天津城市大气污染物浓度垂直分布特征

利用2007年10月10日~2008年9月30日天津边界层气象观测塔得到的PM2.5质量浓度、O3和NO2体积分数等梯度资料，对比分析了不同高度上各污染物数据统计特征，并对各污染物数据的时间变化特征及垂直分布进行了讨论.结果表明，天津市PM2.5污染严重，且易发生光化学污染事件.各高度层PM2.5浓度在12、1和2月份存在较大差异，其他月份差异较小；O3体积分数均表现出夏季高冬季低的典型特征；NO2体积分数在220m高度处变化较为复杂且全年波动较大，120m处变化平稳，40m处则表现出春夏季高、秋冬季低的特点.PM2.5体积分数和NO2体积分数日变化均呈现双峰型，峰值的出现与早晚出行高峰以及边界层的变化有关，且污染物出现峰值的时间由低到高存在2~3h的延迟.O3体积分数与太阳辐射强度关系密切，各层均在14：00前后达到最大，而夜间的还原反应使各层臭氧体积分数下降.40m和120m处NO2体积分数变化较为一致，全天波动很小，而220m处波动较大，昼夜差异明显.

Vertical distribution of air pollutants in the atmosphere in Tianjin

The statistical characteristics, temporal variation and vertical distribution of the main air pollutants in Tianjin (PM_(2.5), O_3 and NO_2 ) were analyzed using the vertical data obtained from a 255 m meteorological tower from 10, Oct 2007 to 30, Sept 2008. In Tianjin, the major pollutant is PM_(2.5), and photochemical smog easily occurs due to the high O_3 concentration. The differences of PM_(2.5) concentration among the three heights (220m,120m and 40m) are greater in December, January and February than in other months. All the O_3 concentrations in the three layers are larger in summer,but smaller in winter. The NO_2 concentration fluctuates obviously at 220m, but is relatively stable at 120m and at 40m. The NO_2 concentration is greater in spring and summer than in autumn and winter. The daily PM_(2.5) and NO_2 concentrations both have two peaks at the morning and evening rush hours and the boundary layer moves. According to the times of appearance of each peak at each layer, 2-3 hours are required to transfer the pollutants from the ground to the top layer. The O_3 concentration has a close relationship with the solar radiation intensity and reaches to a maximum at about 14:00 and decreases at night because of the deoxidization reactions in each atmospheric layer. Both at 40 m and 120 m, the concentration of NO_2changes similarly and oscillates little, but at 220 m it fluctuates obviously, and in addition, shows a greater diurnal variation.