Changes in the distribution of dicarboxylic acids, kotocarboxylic acids and dicarbonyls in the rain and aerosol samples simultaneously collected during wet precipitation events

摘要

Rain and aerosol samples were simultaneously collected from Tokyo and analyzed for the molecular distribution of dicarboxylic acids (C_2-C_(11)), ketoacids (C_2-C_6, pyruvic acid) and #alpha#-dicarbonyls (glyoxal and methylglyoxal) using a capillary GC and GC/MS. The samples were also analyzed for rainwater total organic carbon (TOC) and aerosol water soluble organic carbon (WSOC). Concentrations of total dicarboxylic acids in rain (C_2-C_(11), 25.8-572#mu#G L~(-1)) as well as rain flux of diacids significantly decreased as a function of time. TOC in rain also showed a decrease with time. In contrast, the aerosol concentrations (300 rpprox 1720 ng m~(-3)) of diacids did not decrease with time during the wet precipitation process, rather they increased in the middle of rainfall events. These results suggest that dicarboxylic acids present in the upper levels of the air column were scavenged in an early stage of rainfall probably by in-cloud scavenging process, however, dicarboxylic acids in the lower atmosphere were not effectively removed by below-cloud scavenging. Air masses containing more dicarboxylic acids were suggested to be supplied over the sampling site during rain events probably by lateral and/or vertical transport mechanism.