Characteristics Of Size Distribution Of Atmospheric Particulate Matter Components In Nanjing

At present,the pollutant ranked first in most cities in China is still atmospheric particulate matter,and its climatic and health effects are closely related to particle size and chemical composition.The chemical composition of atmospheric particulate matter is very complex.The main components include carbon-containing components,inorganic metal elements,and water-soluble ions.These components exhibit different distribution characteristics at different particle sizes.At present,there are relatively few studies on the particle size distribution characteristics of different components of atmospheric particulate matter,and they mainly focus on the two particle sizes of coarse particulate matter(PM₁₀)and fine particulate matter(PM_2.5).The distribution characteristics are not fully understood.This study is based on the monitoring data of particulate matter components?water-soluble ions,carbon-containing components,and elements?with eight-level particle size in the eastern part of Nanjing City from 2016 to2017?the typical months of four seasons each year?.The mass concentration and the particle size distribution characteristics of main chemical components throughout the year and different seasons;quantitative analysis of the sources of atmospheric particulate matter and chemical components of different particle sizes;combined with meteorological conditions,the particle size distribution of atmospheric particulate matter chemical components was further explored Factors affecting the source.The main findings are as follows:?1?The mass concentration of particulate matter in Nanjing's atmosphere has a bimodal distribution throughout the year and in different seasons.The main peak is distributed in the 0.4-1.1?m particle size segment and the secondary peak is distributed in the 3.3-9?m particle size segment.The peak values of the main peak and the secondary peak are similar in spring and winter.The mass concentration in spring is higher in the coarse particle size section?>9?m?,and the mass concentration in winter is the highest throughout the year.The peak size in the fine particle size section is in summer and Autumn is significantly higher than the coarse particle size segment,the summer mass concentration is the lowest throughout the year,and the main peak shifts to a finer particle size segment,while the autumn mass concentration is mostly concentrated between 0.4-0.7?m.?2?According to the difference in peak performance,the particle size distribution of metal elements in particles is divided into three categories.The first type is the single-peak type of coarse particles,the peak distribution is in the 3.3-5.8?m particle size segment,mainly Na,Mg,Ba,Elements such as Al,Ca,Ni,Co,and Sr;the second type is fine-particle single-peak type,with peaks distributed in the 0.4-1.1?m particle size segment,mainly Zn,Cd,Tl,As,and Pb;the third type It is a multimodal type,of which the bimodal type of coarse and fine particles is the most common.The peaks are roughly distributed in the 1.1?m and 5?m particle sizes,mainly Fe,K,Mn,Se,Li,Be,V,Cu Elements such as Cr,Ce and Ag.According to the value of the enrichment factor,the metal elements in the particulate matter in Nanjing are divided into three types.The first type is the low-enriched elements,which are Mn,Mg,Ba,Be,Ca,Ce,Co,Sr,Fe and V.Most of the particle size ranges are not much different;the second type is medium-enriched elements,with Na,Ni,K,Li and Cr,the enrichment is very obvious in the particle size section<2.1?m;There are As,Ag,Cu,Tl,Pb,Zn,Cd and Se.As the particle size decreases,the enrichment factor of most elements gradually increases,indicating that the impact of human activities increases as the particle size decreases.?3?In general,the particle size distribution of carbon components?OC,EC?in atmospheric particles is bimodal,with the main peak of OC in the 0.7-2.1?m particle size segment and the secondary peak in the 3.3-5.8?m particle size segment.In the fine particle size segment,the mass concentration of OC is higher in autumn and winter than in spring and summer,and the peak position tends to increase toward the coarse particle size.In contrast,in the coarse particle size section,the mass concentration of OC is higher in spring and summer than in autumn and winter.In terms of EC,from the annual average,the main peak is distributed in the 3.3-5.8?m particle size segment,and the secondary peak is distributed in the 0.4-1.1?m particle size segment.From different seasons,in the fine particle section,the concentration in spring and winter is higher than that in summer and autumn,and the peak particle size in winter is larger;in the coarse particle section,the mass concentration in winter is the highest and the mass concentration in summer is the lowest.?4?Due to different types of water-soluble ions,the particle size distribution characteristics show a large difference.NH₄⁺,K⁺,and SO₄^2-are fine-particle single-peak distributions,and the peaks are distributed in the 0.4-2.1?m particle size segment,0.7-2.1?m particle size segment,and 0.7-2.1?m particle size segment,respectively.Ca²⁺and Mg²⁺showed a unimodal distribution of coarse particles,with peaks distributed in the>9?m particle size segment and 2.1-9?m particle size segment,respectively.Na⁺and F-have a bimodal distribution.The main peaks are located in the2.1-5.8?m particle size segment and the 2.1-9?m particle size segment,respectively.The peaks of the secondary peaks are similar,both in the 0.4-1.1?m particle size segment.In addition,there are significant seasonal differences between NO₃^-and Cl^-.NO₃^-has a bimodal distribution in the spring,with peaks in the 0.4-2.1?m and 3.3-9?m particle sizes,respectively,and coarse-particle single-peak type in the summer,with peaks in the 2.1-9?m particle size range.The autumn and winter seasons are fine-particle single-peak types,with peaks distributed in the 0.7-2.1?m particle size segment.Cl^-is distributed evenly in all particle sizes in the spring and autumn seasons.In summer,it is a coarse particle single-peak type with a peak distribution in the 3.3-9?m particle size section,and in winter it is a fine particle single-peak type with a peak distribution in the range of 0.7-2.1?m particle size segment.?5?The particle size distribution of the mass concentration of particulate matter is obviously related to meteorological factors,and it varies greatly in different seasons.PM_>2.1 concentration is significantly positively correlated with wind speed in spring and negatively correlated with winter.The correlation between PM_2.1 concentration and wind speed is low in all seasons.PM_>2.1 was significantly negatively correlated with relative humidity in spring and autumn,and PM_2.1 was significantly positively correlated with humidity in winter.The humidity threshold of PM_2.1 is about 70%,and when it is greater than this value,the increase in hygroscopicity increases rapidly.?6?The source analysis results of all components of atmospheric particulate matter show that the sources of particulate matter in different particle size segments are obviously different.The primary source of coarse particulate matter?PM>2.1?is the dust source,followed by industrial sources,metallurgical sources,motor vehicle pollution sources and coal combustion sources.The biomass combustion source has the smallest contribution,and the primary source of fine particulate matter?PM2.1?is combustion.Coal sources,the remaining main sources are secondary generation,dust sources,traffic pollution sources and garbage incineration sources in order of contribution.