华北背景地区大气能见度变化特征及影响因素分析

Variation Characteristics of Atmospheric Visibility and Its Influence Factors in the background area of North China

基于1980～2014年上甸子国家级地面气象台站人工观测的大气水平能见度数据和大气成分站资料,采用Mann-Kendall趋势分析及突变检验法对大气能见度进行分析,并结合气象和污染要素进行相关性检验,以了解华北背景地区大气能见度的变化趋势及其影响因素。结果表明:上甸子地区年均能见度呈下降趋势,能见度最大和最小变率出现在夏季和春季,分别为3.4 km (10 a)-1和1.7 km (10 a)-1;冬季能见度(38.1 km)最高,秋季(36.2km)次之,春季(32.8 km)和夏季(31.4 km)较低;突变分析表明上甸子地区的年均能见度未出现明显突变。能见度受各类气象因子的综合影响。根据Person相关和偏相关的统计结果,能见度与相对湿度和风速均呈明显负相关;与气压呈明显的正相关;而与气温的相关系数时正时负,表明气温对能见度的影响具有两面性。能见度下降的主要原因为大气污染,能见度随着大气细颗粒物增加呈幂指数降低(决定系数R2=0.98,显著性水平p<0.01);能见度为10km时对应的细颗粒物(PM2.5)的边界浓度为74μg/m^3;在现行的国家环境空气质量标准二级标准(75μg/m^3)下,可以使华北背景地区保持较高的大气能见度(≥10 km)。

In virtue of Mann-Kendall rank statistics, the trends and the abrupt variations of visibility were analyzed using the data of manual air horizontal visibility at the Shangdianzi meteorological station, Beijing from 1980 to 2014.In addition, factors affecting the trend of visibility were analyzed by exploring the relationships between visibility and meteorological elements, as well as atmospheric pollutants, at the background area of North China. The results showed that annual means of visibility experienced a significant decrease, the maximum and the minimum trends of the annual mean visibility were 3.4 km (10 a)^-1 in summer and 1.7 km (10 a)^-1 in spring, respectively. The best visibility appeared in winter (38.1 km), and then in autumn (36.2 km).The worst values were observed in spring (32.8 km) and summer (31.4 km). The annual mean visibility showed no significant abrupt changes. In this analysis, the visibility had a negative correlation with relative humidity and wind speed, and a positive correlation with pressure, and a positive or negative correlation with temperature, which indicated that the influence of temperature on visibility has two sides. The further study pointed out that the degradation of visibility was mainly caused by the high concentration of aerosol particles (PM2.5)(R^2 =0.98, p<0.01), which suggested that the concentration of PM2.5 should be controlled below 74 μg/m^3 to make a good visibility (≥10 km) in Shangdianzi. Keeping the PM2.5 mass concentration equal or below the secondary standards of the National Ambient Air Quality Standard (75 μg/m^3) is expected to perform good visibility (≥10 km) in the background area of North China.