| Atmospheric ozone plays an important role in global and regional environment change.It has a significant impact on the solar radiation budget.As one of primary gaseous contaminant in urban ambient,ozone has an important effect on the urban and suburbant atmospheric environment. Based on the data of air pollutants and meteorological parameter collected in Beijing, Characteristics of ozone precursor are explored.Trace gases NOx and CO,VOCs,temperature and solar radiation are associated with ozone formation.The major contents and conclusions are presented as follows:Firstly,O3 pollution is very serious,and O3 concentrations fluctuate periodically.The photochemical pollution in Beijing is most serious in summer.The peak O3 and oxidant (OX=O3+NO2)concentration in Beijing often appear about 15:00 in the early afternoon;the diurnal variation of NOx concentrations show a very clear cycle with two peaks;one appears about 07:00 in the morning and the other is at 23:00 in the evening.The highest photolysis rate coefficient of NO2(J3)appears in summer.The greatest J3 in daytime appears at noon.The NOx crossover point occurs at about 100×10-9NOx At lower levels,NO2 is the major component of NOx,whereas NO dominates at higher mixing ratios.It is also shown that the level of OX is made up of two contributions,regional contribution and local contribution.The former is affected by regional background O3 level,with the maximum in spring,whereas the latter is effectively correlates with the level of primary pollution,with the maximum in summer.Diurnal variation also appears in the concentrations of the components of oxidants.Owing to changes of traffic in urban,NOx concentrations on weekends are higher than weekdays.Variations of O3 concentrations in daytime in weekend are a little different from weekdays,but O3 concentrations in night on weekends are lower than weekdays.Secondly,average total ozone content in Beijing is 329 DU and higher in winter and spring, lower in summer and autumn.The inverse relationship exists between ground level UV radiation and total ozone content.This study also shows that a substantial reduction(up to 50%)in the UV radiation on days with high levels of air pollution.Larger fluctuations are found in UV radiation in the summer.The effects of clouds and air pollution on UV are higher than on total solar radiation, and the reduction in UV is about twice as large as the total solar radiation values.Strong reduction in the UV radiation reaching the ground is associated with the increase of tropospheric ozone and nitrogen oxides in Beijing.The correlation coefficient between ozone concentration and decrease in UV radiation is 0.70 in the early afternoon.Both temperature and wind speed have significant positive correlation with ozone.Relative humidity has a significant negative correlation with ozone.Ozone concentrations have signficant correlation with temperature in summer and with wind speed in winter.The distant transport associated with southeastern,southern and western winds contributes substantially to the ozone because the air mass is polluted.The main relationships we could observe in these analyses are then used to obtain a regression equation linking diurnal ozone concentration in summer with meteorological parameters.The characteristics of CO concentration and wind-speed data distribution show that there is an obviously seasonal cycle of CO concentration,with the maximum in winter and minimum in summer.The seasonal variations are believed to be due to the combination results of emission sources and atmospheric diffusion.Data show an inverse relationship between opposing percentiles of the distribution of CO concentration and mean wind speed,and its correlation coefficient is 0.93.The value of K is 3.5±0.5.CO concentrations when prevailing wind direction is from East sector may be 2.3 times higher as compared from West sector,which are affected by where the sample is located and the advection of pollution air from high traffic density area nearby.Thirdly,the highest mean extent of reaction appears in summer.Hourly average extent of reaction in summer is 0.25.The diurnal variation of extent of reaction shows a very clear cycle with single peak,the peak often appears at about 15:00 in the early afternoon.With the availability of radicals and oxides of nitrogen,the mean of reaction increase may be 5.3 times higher at high level as compared at low level.The reactivity of NMHCs is dominated by anthropogenic NMHCs and of the anthropogenic NMHCs,reactive aromatics dominate in which eth-benzene is the most important.Ozone production efficiency is 4.0.Oxidant production rate increases with increasing NOx,with the average of(12.5±8.3)×10-9·h-1.The highest net ozone production rate appears in the noontime.Generally the formation of ozone throughout of Beijing area is limited by VOCs,in which reactive aromatics and alkene are dominant.
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