宁波地区空气质量及大气自净能力海陆差异对比

Comparison of air quality and atmospheric self-purification capacity between coastal and inland areas of Ningbo

以镇海、奉化分别作为宁波沿海和内陆空气质量代表站。基于代表站2013-2017年污染物资料和2015年12月至2017年2月冬季激光雷达资料,对比分析宁波地区沿海和内陆站点的空气质量差异;利用NCEP的GDAS(Global Data Assimilation System)资料和ERA-Interim高分辨率再分析资料评估两地气溶胶来源及大气自净能力差异。结果表明:宁波沿海和内陆地区中度及以上污染主要集中于冬季,冬季首要污染物以PM2.5为主;镇海NO2浓度较奉化显著偏高,而两地PM2.5 和PM10 浓度差异较小。冬季镇海和奉化3km以下都存在消光系数大的气溶胶集中层,镇海3km内消光系数平均值较奉化偏高约40%。两地中度及以上污染时,镇海和奉化的气溶胶粒子主要来自宁波西北方向的内陆地区,比例分别为90%和63%,镇海地区其余10%左右来自近距离低空偏东气流的输送,而奉化地区有37%来自浙江西南部的短距离输送。冬季当宁波地区出现区域性优和中度以上污染时,浙江北部沿海分别盛行东北风和西北风,空气质量优时混合层内平均风速大于中度以上污染时。浙江省大气自净能力比值呈自西北向东南减小,宁波地区优等空气质量大气自净能力约为中度以上污染的 1.5倍。大气自净能力在不同空气质量等级下差异显著,可作为大气污染发生、发展和消退判定的参考依据。

Based on air pollutant monitoring data from 2013 to 2017 and the LiDAR data from December of 2015 to February of 2017 observed at Zhenhai (a coastal station) and Fenghua (an inland station) in Ningbo,the characteristics of air quality at the two stations were comparatively analyzed,and the aerosol sources and difference of atmospheric self-purification capacity at the two stations were evaluated using the reanalysis data from National Centre for Environment Prediction (NCEP) Global Data Assimilation System (GDAS) and ERA-Interim high-resolution dataset.The results showed that moderate and heavier air pollution occur mostly in winter in the coastal and inland areas of Ningbo,with PM 2.5 as the primary pollutants commonly.The NO 2 concentrations in Zhenhai area are significantly higher than that in Fenghua,and concentrations of PM 2.5 and PM 10 between the two areas are close to each other.In winter,an aerosol layer below 3 km with large extinction coefficient are observed at both stations,and the average of extinction coefficient below 3 km at Zhenhai station is about 40% larger than that observed at Fenghua station.When moderate and heavier pollution occur at both stations,aerosols are mainly originated from the northwestern inland region of Ningbo,reaching 90% for Zhenhai and 63% for Fenghua,respectively.The rest aerosols in Zhenhai are mainly related to the short-range transport by easterly flows at low levels,and that in Fenghua are primarily due to the short-range transport from the southwestern region of Zhejiang province.The northern coastal areas in Zhejiang province is usually dominated by northeasterly and northwesterly winds when air quality in Ningbo region reaches grades of excellence,moderate,and heavier pollution during winter,with mean wind speed of the former higher than the latter. The ratio of atmospheric self-cleaning capacity between air quality grades of excellence and moderate and heavier pollution decreases from the northwest to the southeast in Zhejiang province,with the value about 1.5 times Ningbo area.The difference of atmospheric self-purification capacity under different air quality grades can be used as a reference for forecasting the occurrence,development and dissipation of air pollution.