Chemical characteristics of continental outflow from Asia to the troposphere over the western Pacific Ocean during September–October 1991: Results from PEM‐West A

Abstract

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.

Global distributions of C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, HCN, and PAN retrieved from MIPAS reduced spectral resolution measurements

“…50 pptv) mixing ratios very close to our MI-PAS RR monthly mean mixing ratios. Singh et al (1996) measured median mixing ratios in polluted air masses by in situ measurements above the southern Atlantic Ocean of 160 pptv and 50 pptv as background at 11.5 km in September andOctober 1992. González Abad et al (2011) reported long-term and global averaged mixing ratios profiles of C 2 H 2 measured by ACE.…”

“…Liang et al, 2007;Wolfe et al, 2007), to assess chemical plume aging (e.g. Talbot et al, 1996;Xiao et al, 2007), to assign polluted air masses to particular pollution events (e.g. von Glatthor et al, 2007Glatthor et al, , 2009Shim et al, 2007), and to assess their potential transport into the stratosphere (e.g.…”

Interannual variability of ozone and carbon monoxide at the Whistler high elevation site: 2002–2006

“…Major field campaigns over the Pacific since the early 1980s have provided coupled CO and O 3 measurements (e.g. Talbot et al, 1994;Heald et al, 2003;Bertschi et al, 2005;Liang et al, 2007). Satellite observations also expand the spatial and temporal scale of both emission and transport of pollutants.…”

Chemical characteristics of air from differing source regions during the Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A)

“…Although all chemical species measured aboard the DC-8 were considered, we will focus on species that are most important to the given geographical categories. Previous studies that have used somewhat similar approaches include Gregory et al [1996,1999] and Talbot et al [ , 1996a …”