occuring 8-18% of the time. Westerly flow patterns were the strongest and most frequent (37-51% occurrence). They were consistently cyclonic, usually reflecting storms in the Ross Sea area, the average center of the curcumpolar vortex. Strong northerly flow occurred more often in 1987 that in other years. Year-to-year variability was also evident in southwesterly flow, which was enhanced in 1988, and weaker in 1987, compared with other years. The lightest winds over the South Pole occur during January, while the most vigorous long-range transport to South Pole occurs from July through October. Selected isentropic trajectories were examined to determine errors inherent in the isobaric estimates. Isentropic trajectories from the east showed little vertical motion and good agreement with isobaric ones. Over west Antartica, however, isentropic trajectories consistently showed positive vertical motion. As a result, their isobaric counterparts were too long and overestimated the cyclonic curvature in the flow. Preferred transport from the west with warm air advection results from the circumpolar vortex being asymmetrical, and the average isotherms, though roughly circular, being offset to the east of the South Pole.

HARRIS, J.M., P.P. TANS, E.J. DLUGOKENCKY, K.A. MASARIE, P.M. LANG, S. Whittlestone, and L.P. Steele. Variations in the atmospheric methane at Mauna Loa Observatory related to long-range transport. Journal of Geophysical Research 97(D5):6003-6010 (1992).

Methane measurements, radon measurements, and air mass trajectories calculated for Mauna Loa Observatory (MLO) are examined to determine relationships among methane source/sink regions, flow patterns for MLO, and methane variations on the synoptic-to-seasonal scale. We present evidence that the methane seasonal cycle observed at MLO is in large part driven by seasonal variations in transport. Furthermore, the variability in methane mixing ratio at MLO is higher in winter than in summer because of greater variability in flow patterns. Ten-day back trajectories are classified according to wind speed and direction using cluster analysis to determine six typical transport regimes. The methane data are then grouped according to transport cluster. The median methane mixing ratio corresponding to tradewind flow was 17.2 ppbv (parts per billion by volume) lower than that corresponding to strong westerly flow. This difference is attributed to transport from source/sink regions, flow across the methane latitudinal gradient, and seasonality of flow patterns. Case studies utilizing individual trajectories and radon measurements to determine probable air parcel origins illustrate the effects of long-range transport on the methane mixing ratio at MLO. Changes in flow pattern from sink to source origins can result in a 50 ppbv rise in methane mixing ratio over a period of a few days. During winter, alternation of westerly winds, tradewinds and anticyclonically curving flows contribute to the large variability in the methane mixing ratio. During summer this variability is reduced with the cessation of strong westerly flows from methane source regions. In July and August, air parcels originate far from methane source regions and in the area of highest modeled OH concentration. At the same time, methane mixing ratios decrease to the lowest values for the year. In this way, the seasonality of flow patterns exerts a major influence on the observed seasonal cycle of methane at MLO.

Harriss, R.C., G.W. Sachse, G.F. Hill, L. Wade, K.B. Bartlett, J.E. Collins, L.P. STEELE, and P.C. NOVELLI. Carbon monoxide and methane in the North American Arctic and subarctic troposphere: July-August 1988. Journal of Geophysical Research 97(D15):16,589-16,599 (1992).

Measurements of carbon monoxide (CO) and methane (CH₄) were made in the North American Arctic during JulyAugust 1988. The distribution of CH₄ was variable in the atmospheric mixed layer (0-2 km), with concentrations determined primarily by interactions of biogenic emissions from wet tundra and turbulent mixing processes. Carbon monoxide exhibited little variation in unpolluted mixed layer environments indicating a minor role for biogenic sources and/or sinks in determining its distribution. In the free troposphere (2-6 km) both CO and CH₄ were variable. Concentration gradients were most frequently associated with intrusions of upper tropospheric or stratospheric air into the midtroposphere, emissions from forest and tundra fires, and long-range transport of enhanced concentrations of these gases from unidentified sources. Summertime haze layers exhibited midtropospheric enhancements of CH₄ similar to those measured in winter Arctic haze events. However, these summer pollution episodes did not exhibit positive correlations with particulate sulfate. The summer Arctic and subarctic haze events observed during the Arctic Boundary Layer Expedition (ABLE 3) were primarily a result of forest and tundra fires of natural origin. The tendency for relatively high variability of CO and CH₄ at altitudes of 3-6 km indicates that ground-based monitoring will not provide an adequate assessment of the chemical composition of the Arctic troposphere to support future global change studies.

