Assessing the Intensity of Marine Biogenic Influence on the Lower Atmosphere: An Insight into the Distribution of Marine Biogenic Aerosols over the Eastern China Seas.

Marine biological activities make a non-negligible contribution to atmospheric aerosols, leading to potential impacts on the regional atmospheric environment and climate. The eastern China seas are highly productive with significant emissions of biogenic substances, but the spatiotemporal variations of marine biogenic aerosols are not well known. Air mass exposure to chlorophyll a (AEC) can be used to indicate the influence of biogenic sources on the atmosphere to a certain degree. In this study, the 12 year (2009-2020) daily AEC were calculated over the eastern China seas, showing the spatial and seasonal patterns of marine biogenic influence intensity which were co-controlled by surface phytoplankton biomass and boundary layer height. By combining the AEC values, relevant meteorological parameters, and extensive observations of a typical biogenic secondary aerosol component, methanesulfonate (MSA), a parameterization scheme for MSA simulation was successfully constructed. This AEC-based approach with observation constraints provides a new insight into the distribution of marine biogenic aerosols. Meanwhile, the wintertime air mass retention over land exhibited a significant decrease, showing a decadal weakening trend of terrestrial transport, which is probably related to the weakening of the East Asian winter monsoon. Thus, marine biogenic aerosols may play an increasingly important role in the studied region.

Aerosol sources and transport paths co-control the atmospheric bacterial diversity over the coastal East China Sea.

Airborne bacteria along with chemical composition of aerosols were investigated during five sampling seasons at an offshore island of the East China Sea. Bacterial diversity was the lowest in spring, the highest in winter, and similar between the autumns of 2019 and 2020, suggesting remarkably seasonal variation but little interannual change. Geodermatophilus (Actinobacteria) was the indicator genus of mineral dust (MD) showed higher proportion in spring than in other seasons. Mastigocladopsis_PCC-10914 (Cyanobacteria) as the indicator of sea salt (SS) demonstrated the highest percentages in both autumns, when the air masses mainly passed over the ocean prior to the sampling site. The higher proportions of soil-derived genera Rubellimicrobium and Craurococcus (both Proteobacteria) and extremophile Chroococcidiopsis_SAG_2023 (Cyanobacteria) were found in summer and winter, respectively. Our study explores the linkage between aerosol source and transport path and bacterial composition, which has implication to understanding of land-sea transmission of bacterial taxa.

East Asian monsoon manipulates the richness and taxonomic composition of airborne bacteria over China coastal area.

Airborne bacteria may have significant impacts on aerosol properties, public health and ecosystem depending on their taxonomic composition and transport. This study investigated the seasonal and spatial variations of bacterial composition and richness over the east coast of China and the roles of East Asian monsoon played through synchronous sampling and 16S rRNA sequencing analysis of airborne bacteria at Huaniao island of the East China Sea (ECS) and the urban and rural sites of Shanghai. Airborne bacteria showed higher richness over the land sites than Huaniao island with the highest values found in the urban and rural springs associated with the growing plants. For the island, the maximal richness occurred in winter as the result of prevailing terrestrial winds controlled by East Asian winter monsoon. Proteobacteria, Actinobacteria and Cyanobacteria were found to be top three phyla, together accounting for 75 % of total airborne bacteria. Radiation-resistant Deinococcus, Methylobacterium belonging to Rhizobiales (related to vegetation) and Mastigocladopsis_PCC_10914 originating from marine ecosystem were indicator genera for urban, rural and island sites, respectively. The Bray-Curits dissimilarity of taxonomic composition between the island and two land sites was the lowest in winter with the representative genera over island also typically from the soil. Our results reveal that seasonal change of monsoon wind directions evidently affects the richness and taxonomic composition of airborne bacteria in China coastal area. Particularly, prevailing terrestrial winds lead to the dominance of land-derived bacteria over the coastal ECS which may have a potential impact on marine ecosystem.

Nonagricultural emissions enhance dimethylamine and modulate urban atmospheric nucleation.

