Showing papers in "Journal of Atmospheric Chemistry in 1985"

Tropospheric chemical composition measurements in Brazil during the dry season

Abstract: Field measurement programs in Brazil during the dry seasons in August and September 1979 and 1980 have demonstrated the large importance of the continental tropics in global air chemistry. Many important trace gases are produced in large amounts over the continents. During the dry season, much biomass burning takes place, especially in the cerrado regions, leading to a substantial emission of air pollutants, such as CO, NO x , N2O, CH4 and other hydrocarbons. Ozone concentrations are enhanced due to photochemical reactions. The large biogenic organic emissions from tropical forests play an important role in the photochemistry of the atmosphere and explain why CO is present in such high concentrations in the boundary layer of the tropical forest. Carbon monoxide production may represent more than 3% of the net primary productivity of the tropical forests. Ozone concentrations in the boundary layer of the tropical forests indicate strong removal processes. Due to atmospheric supply of NO x by lightning, there is probably a large production of O3 in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer.

Distribution, speciation, and budget of atmospheric mercury

Abstract: Total gaseous mercury (TGM) concentrations over the Atlantic Ocean and over Central Europe were measured repeatedly in the years 1978–1981. The latitudinal TGM distribution showed a pronounced and reproducible interhemispherical difference with higher TGM concentrations in the Northern Hemisphere. TGM was found to be vertically well mixed within the troposphere. The TGM concentration seems to increase with time at a rate of 10±8%/yr in the Northern and 8±3%/yr in the Southern Hemisphere. Measurements of mercury speciation showed that elemental mercury is the main TGM component contributing more than 92% and 83% of TGM in marine and continental air, respectively. The tropospheric mercury burden was calculated to be 6×109g. The interhemispheric distribution and temporal and spatial variability of TGM imply a tropospheric residence time of TGM of about 1 yr. Sink strengths calculated independently from the measured mercury concentration on particles and in rainwater are consistent with the above figures.

Evaluation of a catalytic reduction technique for the measurement of total reactive odd-nitrogen NOy in the atmosphere

Abstract: A catalytic reduction technique for the measurement of total reactive odd-nitrogen NO y in the atmosphere was evaluated in laboratory and field tests. NO y component species include NO, NO2, NO3, HNO3, N2O5, CH3COO2NO2(PAN), and particulate nitrate. The technique utilizes the reduction of the higher oxides to NO in reaction with CO on a metal catalyst and the subsequent detection of NO by chemiluminescence produced in reaction with O3. The efficiency and linearity of the conversion of the principal NO y species were examined for mixing ratios in the range of 0.1 to 100 parts per billion by volume (ppbv). Results of tests with Au, Ni, and stainless steel as the catalyst in the temperature range of 25–500°C showed Au to be the preferred catalyst. NH3, HCN, N2O, CH4, and various chlorine and sulfur compounds were checked as possible sources of NO y interference with the Au catalyst. The effects of pressure, O3, and H2O on NO y conversion were also examined. The results of the checks and tests in the laboratory showed the technique to be suitable for initial NO y measurements in the atmosphere. The technique was subsequently tested in ambient air at a remote ground-based field site located near Niwot Ridge, Colorado. The results of conversion and inlet tests made in the field and a summary of the NO y data are included in the discussion.

Deposition of atmospheric mineral particles in the north pacific ocean

Abstract: Total deposition of atmospheric mineral particles (wet plus dry) has been measured during consecutive two-week sampling intervals from January, 1981 to March, 1982 at four island stations (Midway, Oahu, Enewetak, and Fanning) of the SEAREX Asian Dust Study Network in the North Pacific. The total deposition of mineral aerosol during the period from February to June is higher than that during the period from July to January at most of the stations. A systematic geographical trend is apparent in the dust flux, with greater fluxes at higher latitudes. The deposition values are correlated with the atmospheric mineral particle concentrations at these stations. The mineral particles are transported from arid regions in Asia to the North Pacific, and the annual dust deposition to the ocean appears to be dominated by sporadic dust events of short duration. Wet deposition dominates the removal of dust particles from the atmosphere over the North Pacific. The total deposition of atmospheric mineral material to the central North Pacific is estimated to be ∼20×1012 g yr-1.