HOFMANN, D.J., S.J. OLTMANS, J.M. HARRIS, S. Solomon, T. Deshler, and B.J. JOHNSON. Observation and possible causes of new ozone depletion in Antarctica in 1991. Nature 359:283-287 (1992).

Local ozone reductions approaching 50% in magnitude were observed during the Antarctic spring in the 11-13 and 25-30 km altitude regions over South Pole and McMurdo Stations in 1991. These reductions, at altitudes where depletion has not been observed previously, resulted in a late September total ozone column 10-15% lower than previous years. The added depletion in the lower stratosphere was observed to coincide with penetration into the polar vortex of highly enhanced concentrations of aerosol particles from volcanic activity in 1991.

HOFMANN, D.J., and S.J. OLTMANS. The effect of stratospheric water vapor on the heterogeneous reaction rate of C1ONO and H₂O for sulfuric acid aerosol. Geophysical Research Letters 19(22):2211-2214 (1992).

Although it is well known that temperature affects the heterogeneous reaction probability (g) C1ONO₂ and H₂O on sulfuric acid aerosol surfaces by determining the amount of water which will co-condense with H₂SO₄ vapor, the effect of the ambient water vapor concentration, which also affects the aerosol composition, has not been investigated in detail. A nearly constant stratospheric water vapor mixing ratio dictates that the water vapor partial pressure vary proportional to atmospheric pressure and thus increase rapidly in the lower stratosphere. In addition, the water vapor mixing ratio increases dramatically in the lower stratosphere following tropospheric-stratospheric exchange. The increase in water vapor partial pressure results in a large increase in g and may be a factor contributing to ozone destruction in the lower stratosphere. Comparison of the lifetime of C1ONO₂ to heterogeneous reactions with that expected from gas phase photochemistry is used to estimate the relative importance of these processes and indicates that winter and spring polar regions are the most likely to be affected.

Hubler, G., D.D. Montzka, R.B. Norton, P.C. Murphy, F.C. Fehsenfeld, S.C. Liu, B.A. Ridley, J.G. Walega, E. Atlas, F.E. Grahek, L.E. Heidt, J. Merrill, B.J. Huebert, and B.A. BODHAINE, Total reactive oxidized nitrogen (NO_y) in the remote Pacific troposphere and its correlation with O₃ and CO: Mauna Loa Observatory Photochemistry Experiment 1988. Journal of Geophysical Research 97(D10):10,427-10,447 (1992).

