北京秋季城区和近郊近地层O_3特征

Characteristics of Surface O_3 over Beijing Urban and Rural Areas in Autumn

北京十三陵地区出现O3高值,一直是人们所关心的环境问题,秋季是北京地区高O3浓度季节,为此2001年9月7～17日在北京城区舞蹈学院楼顶和十三陵地区昭陵进行了一次以O3为主,并结合其前体物的综合比对实验.对北京城区和郊区地面O3特征进行了比对分析,目的是了解北京秋季近地面城乡O3差异的原因.结果表明郊区O3浓度日均值普遍大于城区O3日均值,城区和郊区白天O3浓度接近,城乡O3平均浓度的差异是由于不同天气条件下城区夜间地面O3浓度很低,有时甚至接近于零,而郊区夜间O3依然维持一定浓度.其主要原因在于城区有较多的污染排放源,致使夜间NO浓度维持相对高值,其通过滴定过程大量消耗O3所致.观测中发现无论城区或郊区当小时平均NO浓度大于10×10-9(体积混合比)时,相应小时平均O3浓度接近于零.NO2/NO低值区对应于地面O3低浓度,城区夜间NO2/NO值低于郊区.由此可见城区O3日平均值较低和城区空气污染重于郊区有密切关系.

The high concentration of surface ozone at Ming Tombs has widely been concerned and the concentration of ozone in the Beijing region in Autumn is very high; therefore, a comprehensive observational experiment was conducted on surface ozone and its precursors at a urban site and a rural site in Beijing from 7 to 17 of September 2001. The characteristics of surface ozone between the urban and rural sites were compared, and the reasons of the differences were analyzed. The primary results indicate that the daily mean concentration of surface ozone at the rural site was higher than that at urban site, but the daytime mean ozone concentrations at two sites were quite close. The big difference of mean ozone concentrations between urban and rural sites attributes to the very low （smetime near zero） concentration of ozone at night in the urban area while ozone in the rural area was relatively high. The reason is that in the urban areas there are many NO sources resulting in the highlevel NO at night, which destructs ozone through “titration” process. It is found that whether at urban or rural sites, when hourly averaged NO was greater than 10×10^-9, the corresponding hourly averaged surface ozone was close to zero; the low ratio of NO2/NO was in good agreement with low surface ozone at both sites; the ratio of NO2/NO at night in the urban area was lower than that in the rural area; and the lower daily mean concentration of ozone in urban areas relative to rural areas was highly related with the more serious air pollution in urban areas than in rural areas.