Study On Variation Of Ozone And Nitrogen Concentration In Summer In South Second Ring Of Xi'an

With the development of the city, there are more and more tall buildings, the range of the human activities gradually rise to the near surface layer. It’s increasingly important to research variation of the surface ozone and nitrogen oxides concentrations. Understanding the change law of ozone and nitrogen oxides has scientific significance. Study on the ozone and nitrogen oxides in urban area has practical significance to control ozone and nitrogen oxides pollutions.In June and August, ozone and nitrogen oxides concentrations and meteorological factors in a range of88m of the South second ring road of Xi’an were observed round the clock in seven days. The paper studied the change laws of ozone and nitrogen oxides concentrations of the South second ring road of Xi’an in summer, and its vertical distribution and the effects of meteorological factors on the pollutants concentrations. The main conclusions were described as follows:(1) In a day and night, the variation of ozone concentrations was divided into3periods: high-midlle-low. In June, ozone concentrations in a range of26～62ppb. In August, ozone concentrations in a range of29-69ppb. The variation of nitrogen oxides concentrations was divided into4periods:higher-lowest-highest-lower. In June, nitrogen oxides concentrations in a range of28～68ppb. In August, nitrogen oxides concentrations in a range of32-76ppb. Ozone concentrations at day (8:00am～18:00pm) was higher than night (20:00pm～next day6:00am), nitrogen oxides concentrations at night was slightly higher than day. It found that the mean concentrations of ozone and nitrogen oxides in August were higher than June, and the change range in August was larger.(2) With the increase of altitude, ozone concentrations increased. There was significant positive correlation between ozone concentrations and altitude. In10:00-16:00、18:00-0:00、2:00-8:00, correlation coefficient in June and August was0.98. With the increase of altitude, nitrogen oxides concentrations decreased. A negative correlation could be found between nitrogen oxides concentrations and altitude.In8:00～10:00、12:00-16:00、18:00～2:00、4:00～6:00, correlation coefficient in June and August was-0.99.(3) In June, ozone concentrations of the South second ring of Xi’an usually at the range of21-70ppb, the first over standard rate of ozone was1.4%. In August, ozone concentrations usually at the range of21～70ppb, the first over standard rate of ozone was3.8%. In June, Nitrogen oxides concentrations in June usually at the range of21-80ppb, the first over standard rate of nitrogen oxides was13.5%. In August, Nitrogen oxides concentrations in August usually at the range of31～80ppb, the first over standard rate of nitrogen oxides was4.2%.(4) In June and August, a positive correlation could be found between ozone concentrations and temperature, correlation coefficient were0.83and0.75. There was negative correlation between ozone concentrations and relative humidity, correlation coefficient were-0.72and-0.62respectively.(5) Vehicle flow at weekday was more than weekend. Jobs and other demand caused the differences between weekday and weekend. Because of the emission of tail gas at weekday was higher than weekend, ozone and nitrogen oxides concentrations at weekday were also higher than weekend. Ozone concentrations and vehicle flow had a positive correlation. Correlation coefficient at weekday was0.55, and it at weekday was0.76.(6) There was faintly negative correlation between ozone concentrations and vehicle flow. The main reason was that ozone concentrations were not only affected by nitrogen oxides concentrations, but also influenced by other precursor (CO and VOCs et.al) and meteorological factors.