[1] Airborne measurements of a large number of oxygenated volatile organic chemicals (OVOC) were carried out in the Pacific troposphere (0.1-12 km) in winter/spring of 2001 (24 February to 10 April). Specifically, these measurements included acetone (CH 3 COCH 3 ), methylethyl ketone (CH 3 COC 2 H 5 , MEK), methanol (CH 3 OH), ethanol (C 2 H 5 OH), acetaldehyde (CH 3 CHO), propionaldehyde (C 2 H 5 CHO), peroxyacylnitrates (PANs) (C n H 2n+1 COO 2 NO 2 ), and organic nitrates (C n H 2n+1 ONO 2 ). Complementary measurements of formaldehyde (HCHO), methyl hydroperoxide (CH 3 OOH), and selected tracers were also available. OVOC were abundant in the clean troposphere and were greatly enhanced in the outflow regions from Asia. Background mixing ratios were typically highest in the lower troposphere and declined toward the upper troposphere and the lowermost stratosphere. Their total abundance (SOVOC) was nearly twice that of nonmethane hydrocarbons (SC 2 -C 8 NMHC). Throughout the troposphere, the OH reactivity of OVOC is comparable to that of methane and far exceeds that of NMHC. A comparison of these data with western Pacific observations collected some 7 years earlier (February-March 1994) did not reveal significant differences. Mixing ratios of OVOC were strongly correlated with each other as well as with tracers of fossil and biomass/biofuel combustion. Analysis of the relative enhancement of selected OVOC with respect to CH 3 Cl and CO in 12 plumes originating from fires and sampled in the free troposphere (3-11 km) is used to assess their primary and secondary emissions from biomass combustion. The composition of these plumes also indicates a large shift of reactive nitrogen into the PAN reservoir thereby limiting ozone formation. A three-dimensional global model that uses state of the art chemistry and source information is used to compare measured and simulated mixing ratios of selected OVOC. While there is reasonable agreement in many cases, measured aldehyde concentrations are significantly larger than predicted. At their observed levels, acetaldehyde mixing ratios are shown to be an important source of HCHO (and HO x ) and PAN in the troposphere. On the basis of presently known chemistry, measured mixing ratios of aldehydes and PANs are mutually incompatible. We provide rough estimates of the global sources of several OVOC and conclude that collectively these are extremely large (150-500 Tg C yr À1 ) but remain poorly quantified.

[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.

Methyl chloride, methyl bromide, and methyl iodide measurements in and over the eastern Pacific (40°N and 32°S latitude) show mean air concentrations of 633 parts per trillion (ppt), 23 ppt, and 2 ppt, and mean surface seawater concentrations of 11.5 ng/l, 1.2 ng/l, and 1.6 ng/l respectively. Long‐term ambient measurements at a marine Pacific site (39°N) show an essentially unchanging background, with some indication of high concentrations of methyl bromide and methyl iodide during summertime. The oceanic data indicate a mean surface supersaturation of 275%, 250%, and 340%, respectively, for these three methyl halides. Depth profiles show that methyl halides are most abundant in the top mixed layer of the ocean. Oceanic concentrations of methyl chloride and methyl bromide are significantly correlated (linear regression coefficient of 0.85), suggesting a common source. No relationship between oceanic methyl iodide concentrations and the other two halides could be found. Coexistence of high concentrations of methyl iodide with relatively low concentrations of methyl chloride and vice versa provided no direct support for the hypothesis that chloride ion reactions with methyl iodide may be the dominant oceanic source of methyl chloride. For the eastern Pacific, mean ocean to air fluxes (in units of 10−7 g cm−2 yr−1) of 13, 1, and 1 are determined for methyl chloride, methyl bromine, and methyl iodide, respectively. When extrapolated to global waters, they provide an adequate source to explain the atmospheric reservoir of these organic halides. Total organic bromine and iodine measurements would suggest that methyl bromide and methyl iodide contribute predominately to the tropospheric bromine and iodine organic reservoir.

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.

The global distribution of fluorocarbon-12 and fluorocarbon-11 is used to establish a relatively fast interhemispheric exchange rate of 1 to 1.2 years. Atmospheric residence times of 65 to 70 years for fluorocarbon-12 and 40 to 45 years for fluorocarbon-l1 best fit the observational data. These residence times rule out the possibility of any significant missing sinks that may prevent these fluorocarbons from entering the stratosphere. Atmospheric measurements of methyl chloroform support an 8-to 10-year residence time and suggest global average hydroxyl radical (HO) concentrations of 3 x 10(5) to 4 x 10(5) molecules per cubic centimeter. These are a factor of 5 lower than predicted by models. Additionally, methyl chloroform global distribution supports Southern Hemispheric HO levels that are a factor of 1.5 or more larger than the Northern Hemispheric values. The long residence time and the rapid growth of methyl chloroform cause it to be a potentially significant depleter of stratospheric ozone. The oceanic sink for atmospheric carbon tetrachloride is about half as important as the stratospheric sink. A major source of methyl chloride (3 x 10(12)grams per year), sufficient to account for nearly all the atmospheric methyl chloride, has been identified in the ocean.