长沙市冬季人行道PM_(2.5)污染特征及影响因素

Characteristics and Influencing Factors of PM_(2.5) Pollution on the Pavement in Winter in Changsha City

了解不同气象条件下城市人行道细颗粒物(PM_(2.5))时空分布特征对于指导城市环境评价及街道空间规划布局具有重要意义。选取长沙市车流量及人流量较大的4条道路旁0、5、10 m处的人行道,在冬季晴天、阴天和大风天开展PM_(2.5)质量浓度、风速、温度及相对湿度监测,探讨PM_(2.5)分布特征与气象因子的关系。结果表明:冬季晴天、阴天及大风天的人行道PM_(2.5)质量浓度变化呈现双峰双谷特征,峰值均出现在06:00—08:00,其次为18:00—20:00,谷值出现在14:00—16:00及22:00—24:00;距离机动车道10m处的人行道PM_(2.5)含量低于机动车道旁(即距离机动车道0 m)的人行道PM_(2.5)含量,这种差异在大风天气下更为显著;人行道PM_(2.5)质量浓度与温度、风速呈显著负相关关系,与空气湿度呈显著正相关关系,低温不利于PM_(2.5)扩散,但在大风天温度对PM_(2.5)的影响极小,风对PM_(2.5)含量的变化影响极大,在远离机动车道的人行道更为显著,而高湿度天气有利于PM_(2.5)的凝结。低温、高湿天气下06:00—08:00、18:00—20:00人行道PM_(2.5)质量浓度较高,大风对PM_(2.5)质量浓度具有一定削减作用,早晚高峰减少人行道洒水以降低空气湿度,有利于PM_(2.5)质量浓度的降低,减少PM_(2.5)积累。

Understanding the spatiotemporal distribution characteristics of urban pedestrian PM_(2.5) under different meteorological conditions is of crucial importance in guiding urban environmental assessment and street space planning and layout.This study monitored PM_(2.5) concentration,wind speed,temperature and relative humidity on the sidewalks at 0m,5m,and 10m from four major roads in Changsha during winter sunny,cloudy and windy days.The results showed that the PM_(2.5) concentration on Changsha's sidewalks exhibited a bimodal pattern with two peaks and two valleys during winter sunny,cloudy and windy days.The peaks occurred between 06:00-08:00 and 18:00-20:00,while the valleys occurred between 14:00-16:00 and 22:00-24:00.The PM_(2.5) concentration on the sidewalks 10m away from the road was lower than that on the sidewalks 0m away,and this difference was more significant on windy days.The PM_(2.5) concentration on the sidewalks was significantly negatively correlated with temperature and wind speed but significantly positively correlated with humidity.Low temperature was unfavorable for the diffusion of PM_(2.5),but the temperature had little effect on PM_(2.5) on windy days.The wind had a strong diffusion effect on PM_(2.5),especially on the sidewalks farther from the road,while high humidity was unfavorable for the condensation of PM_(2.5).During low-temperature and high-humidity weather conditions,the PM_(2.5) concentration on the sidewalks was high between 06:00-08:00 and 18:00-20:00,and the wind could reduce the PM_(2.5) concentration to some extent.Reducing the humidity by reducing sidewalk watering during peak hours could also help reduce the PM_(2.5) concentration and accumulation.