北京平原和延庆地区山谷风异同及对污染的影响

Similarities and Differences of Valley Winds in the Beijing Plain and Yanqing Areas and Its Impact on Pollution

在一定的地形与天气条件下,山谷风环流是影响山地和平原气溶胶污染的主要气象因素之一.本研究基于2015~2019年京津冀地区生态环境监测数据和多源气象数据,对比分析了北京平原和延庆地区山谷风异同,结合典型污染事件揭示了山谷风不同阶段对PM_(2.5)浓度的影响机制.经分析发现,观象台山谷风为偏西南风转偏东北风,延庆站为偏东南风转偏东北风,随着污染等级加重,山谷风强度减弱17.7%~32.4%;观象台风速2~6 m·s^(-1)时,最大为SE风向PM_(2.5)浓度83μg·m^(-3),东南风浓度高于西南;延庆站风速2~6 m·s^(-1)时,偏东南方向浓度高于其他风向20~40μg·m^(-3),谷风阶段PM_(2.5)浓度高于近5年均值10~12μg·m^(-3).以2015年3月5~8日重污染事件为例,山谷风的影响作用主要体现在谷风时段东南风的高湿性及区域传输作用,延庆站3月6~7日谷风阶段PM_(2.5)浓度上升100~130μg·m^(-3);山风时段逆温发展至1000 m,观象台和延庆站露点先后抬升18℃左右,延庆站露点峰值滞后观象台2 h,高湿环境下PM_(2.5)浓度小幅上升.同时,3月6~7日延庆站400 m高度和玉渡山站热力梯度逐渐减小,山谷风分别减小8%和6%,局地环流减弱可能与边界层和高浓度气溶胶双向反馈机制有关.

Under certain terrain and weather conditions,mountain-valley circulation is one of the main meteorological factors affecting aerosol pollution in plain-mountain area.Based on environmental monitoring data and multi-source meteorological data for the Beijing-Tianjin-Hebei region between 2015 and 2019,the characteristics,similarities,and differences of mountain-valley winds in the Beijing Plain and Yanhuai Basin regions were compared.The results show that the mountain-valley winds recorded at the Beijing Observatory are from southwest to northeast compared to from the southeast to northeast at Yanqing station.With the aggravation of pollution levels,the mountain-valley wind intensity decreased by 17.1%-32.4%.When the wind speed at Beijing Observatory was 2-6 m·s^(-1),the maximum PM_(2.5)concentration in southeast was 83μg·m^(-3),which was higher than in the southwest.When the wind speed at the Yanqing station was 2-6 m·s^(-1),the PM_(2.5)concentrations in SE-SSE area was 20-40μg·m^(-3)higher than in other directions,and the concentrations in the valley winds were 10-12μg·m^(-3)higher than the average value for the last five years.Taking the typical heavy pollution event on March 5-8,2015,as an example,the influence of mountain-valley winds is mainly reflected in the high humidity and regional transmission of southeast winds during the valley wind stage.The PM_(2.5)concentrations at the Yanqing station increased by 100-130μg·m^(-3)during the valley wind stage on March 6 and 7,2015.The inversion temperature developed to 1000 m during the mountain wind stage,the local dew point at the Beijing Observatory and the Yanqing station rose by approximately 18℃.The peak dew point at the Yanqing station occurring 2 hours after the Beijing Observatory,and the concentrations of PM_(2.5)rose slightly under high humidity conditions.Meanwhile,the thermal gradient between the 400-m-high Yanqing Station and Yudu Mountain gradually decreased,and the mountain-valley wind decreased by 8%and 6%,respectively.The weakening of local circulation may be related to the bidirectional feedback mechanism of the boundary layer and high concentrations of aerosols.