Characteristics and emissions of isoprene and other non-methane hydrocarbons in the Northwest Pacific Ocean and responses to atmospheric aerosol deposition.

Field investigations in the Northwest Pacific Ocean were carried out to determine the distributions of marine and atmospheric non-methane hydrocarbons (NMHCs), sources and environmental effects. We also conducted deck incubation experiments to investigate the effects of atmospheric aerosol deposition on NMHCs production. The marine NMHCs displayed an increasing trend from the South Equatorial Current to the Oyashio Current. The enhanced phytoplankton biomass and dissolved organic materials (DOM) content in the Kuroshio-Oyashio Extension contributed significantly to isoprene and NMHCs production compared with those in tropical waters and the North Pacific subtropical gyre. The Northwest Pacific Ocean was a significant source of atmospheric NMHCs, with average sea-to-air fluxes of 28.0 ± 38.9, 65.2 ± 73.3, 21.0 ± 26.7, 48.7 ± 62.6, 12.7 ± 15.9, 14.2 ± 16.8, and 41.7 ± 80.4 nmol m-2 d-1 for ethane, ethylene, propane, propylene, i-butane, n-butane, and isoprene, respectively. Influenced by seawater release and OH radical consumption, the atmospheric NMHCs apart from isoprene displayed upward trends with increasing latitude. The deck incubation showed that the addition of aerosols and acidic aerosols significantly boosted phytoplankton biomass, altered community structure, and accelerated the production of isoprene. However, the other six NMHCs showed no obvious responses to atmospheric aerosol deposition in the incubation experiments. In summary, ocean current movements and atmospheric deposition could influence the production and release of isoprene in the Northwest Pacific Ocean.

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.

Emissions and potential controls of light alkenes from the marginal seas of China.

Marine-derived reactive gases constitute a substantial fraction of volatile organic compounds and directly impact atmospheric chemistry and the global climate. Light alkene emissions from marginal seas are limited, and their contribution to atmospheric concentrations is likely underestimated. We surveyed oceanic emissions of ethylene, propylene, and isoprene, as well as their potential controlling factors in the marginal seas of China during the cruises in 2014-2015. Significant temporal-spatial variations in ethylene, propylene, and isoprene concentrations were observed, with the highest occurring in summer near the coastal regions. Isoprene concentrations were primarily controlled by phytoplankton biomass (i.e., Chl-a) in coastal regions, while the elevated concentrations of ethylene and propylene were attributed to photochemical reactions with the high levels of dissolved organic matter (DOM). Additionally, the vertical distributions of ethylene and propylene mirrored light penetration, with exponential decrease in concentrations with depth. However, there were high values of ethylene and propylene observed at deep chlorophyll maximum, suggesting the existence of non-photochemical production pathways, most likely biological origin. Emissions of ethylene, propylene, and isoprene from the marginal seas of China were estimated to be 0.022, 0.024, and 0.011 Tg C yr-1, respectively, indicating they are important contributors to global non-methane hydrocarbons. Due to the scarcity of alkene emission data for marginal seas, current global emissions have been underestimated to some extent. It is essential to incorporate the contributions from marginal seas to accurately estimate alkene budgets on global scales.