Numerical Simulation Of Main Air Pollution And Its Pollution Characteristics In Yangtze River Delta

With the rapid development of economy and the increasing of pollution emission in Yangtze River Delta,the air pollution,which is dominated by ozone and particulate matter,is becoming more and more serious.The study on the characteristics of ozone and particulate matter and its impact factors can provide a scientific basis for improving the air quality in the region.To investigate the spatial and temporal characteristics of air pollutants and its impact factors,the hourly concentrations of six pollutants and meteorological data collected at environment monitoring stations in 33 cities and meteorological monitoring stations in 4 provincial cities of the region in 2016 were analyzed.The WRF-Chem model was used to simulate ozone in August and particulate matter in December to analyze the characteristics of high concentration ozone,its process of generation and elimination and the characteristics of typical particulate matter.Results showed that:（1）The annual concentration of O₃ ranged from 50μg·m^-33 to 73μg·m^-3 with an average of61μg·m^-3 in Yangtze River Delta.O₃ concentrations in 31 cites exceeded the classⅡAmbient Air Quality Standard（GB 3095-2012）to different degrees except Wuhu and Xuancheng in the region.The O₃ exceedance rate ranged from 0.34%to 18.86%with an average of 5.68%.The monthly average concentration of O₃ reached high values in May and September.The diurnal variation of O₃ concentration showed a single peak distribution,with the peak value appeared around 15:00 in all the seasons.The highest peak value was157μg·m^-3 in summer.The O₃ concentrations in coastal cities were generally higher than those in inland cities.Suqian-Huai’an-Chuzhou region was more polluted in summer.O₃was negatively correlated with NO₂ and CO,and the correlation was strong with NO₂.O₃was positively associated with temperature and sunshine duration while it was negatively correlated with relative humidity and rainfall.The annual concentrations of NO₂ and CO ranged from 20μg·m^-33 to 51μg·m^-3 and 0.66 to 1.33mg·m^-3,respectively.The NO₂exceedance rate ranged from 0.34%to 7.41%.The monthly average concentrations of CO in Xuzhou,Tongling and Ma’anshan were higher than the average level in the region.The diurnal variation of NO₂ and CO showed two peaks in all the seasons.Two peaks of NO₂appeared around 08:00 and 19:00 to 20:00,and two peaks of CO appeared at 08:00 and22:00.NO₂ and CO was negatively correlated with temperature and wind speed.The annual concentrations of SO₂ ranged from 8μg·m^-33 to 40μg·m^-3.The monthly average concentrations of SO₂ in Xuzhou and Tongling were higher than other cities.SO₂ was negatively correlated with temperature,relative humidity,rainfall.The annual concentration of PM_2.5.5 and PM₁₀0 ranged from 25μg·m^-33 to 62μg·m^-3 and 42μg·m^-3 to 121μg·m^-3.The concentrations of PM_2.5.5 exceeded the standard in all cites,with the highest exceedance rate was 23.91%in Chuzhou.PM₁₀ exceeded the standard in other cities except Zhoushan and Lishui,with the highest exceedance rate was 22.9%in Xuzhou.The monthly average concentration of particulate matter exhibited two peaks in March and December or January.and the diurnal variation of it showed two peaks,with two peaks appeared around 09:00 to10:00 and 22:00 to 23:00,respectively.In winter,the highest concentration of PM_2.5 and PM₁₀ in Xuzhou was 102μg·m^-33 and 175μg·m^-3,respectively.Particulate matter was significantly positive correlation with NO₂,CO,SO₂,while it was negative correlation with temperature,wind speed and rainfall.（2）The WRF-Chem model could reproduce the evolution characteristics of meteorological fields and the concentration levels and variation tendency of ozone and particulate matter in the YRD.Analysis of high-concentration ozone episode found that the concentration level and distribution of O₃ in the region vary greatly in day and night,and the spatial distribution is mainly influenced by its precursors,solar radiation intensity and wind field.The convergence of wind field led to local ozone pollution;and airflow transported high-concentration ozone to the downwind region.Based on the analysis of the typical particulate pollution process in the area,it was found that the short-term pollution experienced in the YRD on December 1st was caused by the high concentrations particles in northern Jiangsu and Wuxi,Suzhou,and Huzhou,which were transported southward under the influence of the northerly wind.On the 4th,the high concentrations particles in Wuxi-Changzhou-Zhenjiang area were transferred to Shanghai and Jiangsu under the transmission of wind fields.On the 5th,high concentrations particulates in northern Jiangsu,Suzhou,and Nantong affected the central and southern of Jiangsu,Shanghai,and Anhui successively under the effects of airflow transport.From the 4th to5th,the northerly and southerly winds switch back and forth.The variations of wind fields made it difficult for pollutants to be exported to the region,causing particulate pollution in the area.The pollution level and distribution of particles were affected by local emissions,air pollution transportation and the variations of local wind fields.