As part of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) total reactive oxidized nitrogen (NO_y) was measured during May and early June of 1988 at the Mauna Loa Observatory, the NOAA-Geophysical Monitoring for Climatic Change Baseline Monitoring Station, located at 3.4-km elevation on the island of Hawaii. Gold catalytic surface conversion of individual reactive oxidized nitrogen species to NO and subsequent quantification of the NO by NO/O₃ chemiluminescence was used to measure the NO_y mixing ratio. The NO_y abundance at the site was governed by the local downslope/upslope wind systems as well as synoptic-scale transport. With some exceptions, downslope wind brought air representative of the free troposphere, while upslope winds transported air from below the trade wind inversion to the site. The upslope air masses could be a mix of marine boundary layer air and free tropospheric air modified by anthropogenic and natural emissions from island sources. It was possible to identify free tropospheric air in the downslope flow through meteorological and chemical tracers. Reflecting the remote location, low NO_y mixing ratios with median values of 262 and 239 pptv were found in free tropospheric and upslope air masses, respectively. The median NO_y levels in free tropospheric air are consistent with airborne NO_y measurements made during NASA�s Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (CITE 2) program over the northeastern Pacific Ocean at corresponding altitudes. The median NO_y values in upslope flow are significantly higher than those measured in the remote marine boundary layer during CITE 2, reflecting probably the influence of island source and/or mixing of free tropospheric air with boundary layer air. The low correlation found between NO_y and tracers of anthropogenic sources, such as carbon monoxide, tetrachloroethylene, and n-propyl nitrate, in free tropospheric air samples is consistent with a stratospheric or upper tropospheric source for NO_y. Simultaneous particular nitrate (NO₃^-) measurements suggest that at times not all aerosol NO₃^- was quantitatively converted to NO by the Au-surface converter technique. These episodes were usually found during upslope flow and were characterized by high sodium concentrations, suggesting that possibly the sodium nitrate contained in these aerosols was not converted efficiently by the Au converter.

Kahl, J.D., M.C. Serreze, and R.C. SCHNELL. Tropospheric low-level temperature inversions in the Canadian Arctic. Atmospheric-Ocean 39(4):511-529 (1992).

Climatological characteristics of the low-level tropospheric temperature inversion in the Canadian Arctic are examined using 10-40 year records of upper-air meteorological data. Inversions at the northern sites are primarily surface-based in winter, and elevated from mid-spring through summer. At the southern sites, a bimodal pattern is observed with surface-based inversions occurring during late summer, as well as during winter. From comparisons of our results with other published climatologies, it appears that this bimodal pattern reflects interactions between short-and long-wave radiation, synoptic activity and snowmelt. Maxima in inversion depth and temperatures difference across the inversion layer occur in February and March; minima occur in August and September. The annual progression of inversion characteristics closely follows the annual pattern of clear-sky percentages, reflecting the controlling influence of cloud and clear-sky radiative forcings on the inversion layer.

Kahl, J.D., M.C. Serreze, S. Shiotani, S.M. Skony, and R.C. SCHNELL. In situ meteorological sounding archives for Arctic studies. Bulletin of the American Meteorologial Society 73(11):1824-1830 (1992).

Two new databases containing Arctic in situ meteorological soundings have been constructed and are now available for distribution to interested researchers. The Historical Arctic Rawinsonde Archive is a comprehensive collection of over 1.2 million rawinsonde soundings north of 65°N. For most stations the record begins in 1958 and extends to 1987; however, for some stations the record begins as early as 1948. The Ptarmigan Dropsonde Archive contains more than 10,000 lower-tropospheric soundings over the Beaufort Sea and western Arctic Ocean during the period 1950-1961.

LANG, P.M., L.P. Steele, L.S. WATERMAN, R.C. MARTIN, K.A. MASARIE, and E.J. DLUGOKENCY. NOAA/CMDL atmospheric methane data for the period 1983-1990 from shipboard flask sampling. NOAA TM ERL CMDL-4 (PB93136489), 88 pp. (1992).

This memorandum presents atmospheric methane data obtained through the shipboard sampling component of the NOAA/CMDL global cooperative flask sampling program. A significant part of this program has involved flask sampling from a commercial container ship, the Southland Star, on regular crossings of the Pacific Ocean between the U.S. west coast and New Zealand. Shipboard flask sampling has also been carried out on a variety of oceanographic research expeditions. Tabulations are provided for individual flask measurements and annual mean methane mixing ratios for 14 sites spaced every five degrees of latitude across the Pacific Ocean between 30°N and 35°S. The methane data from the Southland Star are also shown as time series plots. The locations of flask sampling on the oceanographic research expeditions are shown in a series of maps. The flask methane data from these expeditions are shown as a series of plots of methane versus latitude. A brief history of the development of the sampling program is included. Flask sampling methods and analytical and calibration procedures are documented.