Source terms and source strengths of the carbonaceous aerosol in the tropics

Abstract: Atmospheric aerosol samples were collected in the Ivory Coast, primarily at Lamto (6°N, 5°W) between 1979 and 1981. The samples were analysed for total particulate carbon concentration and isotopic composition (13C/12C) by mass spectrometry. Observed concentrations were found high compared to values reported for temperate regions. Fine particulate carbon in the submicrometersize range accounted for 50 to 80% of the reported concentrations. At Lamto, both particulate carbon concentrations and isotopic ratios exhibit a large temporal variability which is shown to reflect the diversity of sources and their seasonal evolution. Natural emissions from the equatorial forest during the wet season, and biomass burning during the dry season, appear to be the major sources. The latter, though active during only a third of the year, is, on an annual basis, the most important source. Based on the data obtained at Lamto, an attempt has been made to estimate the flux of fine particulate carbon emitted from the tropical regions into the global troposphere. This flux, which is of the order of 20×1012 g C/yr, appears to be equivalent to the flux of fine particulate carbon emitted from industrial sources. These results suggest that the tropospheric burden of fine particulate carbon in lowlatitude regions is dominated by the long-range transport of carbonaceous aerosols originating from the Tropics.

Measurements of various sulphur gases in a coastal marine environment

Abstract: Measurements of several sulphur gases have been made in coastal seawaters (including microlayers) and marine air off Great Yarmouth, U.K., and in a freshwater lake. The results show dimethyl sulphide to be the dominant sulphur gas in all the waters examined, with lesser amounts of carbonyl sulphide and carbon disulphide. For the marine air and water samples carbonyl sulphide showed no significant seasonal variation in concentration. The seawater was always supersaturated with respect to the carbonyl sulphide concentration in the air; the mean saturation value being 4.6. Likewise the seawater was always supersaturated with dimethyl sulphide, but for this gas the concentrations in the water showed substantial seasonal variation (× 40), with a maximum value of about 500 ng(S) l-1 in late June, approximately contemporaneous with the second plankton bloom in the region. Sea surface microlayers harvested cryogenically showed a mean enrichment of 2.4 relative to subsurface water for carbonyl sulphide. Some part of the observed microlayer enrichment for this gas may be due to freezing-on of atmospheric carbonyl sulphide onto the frozen microlayer sample. In general, microlayer samples did not exhibit a significant enrichment for dimethyl sulphide. However, under conditions of high biological production, enrichments of several-fold were found, but may be attributable, at least in part, to biological production of dimethyl sulphide in the microlayer water in the period between collection and analysis.

Photochemical aspects of tropospheric iodine behaviour

Abstract: The I-atom sensitised decomposition of ozone in air at 1 atm pressure and ambient temperature has been investigated. Iodine atoms were produced by photolysis of I2 using visible light or of CH3I using ultraviolet light. In both cases, the quantum yield for O3 decomposition was 1.25 (±0.11) per I atom. An important role is proposed for the self-reaction of IO radicals leading to higher oxides of iodine, IO+IO(+M)→I2O2(+M)→higher oxides, which predominated over the bimolecular reaction leading to regeneration of I atoms, IO+IO→2I+O2, with k 2a/k 2b≥4. Simple computer modelling calculations indicate that reaction (2a) may be important in determining the fate of photolabile iodine species in the atmosphere. The consequences for the behaviour of radioiodine releases are also discussed.

