成都市2015—2019年臭氧浓度夜间变化及成因分析

利用2015—2019年成都市每日逐时地面O₃监测资料和同期气象数据,通过模拟和计算区域水平、铅直流场和大气静力稳定度支配参数(R_i),对成都市夜间O₃浓度第二峰值的反常现象进行统计分析和原因追踪。研究结果表明:成都市2015—2019年夜间O₃浓度第二峰值出现频率为17%,造成O₃浓度夜间反常现象的原因是雅安市山风将高空O₃输送至地面,而后平流至成都市,或本地高空湍流破坏夜间稳定层,将上层残留层储存的白天高浓度O₃送至近地面,加之夜晚绝大部分污染源停止排放,消耗O₃的物质大幅减少,造成地面O₃浓度的夜间反常变化。引起高空湍流的方式有2种:一是风向切变,且至少切变45°,风向切变角度越大,湍流强度越大,引起残留层向下增长的幅度越大;二是风速切变,且切变层风速要大于上、下层风速2 m/s,切变风速越大,湍流强度就越大,残留层向下增长的幅度就越大,低空急流是风速切变的极端表现。

Analysis of Nighttime Changes and Causes of Ozone Concentration in Chengdu from 2015 to 2019

Using daily hourly ground O₃ monitoring data and meteorological data over the same period in Chengdu from 2015 to 2019,through simulation and calculation of regional level,lead direct current field,and the dominant parameter R_i(Richardson number) of atmospheric static stability,statistical analysis and cause tracking were conducted on the abnormal phenomenon of the second peak of nighttime O₃ in Chengdu. The research results showed that the frequency of the second peak of O₃ at night in Chengdu from 2015 to 2019 was 17%. The reason for the abnormal phenomenon of O₃ at night was that the mountain winds in Ya''an City input O₃ at high altitude to the ground and then advection to Chengdu City, or the local high altitude turbulence destroyed the nighttime stable layer and injected the daytime high concentration O₃ stored in the upper residual layer into the ground,in addition to the fact that most pollution sources stopped discharging at night,resulting in a significant reduction in the consumption of O₃, thereby causing abnormal changes in ground O₃ at night. There were two ways to cause high altitude turbulence:First,the wind direction should be sheared by at least 45°. At the same time,the greater the shear angle along the wind direction,the greater the turbulence intensity,and the greater the downward growth of the residual layer; The second was wind speed shear,and the wind speed in the shear layer should be greater than the wind speed in the upper and lower layers by more than 2 m/s. At the same time,as the shear wind speed increased,the turbulence intensity became stronger,and the depth of the residual layer growing downward became deeper. Low level jets were the extreme manifestations of wind speed shear.