Luria, M., J.F. Boatman, J.M. HARRIS, J. Ray, T. Straube, J. CHIN, R.L. Gunter, G. HERBERT, T.M. Gerlach, and C.C. Van Valin. Atmospheric sulfur dioxide at Mauna Loa, Hawaii. Journal of Geophysical Research 97(D5): 6011-6022 (1992).

Measurements of sulfur dioxide (SO₂) were made at the National Oceanic and Atmospheric Administration's Mauna Loa Observatory in Hawaii, during a 12-month period beginning in December 1988. SO₂ concentrations varied from background levels of less than 0.05 ppbv to a maximum of 50 ppbv, during episodes that lasted from 2 to 24 hours. Emissions from the Kilauea crater, approximately 35 km southeast of the observatory at an elevation of about 1000 m above sea level (asl), and the current eruptionn at Puu O'o 50 km east-southeast, are the most likely sources for the higher concentrations. These episodes occurred 10-25 times each month, mostly during the day; peak concentrations were usually recorded at mid-day. The SO₂ concentrations can be grouped into three periods; low (June-September), high (October-January) and intermediate (February-May). A clear diurnal cycle of SO₂ concentration exists throughout the year, although day-night changes were greatest during October-January and were barely detectable during the June-September period. The highest SO₂ concentrations were recorded when the predominant wind direction was notherly to northwesterly, even though the apparent sources are in the southeastern sector. Nighttime concentrations were usually at background levels; however, many exceptions were observed. A few cases of higher than background SO₂ were observed when free tropospheric (FT) conditions were identified. The possibility that long-range transport was the cause for elevated SO₂ concentrations under FT conditions was examined using air mass back trajectories analyses. The highest nighttime SO₂ concentrations, under FT conditions, were observed during periods with slow easterly trajectories, and the lowest concentrations were found during westerly flows. Twenty-four nighttime free tropospheric events were recorded when the SO₂ concentration exceeded 0.2 ppbv. During 18 of these episodes, unusually high CO₂ concentrations were observed.

Martinsson, B.G., E. Swietlicki, H.-C. Hansson, A. Wiedensohler, K.J. Noone, J.A. OGREN, and A. Hallberg. Elemental composition of fog interstitial particle size fractions and hydrophobic fractions related to fog droplet nucleation scavenging. Tellus 44B:593-603 (1992).

The cloud nucleation scavenging process was studied during a joint campaign of the EUROTRAC sub-project Ground-based Cloud Experiment. It was found that the particle size has a strong influence on the partitioning of particles between the cloud droplet and the interstitial aerosol reservoirs. A new aerosol sampling unit, the relative humidity processing system, was employed for the extraction of particles with a low growth-ability with respect to increased relative humidity. The system supplied tracer elements on the particle growth-ability. These elements could be used to identify a factor related to particle hygroscopic properties, which was in effect as a selector of cloud condensation nuclei.

Noone, K.J., J.A. OGREN, A. Hallberg, H.-C. Hansson, A. Wiedensohler, and E. Swietlicki. A statistical examination of the chemical differences between interstitial and scavenged aerosol. Tellus 44B:581-592 (1992).

The difference in chemistry between interstitial aerosol particles and particles that were scavenged into fog droplets is examined using multivariate statistical techniques. Fifteen (15) trace elements (P, S, Cl, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Pb, EC) were used in the analysis. There was a significant difference in composition between the two types of particles. S, Fe, Mn, and Cu were among the elements best describing the scavenged aerosol, while the interstitial aerosol was best described by elemental carbon (EC).

