Chemical Pollution Characterization And Source Apportionment Of Atmospheric Precipitation In Nanchang

This article is aiming to identify the sources and origins of atmospheric precipitation ions in Nanchang City.The rainwater samples were collected since April 2016 till April2017,in which the chemical characteristics of major ions were analyzed.Additionally,the PMF?positive definite matrix factorization?model was used to distinguish the source and HYSPLIT Trajectory Model to simulate the backward trajectory.The results showed that:?1?NH₄⁺and Ca²⁺are the main cations.On average,we measured rainfall-weighted concentrations of 67.2?eq/L and 46.4?eq/L,accounting for 47%and 33%of the total cations respectively.SO₄^2-and NO₃^-are the major anions,of which the average rainfall-weighted concentrations are 126?eq/L and 25.09?eq/L,accounting for 73%and 14%of the total anions respectively.During the study,the type of atmospheric precipitation pollution was of medium pollution.?2?The order of the rainfall-weighted average concentration of total inorganic ions is winter>summer>autumn>spring,and the change of precipitation is negatively correlated with it.The concentration of SO₄^2-in winter is significantly higher than in other seasons and lowest in autumn.The concentrations of Na⁺,Cl^-and K⁺are the lowest in the spring and the trend of change is similar.?3?The significant correlations among NH₄⁺,Ca²⁺,K⁺,Mg²⁺,Na⁺,Cl^-and NO₃ indicate their similar sources or the formation of compounds with them.NH₄⁺is preferentially combined with NO₃^-in the atmosphere,and the contribution of NH₄⁺to the acid neutralization of rainwater is greater than Ca²⁺.Maybe they can exist in the form of NH₄NO₃,NH₄HSO₄ and?NH4?₂SO₄ in the atmosphere.?4?The ratio of SO₄^2-/NO₃^-is 5.02,which belongs to sulfuric acid type acid rain.The contribution of SO₄^2-to rain acidification increases gradually,and the type of rainfall gradually shifts from mixed type to sulfuric acid type.In August,September and October,the concentration of alkaline ions in the atmosphere is relatively high,and Ca²⁺is the main factor in neutralizing the acidic substances in rainfall.?5?NH₄^+/Ca²⁺is relatively large in winter,and has the highest value in spring,which may be related to agricultural fertilization or soil organic matter decomposition.The lowest value of(Ca²⁺+NH₄⁺)/(NO₃^-+SO₄^2-)occurs in winter and which may be related to the increase of coal burning.?6?Ca²⁺and NH₄⁺are the most important neutralization components in precipitation.Na⁺also has a certain neutralization effect on anions.During the summer and autumn alternate seasons?August and September?,the neutralization effect of K⁺on precipitation anions is obviously greater than that in other months.?7?Based on the PMF model,four potential sources of atmospheric chemical composition in Nanchang City were identified:secondary pollution?35%?,coal burning?30%?,soil?20%?,sea salt?15%?.Na⁺,Cl^-,K⁺are obviously affected by sea salt,also affected by coal burning,soil and secondary pollution;Mg²⁺and Ca²⁺are mainly come from soil;almost all of the SO₄^2-and F^-come from Gas emissions from coal burning;major NH₄⁺,NO₃^-,and part of the SO₄^2-mainly contributed by secondary pollution sources.The secondary pollution caused by human activities and coal burning are still the main causes of atmospheric pollution in Nanchang.?8?Backward trajectory analysis shows that the precipitation in Nanchang is mainly affected by air mass origin from local areas.The sources of rainfall air masses vary greatly in different seasons.Pollutants in spring are mainly affected by the transmission from the local area and the surrounding provinces;The precipitation air mass in summer mostly comes from the surrounding areas and local areas,and also from the southeast coast of China and the South China Sea.The oceanic ions were diluted or settled when they through the inland,resulting in rainfall air mass origin from ocean in spring and summer impacted a little on Nanchang;In addition to the influence of local air and surrounding provinces during the autumn,the cold air transmitted from north to south will have a certain impact on Nanchang,and at the same time it will be greatly affected by marine air masses in the autumn.The air mass in winter come from the local area and the surrounding areas.The surrounding provinces have the greatest impact on precipitation pollution.