Research On The Seasonal Distribution Patterns Of Water-soluble Ions And Heavy Metals In Atmospheric Particulates

The national standard gravimetric method was applied to collect PM_2.5 samples under the polluted weather days in Baoding in 2018.The water-soluble ions（WSIs）in the PM_2.5 samples were determined by ion chromatography and their distribution characteristics in different seasons were analyzed.The PMF model and backward trajectory model were used for source apportionment.Arsenic in PM_2.5 was determined,and the geological accumulation index method,potential ecological hazard method were used to evaluate the potential health risks.The results are as follows:During the sampling period,the PM_2.5 concentration in Baoding was18.4—258.0μg·m^-3,and the annual average value was 91.5±62.5μg·m^-3;The seasonal distribution pattern was winter(160.6μg·m^-3)>autumn(105.3μg·m^-3)>spring(57.6μg·m^-3)>summer(53.2μg·m^-3).Seasonal changes of PM_2.5 are related to meteorological conditions and gaseous pollutants.The annual average value of WSIs was 49.20μg·m^-3,accounting for 63.95%of PM_2.5.The seasonal pattern of WSIs was consistent with that of PM_2.5.The secondary pollution ions were the dominant components,accounting for 77.12%.The change of the secondary pollution ions in each season was not big,and the proportion was stable.PM_2.5 was slightly acidic in spring,summer and autumn,alkaline in winter,and alkaline throughout the year.During the sampling period,Baoding city had strong secondary transformation（SOR and NOR）,which was positively correlated with humidity and temperature.The water-soluble ions mainly existed in spring and summer as Na₂SO₄ and Na NO₃,in autumn as NH₄HSO₄ and NH₄NO₃,and in winter as（NH₄）₂ SO₄ and NH₄NO₃,and partly as NH₄Cl.The annual average value of NO₃^-/SO₄^2-was 1.16,indicating that most of secondary ions in Baoding came from mobile sources.PMF model source analysis obtains 4 pollution sources,secondary pollution source（11.90%）,biomass combustion/traffic source（41.13%）,industrial source/coal combustion source（31.94%）,and dust source（15.03%）.Backward trajectory cluster analysis showed that PM_2.5 in spring and summer may be mainly affected by local air masses,while air masses from the northwest in autumn and winter contribute more to PM_2.5,and the source of Na⁺was related to offshore air masses.The annual average value of arsenic in PM_2.5 was 21.88 ng·m^-3,and the seasonal variation varies from small to large in spring,summer,autumn and winter.The annual average I_geo value of As was 2.90,and the summer was severely polluted.The other three seasons and the whole year have moderate to severe pollution.The average annual E_r value of As was 205.26,which was a high ecological hazard.Heavy ecological hazard in summer,high ecological hazard in autumn,and slightly heavy ecological hazard in winter and spring.The health risk assessment model showed that the annual average HQ value of arsenic in PM_2.5 was 1.40.Except for spring less than 1.0,it was greater than 1.0 in summer,autumn and winter,indicated that arsenic in PM_2.5 in spring has no non-carcinogenic health risks,and other seasons have non-carcinogenic health risks;CR_adults and CR_children are 3.09×10^-5 and7.73×10^-6(>1×10^-6)respectively,indicated that arsenic in PM_2.5 in four seasons had carcinogenic risk and should be paid attention to.