Noone, K.J., J.A. OGREN, A. Hallberg, J. Heintzenberg, J. Strom, H.-C. Hansson, B. Svenningsson, A. Widensohler, S. Fuzzi, M.C. Facchini, B.G. Arends, and A. Berner. Changes in aerosol size and phase distributions due to physical and chemical processes in fog. Tellus 44B:489-504 (1992).

Measurements of the scavenging efficiency of aerosol particles in fog are presented. The scavenging efficiency as a function of size for accumulation-mode particles is presented, along with efficiencies for the total number, accumulation-mode number, and accumulation-mode volume. Particles below ca. 0.3 m diameter were not efficiently scavenged in the fogs. The scavenging efficiency for accumulation-mode particles showed two steps, indicating that the hygroscopic/hydrophobic nature of the aerosol appeared to have been a controlling factor in determining scavenging efficiencies Observed changes in the aerosol size distributions are discussed in reference to the processes (i.e., in-cloud scavenging, aqueousphase reactions) potentially influencing them.

NOVELLI, P.C., L.P. STEELE, and P.P. TANS. Mixing ratios of carbon monoxide in the troposphere. Journal of Geophysical Research 97(D18):20,731-20,750 (1992).

Carbon monoxide (CO) mixing ratios were measured in air samples collected weekly at eight locations. The air was collected as part of the NOAA/CMDL cooperative flask sampling program (National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory, formerly Geophysical Monitoring for Climatic Change, Air Resources Laboratory) at Point Barrow, Alaska (71°N), Niwot Ridge, Colorado (40°N), Mauna Loa and Cape Kumakahi, Hawaii (19°N), Guam, Marianas Islands (13°N), Christmas Island (2°N), Ascension Island (8°S) and American Samoa (14°S). Half-liter or 3-L glass flasks fitted with glass piston stopcocks holding Teflon O rings were used for sample collection. CO levels were determined within several weeks of collection using gas chromatography followed by mercuric oxide reduction detection, and mixing ratios were referenced against the NOAA/CMDL carbon monoxide standard scale. During the period of study (mid-1988 through December 1990) CO levels were greatest in the high latitudes of the northern hemisphere (mean mixing ratio from January 1989 to December 1990 at Point Barrow was approximately 154 ppb) and decreased towards the south (mean mixing ratio at Samoa over a similar period was 65 ppb). Mixing ratios varied seasonally, the amplitude of the seasonal cycle was greatest in the north and decreased to the south. Carbon monoxide levels were affected by both local and regional scale processes. The difference in CO levels between northern and southern latitudes also varied seasonally. The greatest difference in CO mixing ratios between Barrow and Samoa was observed during the northern winter (about 150 ppb). The smallest difference, 40 ppb, occurred during the austral winter. The annually averaged CO difference between 71°N and 14°S was approximately 90 ppb in both 1989 and 1990; the annually averaged interhemispheric gradient from 71°N to 41°S is estimated as approximately 95 ppb.

OGREN, J.A., K.J. Noone, A. Hallberg, J. Heintzenberg, D. Schell, A. Berner, I. Solly, C. Kruisz, G. Reischl, B.G. Arends, and W. Wobrock. Measurements of the size dependence of the concentration of non-volatile material in fog droplets. Tellus 44B:570-580 (1992).

Measurements of the size dependence of the mass concentration of non-volatile material dissolved and suspended in fog droplets were obtained with three complementary approaches, covering a size range from ca. 1-50 m diameter: a counterflow virtual impactor, an eight-stage aerosol impactor, and a two-stage fogwater impactor. Concentrations were observed to decrease with size over the entire range, contrary to expectations of increasing concentrations at larger sizes. It is possible that the larger droplets had solute concentrations that increased with increasing size, but that the increase was too weak for the measurements to resolve. Future studies should consider the hypothesis that the droplets were coated with a surface-active substance that hindered their uptake of water.

OLTMANS, S.J., and H. Levy, II. Seasonal cycle of surface ozone over the western North Atlantic. Nature 358:392-394 (1992).

