Occurance, emission and environmental effects of non-methane hydrocarbons in the Yellow Sea and the East China Sea

The spatial distributions, fluxes, and environmental effects of non-methane hydrocarbons (NMHCs) were investigated in the Yellow Sea (YS) and the East China Sea (ECS) in spring. The average concentrations of ethane, propane, i-/n-butane, ethylene, propylene and isoprene in the seawater were 18.1 ± 6.4, 15.4 ± 4.7, 6.8 ± 2.9, 6.4 ± 3.2, 67.1 ± 26.7, 20.5 ± 8.7 and 17.1 ± 11.1 pmol L⁻¹, respectively. The alkenes in the surface seawater were more abundant than their saturated homologs and NMHCs concentrations (with the exception of isoprene) decreased with carbon number. The spatial variations of isoprene were consistent with the distributions of chlorophyll a (Chl-a) and Chaetoceros, Skeletonema, Nitzschia mainly contributed to the production of isoprene, while the others’ distributions might be related to their photochemical production. Observations in atmospheric NMHCs indicated alkanes in the marine atmosphere decreased from inshore to offshore due to influence of the continental emissions, while alkenes were largely derived from the oceanic source. In addition, no apparent diurnal discrepancy of atmospheric NMHCs (except for isoprene) were found between daytime and night. As the main sink of NMHCs in seawater, the average sea-to-air fluxes of ethane, propane, i-/n-butane, ethylene and propylene were 31.70, 29.75, 18.49, 15.89, 239.6, 67.94 and 52.41 nmol m⁻² d⁻¹, respectively. The average annual emissions of isoprene accounted for 0.1–1.3% of the global ocean emissions, which indicated that the coastal and shelf areas might be significant sources of isoprene. Furthermore, this study represents the first effort to estimate the environmental effects caused by NMHCs over the YS and the ECS and the results demonstrated contributions of alkanes to ozone and secondary organic aerosol (SOA) formation were lower than those of the alkenes and the largest contributor was isoprene.