1961~2019年黄河流域大气自净能力指数变化特征分析

利用2015~2019年环境空气质量监测数据和黄河流域73个站点1961~2019年的气象观测资料，对11个站点的大气自净能力指数的适用性及其与环境空气质量之间的关联性进行了验证，并分析了黄河流域大气自净能力指数的时空变化特征及影响因子.结果表明，1961~2019年黄河流域大气自净能力指数整体呈下降趋势，下降速率为每10a下降0.18t/（d×km²），平均值为4.44t/（d×km²），且在1969年达到最大值，为5.32t/（d×km²），2011年达到最小值，为3.81t/（d×km²）；黄河流域73个站点中有64个站点大气自净能力指数呈下降趋势，50个站点呈显著和极显著下降趋势.从年内变化看出，黄河流域大气自净能力指数最高值出现在4月，为5.30t/（d×km²），最低值出现在1月，为3.48t/（d×km²）.在年空间分布上，黄河流域大气自净能力指数分布以青海西南部，山东、四川大部分地区，内蒙古、宁夏以及甘肃少部分地区，陕西西安，山西的五寨和右玉等大气自净能力较好，大气自净能力指数在4.69~7.18t/（d×km²），其余地区大气自净能力相对较差.影响因子中，混合层高度与大气自净能力指数呈极显著正相关，相关系数为0.63（n=4307）；小风日数与大气自净能力指数呈极显著负相关，相关系数为-0.78（n=4307），日平均风速³2.5m/s的日数及日平均风速³5.5m/s的日数与大气自净能力指数均呈极显著正相关，相关系数分别为0.78和0.55（n=4307）；降水日数与大气自净能力指数呈极显著正相关，相关系数为0.18（n=4307），中雨及以上日数与大气自净能力指数呈显著正相关，相关系数为0.03（n=4307），黄河流域小雨对大气自净能力的影响明显高于中雨.逐步回归分析显示，大气自净能力指数主要受日平均风速³2.5m/s的日数、降水日数和混合层高度的综合影响，其中，日平均风速³2.5m/s的日数对大气自净能力指数的贡献率最大，其贡献为正.

Variation characteristics of atmospheric self-purification capacity index over the Yellow River Basin during 1961~2019

Based on the ambient air quality monitoring data from 2015 to 2019 and the meteorological observation data from 73 stations in the Yellow River Basin from 1961 to 2019, the applicability of the atmospheric self-purification capacity index of 11 stations and its correlation with the ambient air quality were verified. The spatial and temporal variation characteristics and influencing factors of atmospheric self-purification capacity index in the Yellow River Basin were analyzed. The results showed that the whole Yellow River Basin presented a downward trend from 1961 to 2019, with a decreasing rate of 0.18t/(d×km²) per 10a, and the average value was 4.44t/(d×km²). The atmospheric self-purification ability index reached its highest value of 5.32t/(d×km²) in 1969, and reached its lowest value of 3.81t/(d×km²) in 2011. Among 73 sites in the Yellow River Basin, 64 sites showed a downward trend in atmospheric self-purification capacity index, and 50 sites showed a significant downward trend. According to the annual variation, the highest value of atmospheric self-purification capacity index in the Yellow River Basin was 5.30t/(d×km²) in April, and the lowest value was 3.48t/(d×km²) in January. In terms of annual spatial distribution, the atmospheric self-purification capacity index of the Yellow River Basin was between 4.69t/(d×km²) and 7.18t/(d×km²) in the southwest of Qinghai, most of Shandong and Sichuan, a small part of Inner Mongolia, Ningxia and Gansu, Xi'an of Shaanxi, Wuzhai and Youyu of Shanxi, etc., which had better atmospheric self-purification capacity. It was relatively poor in other regions. Among the impact factors, the mixing layer height was positively correlated with the self-purification capacity of the atmosphere, and the correlation coefficient was 0.63(n=4307). There was an extremely significant negative correlation between the number of light wind days and atmospheric self-purification ability index, with the correlation coefficient of -0.78(n=4307). The number of ³2.5m/s and ³5.5m/s days with daily average wind speed had extremely significant positive correlation with atmospheric self-purification capacity index, the correlation coefficients were 0.78and 0.55(n=4307), respectively. There was an extremely significant positive correlation between the number of rainy days (³0.1mm) and atmospheric self-purification capacity, and the correlation coefficient was 0.18(n=4307). The number of days with moderate rain (³10.0mm) and above were significantly positively correlated with atmospheric self-purification capacity, with a correlation coefficient of 0.03(n=4307). The effect of light rain on atmospheric self-purification capacity was obviously higher than that of moderate rain in the Yellow River Basin. Stepwise regression analysis showed that the index of atmospheric self-purification capacity was mainly affected by the number of days with daily average wind speed (³2.5m/s), the number of rainy days and the height of mixing layer. Among them, the number of days with daily average wind speed (³2.5m/s) had the largest contribution to the index, and its contribution was positive.