The possible impact of pollution from North America and Europe on tropospheric ozone throughout the Northern Hemisphere is a major environmental concern. We report here continuous measurements of ozone from Bermuda (32°N, 65°W) and Barbados (13°N, 60°W), which suggest that despite their proximity to the eastern US seaboard, natural processes rather than pollution control surface ozone in these regions. Although springtime daily average ozone concentrations at Bermuda are greater than 70 parts per billion (10) by volume (p.p.b.v.) and hourly values in 1989 sometimes exceeded the Canadian Air Quality limit of 80 p.p.b.v., trajectory analyses indicate that these high levels of ozone are transported from the unpolluted upper troposphere >5 km above the northern United States and Canada. During the summer, when surface ozone concentrations over the eastern United States can exceed 70 p.p.b.v. owing to pollution, typical values at Bermuda are between 15 and 25 p.p.b.v. At Barbados, both the seasonal and diurnal variations in surface ozone are nearly identical to those at Samoa in the tropical South Pacific, where the isolation from anthropogenic sources and low levels of NOx ensure that natural processes control surface ozone.

Parungo, F., B. Kopcewicz, C. Nagamoto, R. SCHNELL, P. SHERIDAN, C. Zhu, and J. HARRIS. Aerosol particles in the Kuwait oil fire plumes: Their morphology, size distribution, chemical composition, transport, and potential effect on climate. Journal of Geophysical Research 97(D14):15,867-15,882 (1992).

Airborne aerosol samples were collected with an impactor in the Kuwait oil fire plumes in late May 1991. A transmission electron microscope was used to examine the morphology and size distribution of the particles, and an X ray energy spectrometer was used to determine the elemental composition of individual particles. A chemical spot test was used to identify particles containing sulfate. The results show that the dominant particles were (1) agglomerates of spherical soot particles coated with sulfate, (2) cubic crystals containing NaCl and , (3) irregular-shaped dust containing Si, Al, Fe, Ca, K, and/or S, and (4) very small ammonium sulfate spherules. The concentrations of small sulfate particles increased at higher levels or greater distances from the fire, suggesting the transformation of SO₂ gas to sulfate particles by photooxidation followed by homogeneous nucleation. The number of soot, salt, and dust particles that were coated with sulfate increased farther from the fire, and the thickness of the coating increased with altitude. This suggested that gas-to-particle conversion had occurred by means of catalytic oxidation combined with heterogeneous nucleation during the plume dispersion. Because the sulfate coating can modify the hydrophobic surfaces of soot and dust particles to make them hydrophilic, most of the particles in the plume apparently were active cloud condensation nuclei that could initiate clouds, fog, and smog, which in turn could affect regional surface temperature, air quality, and visibility. Long-range air trajectories suggested that some aerosols from the fires could have transported to eastern Asia. It seems possible (but is presently unproven) that a severe flood in China in June was influenced by aerosols from the plumes.

Rosen, J.M., B.A. BODHAINE, J.F. Boatman, J.J. DeLuisi, M.J. Post, Y. Kim, R.C. SCHNELL, P.J. SHERIDAN, and D.M. Garvey. Measured and calculated optical property profiles in the mixed layer and free troposphere. Journal of Geophysical Research 97(D12):12,837-12,850 (1992).

Nearly simultaneous measurements of the physical and optical properties of mixed layer and free tropospheric aerosols near Boulder, Colorado, were made on several occasions using aircraft, balloon, and ground-based sensors. This effort (Front Range Lidar, Aircraft, and Balloon experiment (FRLAB)) was conducted with the purpose of obtaining a diverse, self-consistent data set that could be used for testing optical model calculations based on measured physical characteristics such as apparent size distribution, composition, and shape. It was found that even with the uncertainties involved, the model predictions are in good agreement with the measurements in the visible and near infrared wavelength regions. At CO₂ lidar wavelengths there is considerably more uncertainty in both the calculated and measured values; however, within the estimated errors there appears to be satisfactory agreement except for the highest free tropospheric layer studied. The results also indicate that during FRLAB the aerosol in the boundary layer and free troposphere behaved as spherical particles for optical modeling purposes. The utility of the observations for determining the extinction-to-backscatter ratio relevant to aerosols in the boundary layer and free troposphere is described with typical measured values being in the 20 to 30 sr range.

