哈尔滨秋季一次持续性重污染过程分析

利用气象与环境监测数据,结合后向轨迹和秸秆焚烧火点监测资料,从环流形势、气象要素、污染源和污染传输特征等方面,对哈尔滨2017年10月18—20日持续性重污染天气过程进行分析。结果表明:这次重污染过程连续48h为重度或严重污染,首要颗粒物为PM2.5,PM2.5平均浓度为438μg·m^-3,局地PM2.5浓度高达1487μg·m^-3。重污染过程分为两个阶段,每个阶段主要污染物呈双峰分布。在重污染过程中,高空环流平直,浅槽前暖平流占主导地位,地面为弱低压均压场控制。地面风速小,平均风速仅为1.5m·s^-1,风速≤1.5m·s^-1静小风频率为71%,风场辐合,有利于污染物积聚。在重污染发展的过程中,地面相对湿度(RH)增大有利于颗粒物吸湿增长和污染加剧;在重污染减弱的过程中,PM2.5浓度减少至每阶段谷值时间比RH减小至谷值时间滞后4—5h。在边界层内有逆温层顶高为200m左右、逆温强度>2.0℃·(100m)^-1的贴地逆温层,层结稳定,垂直扩散条件差。污染物主要来源于秸秆焚烧,其次来源于取暖燃煤。静稳气象条件下本地污染物积累叠加远距离较高浓度的秸秆焚烧污染物输送导致哈尔滨这次重污染过程。

Analysis of a persistent heavy air pollution event during Autumn in Harbin

Using meteorological and environmental monitoring data,the backward trajectory analysis,and satellite fire-monitoring data,the characteristics of a persistent heavy air pollution event in Harbin from October 18 to 20,2017 were analyzed,including atmospheric circulation,meteorological elements,pollutant sources,and transport.The results indicate that the heavy and severely heavy air pollution periods last for 48 h,with the mean and maximum PM_2.5 (primary air pollutant) concentration reaching 438 μg·m^-3 and 1487 μg·m^-3,respectively.This heavy pollution event can be divided into two stages where double peaks of pollutant concentrations are observed.During this heavy pollution event,atmospheric circulation at upper levels are smooth and dominated by warm advection ahead of a shallow trough,and meanwhile,the surface is controlled by a weak low pressure.The surface wind speed is low,about 1.5 m·s^-1 on average,and the occurrence frequency of wind speed ≤ 1.5 m·s^-1 is 71%.The convergence of wind field favored the accumulation of air pollutants.During the development of heavy pollution,the increase of relative humidity (RH) contribute to the hygroscopic growth of particulate matters and thus enhance the pollution process.The decrease of PM_2.5 concentration to the minimum lags 4-5 h behind that of RH to its minimum value.A strong surface temperature inversion layer is observed in the planetary boundary layer,with the top up to about 200 m and the intensity larger than 2.0℃·(100 m)^-1.The stable stratification makes poor vertical diffusion.These air pollutants dominantly come from straw burning,followed by the coal combustion for building heating.The heavy pollution event in Harbin is due to the accumulation of local pollutants under stable meteorological conditions and the long-distance transport of massive pollutants caused by straw burning.