气溶胶辐射效应对气象和环境影响的观测与模拟研究

Observation and modeling study of the influence of aerosol radiation effect on meteorology and environment

选取2015年和2019年不同代表年份,结合外场观测和数值模拟,分析了天津地区不同季节不同天气(晴天、多云、霾)下,气溶胶辐射效应对整层大气透过率和地表入射太阳辐射的影响,以及这种影响在不同年份的差异.借助WRF-Chem模式模拟分析了重污染期间气溶胶辐射效应对垂直方向上气象要素廓线、边界层结构以及PM_(2.5)浓度的反馈机制.结果表明:霾污染可导致大气透过率明显下降,春、秋、冬不同季节,霾污染导致中午大气透过率分别下降0.09,0.11和0.09.全年平均霾污染可导致大气透过率降低约15.5%.云量的增多也可导致大气透过率明显下降,多云天气下大气透过率相比晴天减小约22.4%.霾和云对大气透过率的影响还与太阳高度角有关,当太阳高度角>60°时,霾污染导致大气透过率下降8.6%.随污染等级提高,气溶胶对太阳辐射的衰减作用也越强,天津地区空气质量分别为Ⅰ~Ⅰ级时,中午地表入射短波辐射呈稳定下降趋势,依次为484,446,439,342,328和253W/m^(2).重污染期间,气溶胶辐射效应导致大气低层(250m以下)降温(0.8℃)增湿(3.8%),而中高层(300~1900m)增温(0.5℃)降湿(2.4%),边界层逆温趋势增强,大气垂直扩散能力减弱,最终形成气溶胶-辐射-边界层-污染正反馈机制,极端情况下可使得近地面PM_(2.5)浓度进一步升高约40μg/m^(3),且这种反馈效应在午后16:00最明显.随大气污染防治行动持续深入,天津空气质量明显改善,与2015年相比,2019年天津年均PM_(2.5)浓度下降27.1%,污染超标天数减少43.8%,受此影响,气溶胶对太阳辐射的衰减作用减弱,2019年冬季霾污染导致中午大气透过率减小0.05,Ⅳ级以上污染天气地表入射短波辐射通量下降85.3W/m^(2),但重污染期间,气溶胶辐射反馈机制仍可通过改变垂直温度层结,对污染的加剧(约20μg/m^(3))产生不容忽视的影响.

Two representative years(2015 and 2019) were selected to investigate the impact of aerosol radiation effect on bulk atmospheric transmissivity and incoming solar radiation, as well as the evolution of such effect, on the basis of in-situ observation and numerical simulation. With the application of the online coupled atmospheric chemistry model WRF-Chem, the feedback mechanism of aerosol radiative effect on the vertical distribution of meteorological factors, the boundary layer structures and the PM_(2.5)concentration during heavy pollution episodes were analyzed. Results showed that: haze pollution could lead to the obvious decline of bulk atmospheric transmissivity and this effect was dominant at noon. In spring, autumn and winter, haze pollution could lead to the reduction of bulk atmospheric transmissivity by 0.09, 0.11 and 0.09 at noon, respectively. The annual mean atmospheric transmissivity was reduced by about 15.5% due to haze pollution. While atmospheric transmissivity reduction due to cloud cover was about 22.4%, compared to clear days. The impact of aerosol and cloud on atmospheric transmissivity was also related to solar elevation angle. When the solar elevation angle was higher than 60°, haze pollution could lead to a reduction of atmospheric transmissivity of 8.6%. The attenuation of aerosol radiation effect on solar radiation would be enhanced with the aggravation of haze pollution. As the air quality level in Tianjin changing from I to Ⅵ, the mean incoming shortwave radiation flux at noon would be 484,446, 439, 342, 328 and 253W/m^(2), respectively. During heavy pollution episode, the aerosol radiation effect could lead to cooling(0.8℃) and moistening(3.8%) of near-surface layer(below 250m), as well as heating(0.5℃) and drying(2.4%) of upper layer(300~1900m), which would then lead to the enhancement of inversion intensity and the weakening of vertical diffusion. This would finally form the positive aerosol-radiation-boundary layer-pollution feedback, hence lead to the further enhancement of PM_(2.5)concentration(up to 40μg/m^(3)) near the surface, and this effect was more evident at about 16:00 in the afternoon. Since the implementation of atmospheric pollution prevention and control actions, the air quality in Tianjin has been continuously improved.Compared to 2015, the annual average PM_(2.5)concentration of 2019 in Tianjin was reduced by 27.1% and the number of polluted days was reduced by 43.8%. As a result, the attenuation effect of aerosol on solar radiation was weakened, as the haze pollution would lead to the reduction of noontime atmospheric transmissivity by 0.05 in the winter of 2019. Air pollution(AQI grade higher than Ⅳ) would reduce the incident shortwave radiation by 85.3W/m^(2) at noontime. Nonetheless, during heavy pollution episode in 2019, the aerosol radiation effect could still exert a nonnegligible impact on the aggravation of pollution levels(up to 20μg/m^(3))through the modification of vertical atmospheric stratification.