Variation Of Surface Ozone And Its Precursors In Beijing And The Effect Of Meteorological Parameters

In recent years,with the expansion of the scale of cities and the number of motor vehicle, many densely populated cities are faced with the threat from the photochemical pollution,and high ozone concentrations are reported frequently.High ozone concentrations would cause great harm on humans,animals,plants and buildings.Therefore,it is very meaningful to enhance the study of surface ozone.Based on the continuous measurements of O₃,NO,NO₂,NO_x,CO and meteorological parameters at the ground layer in Institute of Atmospheric Physics,China Academy of Sciences, from September 2004 to July 2005,the temporal variations of ozone and its precursors and the relationship between ozone and its precursors are studied.In addition,the correlation of ozone and its precursors with meteorological parameters are analysed.The key findings in this study are summarized as follows:(1)During period of obeservation,diurnal variations in ozone and its precursors are different between precipitation and non-precipitation days.In non-precipitation days,the diurnal variation in ozone accompanied with unimodal distribution shows a peak value around 15:00 at noon and a foot value around 7:00 in the morning,and ozone concentrations with small variation keeps in low values from 20:00 to 07:00 next day.NO,NO₂,NO_x and CO accompanied with bimodal distribution show a similar trend in daily variation,but the time corresponding to peak-value and foot-value and the daily amplitude are different.In precipitation days,daily averaged concentration in ozone and its precursors rebound in 0:00.(2)Ozone and its precursors have a regular seasonal variation.O₃ shows:Summer＞spring＞autumn＞winter;NO₂ and NO_x show:Autumn＞winter＞spring＞summer;NO and CO show: Winter＞autumn＞spring＞summer.(3)The coherence of hourly averaged concentrations between ozone and its precursors is not fit for linear correlation.Hourly concentrations in its precursors have a critical value, respectivelly.When the hourly averaged concentration in precursors below their critical value, some that in ozone would beyond the Chinese National Air Quality Standard Grade 2(hourly average concentration 93.3 ppb).The frequency of days with O₃ concentration exceeding the Chinese National Air Quality Standard Grade 2 in these ranges is 2.7%for NO,1.7%for NO₂, 2.3%for NO_x and 1.9%for CO,respectively.On the contrary,when the hourly averaged concentration in precursors beyond their critical value,O₃ hourly averaged concentration does not beyond the Standard.(4)In order to focus on the influence of a local individual meteorological parameter,we performed an analysis on the hourly air pollutant concentrations and meteorological hourly data to analyze the relationships between air pollutants and meteorological parameters after excluding the data for precipitation days.The results show that,O₃ has a significant negative correlation with relative humidity and positive correlations with radiation,temperature and wind speed for yearly value,on the contrary,the precursors show positive correlations with relative humidity, and significant negative correlations with radiation,temperature and wind speed,for yearly value. But the correlation of O₃ and its precursors with meteorological element for every month would appear abnormality.For instance,NO has negative correlation with relative humidity in June,and has non-significant with relative humidity in July.(5)Taking into the common effects of local wind direction and wind speed,frequency and pollution coefficient in different wind direction would be analysed.The results show that the high-value of each pollutants mainly concentrated in the east,north,south direction,and the low-value almost concentrated in the west direction.