Research On The Characterization Of Inorganic Ions Of PM_2.5 In A City

With the rapid development of China's economy and society,coal and other energy consumption rising,rapid incresing of the number of motor vehicles,many cities are facing enormous pressure on air pollution.As an important city in the Yangtze River Delta,it is necessary to research the characteristics of inorganic ions of PM_2.5 and pollution formation mechanism in the city.In this study,the atmospheric pollution monitoring system was used to observe the multi parameter of air quality in long term.The pollution characteristics and formation mechanism of atmospheric PM_2.5 and inorganic ions were analyzed,which present a certain theoretical and scientific value.The results were summarized as follows:?1?PM_2.5 was the main pollutant that affected the current ambient air quality.PM₁₀ concentration showed a downward trend since the year of 2000 and rebounded in 2013.Air quality was mainly polluted by particulate matter.77.2% of the main pollutants was PM_2.5 in 2013,half of which occured in winter,and about 20% in spring and autumn.?2?The concentration of coarse particulate matter and dust in the city was declining.The concentration of PM₁₀ showed a downward trend,at the same time,the dust concentration in the main city showed a downward trend from 2001 to 2013,but the amount of dust in 2013 than the previous two years have a substantial rebound.?3?PM_2.5 and the main inorganic ions of the city showed different diurnal trends,mainly influenced by industrial activities,traffic emissions,solar radiation and weather conditions.PM_2.5 and NO₃^-showed two peaks during the early peak and late peak of traffic.SO₄^2-exhibited a higher concentration at about 9:00 to 15:00 during the day and a lower concentration at other times,similar to the diurnal variation of its precursor SO2,which is significantly influenced by industrial emissions.?4?The PM_2.5 and the main inorganic ions showed different weekly trends,mainly influenced by the working days and the unique characteristics of the tourism city.The higher concentration from Monday to Thursday was affected by the busy work.The total concentration of chemical components decreased significantly on Friday and Saturday,indicating the effect of reduced anthropogenic emissions at weekends.While the concentration of chemical components on Sunday showed a significant increase,almost reached the most serious pollution of the day in one week.?5?Relative humidity is an important meteorological factor that affects the formation of inorganic ions and PM_2.5.In the low humidity range,the concentration of NO₃^-increases with the increase of humidity and decreases in the range of high humidity of 75-85%.Under the influence of liquid phase reaction,SO₄^2-tends to grow at high humidity,its concentration more than doubled above 80% humidity,indicating that under high humidity,the formation of sulfate will take precedence over nitrate.?6?The wind speed is another important meteorological factor which affects the inorganic ions and PM_2.5.The removal rate of fine particles is relatively low,and the removal rate of coarse particles is relatively high.SO₄^2-,NO₃^-,NH₄⁺?,OC and EC have a removal rate of 12%,31%,21%,35% and 48%,respectively,in the wind speed range of 4 m/s,SO₄^2-,NO₃^-,NH₄⁺.The removal rate is lower,and the particle size of secondary particles is smaller,and the removal rate of OC and EC is higher.?7?Liquid phase reaction is the main production route of sulfate,the city is in high humidity,high frequency fog environment,so liquid phase reaction is one of the important ways to generate sulfate.In contrast,the effects of temperature and wind speed on SO₄^2-conversion formation are small.Vapor phase oxidation is the main production route of nitrate.The effect of temperature on NO₃^-generation is significant.At low temperature,the oxidation rate of NO₂-is obviously improved and the amount of nitrate is high.The correlation and source analysis show that Cl^-in PM_2.5 comes from the source of fireworks,coal combustion and waste incineration.K⁺ is derived from biomass burning and fireworks except for its mineral source.