Day And Night Variation Characteristics And Source Analysis Of Chemical Composition Of Fine Particulate Matter In Changzhou City

To investigate temporal fine particulate matter mass levels and chemical compositions in Changzhou,Yangtze River Delta region,a total of 110 PM_2.5 samples were collected in summer?July-August 2016?and winter?January-February 2017?at an urban site?Jiangsu University of Technology,JSUT?.Seasonal and diurnal variations of PM_2.5 mass concentrations,water-soluble inorganic ions?WSII?,elements and carbon components?OC,EC?were discussed in this study.Furthermore,the concentration as well as light absorption characteristics of humic-like substances carbon?HULIS-C?were examined.Finally,source apportionment analysis was conducted on the dataset using the principle component analysis?PCA?method,hoping to provide the basic database in the distribution of PM_2.5 as well as scientific evidences of control countermeasures on air pollution in Changzhou.The results showed as following:?1?Averaged daytime and nighttime PM_2.5 in winter were 122.60±63.09?g·m^-3 and111.72±65.86?g·m^-3,significantly higher than the Class 2 limit values of the National Ambient Air Quality Standard(NAAQS,75?g·m^-3),while daytime and nighttime PM_2.5 in summer were 78.83±18.03?g·m^-3 and 70.39±25.68?g·m^-3.High PM_2.5 levels indicate PM_2.5pollution was serious in winter in Changzhou.?2?With regard to the seasonal comparison,WSII concentrations in winter were about twice higher than those in summer.More specifically,SO₄^2-?NO₃-?NH₄⁺?Cl^-and K⁺concentrations in winter were much higher than those in summer.High Ca²⁺in summer was caused by dust emissions from the construction nearby.For carbonaceous components,OC3,OC4 and EC1 accounted for more than 73%of TC,indicating coal combustion and motor vehicle emissions were the dominant contributors.Proportion of OC1 in TC was higher in winter than that in summer,with good correlations between OC and K⁺in daytime winter,indicating the carbonaceous aerosol were impacted by biomass burning.While in summer,high OPC/TC and OC2/TC ratios might be influenced by the over loading of the dust in the samples.Of the elements,Fe,Al and Zn accounted for more than 85%of all elements.Enrichment factor results for As,Cu,Pb and Zn were in the range of 100⁵00,suggesting an anthropogenic sources origin.Ion balance calculations showed that the particles in winter were nearly neutral while those in summer were alkaline.Overall,slightly differences were found in the PM_2.5 chemical components concentrations between daytime and nighttime,while obviously seasonal differences were found in PM_2.5 species.?3?PM_2.5 mass reconstruction showed that OM,dust and SO₄^2-were the dominant PM_2.5species in summer.while in winter,the percentage of NO₃^-increased obviously but OM decreased by⁴0%,indicating nitrates-dominant was the most important pollution pattern in Changzhou.?4?Average HULIS-C concentrations in winter were 4.18?g·m^-3?daytime?and 3.74?g·m^-3?nighttime?,while those in summer were 4.87?g·m^-3and 3.64?g·m^-3,respectively.The correlation analysis of HULIS-C and other chemical components were conducted,which showed that biomass burning,fossil fuel combustion,factory emissions and especially secondary formation were the main influencing factors.Moreover,daytime HULIS were mainly influenced by secondary reaction of anthropogenic precursor contaminants,while nighttime HULIS were affected not only by secondary formation by but also primary combustion emissions.?5?PCA analysis showed that main sources of PM_2.5.5 daytime winter were the mixture of secondary formation and motor vehicle emissions?28.76%?,followed by dust?18.50%?and coal combustion?15.26%?,while comparable contributions were found in dust?18.91%?and secondary formation?18.73%?nighttime summer,followed by coal combustion?14.04%?.In summer,secondary formation was the largest contributor both in daytime and nighttime,accounting for 21.22%and 26.94%of PM_2.5 mass,respectively.Moreover,dust emissions caused by the construction nearby was also the dominate source in daytime.