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.

An aircraft measurement program was undertaken in the savanna regions of central South America in the dry season of 1980 to investigate the atmospheric effects of large-scale biomass burning. The smoke from the fires was found to be largely confined within an approximately 3-km-deep boundary layer capped by a subsidence inversion or a stable layer. This condition typically persists for week-long periods as a result of the synoptic subsidence occurring during the dry season. Photochemical production of ozone occurred in the polluted layer over the entire Cerrado region of central Brazil. The factors controlling the concentration of this ozone are examined, and an estimate of the amount of ozone produced is reported.

Reported here are O3 data recorded during the 1977 and 1978 Gametag field experiments. Nearly two thirds of these data were recorded in the free troposphere over the altitude range of 5–6.5 km. The remaining one third were collected in the atmospheric boundary layer, typically 0.3–1 km above the surface terrain. The latitude range covered by these measurements was 58°S to 70°N and involved flight operations over northern Canada, Alaska, the southeastern/central Pacific (northern hemisphere), and the central/western Pacific in the southern hemisphere. This data base is unique in that all ozone measurements were recorded on the same set of three ozone analyzers, on a single aircraft platform, and over a short time span. Key observations include (1) systematically higher average free tropospheric O3 levels in the northern versus southern hemisphere with the global minimum in ozone occurring at tropical latitudes; (2) extensive O3 layering within the free troposphere over large geographical areas of the northern hemisphere and, to a much lesser extent, remote areas of the southern hemisphere; (3) boundary‐layer O3 concentration levels which were consistently lower than free tropospheric O3 levels in remote areas of the northern hemisphere but only slightly lower than those levels observed in the southern hemisphere; and (4) the finding in April/May 1978 of a latitudinal zone, 13°S to 2°N, virtually devoid of boundary layer O3. A comparison of these data with those of other investigators, together with a discussion of the relevancy of these observations to our present understanding of the tropospheric O3 budget, is presented.

The phase I Gametag (Global Atmospheric Measurements Experiment of Tropospheric Aerosols and Gases) aerosol measurements were designed to provide an initial assessment of the levels, types, and optical effects of tropospheric aerosols in remote marine and continental regions and to examine the possible causal relationships between the observed distributions and the dominant factors controlling aerosol population: chemical and physical transformations, source and sink strengths, and transport. We used size‐number data to determine mass concentrations and to estimate extinction, using nominal optical properties. Filter and impactor data have been used to determine aerosol composition, and correlative aircraft measurements have been used to aid in our data interpretation. Our data have been used to generate latitudinal profiles along our Pacific flight tracks. Our continental measurements, in general, show bimodal aerosol size distributions that reflect different source for each mode. The aerosol population consists primarily of crustal aerosols with r ≥ 0.5 μm and sulfate and combustion aerosols with r < 0.5 μm, with only a minor sea salt component. Owing to vertical mixing, there are no qualitative differences between the boundary layer and the free troposphere. Our data indicate that crustal aerosols represent a significant component of a background tropospheric aerosol in western North America and suggest that the possible contribution of the crustal aerosol to extinction should not be ignored. Pacific marine measurements show a qualitative difference between the boundary layer and the free troposphere. The boundary‐layer aerosol population is dominated by a bimodal sea spray aerosol; optical effects and mass concentration are dominated by a mode with a volume mean radius of ∼1 μm. Our measurements show only a small crustal component of the marine boundary‐layer aerosol. Our data indicate a loss of Cl from the sea spray aerosol, with the greatest loss in the small particles. We have inferred a background concentration of 0.2 ppbm for our measured particles that does not appear to be directly related to the sea spray aerosol. We have identified some of these particles as locally produced secondary aerosols; simultaneous measurements of gaseous species support this interpretation. Our Pacific free tropospheric aerosol measurements show a highly variable aerosol component, with local variations in concentration by 1 order of magnitude within a few kilometers. Our measured total aerosol and crustal component concentrations show a general decrease from north to south. Our lowest mean mid tropospheric concentration was seen south of 20°S; we have identified this mean concentration of 0.08 ppbm as a midtropospheric background aerosol.

We describe modifications of a commercial NOx detector for very high sensitivity and ease of computer assisted data acquisition. These changes include a larger gold-coated reaction chamber, increased ozone flow, a faster vacuum pump, analog outputs to define mode and range status, and enhanced cooling for the PMT. The detection limit, defined as a signal-to-noise ratio of 1:1 at the ±2 σ level is about 10 ppt with a 1/e response time of about 20 s or about 45 ppt for 1 s. Detection of other reactive nitrogen compounds is also discussed.