Pollution Characteristics And Interactions Of PM_2.5 And O₃ In Shenyang Cit

At present,fine particulate matter(PM_2.5)and ozone（O₃）have become two important pollutants in China’s urban air pollution,with important impacts on the ecological environment,climate change and public health,and there are complex links between the two,which can interact in the atmosphere through a variety of ways.As one of the famous heavy industrial cities in China,Shenyang still suffers from fine particulate matter pollution in winter and ozone pollution in summer,despite the remarkable effectiveness of air pollution control in recent years.This paper investigates the pollution characteristics and interaction mechanisms of atmospheric PM_2.5 and O₃ in Shenyang based on hour-by-hour observations throughout the year 2019,including PM_2.5 and water-soluble ions,O₃,NO₂,SO₂,volatile organic compounds（VOCs）,and meteorological elements,etc.The main results are as follows:（1）There was serious fine particulate pollution in Shenyang in the winter of 2019.The average concentrations of SO₄^2-and NH₄⁺among water-soluble ions were highest in summer,NO₃^-and Cl^-were the highest in winter,K⁺was the highest in summer and autumn,and the average concentrations of Ca²⁺,Mg²⁺and Na⁺were lower in all seasons,ranging from 0.05 to0.46μg/m³.The secondary ions(SO₄^2-,NO₃^-and NH₄⁺)in PM_2.5 account for a large proportion of the concentration and the daily trend was similar to that of PM_2.5(except for SO₄^2-in summer).NH₄⁺was combined as（NH₄）₂SO₄ and NH₄NO₃ in spring,summer and autumn,and mainly existed as（NH₄）₂SO₄ or NH₄HSO₄ in winter.Ambient air quality in Shenyang was most affected by secondary pollutants（sulphate and nitrate）,with a contribution of more than 50%in all seasons.Heavy haze occurred in Shenyang from 1-5March 2019,mainly due to straw burning,unfavourable meteorological conditions and long-distance transmission of pollutants.（2）The average O₃ concentration in Shenyang in 2019 was highest in summer（106.39μg/m³）,followed by spring（70.20μg/m³）and autumn（46.84μg/m³）,and lowest in winter（26.65μg/m³）.O₃ concentrations in all four seasons showed single-peak daily variation characteristics,with peak concentrations occurring at around 2pm.O₃ concentrations showed positive correlations with temperature and wind speed in all seasons,and inverse correlations with humidity in all seasons.The O₃ concentrations were also inversely correlated with NO₂ concentrations,with the maximum O₃ concentration corresponding to a NO₂concentration ranged of 20-30μg/m³.The annual Ozone formation potential（OFP）for all types of VOCs met the criteria of olefins>aromatic hydrocarbons>alkanes>alkynes,which was consistent with the ranking of the OFP contributions of all types of VOCs in all seasons.Strengthening the regulation of traffic,chemicals,solvent use and fuel volatilisation is an effective way to reduce O₃ concentration levels in Shenyang.（3）The number of PM_2.5 pollution hours in winter in Shenyang in 2019 accounted for56.7%of the year（1499h）.The total number of O₃ pollution hours was 57h,and July was the month of high O₃ pollution.PM_2.5-O₃ showed a significant negative correlation in winter,a weak negative correlation in spring and autumn,and a weak positive correlation in summer in Shenyang,the correlation coefficients were-0.45,-0.14,-0.07,and 0.15,respectively.PM_2.5had the most significant effect on the photochemical production of O₃ in winter.Atmospheric AOCidation（AOC）was strongest in summer,followed by spring and autumn,and weakest in winter.The O₃-dominated atmospheric AOCidation contributed to the production of PM_2.5.Atmospheric AOCidation had a significant contribution to the secondary production of sulphate,but was not a major control factor for the secondary production of nitrate.