Atmospheric chemistry of alkanes

Abstract: The reactions of the alkanes under atmospheric conditions and in the presence of oxides of nitrogen are reviewed and evaluated. Particular emphasis is placed upon their subsequent reactions after the initial OH radical reaction under conditions where the alkyl peroxy radicals produced react predominantly with NO, rather than with HO2 and/or RO2 radicals. Methods are discussed for estimating the overall OH radical rate constants, the number of molecules of NO consumed per alkane molecule reacted, and the products formed and their yields.

Nonmethane hydrocarbons in an oceanic atmosphere

Abstract: C2−C6 Nonmethane hydrocarbons (NMHC) and radioactive continental tracers were measured during two oceanographic cruises, in June 1982 in the Mediterranean and Red Sea, and in November 1982 across the North Atlantic and South Pacific oceans. Typical concentrations in marine atmosphere are between 0.05 and 0.2 ppbv. Owing to their similar lifetimes, propane and radon-222 are found to be well correlated. This relationship establishes that propane is mainly produced over lands and enables us to estimate its continental source strength at about 60×106 tons of carbon per year.

An improved method of measuring tropospheric NO2 and RO2 by matrix isolation and electron spin resonance

Abstract: A cryogenic system for the airborne and ground based sampling of ambient radicals by matrix isolation is described. The trapped radicals, e.g., NO2 and RO2, are analyzed by ESR. The technique has been improved, mainly by addition of water vapor to the sampled air, to yield a collection efficiency of (90±10)% and a lower detection limit of about 20 ppt, but it still does not distinguish between the different RO2. Careful calibration reduced the measurement error (1 σ) to ±10% for NO2 and ±15% for HO2. Two diurnal variations of RO2 and NO2 at ground level and vertical profiles in the lower troposphere are presented.

An optimized chemiluminescence detector for tropospheric NO measurements

Abstract: A detector for the chemiluminescent measurement of NO in background air is described. A large reduction of interferences is achieved by using a stabilized ozone generator which allows operation of the instrument at lower O3 concentrations. Purification and humidification of the O3 stream further reduces interferences and shortens the instrumental clean-up time, which is important for aircraft missions. From a series of laboratory tests and from measurements performed aboard an aircraft it is demonstrated that the remaining interferences are acceptable for measurements in the undisturbed troposphere. In particular, no remnant NO signal is observed in clean air at night. During flight, a detection limit (2σ) of 20 ppt is achieved for a 1 min integration time.

Measurements of selected C2-C5 hydrocarbons in the background troposphere: Vertical and latitudinal variations

Abstract: Meridional cross sections of the concentration of light hydrocarbons are reported. They were obtained from 20. April to 10. May, 1980, during the French research flight STRATOZ II, and cover the latitudes between 60° N and 60° S and the altitudes between 800 mb and 200 mb. The mixing ratios of ethane, ethene, acetylene, propane, propene, n-butane, i-butane, n-pentane, and i-pentane range between 2.0 and 0.02 ppb. Globally, a decrease in concentration with increasing altitude and -in most cases-with decreasing latitude is observed. In addition the 2-dimensional concentration fields show structures of different scales. In particular, isolated maxima of high concentrations are found in the upper troposphere. They point to fast vertical transport between the boundary layer and the upper troposphere. In the present case these maxima seem to be correlated with large scale meteorological systems, such as low pressure regions or the Inter Tropical Convergence Zone. It is argued that the NMHC provide a set of tracers well suited to the detection of fast vertical transport.

Model analysis of the measured concentration of organic gases in the Norwegian Arctic

Abstract: A 2-D meridional model for the chemistry and transport in the troposphere is used to study the seasonal variation of the concentration of organic gases like C2H2, C2H6, C3H8, C6H6, C7H8. CHCl3 and C2Cl4 at high latitudes. The anthropogenic sources for these species were estimated, and the temporal and latitudinal distribution of OH and O3 was calculated using a complex photochemical reaction system. There is fair agreement between the calculated annual variation and the measured concentrations for C2H2, C2H6, C3H8, C7H8 and C2Cl4 at Spitsbergen during July 1982 and March/April 1983, with a distinct late winter maximum and summer minimum. For CHCl3, the direct anthropogenic source is minor compared to indirect anthropogenic or natural sources. For benzene, emission in car exhaust is important, but other anthropogenic sources are required for the calculations to agree with the measurements. Measured C2H4 and C3H6 concentrations are much higher than the calculated ones based on anthropogenic emissions, and show opposite seasonal trends. This indicates biogenic sources for these compounds.

