Compound-specific carbon isotope compositions of individual long-chain n-alkanes in severe Asian dust episodes in the North China coast in 2002

摘要

The molecular compositions and compound-specific carbon isotope compositions of individual long-chain n-alkanes of atmospheric aerosols collected during two severe Asian dust episodes in Qingdao in spring of 2002 were analyzed using gas chromatography/mass spectrometry (GC/MS) and gas chromatography/isotope ratio mass spectrometry (GC/IRMS). Typical plant wax n-alkanes (C_(29) and C_(31)) had lower delta ~(13)C values than those from anthropogenic (engine exhaust) sources (C_(21) - C_(23)). The av-. erage delta ~(13)C value of plant wax n-alkane C_(29) in non-dust episode periods was -30.5 per thousand (-30.3 per thousand - -31.9 per thousand), while -31.3 per thousand (-31.1 per thousand -31.5 per thousand) in dust episode periods; for C31, it was -31.4 per thousand (-31.1 per thousand - -33.0 per thousand) in non-dust episode periods, and -31.7 per thousand (-31.3 per thousand - -32.6 per thousand) in dust episode periods. Plant wax in the dust episode samples was mainly from herbaceous plants via long-range transport, while local plant wax was mainly from deciduous plants and woody plants. In North China coast, 83.3 percent of the plant wax in the severe dust episode samples was from C_3 plants while 80.0 percent for the non-dust samples, indicating that plant wax transported to the northwestern Pacific Ocean by airborne dust from East Asia was mainly from C_3 plants. The results suggest that the molecular and molecular-isotopic compositions of individual long-chain n-alkanes can, as an effective indicator, identify the terrestrial organic components in the dust from East Asia and sediments in the northwest Pacific Ocean.