Abstract.An important objective of the Pacific Exploratory Mission-West A (PEM-West A) was the chemical characterization of the outflow of tropospheric trace gases and aerosol particles from the Asian continent over the western Pacific Ocean. This paper summarizes the chemistry of this outflow during the period September -October 1991. The vertical distributions of CO, C2H6, and NO× showed regions of outflow at altitudes below 2 km and from 8 to 12 km. Mixing ratios of CO were =130 parts per billion by volume (ppbv), =1000 parts per trillion by volume (pptv) for C2H6, and =100 pptv for NOx in both of these regions. Direct outflow of Asian industrial materials was clearly evident at altitudes below 2 kin, where halocarbon tracer compounds such as CH3CCI 3 and C2C14 were enhanced about threefold compared to aged Pacific air. The source attribution of species outflowing from Asia to the Pacific at 8 -12 km altitude was not straightforward.Above l0 km altitude there were substantial enhancements of NOy, 03, CO, CH 4 SO2, C2H6, C3H 8, C2H 2, and aerosol 21°pb but not halocarbon industrial tracers. These air masses were rich in nitrogen relative to sulfur and contained ratios of C2H2/CO and C3Hs/C2H6 (=1.5 and 0.1 respectively) indicative of severalday-old combustion emissions. It is unclear if these emissions were of Asian origin, or if they were rapidly transported to this region from Europe by the high wind speeds in this tropospheric region (60 -70 m s_). The significant cyclonic activity over Asia at this time could have transported to the upper troposphere emissions from biomass burning in Southeast Asia or emissions from the extensive use of various biomass materials for cooking and space heating. Apparently, the emissions in the upper troposphere were brought there by wet convective systems since water-soluble gases and aerosols were depleted in these air masses. Near 9 km altitude there was a distinct regional outflow that appeared to be heavily influenced by biogenic processes on the Asian continent, especially from the southeastern area. These air masses contained CH4 in excess of 1800 ppbv, while CO 2 and OCS were significantly depleted (349 -352 ppmv and 450 -500 pptv, respectively). This signature seemingly reflected CH 4 emissions from wetlands and rice paddies with coincident biospheric uptake of tropospheric CO 2 and OCS.

Biomass-burning impacted air masses sampled over central and eastern Canada during the summer of 1990 as part of ABLE 3B contained enhanced mixing ratios of gaseous HNO3, HCOOH, CH3COOH, and what appears to be (COOH)2. These aircraft-based samples were collected from a variety of fresh burning plumes and more aged haze layers from different source regions. Values of the enhancement factor, delta X/delta CO, where X represents an acidic gas, for combustion-impacted air masses sampled both near and farther away from the fires, were relatively uniform. However, comparison of carboxylic acid emission ratios measured in laboratory fires to field plume enhancement factors indicates significant in-plume production of HCOOH. Biomass-burning appears to be an important source of HNO39 HCOOH, and CH3COOH to the troposphere over subarctic Canada

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et al., 1985; Merrill et al., 1989; Gao et al., 1992]. This transport pattern, combined with increasing industrialization in the Copyright 1996 by the American Geophysical Union.Paper number 94JD03117. 014g-0227/96/94JD-03117505.00 NH4 +, K*, Mg 2+, and Ca 2+) and the natural radionuclides 2'°Pb and 7Be were determined.Lead 210 AnalysisThe filters for soluble ionic analyses were extracted in the field within 12 hours of each flight, following procedures that have been previously described [Talbot et aL, 1986[Talbot et aL, , 1992. These extracts were analyzed for anionic species by ion chromatography immediately after extraction. Aliquots preserved with chloroform were subsequently analyzed for cationic species, again by ion chromatography, in the laboratory at the University of New Hampshire (UNH) after completion of the mission.All filters for radionuclide analyses were subjected to nondestructive gamma spectrometry at UNH within 2 -4 weeks of collection to quantify _Be activities [Dibb, 1990a; Dibbet al., 1992].(Groups of filters were express mailed to New Hampshire from the field sites at weekly intervals.) Uncertainties in 7Be activity due to counting statistics were below 20°/, for 16-hour counting periods when the activity exceeded 100 fCi m 3 but increased for samples with lower activity. The small air volumes sampled precluded quantification of 2t°Pb by direct gamma counting. We determined z_°Pb activities by alpha spectrometric determination of 21°Po (with Z°_Po tracer added and plating onto Ag planchets) [Flynn, 1968; Dibb, 1990b] after allowing 1 year for 21°poingrowth.The zt°po/Zt°Pb ratio will be 85-90% of its value at secular equilibrium al_er 12 -14 months (the last samples were processed 2 months after the first), assuming that the aerosols were so young at collection that no 2'°Po was present. We did not correct the zt°pb activities reported below for this departure from equilibrium, hence they may be as much as 10 -15% low. ResultsA total of 98 aerosol samples were collected during PEM-West A. All of the samples had 2_°Pb activities that could be quantified by our techniques, while 7Be and SO4 _ were quantified in 82 and 90 samples, respectively. Nitrate and NH4 ÷ mixing ratios were also high enough to quantify in more than I/2 the samples, but all other soluble ionic species were below our detection limits more often than not (Table 1). Mean concentrations of all aerosolassociated species, except 7Be, were higher in the 0-to 2-km altitude range than at higher elevations. This difference would be accentuated for most of the ionic species if all samples below detection limit were included in the averaging process (Table 1). We expected 2_°Pb activities to decrease rapidly with altitude and 7Be activities to increase. However, the observed contrasts between boundary layer and free tropospheric activities of 7Be and z_°Pb were quite small. Nearly 1/2 of the samples above 2 km were collected between 6 and 13 km where 2_°Pb activities near or below 2 fCi ms STP were expected [e.g., Moore ...

As part of NASA's Arctic Boundary Layer Expedition 3A and 3B field measurement programs, measurements of NOx, HNO3, PAN, PPN, and NOy were made in the middle to lower troposphere over Alaska and Canada during the summers of 1988 and 1990. These measurements are used to assess the degree of closure within the reactive odd nitrogen (NxOy) budget through the comparison of the values of NOy measured with a catalytic convertor to the sum of individually measured NOy (i) compounds (i.e., ΣNOy (i) = NOx + HNO3 + PAN + PPN). Significant differences were observed between the various study regions. In the lower 6 km of the troposphere over Alaska and the Hudson Bay lowlands of Canada a significant fraction of the NOy budget (30 to 60%) could not be accounted for by the measured ΣNOy (i). This deficit in the NOy budget is about 100 to 200 parts per trillion by volume (pptv) in the lower troposphere (0.15 to 3 km) and about 200 to 400 pptv in the middle free troposphere (3 to 6.2 km). Conversely, the NOy budget in the northern Labrador and Quebec regions of Canada is almost totally accounted for within the combined measurement uncertainties of NOy and the various NOy (i) compounds. A substantial portion of the NOy budget's “missing compounds” appears to be coupled to the photochemical and/or dynamical parameters influencing the tropospheric oxidative potential over these regions. A combination of factors are suggested as the causes for the variability observed in the NOy budget. In addition, the apparent stability of compounds represented by the NOy budget deficit in the lower‐altitude range questions the ability of these compounds to participate as reversible reservoirs for“active”odd nitrogen and suggest that some portion of the NOy budget may consist of relatively unreactive nitrogen‐containing compounds.