Gas-phase dimethylamine (DMA) has recently been identified as one of the most important vapors to initiate new particle formation (NPF), even in China's polluted atmosphere. Nevertheless, there remains a fundamental need for understanding the atmospheric life cycle of DMA, particularly in urban areas. Here we pioneered large-scale mobile observations of the DMA concentrations within cities and across two pan-region transects of north-to-south (∼700 km) and west-to-east (∼2000 km) in China. Unexpectedly, DMA concentrations (mean ± 1σ) in South China with scattered croplands (0.018 ± 0.010 ppbv, 1 ppbv=10-9 L/L) were over three times higher than those in the north with contiguous croplands (0.005 ± 0.001 ppbv), suggesting that nonagricultural activities may be an important source of DMA. Particularly in non-rural regions, incidental pulsed industrial emissions led to some of the highest DMA concentration levels in the world (>2.3 ppbv). Besides, in highly urbanized areas of Shanghai, supported by direct source-emission measurements, the spatial pattern of DMA was generally correlated with population (R2 = 0.31) due to associated residential emissions rather than vehicular emissions. Chemical transport simulations further show that in the most populated regions of Shanghai, residential DMA emissions can contribute for up to 78% of particle number concentrations. Shanghai is a case study for populous megacities, and the impacts of nonagricultural emissions on local DMA concentration and nucleation are likely similar for other major urban regions globally.

Change of dominant phytoplankton groups in the eutrophic coastal sea due to atmospheric deposition.

Nutrient stoichiometry and input of trace metals may profoundly affect the growth and community structure of phytoplankton. A bioassay experiment was designed to explore the key components in atmospheric deposition that affect marine phytoplankton growth by adding aerosols and analogues nutrients and Cu to the surface water of the coastal East China Sea (ECS). Our results showed that atmospheric deposition along with the input of phosphate could largely enhance the chlorophyll a (Chl a) concentrations in this eutrophic water. Phosphorus addition lifted the proportions of T. oceanica in Diatoms and B. brevisulcata in Dinoflagellates. T. oceanica replaced S. costatum and became the dominant diatom species after the Chl a peak, probably associated with the N/P ratio approaching to 16. Atmospheric aerosols containing affluent N and little P showed limited promotion to Chl a, and the positive effect was very likely due to the soluble Cu and other trace metals supplied by the aerosol. Moreover, soluble aerosol Cu was found to be conducive to the relative abundance of most dominant class Coscinodiscophyceae, and both soluble aerosol Fe and Cu seemed to be very important for increasing the proportion of S. costatum. Soluble metals could be the key components in aerosols controlling the phytoplankton composition in the eutrophic sea and such impact might exceed affluent P provided by other exogenous sources.

Regional and Urban-Scale Environmental Influences of Oceanic DMS Emissions over Coastal China Seas.

Marine biogenic dimethyl sulfide (DMS) is an important natural source of sulfur in the atmosphere, which may play an important role in air quality. In this study, the WRF-CMAQ model is employed to assess the impact of DMS on the atmospheric environment at the regional scale of eastern coastal China and urban scale of Shanghai in 2017. A national scale database of DMS concentration in seawater is established based on the historical DMS measurements in the Yellow Sea, the Bohai Sea and the East China Sea in different seasons during 2009~2017. Results indicate that the sea-to-air emission flux of DMS varies greatly in different seasons, with the highest in summer, followed by spring and autumn, and the lowest in winter. The annual DMS emissions from the Yellow Sea, the Bohai Sea and the East China Sea are 0.008, 0.059, and 0.15 Tg S a-1, respectively. At the regional scale, DMS emissions increase atmospheric sulfur dioxide (SO2) and sulfate ( SO 4 2 - ) concentrations over the East China seas by a maximum of 8% in summer and a minimum of 2% in winter, respectively. At the urban scale, the addition of DMS emissions increase the SO2 and SO 4 2 - levels by 2% and 5%, respectively, and reduce ozone (O3) in the air of Shanghai by 1.5%~2.5%. DMS emissions increase fine-mode ammonium particle concentration distribution by 4% and 5%, and fine-mode nss- SO 4 2 - concentration distributions by 4% and 9% in the urban and marine air, respectively. Our results indicate that although anthropogenic sources are still the dominant contributor of atmospheric sulfur burden in China, biogenic DMS emissions source cannot be ignored.

