Atmospheric visibility in Ningbo has been observed and analyzed.The mean value of visibility in autumn and winter was 11.6 km.The probability of haze was 31.6％.The average visibility in haze days was 6.6 km,and the maximum frequency of concentration range of PM2.5 was 100-120 μg/m3.Visibility declined exponentially with the growth of PM2.5 concentration.Under the same PM2.5 concentration,higher RH made lower visibility.When the visibility equaled to 10 km,the critical value of PM2.5 concentration was 67.5 μg/m3.Moreover,under different RH,the critical PM2.5 concentration corresponding to the visibility of 10 km was different.By establishing regression equation of visibility in different RH and PM2.5 concentrations,it was found that PM2.5 had the maximum weight under low RH (RH≤30％) and RH had the maximum weight under high RH (RH ＞60％).In addition,the weight of RH increased with the growth of PM2.5 concentration when RH was under 60％,and the weight of RH decreased with the growth of PM2.5 concentration when RH exceeds 60％.The conclusions are of great realistic significance for haze governance and improving visibility in Ningbo.%针对宁波市大气能见度的观测研究表明,宁波市秋冬季大气能见度均值为11.6 km,霾日发生率为31.6％,霾日的能见度均值为6.6 km,且PM2.5质量浓度在100～ 120 μg/m3范围内的频率最高.能见度随着PM:5浓度增大呈指数下降,且相同的PM2.5浓度情况下,相对湿度越大,能见度越低.能见度为10 km的临界点上,PM2.5质量浓度值对应为67.5μg/m3.不同相对湿度时,能见度为10 km对应的PM2 5质量浓度临界值不同.通过建立能见度回归方程发现,低相对湿度(RH≤30％)时,PM2 5对能见度的影响权重最大;高相对湿度(RH＞ 60％)时,相对湿度的权重最大;RH低于60％时,RH的权重随着PM2.5浓度的增加而增大;而RH高于60％时,RH的权重随着PM2.5浓度的增加而减小.分析结果可为宁波市灰霾防治和采取合适的管控措施提高能见度提供一定参考.
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