北京山谷风环流特征分析及其对PM2.5浓度的影响

利用北京地区2013~2015年秋冬季各自动站气象要素数据、大气所铁塔资料以及海淀气象站风廓线数据和该地区PM2.5浓度数据,挑选典型个例分析山谷风环流特征及其对PM2.5浓度的影响.经过分析发现,谷风(山风)平均风速为0.55m·s~(-1)(0.31 m·s~(-1)).秋季(冬季)谷风平均持续时间为9h(6h),秋季(冬季)谷风开始时刻为11:00(13:00);秋季(冬季)山风持续时间为13 h(16 h),秋季(冬季)山风开始时刻为21:00(20:00);受北京地区地形等的影响,山谷风转化的风向分界线为东北-西南向,秋季山风前沿压到南二环,冬季山风前沿压到南三环;山、谷风在形成及发展变化的过程中,其厚度有着明显的变化,谷风(山风)秋冬季的平均厚度为700~1 000 m(300~600 m);无论是秋季还是冬季,一天中平均PM2.5浓度开始上升的时刻南部早于北部,秋季PM2.5浓度开始上升的时刻要早于冬季,而开始下降的时刻秋季会晚于冬季.北京地区秋(冬)季空气污染南北差异较大的过渡区处于南二环(南三环),并会随着时间的推移向南移动.秋(冬)季该现象的持续时间为4 h(2h).并且,在研究中发现,PM2.5与山谷风之间可能存在着一定的正负反馈作用.

Impact of Mountain-Valley Wind Circulation on Typical Cases of Air Pollution in Beijing

The impact of mountain-valley wind circulation on the typical examples of pollution was analyzed through the selected pollution process, combining with the hourly PM_2.5 concentrations and meteorological data in Haidian, Shangdianzi and Lishuiqiao in Autumn and Winter from 2013 to 2015, and also the data of Tower of atmospheric, wind profile of Haidian and automatic meteorological stations in the same period. The analysis showed that the average wind speed of valley wind was greater than that of the mountain wind, and they both would be "broken" during the conversion time in the mountain-valley wind days. In contrast with the mountain wind, the average duration of valley wind in autumn was longer than that in winter, and the start time of valley wind in autumn was earlier than the same wind in winter; influenced by the topography of Beijing area, the direction boundary of the transformation between mountain-valley wind was northeast-southwest. The frontier of mountain wind in autumn could fall down to the South Second Ring Road, and it could be pressed to the South Third Ring Road in winter; the average thickness of valley wind was greater than the mountain wind. Whether the moment was in autumn or winter, in the south, the average time when the PM_2.5 concentration began to rise, was earlier than in the north in a day; the time when concentration of pollutants began to rise in the fall was earlier than in the winter, but the time when the concentration began to decline showed the opposite trend. The transition zone of different PM_2.5 concentration in Beijing in autumn or winter located in South Second Ring Road (South Third Ring Road), and it would move to south over time. Duration autumn and winter seasons, this phenomenon lasted about 4 and 2 hours, respectively. Furthermore, the positive and negative feedback effects may exist between pollutant concentrations and mountain-valley wind.