Chemical Characterization Of Atmospheric Aerosol Over The South China Sea And At A Coastal Regional Station

The South China Sea?SCS?is the biggest marginal sea of China.The chemical characteristics of atmospheric aerosols over the SCS is influenced by the physical,chemical,biological processes and the emissions in the surrounding regions.There is still a lack of studies on chemical characterization on marine aerosols over the SCS.Here,filter samples of total suspended particle?TSP?were collected during two cruise campaigns over the northern?2013?and western?2014?SCS,respectively.In addition,a 1-year campaign was conducted at a coastal regional site,Tianhu?TH?,Guangzhou,to collect fine particulate matter(PM_2.5)from March 2012 to February 2013.Non-polar organic compounds?NPOCs?as well as organic carbon?OC?,elemental carbon?EC?and water-soluble ions?WSI?were detected in the TSP samples collected in the northern SCS.The NPOCs species were grouped into 10 groups including n-alkanes,PAHs,hopanes etc.Some important results were obtained as follows.?The concentrations of total NPOCs ranged from 19.8 to 288.2 ng/m3 with an average of 87.8 ng/m3,which accounted for 0.8-1.7%?average 1.0%?of organic matter?OM?.n-Alkanes was the predominant group,accounting for 43.1-79.5%,followed by PAHs?5.5-44.4%?and hopanes?1.6-11.4%?.?We found that primary combustion?biomass burning/fossil fuel combustion?was the dominant source for the majority of NPOCs.Biomass burning in southern/southeastern China via long-range transport was proposed to be a major contributor of NPOCs in marine aerosols over the northern SCS,suggested by the significant correlations between nss-K+ and NPOCs groups as well as the analysis of air mass back-trajectory and fire spots.?For the samples with strong continental influence,the strong enhancement in concentrations of n-alkanes,PAHs,hopanes and steranes were attributed to fossil fuel?coal/petroleum?combustion.?Terrestrial plants waxes were another contributor to NPOCs.OC,EC,water-soluble ions,total carbon?TC?and its stable isotopic ratio??13C?were measured in the TSP samples collected in the western SCS.The major results are showed as follows.?The average concentrations of OC and EC were 2.1±1.2?g/m3 and 0.3?0.2?g/m3,respectively.The results of OC/EC and ?13C showed that biomass burning and the secondary formation during long-range transport were the major sources for the carbonaceous aerosols over the western SCS.In addition,secondary formation via the oxidation of biogenic volatile organic compounds derived from the ocean was an important contributor for the TSP samples with high OC/EC.?Secondary ions(SO₄^2-,NO₃^-,NH₄⁺ and C₂O₄²)accounted for 55.3%of total WSI ?EWSI?while sea salt ions?Na+ and Cl-?accounted for 37.5%of total ?WSI.?Marine emission was the major source for the fresh air mass influenced samples?Cl-depletion:20.6%-67.8%?while long-range transport of continental outflow was the dominant contributor for aged air mass influenced samples?Cl-depletion:80.7%-99.3%?.?Strong enhancements in concentrations of ?WSI were observed in the typical aged air mass influenced sample compared with fresh air mass influenced sample.The mass concentrations of PM_2.5 and the major chemical components including water-soluble ions,OC,EC and elements were detected in the PM_2.5 samples collected in TH.The main conclusions are drawn as follows.?The annual average concentration of PM_2.5 was 44.2±25.8 ?g/nm3.Sulfate was the most dominant component,accounting for 28.6%of PM_2.5,followed by organic matter?21.9%?.Both sea salt and crustal material accounted for only a small fraction of PM_2.5?<5%?.?Seasonal enhancement of PM_2.5 was observed in autumn 2012,especially with high-PM_2.5 events?more than 100 ?g/m?in October.?The backward Lagrangian particle dispersion modeling?LPDM?and the cluster analysis of the back-trajectories indicate that the northern area is an important source region of long-range transport.However,the footprint retroplume of the samples shows that the sources in the Pearl River Delta Region should also be considered,especially secondary aerosol formation and biomass/biofuel burning.?Two high-PM_2.5 case studies show that both local and long-range transport can play important roles in the PM_2.5 elevation episode.