Distribution characteristics and environmental effects of non-methane hydrocarbons in the East China Sea

Abstract

Non-methane hydrocarbons (NMHCs) are important reactive compounds in the atmosphere which are crucial to the formation of ozone (O3) and secondary organic aerosol (SOA). In this study, the distribution characteristics, sea-to-air fluxes, and environmental effects of NMHCs were investigated in the East China Sea during spring and autumn. Affected by abundant nutrients and dissolved organic matter in the coastal area, NMHCs concentrations inshore were higher than those offshore. The mean concentrations of ethane, ethene, propane, propene, and isoprene were 5.1, 3.8, 6.0, 2.3, and 4.0 times higher in spring than autumn, respectively. In spring, the higher isoprene concentrations might have been due to the higher phytoplankton biomass and outbreak of dinoflagellates, while elevated concentrations of other NMHCs were primarily due to photochemical processes associated with high level of solar radiation. Influenced by terrestrial input and atmospheric chemical reactions, atmospheric concentrations of NMHCs were significantly higher in autumn than in spring. The mean concentrations of ethane, ethene, propane, propene, and isoprene were 221 ± 92.4, 182 ± 112, 198 ± 184, 46.4 ± 25.4, and 7.0 ± 2.9 pptv in spring, and 1090 ± 353, 655 ± 519, 701 ± 329, 476 ± 388, and 35.0 ± 23.2 pptv in autumn, respectively. The mean sea-to-air fluxes of the five NMHCs were 132 ± 126, 658 ± 591, 123 ± 128, 93.4 ± 89.0, and 120 ± 98.6 nmol m−2 d−1 in spring and 31.1 ± 25.9, 352 ± 212, 36.5 ± 40.5, 71.2 ± 43.9, and 78.6 ± 64.8 nmol m−2 d−1 in autumn, respectively. In addition, according to the environmental effects of NMHCs, alkenes exhibited higher atmospheric chemical reactivity and were the major contributors to O3 and SOA formation.