2006~2021年夏半年上海臭氧浓度特征及其大气环流背景分析

Characteristics of Ozone Concentration in Shanghai and Its Associated Atmospheric Circulation Background During Summer Half-years from 2006 to 2021

基于上海地区2006~2021年逐日臭氧浓度数据以及同期气象要素和美国环境预报中心/国家大气研究中心(NCEP/NCER)再分析数据,分析了2006~2021年上海地区臭氧浓度变化特征和气候背景,进一步对比分析臭氧浓度异常年份的高空大气环流形势差异,并加入关键气象影响因子建立臭氧浓度月预报模型.结果表明,上海地区全年和夏半年臭氧浓度的平均值均呈现波动式上升趋势,且夏半年臭氧浓度和风速呈显著负相关(相关系数达-0.826),与静风出现频率以及低云量<20%出现日数呈显著正相关(相关系数分别为0.836和0.724).当夏半年西太平洋副热带高压强度偏强且位置偏西偏南时,上海易受偏西风异常环流影响,不利于海上洁净空气向上海输送,易引起高浓度臭氧污染.当夏半年地面射出长波辐射偏低时,有利于地面升温,易引起高浓度臭氧污染.加入太阳直接辐射、最高气温和风速作为外生变量的臭氧月预报模型对月预报效果提升明显,均方根误差减少47.7%,相关系数提升11.2%.

It is of great importance to scientifically evaluate the impact of weather and climate conditions on the occurrence of O_(3) pollution in order to improve the accuracy of O_(3) pollution forecasts,as well as to reasonably control and reduce the adverse effects of O_(3) pollution.The characteristics of O_(3) concentration and climate background were analyzed based on daily O_(3) concentration data,meteorological factors,and NCEP/NCER reanalysis data from 2006 to 2021 in Shanghai.In addition,the differences in atmospheric circulation situations during years with anomalous O_(3) concentrations were compared and diagnosed from the perspective of climatology.Additionally,the monthly O_(3) concentration prediction model(seasonal autoregressive integrated moving average with exogenous regressors,SARIMAX)was further established by adding the key meteorological factors.The results indicated that both the whole-year average and summer half-year average O_(3) concentrations in Shanghai were increasing with fluctuation,and the summer half-year average was much higher than the annual average,up to 36.2%.Furthermore,there was a significant negative correlation between O_(3) concentration and wind speed(correlation coefficient of -0.826)and a significant positive correlation with the frequency of static wind and the number of days in which the low cloud cover was less than 20%(correlation coefficients of 0.836 and 0.724,respectively).The monthly mean O_(3) concentration had a clear periodicity,showing a pattern with a high concentration in the middle period(April to September)and a low concentration at the beginning and end of the periods.High O_(3) concentration years(2013-2021)were accompanied by more polluted days,lower average wind speed,more small wind(≤1.5 m·s^(-1))days,more days of low cloud cover of less than 20%,more days of high temperature,higher direct solar radiation,and more sunshine hours.When the location of the stronger West Pacific subtropical high was westward and southward in the summer half-year,Shanghai was influenced by an anomalous westerly wind,which was not conducive to the transportation of clean air from the sea to Shanghai and thus led to the high concentration of O_(3) pollution.When the long wave radiation emitted from the ground was low in the summer half-year,it was favorable for the increase in ground temperature and caused a high concentration of O_(3) pollution.Adding direct solar radiation,maximum temperature,and wind speed as exogenous variables to the monthly O_(3) forecast model could significantly improve the effectiveness of the monthly forecast,with the root mean square error decreasing by 47.7%(from 22 to 11.5)and the correlation coefficient increasing by 11.2%(from 0.819 to 0.911),which could be applied to the practical prediction of monthly O_(3) concentration.