Mesoscale modelling study of the interactions between aerosols and PBL meteorology during a haze episode in China Jing–Jin–Ji and its near surrounding region – Part 2: Aerosols' radiative feedback effects

Abstract

Abstract.Two model experiments, namely a control (CTL) experiment without aerosol-radiation feedbacks and a experiment with online aerosol-radiation (RAD) interactions, were designed to study the radiative feedback on regional radiation budgets, planetary boundary layer (PBL) meteorology and haze formation due to aerosols during haze episodes over Jing-Jin-Ji, China, and its near surroundings (3JNS region of China: Beijing, Tianjin, Hebei, East Shanxi, West Shandong and North Henan) with a two-way atmospheric chemical transport model. The impact of aerosols on solar radiation reaching Earth's surface, outgoing long-wave emission at the top of the atmosphere, air temperature, PBL turbulence diffusion, PBL height, wind speeds, air pressure pattern and PM 2.5 has been studied focusing on a haze episode during the period from 7 to 11 July 2008. The results show that the mean solar radiation flux that reaches the ground decreases by about 15 % in 3JNS and 20 to 25 % in the region with the highest aerosol optical depth during the haze episode. The fact that aerosol cools the PBL atmosphere but warms the atmosphere above it leads to a more stable atmospheric stratification over the region, which causes a decrease in turbulence diffusion of about 52 % and a decrease in the PBL height of about 33 %. This consequently forms a positive feedback on the particle concentration within the PBL and the surface as well as the haze formation. Additionally, aerosol direct radiative forcing (DRF) increases PBL wind speed by about 9 % and weakens the subtropical high by about 14 hPa, which aids the collapse of haze pollution and results in a negative feedback to the haze episode. The synthetic impacts from the two opposite feedbacks result in about a 14 % increase in surface PM 2.5 . However, the persistence time of both high PM 2.5 and haze pollution is not affected by the aerosol DRF. On the contrary over offshore China, aerosols heat the PBL atmosphere and cause unstable atmospheric stratification, but the impact and its feedback on the planetary boundary layer height, turbulence diffusion and wind is weak, with the exception of the evident impacts on the subtropical high.

Impacts of aerosol-radiation feedback on local air quality during a severe haze episode in Nanjing megacity, eastern China

“…For the diurnal cycle, the increase of surface PM 2.5 concentration is more predominant at around 10:00-18:00 LT, with an average value ranging from 10 to 15 μg m −3 (12-16%). Wang et al (2015) also indicated that the more stable atmospheric stratification from diurnal timing (Fig. 6f) and areas ( Fig.…”

“…6e). Wang et al (2015) designed similar experiments and found that atmospheric aerosols cooled the PBL but warmed the atmosphere above it in northern China, leading to a more stable atmospheric stratification and a decrease in PBL height by about 33%.…”

“…During strong air pollution episodes such as wild fire Grell et al, 2011;Jiang et al, 2012) or dust events , it is calculated that aerosols reduced the shortwave radiation and temperature at the surface, and heated the atmosphere at the top of planetary boundary layer (PBL). Recent modelling studies Wang et al, 2015;Gao et al, 2016) also highlighted that the negative radiative forcing of anthropogenic haze aerosols induced a reduction of shortwave radiation by 20-25% over the North China Plain (NCP), with a decrease in surface temperature (0.6-2.8 °C), wind speed (20-60%) and PBL height (5-30%).…”

Mesoscale modeling study of the interactions between aerosols and PBL meteorology during a haze episode in Jing–Jin–Ji (China) and its nearby surrounding region – Part 1: Aerosol distributions and meteorological features

“…The relationship between key PBL meteorological factors, PM 2.5 and the haze episode is analyzed. The impact of aerosols on local PBL is presented in a companion paper (Part 2, Wang et al, 2015).…”

Investigation of Particulate Matter Regional Transport in Beijing Based on Numerical Simulation

“…A more detailed description of CUACE can be found in Gong and Zhang (2008). And it has been evaluated and applied systematically in previous studies Wang et al, 2015b;He et al, 2016b). The FLEXPART model, developed by the Norwegian Institute of Air Research, is a Lagrangian transport and dispersion model that is suitable for the simulation of atmospheric transport processes.…”