基于天气背景天津地区重污染天气特征分析

以天津地区长序列观测PM_(2.5)质量浓度资料为依托,基于天气背景对2014—2016年天津地区重污染天气特征进行分析,并以此为基础评估天津环境气象数值模式(WRF/Chem)在不同天气条件下的模拟效果.结果显示:2009—2016年天津地区重污染天气为341 d,约占全部天数的11.7%,重污染天气主要出现在每年的10月—次年3月,约占全年的82%,重污染天气出现的地面形势主要为锋前低压区、低压槽前、均压场和高压后,4类天气类型占所有重污染天气的73%.同一天气背景下,PM_(2.5)质量浓度模拟值与实况值之间的误差有相似之处,低压槽天气时细颗粒污染浓度模拟明显偏低;冷锋前低压区、华北地形槽和低压过程模拟值略有偏低;高压前和高压底天气模拟值略微偏高;数值模式天津地区重污染TS(Threat score)评分为0.68,漏报与低压槽辐合线模拟位置偏差、冷空气受污染反馈作用影响、小尺度闭合低压区未准确模拟3个因素密切相关;空报主要与冷空气过程影响时间模拟偏差、高压中心位置偏差及其输送通道建立时间影响密切相关.

Analysis of synoptic characteristics of heavy pollution in Tianjin based on weather background

Based on the long-term PM_2.5 mass concentration data in Tianjin, this study analyses characteristics of heavy pollution weather in Tianjin under different backgrounds from 2014 to 2016 and evaluates the simulation results derived from WRF/Chem modelunder different weather conditions. Results showed that the total number of heavy pollution days were 341 in Tianjin during 2009-2016, which accounted for~11.7% of all days.Heavy pollution weather mainly occurs during October-March, which accounted for~82% of all heavy pollution days. The surface patterns favoring the formation of heavy pollution weather mainly include the low pressure in front of cold front,front of the upper trough, the saddle and the high-pressure rear. These four patterns account for 73% of all heavy pollution weather events.The deviation between simulated and observed PM_2.5 mass concentrations showed similarities for the same weather background. Simulation of fine particle pollution is remarkably lower in the background of upper trough, slightly lower in the backgroundof flow pressure in front of cold front, topographic trough and low pressure system, and slightly higher in front of and at the bottom of the high pressure. The TS of numerical model on heavy pollution was 0.68. There were multiple causes for vacancy-forecast, including the simulationof position deviation of convergence line, effects of pollution feedback about cold air, and simulation of small scale closed low pressure area. There were also multiple causes for failed-forecast, including the affecting time of the cold air process, bias of the position of high pressure center and the time for the establishment of pollutants transport channel.