Savoie, D.L., J.M Prospero, S.J. OLTMANS, W.C. Graustein, K.K. Turekian, J.T. Merrill, and H. Levy II. Sources of nitrate and ozone in the marine boundary layer of the tropical North Atlantic. Journal of Geophyical Research 97(D11):11,575-11,589 (1992).

During the period April 1989 through December 1990, O₃ concentrations in the marine boundary layer at Barbados, West Indies, show a pronounced seasonal cycle. Daily averaged values in the winter and spring often fall in the range of 25-35 ppbv for periods of several days, and they seldom fall below 20 ppbv. In contrast, during the summer, values typically fall in the range of 10-20 ppbv. During the winter-spring period, there is a very strong negative correlation between O₃ and a number of aerosol species, including NO₃^-. These anticorrelations appear to be driven by changing transport patterns over the North Atlantic as opposed to chemical reactions involving O₃ and nitrogen species in the atmosphere. Analyses of isentropic trajectories clearly show that high O₃ and low NO₃^- are associated with transport from higher latitudes and high altitudes. Conversely, high NO₃^- and relatively low O₃ are associated with transport from Africa. Our study suggests that North America and the middle tropsphere (and stratosphere) are not strong sources for NO₃^- over the tropical North Atlantic. The strong correlation of NO₃^- with ²¹⁰Pb and the weaker correlation with Saharan dust indicates that NO₃^- is derived principally from continental surface sources, probably in Europe and North Africa, but not from the Saharan soil material itself. During several extended periods, NO₃^- and ²¹⁰PB were strongly correlated and their concentrations were high relative to nss SO₄⁼, these factors, coupled with trajectories originating in Africa, suggest that African biomass burning was a significant source at these times. In contrast, biomass burning appears to be a minor source for O₃ as measured at Barbados, perhaps accounting for an enhancement of about 5 ppbv at most during these periods.

SHERIDAN, P.J., R.C. SCHNELL, D.J. HOFMANN, J.M. HARRIS, AND T. Deshler. Electron microscope studies of aerosol layers with likely Kuwait origins over Laramie, Wyoming during spring 1991. Geophysical Research Letters 19(4): 389-392 (1992).

Upper tropospheric aerosols observed in spring 1991 over Laramie, Wyoming, were sampled using balloon-borne cascade impactors. Three impactor samples were collected; two were in upper tropospheric aerosol layers and one was collected at the same altitude in cleaner, "background" upper air. Optical particle counters measured concentrations of particle with radii ³ 0.15 mm in the layers which were increased 5-10 times over what is normally observed at these altitudes. Electron microscope analyses showed acidic and neutralized sulfate particles to be the dominant aerosol constituents in these layers, although carbonaceous soot aggregates and crustal dust particles were also found. The morphology and elemental composition of these particles closely resembles particles collected in the large mixed smoke plume of the Kuwait oil fires. Meteorological analyses showed favorable transport conditions from the Middle East to the continental U.S. when layers were present over Wyoming, and less than ideal conditions when the layers were absent. Based on these microanalytical results and the corroborating meteorological and air trajectory analyses, the most likely source of these aerosol layers is the oil fires in Kuwait.

STEELE, L.P., E.J. DLUGOKENCKY, P.M. LANG, P.P. TANS, R.C. MARTIN, and K.A. MASARIE, Slowing down of the global accumulation of atmospheric methane during the 1980s, Nature, 358, 318-316 (1992).