Study of background aerosols in the Antarctic troposphere

Abstract: Systematic year-round observations of submicron aerosols were carried out at Syowa Station (69°00’S, 39°35’E) in 1978. On the basis of the results of these observations, it is concluded that two types of aerosols originating from different sources are present in the Antarctic troposphere. With the intrusion of maritime air, mostly in the polar night months, sea salt particles and ammonium sulfate particles contained originally in the clean maritime air are dominant. The size distribution of such aerosols is monomodal, having a single mode at around 0.03 μm in radii. On the other hand, in the sunlit months, sulfuric acid droplets are predominant and the size distribution is bimodal, having an additional mode at around 0.005 μm in radii. Those sulfuric acid particles seem to be formed photochemically within a specific layer in the mid to lower troposphere over Antarctica. Most Antarctic submicron particles are of tropospheric origin, not of stratospheric nor anthropogenic origin.

The photochemistry of synoptic-scale ozone synthesis Implications for the global tropospheric ozone budget

Abstract: The oxidation of nonmethane hydrocarbons represents a source of tropospheric ozone that is primarily confined to the boundary layers of several highly industrialized regions. (Each region has an area greater than one million km2). Using a photochemical model, the global tropospheric ozone budget is reexamined by including the in-situ production from these localized regimes. The results from these calculations suggest that the net source due to this photochemistry, which takes place on the synoptic scale, is approximately as large as the amount calculated for global scale photochemical processes which consider only the oxidation of methane and carbon monoxide. Such a finding may have a considerable impact on our understanding of the tropospheric ozone budget. The model results for ozone show reasonable agreement with the climatological summer distribution of ozone and the oxides of nitrogen at the surface and with the vertical distribution of ozone and nonmethane hydrocarbons obtained during a 1980 field program.

Surface ozone measurements in the Venezuelan tropical savannah

Abstract: A one-year set of surface ozone measurements in a four-station network located in the Venezuelan savannah is reported. The diurnal ozone variation is typical of continental stations with a maximum in the afternoon, when vertical turbulent mixing is strongest. The annual O3 average concentration, based on the monthly averages of daily maxima, was 17±2 ppb, which is in good agreement with values reported for similar latitudes. The boundary-layer ozone levels did not fall below 8 ppb, in contrast with previous sporadic measurements made in tropical latitudes. No evidence was found that mesoscale O3 downdrafts in the ITCZ in the South American continent are an important source of surface ozone. Finally, it is suggested that the relatively high ozone levels observed at the end of the dry season are probably of photochemical origin.

High atmospheric NO x levels and multiple photochemical steady states

Abstract: The rate of removal of atmospheric NO(x) compounds at different NO(x) levels is estimated using a one-dimensional photochemical model. NO(x) removal by wet deposition, surface deposition, and thermochemical processes is examined. NO(x) removal rates at different surface NO mixing ratios are calculated and the data are analyzed. It is revealed that at low NO(x) levels NO(x) is photochemically converted to HNO3 by either wet or dry deposition; however, at high NO(x) levels formation of HNO3 is inhibited due to the disappearance of tropospheric ozone and OH, and the NO(x) is removed by rainout of N2O4 and N2O5, surface deposition of NO and NO2, and direct dissolution of NO and NO2 in rainwater. The effects of NO(x) mixing ratios greater than 10 to the -7th on the ozone and climate are investigated.

