摘要
空气湿度是调节能见度变化和大气污染发展的重要气象因素,利用2015~2020年天津市冬季的相对湿度、比湿、PM_(2.5)质量浓度和能见度的历史数据,分别分析了PM_(2.5)质量浓度和能见度与相对湿度和比湿之间的关系.2015~2020年冬季,天津城区PM_(2.5)质量浓度整体呈下降趋势,6 a下降了28.0%.10 km以上能见度天气的发生频率在2015~2018年冬季逐步上升,但在2019年和2020年的冬季重新下降.其中,2020年1月和2月天津市平均相对湿度达到63%和67%,显著高于30 a的历史同期均值,低于2 km的极端低能见度天气发生频率反弹至与2016年冬季相当的水平,空气湿度的升高在视觉上掩盖了PM_(2.5)的减排效果.天津市水汽的外部来源主要包括西南方向和东部渤海湾方向的输送,其中渤海湾方向传输的水汽占比约为59%,明显高于西南方向的25%.但东风相对清洁,对PM_(2.5)质量浓度的增长贡献有限,更多影响的是能见度.相比之下,当地面主导风向为西南风且比湿>2.0 g·kg^(-1)时,大气污染的发生频率高达83.6%.短时间内,比湿的变化与相对湿度相比较为平稳,冬季利用比湿的变化在一定程度上可以预测大气污染事件的发生及污染程度.冬季平均相对湿度>80%或比湿>3.0 g·kg^(-1)时,PM_(2.5)质量浓度>75μg·m^(-3)的发生频率分别为78%和80%.在冬季的环境气象预报中,要尤其警惕比湿高于3.0 g·kg^(-1)的天气条件.
Air humidity is a key meteorological factor in regulating visibility changes and haze episodes.Based on multi-year historical data of PM_(2.5)mass concentration,visibility,relative humidity(RH),and specific humidity(q)during winter in Tianjin,the impact of air humidity on PM_(2.5)mass concentration and visibility was investigated.Between 2015 and 2020,the PM_(2.5)mass concentration showed an overall decline of 28.0%.The frequency of visibility above 10 km significantly increased between 2015 and 2018,indicating an improvement in visibility during this period.However,the visibility deteriorated again in the winter of 2019 and 2020,with a decreased frequency of visibility above 10 km.Specifically,the mean RH in January and February in 2020 of Tianjin reached 63%and 67%,respectively,which were higher than the historical 30-year average for the same period.The frequency of extremely low visibility(lower than 2 km)rebounded to a level equivalent to that during the winter of 2016.The enhanced air humidity visually obscured the reduction effect of PM_(2.5).For Tianjin,the external sources of water vapor are southwestern and eastern transport.Particularly,water vapor transported from eastern Bohai Bay(59%)is significantly greater than that from southwestern direction(25%).However,the eastern air mass is generally clean,hence,although the condensed water may increase the PM_(2.5)mass concentration in the humid air,the eastern air mass affects visibility to a greater extent.On the other hand,the haze episodes during winter frequently occurred when the southwestern wind dominated and specific humidity was greater than 2.0 g·kg^(-1),with a frequency of 83.6%.In a short period of time,the variation of specific humidity is less significant than RH,therefore,the relationship between specific humidity and PM_(2.5)mass concentration or air quality can be utilized to predict the occurrence of haze episodes and pollution during winter.When the average RH is higher than 80%or the mean specific humidity is greater than 3.0 g·kg^(-1),the frequency of PM_(2.5)mass concentration greater than 75μg·m^(-3)is 78%and 80%,respectively.For the air quality forecast during winter,weather conditions with specific humidity greater than 3.0 g·kg^(-1)should be carefully monitored.
作者
丁净
唐颖潇
郝天依
姚青
蔡子颖
张裕芬
韩素芹
DING Jing;TANG Ying-xiao;HAO Tian-yi;YAO Qing;CAI Zi-ying;ZHANG Yu-fen;HAN Su-qin(Tianjin Environmental Meteorological Center,Tianjin 300074,China;China Meteorological Administration-Nankai University Cooperative Laboratory for Atmospheric Environment-Health Research,Tianjin 300074,China;State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control,College of Environmental Science and Engineering,Nankai University,Tianjin 300350,China)
出处
《环境科学》
EI
CAS
CSCD
北大核心
2021年第11期5143-5151,共9页
Environmental Science
基金
国家自然科学基金项目(41771242)。
作者简介
丁净(1990~),女,博士,主要研究方向为气溶胶物理与化学,E-mail:dingjing0824@126.com;通信作者:张裕芬,E-mail:zhafox@126.com;通信作者:韩素芹,E-mail:sq_han@126.com。
