Studies On The Spatio-temporal Variations,sources And Atmospheric Processes Of Gaseous Organic Pollutants Over The South China Sea

Gaseous organic pollutants originating from different sources show significant variations in concentrations and composition,and thus lead to different impacts on environmental effects and public health.Currently,there is still a lack of studies for investigating the characteristics of gaseous organic pollutants in the coastal and oceanic regions.The South China Sea（SCS）is in the tropical-subtropical rim of the northwestern Pacific Ocean and is one of the largest marginal seas around the world.Under the influence of Asian monsoon,the coastal and oceanic regions of the SCS have significant variations in oceanic and continental source contributions;thereby this region is ideal to investigate the characteristics of gaseous organic pollutants.In this study,the northern SCS and a coastal site（HKUST）were selected to study the characteristics of gaseous organic pollutants.We measured gaseous perfluoroalkyl substances（PFASs）and non-methane hydrocarbons（NMHCs）during a cruise campaign over the northern SCS from September to October 2013.Moreover,five C₁-C₄ alkyl nitrates were measured at a coastal site in four typical months of 2011 and 2012.The results show that:（1）The concentrations of total PFASs ranged from 18.0-109.9 pg m^-3(mean:54.5 pg m^-3)over the northern SCS.Among the measured PFASs,fluorotelomer alcohols（FTOHs）was the predominant PFAS group,accounting for 95.2-99.3%of the total PFASs.The concentrations of total NMHCs ranged from 1.45-9.13 ppbv（mean:3.54 ppbv）.Among the measured NMHCs,alkanes and aromatics were the most abundant NMHC groups,contributing to 29-62%and 11-53%of the total NMHCs,respectively.（2）Based on the diagnostic ratios and air mass back-trajectory analysis,it suggests that PFASs and NMHCs over the northern SCS were significantly influenced by the continental sources via long-range transport,while the contribution of oceanic emissions was minor.Source apportionment results suggest that fossil fuel combustion and industrial emissions were the major sources of alkanes and aromatics over the northern SCS,respectively.（3）We estimated the decay of PFASs concentration during long-range transport by using an air quality model.The results indicate that the removal of longer-lived FTOHs was mainly influenced by atmospheric physical processes（e.g.,deposition and dilution）,while hydroxyl（OH）radical reaction played an important role in the decay of shorted-lived PFAS species.（4）The concentrations of total RONO₂ ranged from 15.4-153.7 pptv（mean:65.9 pptv）at a coastal site,with the predominant species of 2-butyl nitrate（2-BuONO₂）and 2-propyl nitrate（2-Pr ONO₂）.The concentrations of 2-BuONO₂ and 2-Pr ONO₂ were both higher in winter than summer,while methyl nitrate（MeONO₂）showed an opposite seasonal trend.（5）Source apportionment results suggest that C₂-C₄ RONO₂ were mainly derived from photochemical formation and biomass burning,while ocean was a major contributor to MeONO₂.A case study in summer further points out that C₂-C₄ RONO₂ were diluted by the oceanic air masses,while MeONO₂ was contributed by the oceanic emissions.