The influence of terrestrial transport on visibility and aerosol properties over the coastal East China Sea.

Air pollutants from East Asia continent can affect the physio-chemical and optical properties of marine aerosols under seasonal winds. We investigated the change of visibility and haze frequency from 1974 to 2017 over the coastal East China Sea (ECS), and reconstructed the light extinction coefficients according to the chemical compositions of PM2.5 samples collected at Huaniao Island in the ECS. The annual average visibility significantly decreased from over 25 km in the early 1970s to <18 km in recent 4 years. The occurrence of daily maximum haze frequency was approximately 3-h later with respect to land sites, which could be explained by the diffusion of air pollutants from nearby cities (haze peak around rush hour) to the coastal ECS as well as the formation of secondary aerosols enhanced by photochemical reactions around noon at the condition of affluent gaseous precursors. Meanwhile, anthropogenic chloride transported from the land could increase the concentration of Cl- in marine aerosol, which may weaken the Cl- depletion phenomenon over coastal ECS and even induced considerable Cl- enrichment during the severe haze event in Jan. 2013. The largest contributor to the light extinction was (NH4)2SO4 followed by NH4NO3 and OM in almost all seasons. Especially in winter and spring, (NH4)2SO4 accounted for 45% and 52% of total light extinction, respectively. The estimated bext was lower than the monitored values, suggesting that the contribution of some aerosol components (e.g. NH4Cl and large mode components) might be underestimated. Further study on the combination of observation and estimation of specific aerosol contribution to the visibility impairment are needed.

Determination of atmospheric alkylamines by ion chromatography using 18-crown-6 as mobile phase additive.

An improved ion chromatographic method including two elution procedures was proposed for the quantitative determination of atmospheric alkylamines in field atmospheric samples involving high levels of inorganic cations by using 18-crown-6 as mobile phase additive. When 18-crown-6 was added to the mobile phase, the retention times increased significantly for Na+, NH4+, K+ and primary alkylamines but decreased for secondary and tertiary alkylamines due to the complexation with certain cations and interaction with both stationary and mobile phases of 18-crown-6. As a result, the separation of the cations was greatly promoted, which reduced the interference of peak distortion of overloaded inorganic cations on the quantitation of adjacent alkylamines. By using the presented method, five inorganic cations (Na+, NH4+, K+, Mg2+, Ca2+) and six alkylamines (dimethylamine (DMAH+), trimethylamine + diethylamine (TMAH+ + DEAH+), propylamine (MPAH+), triethylamine (TEAH+), ethanolamine (MEOAH+) and triethanolamine (TEOAH+)) were effectively separated and determined, and the relative standard derivations (RSDs) of objective cations were all less than 1% for retention time and 3.1% for peak area (n = 9), respectively. The linearity was excellent for each cation (R2 > 0.993) except for NH4+ and TEOAH+ showing a non-linear response (R2 > 0.998 for theoretical non-linear fitting), and the detection limit of these cations were 0.03-1.19 ng. The proposed method was successfully used in the determination of both alkylamines and inorganic cations in ambient particulate matters and gaseous alkylamines in ceiling duct exhaust. The annual average concentrations of DMAH+, TMAH+ + DEAH+ and TEAH+ were 15.56, 4.35 and 16.00 ng m-3 in PM2.5 over Shanghai in 2013. The concentrations of gaseous DMA and TMA + DEA in ceiling duct exhaust reached a maximum of 940.0 and 112.7 µg m-3, and were positively correlated with the human activity intensity, suggesting that human excreta emissions was a potential important source of atmospheric alkylamines in urban area of Shanghai.