Measurement of the photodissociation coefficient of NO2 in the atmosphere: II, stratospheric measurements

Abstract: The photodissociation coefficient of NO2, J NO 2, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J NO 2 measured were 10.5±0.3 and 10.3±0.3×10-3 s-1 at 24 and 32 km respectively. The decrease in J NO 2 at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J NO 2 using a simplified isotropic multiple scattering computer routine.

Wet deposition due to fog in the Po Valley, Italy

Abstract: Wet deposition due to radiation fog is examined in this paper. The area where the reported measurements were performed, the Po Valley, northern Italy, is characterized by both a high fog occurrence during the fall-winter months and fog water solutions of high ionic concentration and acidity. Estimated wet deposition for NH 4 + , NO inf3 sup- and SO inf4 sup2- ions due to fog droplet settling to the ground accounts for 13.2, 12.1 and 5.3 percent with respect to bulk precipitations over the same period: January–March and October–December (fog season). Fog deposition rates show that this process can be an important pathway of trace gases and particles loss from the air. First indicative results of fog removal efficiency with respect to air particulate matter are presented. Dry deposition parameters should be taken into account in evaluating the potential effect of fog droplet deposition on vegetation.

Stratospheric response to chemical perturbations

Abstract: The paper presents a coupled chemical-radiative one-dimensional model which is used to assess the steady-state and time-dependent composition and temperature changes in relation to the release in the atmosphere of chemicals such as CO2, N2O, CH4, NO x and chlorofluorocarbons. The model indicates that a doubling in CO2 leads to an increase in temperature of 12.7 K near the stratopause and to an increase in total ozone of 3.3% with a local enhancement of 17% at 40 km altitude. Additional release of N2O leads to an ozone reduction in the middle stratosphere. The reduction in the ozone column is predicted to be equal to 8.8% when the amount of N2O is doubled. The chemical effect of CH4 on ozone is particularly important in the troposphere. A doubling in the mixing ratio of this gas enhances the O3 concentration by 11% at 5 km. The predicted increase of the ozone column is equal to 1.4%. A constant emission of CFCl3 (230 kT/yr) and CF2Cl2 (300 kT/yr) leads to a steady-state reduction in the ozone column of 1.9% compared to the present-day situation. The effect of some uncertainties in the chemical scheme as well as the impact of a high chlorine perturbation are briefly discussed. Finally the results of a time dependent calculation assuming a realistic scenario for the emission of chemical species are presented and analyzed.

Trace elements in the atmospheric aerosols at Delhi, North India

Abstract: The total suspended particulate (TSP) levels at Delhi (north India) were measured on 116 days between February and October 1980. The observations were stratified according to season and the values of cross-correlation of the TSP and its components were evaluated. High TSP (209 μg m-3) levels were found during the summer period associated with hot and dry weather in the region and low TSP (109 μg m-3) were found during the monsoon period. Most of the TSP mass was associated with natural soil elements, such as Fe, Al, Mn, Ca, and K. Only a fraction of the mass of the TSP was comprised of elements from anthropogenic sources, e.g., Pb, Ni, Cd, Sb, Cu, and Zn. The aerosols at Delhi were potentially basic in nature, unlike those in European countries which are acidic in nature and cause acid rainfall.

A resonance-fluorescence instrument for the in-situ measurement of atmospheric carbon monoxide

Abstract: The development of an airborne instrument for the in-situ measurement of carbon monoxide is described The technique is resonance-fluorescence of the (A 1Π → X 1Σ) transition of CO in the VUV The instrument achieves a detection limit of 1 ppb for an interaction time of 10 s from ground level up to an altitude of 34 km Interferences from other stratospheric trace gases are negligible

A model investigation of the impact of increases in anthropogenic NOx emissions between 1967 and 1980 on tropospheric ozone

Abstract: The impact of anthropogenic NOx emission on tropospheric ozone has been investigated. Two statistical models were used for estimating annual global emissions of NOx and for driving the trend in the emission for the years 1966-1980. Both models show a steady increase in the NOx emission, except for two brief periods of leveling off: after 1973 and after 1978. The impact was estimated by calculating the rates of emissions as functions of latitude, longitude, and year, with a one-dimensional (latitudinal) model, which included coupled tropospheric photochemistry and diffusive meridional transport. Steady-state photochemical calculations with prescribed NOx emissions appropriate for 1966 and 1980 indicate an ozone increase of 8-11 percent in the Northern Hemisphere, a result compatible with the rise in ozone suggested by the observations.

