Acetone (CH3COCH3) was found to be the dominant nonmethane organic species present in the atmosphere sampled primarily over eastern Canada (0–6 km, 35°–65°N) during ABLE3B (July to August 1990). A concentration range of 357 to 2310 ppt (= 10−12 v/v) with a mean value of 1140±413 ppt was measured. Under extremely clean conditions, generally involving Arctic flows, lowest (background) mixing ratios of 550±100 ppt were present in much of the troposphere studied. Correlations between atmospheric mixing ratios of acetone and select species such as C2H2, CO, C3H8, C2C14 and isoprene provided important clues to its possible sources and to the causes of its atmospheric variability. Biomass burning as a source of acetone has been identified for the first time. By using atmospheric data and three‐dimensional photochemical models, a global acetone source of 40–60 Tg (= 1012 g)/yr is estimated to be present. Secondary formation from the atmospheric oxidation of precursor hydrocarbons (principally propane, isobutane, and isobutene) provides the single largest source (51%). The remainder is attributable to biomass burning (26%), direct biogenic emissions (21%), and primary anthropogenic emissions (3%). Atmospheric removal of acetone is estimated to be due to photolysis (64%), reaction with OH radicals (24%), and deposition (12%). Model calculations also suggest that acetone photolysis contributed significantly to PAN formation (100–200 ppt) in the middle and upper troposphere of the sampled region and may be important globally. While the source‐sink equation appears to be roughly balanced, much more atmospheric and source data, especially from the southern hemisphere, are needed to reliably quantify the atmospheric budget of acetone.

[1] We report the first in situ measurements of hydrogen cyanide (HCN) and methyl cyanide (CH 3 CN, acetonitrile) from the Pacific troposphere (0-12 km) obtained during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) airborne mission (February-April 2001). Mean HCN and CH 3 CN mixing ratios of 243 ± 118 (median 218) ppt and 149 ± 56 (median 138) ppt, respectively, were measured. These in situ observations correspond to a mean tropospheric HCN column of 4.2 Â 10 15 molecules cm À2 and a CH 3 CN column of 2.5 Â 10 15 molecules cm À2 . This is in good agreement with the 0-12 km HCN column of 4.4 (±0.6) Â 10 15 molecules cm À2 derived from infrared solar spectroscopic observations over Japan. Mixing ratios of HCN and CH 3 CN were greatly enhanced in pollution outflow from Asia and were well correlated with each other as well as with known tracers of biomass combustion (e.g., CH 3 Cl, CO). Volumetric enhancement (or emission) ratios (ERs) relative to CO in free tropospheric plumes, likely originating from fires, were 0.34% for HCN and 0.17% for CH 3 CN. ERs with respect to CH 3 Cl and CO in selected biomass burning (BB) plumes in the free troposphere and in boundary layer pollution episodes are used to estimate a global BB source of 0.8 ± 0.4 Tg (N) yr À1 for HCN and 0.4 ± 0.1 Tg (N) yr À1 for CH 3 CN. In comparison, emissions from industry and fossil fuel combustion are quite small (<0.05 Tg (N) yr À1 ). The vertical structure of HCN and CH 3 CN indicated reduced mixing ratios in the marine boundary layer (MBL). Using a simple box model, the observed gradients across the top of the MBL are used to derive an oceanic loss rate of 8.8 Â 10 À15 g (N) cm À2 s À1 for HCN and 3.4 Â 10 À15 g (N) cm À2 s À1 for CH 3 CN. An air-sea exchange model is used to conclude that this flux can be maintained if the oceans are undersaturated in HCN and CH 3 CN by 27% and 6%, respectively. These observations also correspond to an open ocean mean deposition velocity (v d ) of 0.12 cm s À1 for HCN and 0.06 cm s À1 for CH 3 CN. It is inferred that oceanic loss is a dominant sink for these cyanides and that they deposit some 1.4 Tg (N) of nitrogen annually to the oceans. Assuming loss to the oceans and reaction with OH radicals as the major removal processes, a mean atmospheric residence time of 5.0 months for HCN and 6.6 months for CH 3 CN is calculated. A global budget analysis shows that the sources and sinks of HCN and CH 3 CN are roughly in balance but large uncertainties remain in part due to a lack of observational data from the atmosphere and the oceans. Pathways leading to the oceanic (and soil) degradation of these cyanides are poorly known but are expected to be biological in nature.

