The concentration, source and deposition flux of ammonium and nitrate in atmospheric particles during dust events at a coastal site in northern China

摘要

Asian dust has been reported to carry anthropogenic reactivenitrogen during transport from source areas to the oceans. In this study, weattempted to characterize NH and NO in atmosphericparticles collected at a coastal site in northern China during spring dustevents from 2008 to 2011. Based on the mass concentrations of NHand NO in each total suspended particle (TSP) sample, the samplescan be classified into increasing or decreasing types. In Category 1, theconcentrations of NH and NO were 20–440 % higherin dust day samples relative to samples collected immediately before or aftera dust event. These concentrations decreased by 10–75 % in the dust daysamples in Categories 2 and 3. Back trajectory analysis suggested thatmultiple factors, such as the transport distance prior to the reception site,the mixing layer depth on the transport route and the residence time acrosshighly polluted regions, might affect the concentrations of NH andNO. NH in the dust day samples was likely either in theform of ammonium salts existing separately to dust aerosols or as theresidual of incomplete reactions between ammonium salts and carbonate salts.NO in the dust day samples was attributed to various formationprocesses during the long-range transport. The positive matrix factorization(PMF) receptor model results showed that the contribution of soil dustincreased from 23 to 36 % on dust days, with decreasing contributionsfrom local anthropogenic inputs and associated secondary aerosols. Theestimated deposition flux of N varied greatly from event toevent; e.g., the dry deposition flux of N increased by9–285 % in Category 1 but decreased by 46–73 % in Category 2. InCategory 3, the average dry deposition fluxes of particulate nitrate andammonium decreased by 46 % and increased by 10 %, respectively, leadingto 11–48 % decrease in the fluxes of N.