Effects of aerosol-radiation feedback and topography during an air pollution event over the North China Plain during December 2017

Özet

The online coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model was used to investigate aregional haze event, which occurred over the North China Plain (NCP) from 27 to 30 December 2017. Modelingscenarios with and without aerosol-radiation feedback within the planetary boundary layer (PBL) were investigated. By adding aerosol-radiation feedback to the model, we captured the spatial and temporal characteristics of the observed temperature and relative humidity (RH), as well as surface $PM_{2.5}$, $SO_2$, and $NO_2$concentrations during this event. The primary meteorological driver of this event was stable meteorologicalconditions, namely, a low PBL, strong temperature inversion, high RH, and a weak wind field. Aerosol-radiationfeedback mechanisms affected these meteorological fields, causing reductions in maximum surface solar radiation, the surface energy budget, PBL height, surface 2-m temperature and middle atmosphere RH, whileincreasing surface 2-m RH, middle atmosphere temperature, and atmospheric stability. Changes in meteorological variables in turn affected air pollutant distributions and concentrations, with $PM_{2.5}$ increasing by morethan 20 μg/$m^3$ over the NCP during this event. Another sensitivity experiment was carried out over the Taihangand Yanshan mountain areas, in which topography was flattened to a 30-m height to explore the impacts oftopography on air pollution in the NCP region. Modeling revealed various topographic effects on meteorologicalvariables related to these two mountains, including a lowered PBL height, reduced wind speed, blocked uniformsurface winds, and more intense temperature inversion. Consequently, surface air pollutant concentrations increased unevenly over the NCP in this experiment. Implementation of more detailed PBL processes, as well asradiosonde and satellite data products into the WRF-Chem model would improve simulations of haze formationover the NCP.