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Field measurement programs in Brazil during the dry seasons in August and September 1979 and 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, NOx, N20 , CH 4 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 03 in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer.

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Results are presented from the 2‐month Polar Sunrise Experiment 1988, which was undertaken to further investigate the cause of ozone destruction during spring in the lower Arctic atmosphere. A strong anticorrelation between the decrease in ozone and concurrent increase in bromine compounds collected on filters observed during a 21‐day period in 1986 was confirmed. It is shown that the reason for this observation is a meteorological modulation which alternately brings to the sampling location lower boundary layer air, depleted in ozone and enriched in filterable bromine, and free tropospheric air with abundant ozone and few bromine compounds. Several other compounds that may have a bearing on the chemical reactions leading to ozone depletion were measured. Bromoform, a potential source for Br atoms, was found to be present at levels between 1 and 10 parts per trillion by volume (pptv); good evidence was obtained that, as with filterable bromine, it had increased in ozone depleted boundary layer air. The mean NO2 level was 85 pptv with an estimated uncertainty of a factor less than 2. However, this measurement of NO2 may have been the sum of NO2+N2O5. The possibility that Br atoms are formed from an N2O5+NaBr interaction is therefore not ruled out. There was a good indication that apparent NO2 was depleted during episodes of low ozone. An upper limit for the mixing ratio of formaldehyde was found to be 39 pptv, while acetaldehyde was observed at mixing ratios of ca. 65 pptv. Ethylene and acetylene were also found to be depleted concurrently with O3. These compounds do react with Br radicals in air (as do the aldehydes) and it is speculated that they may create a link with HOx. chemistry. Data on several other chemical compounds are also presented. Their participation in the O3 depletion chemistry is less clear. The implications of the measurements with respect to the hypothesis that the ozone depletion are due to a BrOx‐O3 destruction cycle are explored.

The third joint Soviet‐American Gases and Aerosols (SAGA 3) experiment was a research cruise conducted aboard the Akademik Korolev in February and March 1990. The cruise covered a region of the equatorial Pacific Ocean from 15°N to 10°S latitude and 144° to 165°W longitude. On this cruise we collected samples for the measurement of alkyl nitrates (RONO2), nonmethane hydrocarbons (NMHC) and several halocarbon gases. Though there are few data available for comparison in this region of the marine boundary layer, the mixing ratios of the trace gases we measured are within the range of prior measurements in the remote atmosphere. Latitudinal gradients were found for trace gases with predominantly anthropogenic sources, e.g., methylene chloride, tetrachloroethylene, and acetylene; higher concentrations in the North Pacific atmosphere decreased slowly across the Equator to the South Pacific. More stable gases, e.g. methyl chloride and methyl bromide, had no pronounced variation across the equator. A biogenic source of two organobromine compounds, bromoform and dibromochloromethane, was indicated by maximum mixing ratios of these species over the equator where indicators of biological productivity (e.g., chlorophyll) in the surface ocean water also maximized. Alkyl nitrates were found at levels higher than predicted from steady state calculations based on measured mixing ratios of hydrocarbons and NO. The measured levels of RONO2 suggest long‐range transport as one mechanism contributing to elevated concentrations of alkyl nitrates in the remote troposphere. However, the distributions of C2 and C3 alkyl nitrates over the equator were similar to the organobromine gases. This distribution suggests a possible oceanic source for alkyl nitrates to the atmosphere.