Cape Grim isotope measurements ― A preliminary assessment

Abstract: Measurements of the stable carbon isotope ratio in atmospheric CO2 permit a distinction between variations resulting from biospheric and oceanic exchange. In situ extraction of CO2 from Cape Grim air (41°S) for isotopic analysis commenced in 1977; however difficulties with technique reliability were experienced until 1982. Since 1982, 2.6 years of relatively consistent values have accumulated. For a preliminary assessment of the latter data, estimates of the isotopic behaviour from the global transport and inter-reservoir exchange model of Pearman and Hyson (1985) have been employed. The assessment demonstrates the precision requirements of a carbon isotope monitoring program and the relevance of the isotope measurements as a constraint on parameterization of the model. Clear evidence of the changes due to fossil fuel combustion is seen in the year-to-year differences in δ13C, with the mean and standard error of the overall trend being −0.025±0.005‰ yr-1. A significant seasonal variation in δ13C is apparent, despite considerable inter-annual variability possibly associated with the 1982/83 ENSO phenomena. The average peak-to-peak amplitude is 0.055±0.014‰ with a maximum on day 85±15 (approx. 26 March). There is some evidence for a complex seasonal inter-relationship between concentration and isotope ratio, both in the Cape Grim data and in Mook et al. (1983) South Pole data, but with marked differences between the stations, and with both different from the model estimates. In particular, the Cape Grim results suggest that exchange with Southern Hemisphere biosphere is the main contributor to the seasonal variation in isotope ratio at this latitude.

Determination of selected atmospheric aromatic hydrocarbons at remote continental and oceanic locations using photoionization/flame-ionization detection

Abstract: A new gas chromatographic technique with a modified photoionization detector connected in series with a conventional flame ionization detector was used to determine low concentrations of atmospheric hydrocarbons in remote atmospheres. Average mixing ratios of five aromatic hydrocarbons measured between 42°N and 30°S latitude in the Pacific Ocean in October/November 1983 were highest in the Northern Hemisphere. The average mixing ratios in the northern and southern marine atmospheres were 49±25 ppt (n=35) and 10±2 ppt (n=21) for benzene, 20±12 ppt (n=32) and 5.6±1.6 ppt (n=12) for toluene, 7.6±3.7 ppt (n=35) and 3.7±1.6 ppt (n=21) for ethylbenzene, 25±12 ppt (n=35) and 13±5 ppt (n=20) for the sum of m- and p-xylenes, and 14±6 ppt (n=35) and 6.6±3.0 ppt (n=21) for o-xylene, respectively. The first latitudinal gradients for these five aromatic compounds are reported. Benzene and toluene mixing ratios measured between July 1982 and October 1983 at a rural, mid-latitude continental site in eastern Washington state gave average values of 226±108 ppt and 133±84 ppt, respectively, with higher wintertime than summertime benzene levels. These continental samples gave calculated air mass ages averaging six days based on benzene-to-toluene ratios.

Concentration and size variation of condensation nuclei at Mawson, Antarctica

Abstract: Condensation nucleus (CN) concentrations have been measured at Mawson (67.6°S, 62.9°E) since mid 1981. Weekly median concentrations have an annual cycle with a maximum of around 300 to 400 cm-3 in summer and a minimum of a few tens of particles per cm-3 in winter. In this respect Mawson behaves very much like an Antarctic continental location. Preliminary measurements of the size distribution of CN particles taken over a nine month period suggest a seasonal change in typical particle radius from around 0.01 μm in winter to around 0.04 μm in summer. Diurnal variation in the CN concentration is generally very weak and does not show any systematic relation to the pronounced diurnal variation in wind-speed at Mawson.

