| In recent 20 years,regional air pollution in Beijing has become an increasingly crucial issue.A comprehensive knowledge of the time evolution of those air pollutants and the characteristics of meteorological influence can provide a scientific basis for understanding the formation mechanism of air pollution,the forecast model design and air pollution management and control.The present study took Changping District as the research area,collected hourly air quality data(PM2.5,PM10,NO2,O3 and SO2)of Changping park?on behalf of urban?and of Dingling?on behalf of suburban?from 2015to 2017 to conduct time series analysis,which includes the statistical characteristics of the interannual,inter-month and daily changes of air pollutant concentration.Subsequently,by combining the monitoring air quality data and the ground meteorological observations,the impact of four meteorological factors including temperature?T?,relative humidity?RH?,wind speed?WS?and wind direction?WD?on air quality was examined separately.From 2015 to 2017,although elevated air pollution events were still frequently occurred,the year-to-year change of the concentration of PM2.5 and PM10 showed a decreasing trend.The annual concentration of PM2.5 and PM10 in urban site respectively reduced by 24.2%and 23.9%in total.The annual concentration of NO2 in urban site reduced by 7.5%.The annual concentration of O3 remained stable over three years.The concentration of SO2 in urban and suburban sites respectively reduced by 38.1%and46.5%.The monthly average concentration of PM2.5 and PM10 in Changping district presented a marked seasonal pattern.Due to sandstorms impact,the concentration of PM10 increased rapidly in spring.Affecting by the intensity of photochemical reaction,NO2 was lower and O3 was higher in summer and vice versa in winter.Moreover,the concentration of SO2,which mainly be influenced by heating demand,was higher in the heating season and lower in the non-heating season.The daily concentration of PM2.5?PM10?NO2 and SO2 in both urban and suburban had"double peaks",and occurrence time of daily peak of NO2 concentration in four seasons was different.The concentration of O3 had a tendency of"single peak".The relationship between air pollutants and T and RH exhibited very differences in different seasons.In spring and autumn,connections between the concentration of PM2.5,PM10,NO2,SO2 and T were not obvious while the concentration of O3 was positively correlated with T.Furthermore,PM2.5,PM10 and NO2 had a positive relationship with RH.In summer,the concentration of PM2.5,PM10 and O3 was positively correlated with T,but was not clear with RH.In winter,severe air pollution more likely happened in the temperature range of-10°C to 3°C with RH more than 60%,which indicated poor atmospheric ventilation.High concentration of PM10 at urban site was easy to appear with a threshold of about6 m/s when a strong wind came from northwest due to sandstorm effect.The concentration of O3 was low under calm wind condition but was relatively high under strong wind condition in terms of the transmission of O3 and its precursors.Moreover,high concentration of SO2 was frequently occurred with wind from the east and southeast,the process was less affected by wind speed. |
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