天津冬季一次污染过程中NOx和O3的立体分布特征

Three-Dimensional Distribution Characteristics of NO_x and O_3 during a Winter Atmospheric Pollution in Tianjin City

由于大气是一个复杂介质,低层大气中湍流的存在使物质和能量的交换很剧烈,污染物的扩散传输现象明显.对不同高度不同区域的低层大气做立体观测,获取气态污染物浓度分布最直接的资料很有必要.综合利用地面观测站点、系留气球和飞机平台,于2016年11月25—26日在天津武清高村一次污染天气条件下对NO_x和O_3进行立体观测,得到了污染物的地面、垂直和低空区域分布特征,并结合气象因子进行分析研究.观测结果表明,地面φ(NO_x)水平较高,日均值为230×10^(-9),超过了GB 3095—2012《环境空气质量标准》二级标准的限值,反映了高村冬季较高的污染水平,主要受当地交通源排放的影响.φ(NO_x)随高度的上升呈下降趋势,受风速的影响明显,主要积聚在逆温层以下.低空φ(NO_x)市区高于郊区,而处于更远郊区的高村φ(NO_x)与市区相当,也反映了高村本地较高的NO_x污染.高村地面φ(O_3)低,日最大8 h平均值为8×10^(-9),反映了冬季低温辐射弱、光化学反应强度低的特点.随高度增加φ(O_3)呈上升趋势,垂直分布特征主要与温度层结有关.低空φ(O_3)呈郊区高于市区,高村(远郊区)高于近郊区的特征.研究显示,φ(NO_x)的升高导致φ(O_3)下降,这可能与高村冬季的φ(VOCs)/φ(NO_x)偏低有关,需要结合VOCs观测数据做进一步分析.

The atmosphere is a complex medium.The presence of turbulence in lower atmosphere makes the exchange of matter and energy intense,and the diffusion of air pollutants is evident.It is necessary to obtain the concentration distribution of gaseous pollutants in the lower atmosphere in different regions and heights.Theφ(NO x)andφ(O 3)were measured during a heavy air pollution episode in Gaocun of Tianjin City from November 25 th to 26 th,2016 by using ground observation,tethered balloon and aircraft synthetically.The characteristics pollutants at ground,vertical and low-altitude areas were obtained and analyzed combining with meteorological factors.Observation results showed that the level ofφ(NO x)on the ground exceeded GB 3095-2012(the average daily concentration was 230×10-9),which indicated high pollution level in Gaocun in winter were mainly affected by the local traffic sources.Theφ(NO x)decreased with the increase of altitude which was obviously affected by the wind speed,NO x mainly accumulated below the inversion layer.φ(NO x)at low altitude of urban areas was higher than the suburbs.While in the far suburb of Gaocun,showingφ(NO x)was comparable with the urban areas indicating high local NO x pollution in Gaocun.The daily maximum 8 hours average concentration of ozone was 8×10-9.The low groundφ(O 3)reflected the low temperature and low photochemical reaction in winter.With the increase of height,φ(O 3)showed a rising trend and its vertical distribution was mainly related with temperature stratification.The low-levelφ(O 3)was higher in the suburbs than that in the urban areas,and the Gaocun concentration was higher than that in the suburbs.The study shows that the increase ofφ(NO x)leads to the decrease ofφ(O 3),which may be related to the low ratio ofφ(VOCs)φ(NO x)in the winter of Gaocun,and further analysis is needed.