Measurements of methane in modern air and in air trapped in ice cores have shown convincingly that the abundance of atmospheric methane has been rising since the Industrial Revolution. This is a matter of concern because of the important role of methane in determining the radiative balance and chemical composition of the atmosphere. The causes of this increase have not been identified unambiguously because of uncertainties in our understanding of the global budget of atmosphere methane and in how it is changing with time. Here we report on measurements of atmospheric methane from an extensive global network of flask sampling sites, which reveal that, although methane continues to accumulate in the atmosphere, there has been a substantial slowing of the global accumulation rate between 1983 and 1990. If this deceleration continues steadily, global methane concentrations will reach a maximum around the year 2006. Our results hint that changes in methane emissions in the latitude band 30-90°N may be of particular significance to this trend.

STURGES, W.T., G.F. Cota, and P.T. Buckley. Bromoform emission from Arctic ice algae. Nature 358:660-662 (1992).

Destruction of surface ozone in the Arctic environment during the spring is thought to be caused by photochemical reactions involving bromine compounds. Berg et al. reported a pulse of bromine particles and gases in the Arctic lower atmosphere in spring, which may be responsible for this surface ozone destruction and for which biogenic sources have been hypothesized. Here we report laboratory and in situ measurements which indicate that Arctic ice microalgae emit significant quantities of bromoform (CHBr3), which may be converted photochemically into active forms of bromine. Our estimates of total annual bromoform release indicate that polar ice algae might contribute globally significant amounts of organic bromine compounds, comparable with anthropogenic and macrophyte sources.

Svenningsson, I.B., H.-C. Hansson, A. Wiedensohler, J.A. OGREN, K.J. Noone, and A. Hallberg. Hygroscopic growth of aerosol particles in the Po Valley. Tellus 44B:556-569 (1992).

A Tandem Differential Mobility Analyzer (TDMA) was used to study the hygroscopic growth of individual ambient aerosol particles in the Po Valley, Italy. The measurements were made during the GCE fog experiment in November 1989. During fog, the interstitial aerosol (Dp (at ambient relative humidity) <5m) was sampled. Two modes of particles with different hygroscopic growth were found for 0.030 m

Walega, J.G., B.A. Ridley, S. Madronich, F.E. Grahek, J.D. Shetter, T.D. Sauvain, C.J. Hahn, J.T. Merrill, B.A. BODHAINE, and E. Robinson, Observations of peroxyacetyl nitrate, peroxypropionyl nitrate, methyl nitrate, and ozone during the Mauna Loa Observatory photochemistry experiment. Journal of Geophysical Research 97(D10):10,311-10,330 (1992).

Measurements of the title species were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) conducted between May 1 and June 4, 1988, at the Geophysical Monitoring for Climatic Change (GMCC) station at 3.4-km elevation on the Island of Hawaii. Diurnal changes in the organic nitrates primarily resulted from the transition between downslope flow (usually free tropospheric air) and upslope flow (marine boundary layer or a mix of marine boundary layer and free tropospheric air, both influenced by island sources of precursors) characteristic of the site. Longer term trends in the mixing ratios reflected changes in air mass origins from midlatitudes to more tropical latitudes. The average mixing ratios in free tropospheric samples were peroxyacetyl nitrate (PAN, 17 pptv), peroxypropionyl nitrate (PPN, 0.3 pptv), methyl nitrate (MN, 4 pptv), and O₃ (43 ppbv). The organic nitrates (PAN, PPN, MN) represent minor components of the total odd nitrogen budget at the site. In free tropospheric samples, PAN, PPN, and MN constituted average percentages of 7%, <1%, and 2% of total odd nitrogen. In more tropical air masses, MN could constitute as much as 10% of total odd nitrogen. A photochemical model is used to investigate the sensitivity of free tropospheric PAN to local precursor concentrations. The observed mixing ratios of PAN are also contrasted with measurements made at continental surface sites and during aircraft programs.

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