Major sinks of tropospheric CO, C 2H 6, and C 2H 2 are reactions with the hydroxyl radical (OH). Natural gas and automobile emissions are important sources of C 2H 6 and C 2H 2, respectively. In addition, combustion of fossil fuel and oxidation of methane (CH 4) and NMHCs also provide important sources for tropospheric CO. As biomass burning products, CO, C 2H 6, C 2H 2, and HCN have been observed in the field and in laboratory fire experiments. Biomass burning is a significant source of tropospheric CO, nonmethane hydrocarbons (NMHCs), and hydrogen cyanide (HCN). High tropospheric O 3 due to biomass burning in southeast Asia was observed by ozonesondes in Hong Kong (22.2°N, 114.3☎) in April 1994, coinciding with the dry season in southeast Asia. Changes in the tropospheric concentration of these molecules could affect the regional and global tropospheric O 3 budget.
Carbon monoxide (CO), ethane (C 2H 6), and acetylene (C 2H 2) are important tropospheric ozone (O 3) precursors. Trajectory calculations, global fire maps, and satellite smoke images revealed that biomass burning in eastern Siberia from mid-July to early October 1998 was the major cause of the elevated levels in tropospheric CO, C 2H 6, C 2H 2, and HCN observed in northern Japan in 1998. Significant increases of CO, C 2H 6, and C 2H 2 took place in August–October 1998. HCN amounts were found to be much higher than its seasonal mean value throughout 1998 with a 65% maximum increase in August 1998. Abnormally high tropospheric amounts of the four molecules were recorded in 1998. Deviation of HCN relative to its seasonal mean value (ΔHCN) is correlated with the similar deviation of CO (ΔCO), indicating that enhancements of CO and HCN above the mean levels were probably due to the same sources.
Good correlations between CO, C 2H 6, and C 2H 2 indicated that they had similar sources and underwent similar dilution processes. The retrievals show significant seasonal variations in the tropospheric content of the four molecules over northern Japan with maxima in winter-spring (February–April) for CO, C 2H 6, and C 2H 2 and in summer (May–July) for HCN. The spectra were recorded with high spectral resolution Fourier transform infrared (FTIR) spectrometers at Moshiri (44.4°N) and Rikubetsu (43.5°N) in northern Japan from May 1995 to June 2000. Tropospheric column amounts and mixing ratios of CO, C 2H 6, C 2H 2, and HCN were retrieved from ground-based infrared solar spectra using a vertical profile retrieval algorithm (SFIT2).
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