Radon measurements as an aid to the interpretation of atmospheric monitoring

Abstract: Radon has been measured continuously at Cape Grim, Tasmania with a detection limit of about 0.05 Bq m-3 (1.4 pCi m-3). The annual average level from a close continental source is 3.8 Bq m-3, whereas the level in maritime air streams is typically 0.5 Bq m-3. The contribution of the ocean is about 0.04 Bq m-3, which indicates that more than 90% of radon in maritime air is from a continent. Thus radon can provide much less equivocal evidence of the degree of continental influence on an air stream than can other atmospheric constituents, whose sources and loss mechanisms are more complex. A knowledge of the past history of an air stream is important in the interpretation of atmospheric measurements.

Interpretation of Mauna Loa Atmospheric Transmission Relative to Aerosols, Using Photometric Precipitable Water Amounts

Abstract: Precipitable water measurements made coincident in time and space with direct broadband solar irradiance measurements are used in conjunction with an atmospheric transmission model to derive a parameter whose major dependence is on total aerosol extinction. Irradiance measurements are used to calculate an atmospheric transmission factor (ATF) that is independent of the instrument calibration and the extraterrestrial solar constant. The dependency of the ATF on precipitable water is determined using LOWTRAN5, an atmospheric transmission model with high spectral resolution. Precipitable water measurements are then used to adjust the measured ATF to correspond to an ATF value obtained for a constant precipitable water amount. The remaining variability in the adjusted ATF is due mostly to aerosol extinction. The technique is applied to a 6-year period (1978–1983) for clear-sky mornings at Mauna Loa, Hawaii (MLO). MLO ATF aerosol residuals are compared with independently measured monochromatic aerosol optical depth. Results show that the ATF aerosol residual is nearly equal to the 500 nm aerosol optical depth prior to the eruption of E1 Chichon, at which time a nonlinear time-dependent relationship between the two quantities is evident. ATF aerosol residuals reflect the spectrally integrated aerosol influence on transmission and, therefore, could indicate better than monochromatic optical depth the radiation balance perturbations due to aerosols. The 6-year precipitable water record for MLO, determined from a dual-channel sunphotometer, has a mean value of 0.3 cm. An annual cycle in precipitable water is evident, as is a 4-month 5-standard-deviation “drought” from December 1982 through March 1983.

An aerosol climatology of Samoa

Abstract: An atmospheric monitoring station is operated at Cape Matatula, American Samoa, by the Geophysical Monitoring for Climatic Change program under the National Oceanic and Atmospheric Administration. A nearly continuous record of condensation nucleus (CN) concentration and multiwavelength aerosol scattering extinction coefficient (σsp) is available from mid-1977 to the present. This report presents the 1977–1983 data. The long-term mean of CN concentration is 274 cm−3, the long-term mean of σsp(550 nm) is 1.54 × 10−5, and no significant long-term, annual, or diurnal trend is apparent in either data record.

A study of the vertical distribution of methyl chloride (CH3Cl) in the midlatitude stratosphere

Abstract: The vertical distribution of the CH3Cl mixing ratio in the stratosphere has been measured from samples collected during two balloon flights on the 21 October 1982 and 10 September 1983. Measurements were made with two analytical techniques that were also employed for previous analyses of stratospheric samples: gas chromatography (GC) and a gas chromatograph/mass spectrometer (GC/MS) combination. The results from all balloon flights performed to date are combined to derive an average experimental profile of CH3Cl at midlatitudes. The profile shows that the CH3Cl mixing ratio decreases by about one order of magnitude between 20 and 30 km altitude. A comparison of the new observations with model profiles reveals discrepancies in the lower stratosphere that amount to a factor of about 3. Possible causes for these discrepancies are discussed.