Spatiotemporal Variation Characteristics Of Surface Ozone And Its Affecting Factors In Northern Shaanxi

Based on the hourly monitoring data of ozone concentration in Yan'an and Yulin in northern Shaanxi province from 2016 to 2018,the characteristics of monthly,seasonal and diurnal variations of ozone concentration in northern shaanxi as well as its affecting factors were analyzed.It was found that the monthly and diurnal variations of ozone concentration in northern Shaanxi showed single peak and single valley values.In seasonal and monthly changes,the peak ozone concentration in northern Shaanxi appears in summer(June,July,and August),and the valley value in winter(December,January,and February).The highest ozone concentration in Yan'an appears in June,while the highest ozone concentration in Yulin appears in July.The lowest ozone concentration appears in December,the same time as that in Yan'an.In December,the monthly mean ozone concentration of Yan'an was lower than that of Yulin except that the monthly mean ozone concentration of Yan'an was higher than that of Yulin in January,and the difference was more obvious in summer than in winter.In the diurnal variation,the diurnal variation of ozone concentration in Yan'an and Yulin shows the characteristics of higher concentration in daytime thanin nighttime.The highest ozone concentration in Yan'an and Yulin occurred at 16:00 in the afternoon and the lowest at 07:00 in the morning(BJT).According to the average daily change of three years,the average hourly ozone concentration in Yan'an is lower than that in Yulin,and the difference at night is significantly higher than that in daytime.The frequency of exceeding for ozone in Yulin was higher than it in Yanan.The frequency of exceeding for ozone in Yulin was increasing while it was decreasing in Yanan from 2016 to 1018.Further studies found that there was a significant linear negative correlation between ozone and carbon monoxide and nitrogen dioxide concentrations in Yan'an and yulin in the northern Shaanxi,and their linear negative correlation passed the significance test with a significance level of 0.05.Based on the comparison with meteorological factors,it is found that in Yan 'an city,the correlation between ozone and meteorological factors follows: sea level pressure > air temperature > temperature dew point difference > wind speed > wind direction;In Yulin city,the correlation between ozone and meteorological factors follows: sea level pressure > air temperature > wind direction > temperature dew point difference > wind speed.Above all,the convergence and divergence caused by the change of sea level pressure in northern Shaanxi has a strongest correlation with surface ozone concentration,which is the most important meteorological affecting factor.As a result,to control the ozone pollution in northern Shaanxi,the government should limit the discharge of pollution sources according to the change of meteorological factors.