Occurrence and emission of non-methane hydrocarbons in the East China Sea: roles of phytoplankton assemblages

Environmental context Marine-derived non-methane hydrocarbons (NMHCs) are thought to affect atmospheric oxidation balance and aerosol formation, hence playing an important role in regulating climate. In this study, we report the distributions and sea-to-air fluxes of 10 NMHCs in the East China Sea (ECS), and assess the roles of phytoplankton assemblages in the occurrence and emission of NMHCs in the ECS. The results will improve our understanding of the biogeochemical cycling of NMHCs in marine systems. Abstract Non-methane hydrocarbons (NMHCs) are important reactive trace-gases that are emitted from oceanic sources. However, it remains unclear how phytoplankton, either total biomass or specific species, affect the generation and emission of NMHCs. This study conducted field observations of NMHCs in the East China Sea (ECS) in autumn, 2014. The mean concentrations of ethane, propane, i-butane, n-butane, pentane, ethene, propene, 1-butene, 1-pentene and isoprene were 20.1 ± 3.6, 20.3 ± 20.2, 4.5 ± 0.9, 10.5 ± 2.3, 14.8 ± 3.4, 63.7 ± 20.8, 23.6 ± 6.6, 7.4 ± 2.9, 15.9 ± 4.3 and 69.4 ± 24.9 pmol L−1 respectively. Horizontal and vertical profiles of NMHCs showed that different water masses had distinct influences and the coastal areas had generally higher concentrations of NMHCs. There were significant positive correlations between alkanes or alkenes, which suggested that their production and fates in the surface seawater were similar. A significant positive correlation was observed between the isoprene and Chl-a concentrations, while no significant correlation was found between Chl-a and any other NMHCs. These results highlighted that, although NMHCs can be produced by phytoplankton, using Chl-a data or phytoplankton assemblages to estimate the production of other NMHCs in seawater is unreliable. Therefore, future research must determine the factors that control the production of these NMHCs. In addition, the results of estimated sea-to-air fluxes of NMHCs underscored the importance of the ECS as a source of NMHCs and the related atmospheric volatile organic compounds.