A comprehensive group of reactive nitrogen species (NO, NO2, HNO3, HO2NO2, PANs, alkyl nitrates, and aerosol‐NO3−) were measured over North America during July/August 2004 from the NASA DC‐8 platform (0.1–12 km). Nitrogen containing tracers of biomass combustion (HCN and CH3CN) were also measured along with a host of other gaseous (CO, VOC, OVOC, halocarbon) and aerosol tracers. Clean background air as well as air with influences from biogenic emissions, anthropogenic pollution, biomass combustion, convection, lightning, and the stratosphere was sampled over the continental United States, the Atlantic, and the Pacific. The North American upper troposphere (UT) was found to be greatly influenced by both lightning NOx and surface pollution lofted via convection and contained elevated concentrations of PAN, ozone, hydrocarbons, and NOx. Observational data suggest that lightning was a far greater contributor to NOx in the UT than previously believed. PAN provided a dominant reservoir of reactive nitrogen in the UT while nitric acid dominated in the lower troposphere (LT). Peroxynitric acid (HO2NO2) was present in sizable concentrations peaking at around 8 km. Aerosol nitrate appeared to be mostly contained in large soil based particles in the LT. Plumes from Alaskan fires contained large amounts of PAN and aerosol nitrate but little enhancement in ozone. A comparison of observed data with simulations from four 3‐D models shows significant differences between observations and models as well as among models. We investigate the partitioning and interplay of the reactive nitrogen species within characteristic air masses and further examine their role in ozone formation.

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In September/October 1992 an instrumented DC‐8 aircraft was employed to study the composition and chemistry of the atmosphere over the southern tropical Atlantic Ocean. Analysis of measurements, which included tracers of biomass combustion and industrial emissions, showed that this atmosphere was highly influenced by biomass burning emissions from the South American and African continents. Marine boundary layer was generally capped off by a subsidence inversion and its composition to a large degree was determined by slow entrainment from aloft. Insoluble species (such as PAN, NO, hydrocarbons, CO) were enhanced throughout the troposphere. Soluble species (such as HNO3, HCOOH, H2O2) were minimally elevated in the upper troposphere in part due to scavenging during cloud (wet) convection. Ozone mixing ratios throughout the South Atlantic basin were enhanced by ≈20 ppb. These enhancements were larger in the eastern South Atlantic (African emissions) compared to the western South Atlantic (South American emissions). In much of the troposphere, total reactive nitrogen (NOy) correlated well with tracers of biomass combustion (e.g., CH3Cl, CO). Although NOx (NO + NO2) correlated reasonably with these tracers in the lower (0–3 km) and middle troposphere (3–7 km), these relationships deteriorated in the upper troposphere (7–12 km). Stratospheric intrusions were found to be a minor source of upper tropospheric NOx or HNO3. Sizable nonsurface sources of NOx (e.g., lightning) as well as secondary formation from the NOy reservoir species (such as HNO3, PAN, and organic nitrates) must be invoked to explain the NOx abundance present in the upper troposphere. It is found that HNO3, PAN, and NOx were able to account for most of the NOy, in the middle troposphere (3–7 km); but a significant shortfall was present in the upper troposphere (7–12). This shortfall was also most pronounced in air masses with low HNO3. The reasons for the upper tropospheric reactive nitrogen shortfall is probably due to instrumental uncertainties and the presence of unidentified organic and inorganic nitrogen species.