Characteristics And Sources Of Fine Particulate Matter In The Background Region Of The Yangtze River Delta

Atmospheric fine particulate matter(PM_2.5)can not only cause enduring and serious damage to human health,but also have direct or indirect negative effects on visibility and climate change.In recent decades,many cities in China have experienced severe haze pollution,especially in populous and industrial-intensive areas.PM_2.5 has gradually shown the characteristics of wide range of regional pollution,complex formation mechanism and explosive growth,which has become the focus of people’s attention.As the vanguard region of China’s economic development,the Yangtze River Delta（YRD）has a prominent regional haze pollution pattern.In order to promote the high-quality development of the ecological society,the research and prevention of PM_2.5 pollution in the YRD region is very necessary and urgent.At present,the research on PM_2.5 pollution in the YRD is mostly concentrated in cities and suburbs,and there are limited studies on the background sites that can reflect the atmospheric background value.In this study,continuous offline observation was carried out at the regional background site in the YRD（Lin’an background site）from November 24,2015 to June 6,2016.Gaseous pollutants and meteorological data are monitored online at the same time,and the concentration of PM_2.5 is reconstructed based on chemical species analysis.It’s concluded that PM_2.5 was the primary pollutant in winter and spring in the background region of the YRD.The concentration of PM_2.5 was significantly correlated with the concentrations of CO,SO₂ and NO₂,indicating that PM_2.5 was affected by multiple emission sources such as vehicle emissions and coal combustion.The meteorological conditions such as temperature,humidity and precipitation had significant influence on PM_2.5.The atmosphere in the background region of the YRD was rich in ammonia in winter and spring,and the particles were generally neutral.Secondary inorganic salt（SNA）was the most important component in PM_2.5,and the variation trends of their concentrations were the same.The nitrogen-sulfur ratio has increased year by year,indicating that motor vehicle emissions may become the dominant source of pollution in the YRD in the following years,and the control and governance of motor vehicle emissions must be strengthened.The sulfur oxidation rate and nitrogen oxidation rate were 0.46±0.15 and 0.28±0.13,respectively.These values are significantly higher than other regions in China,indicating that the secondary conversion of SO₂ and NO₂ in the background area of the YRD is very strong,with liquid and gas phase oxidation identified as the main production pathway of SO₄^2-and NO₃^-,respectively.The primary source emissions in the background region of the YRD contribute more to the carbonaceous aerosol pollution than the secondary generation.The principal component analysis-multiple linear regression（PCA-MLR）model identified three sources:secondary sources（37.49%）,fossil fuel and biomass combustion sources（36.61%）,and sea salt sources（25.91%）.The combustion source and secondary source made the greatest contribution in winter and spring,respectively.The haze pollution episodes in winter and spring in the background region of the YRD mainly originated from local pollution and were also affected by regional transmission.The formation of SNA mainly dominated by NO₃^-was the main driving factor for the occurrence of heavily polluted days and pollution episodes.Therefore,the coordinated emission reduction of PM_2.5 and gaseous pollutants is the necessary mean for the prevention and control of atmospheric PM_2.5 pollution in the YRD region.