Modeling the feedback between aerosol and meteorological variables in the atmospheric boundary layer during a severe fog–haze event over the North China Plain

摘要

The feedback between aerosol and meteorological variables in the atmosphericboundary layer over the North China Plain (NCP) is analyzed by conductingnumerical experiments with and without the aerosol direct and indirecteffects via a coupled meteorology and aerosol/chemistry model (WRF-Chem). Thenumerical experiments are performed for the period of 2–26 January 2013, duringwhich a severe fog–haze event (10–15 January 2013) occurred, with thesimulated maximum hourly surface PM concentration of ~600 ugm, minimum atmospheric visibility of ~0.3 km, and 10–100 hoursof simulated hourly surface PM concentration above 300 ug mover NCP. A comparison of model results with aerosol feedback againstobservations indicates that the model can reproduce the spatial and temporalcharacteristics of temperature, relative humidity (RH), wind, surfacePM concentration, atmospheric visibility, and aerosol optical depthreasonably well. Analysis of model results with and without aerosol feedbackshows that during the fog–haze event aerosols lead to a significant negativeradiative forcing of −20 to −140 W m at the surface and a largepositive radiative forcing of 20–120 W m in the atmosphere andinduce significant changes in meteorological variables with maximum changesduring 09:00–18:00 local time (LT) over urban Beijing and Tianjin and southHebei: the temperature decreases by 0.8–2.8 °C at thesurface and increases by 0.1–0.5 °C at around 925 hPa, while RHincreases by about 4–12% at the surface and decreases by 1–6% ataround 925 hPa. As a result, the aerosol-induced equivalent potentialtemperature profile change shows that the atmosphere is much more stable andthus the surface wind speed decreases by up to 0.3 m s (10%)and the atmosphere boundary layer height decreases by 40–200 m(5–30%) during the daytime of this severe fog–haze event. Owing to thismore stable atmosphere during 09:00–18:00, 10–15~January, compared to thesurface PM concentration from the model results without aerosolfeedback, the average surface PM concentration increases by10–50 μg m (2–30%) over Beijing, Tianjin, and southHebei and the maximum increase of hourly surface PMconcentration is around 50 (70%), 90 (60%), and80 μg m (40%) over Beijing, Tianjin, and southHebei, respectively. Although the aerosol concentration is maximumat nighttime, the mechanism of feedback, by which meteorological variablesincrease the aerosol concentration most, occurs during the daytime (around10:00 and 16:00 LT). The results suggest that aerosol induces a more stableatmosphere, which is favorable for the accumulation of air pollutants, andthus contributes to the formation of fog–haze events.