Contributions of extremely unfavorable meteorology and coal-heating boiler control to air quality in December 2019 over Harbin, China

The persistent haze events that occurred over Harbin in December 2019 are targeted in this study. To determine the cause of these haze events, December 2018 and December 2019 were selected for modeling runs using the WRF-Chem model, considering December 2018 with good air conditions as the baseline scenario. The emission inventory was identically employed in both periods to predict pollutant concentrations in response to meteorology changes. Additionally, in an abatement case study, the emission inventory was updated to evaluate the role played by low-capacity coal-heating boiler (CHB) control in air quality index (AQI) improvement in December 2019. In December 2019, the mean drop in 10 m wind speed, 2 m air temperature, 2 m relative humidity, and planetary boundary layer height reached up to 0.5 m/s, 4.3 degrees C, 2.1%, and 26.0 m relative to that in December 2018. These changes resulted in increased concentrations of PM2.5, PM10, SO2, NO2, and CO during haze days and correspondingly contributed 33.5%, 33.6%, 39.6%, 26.0%, and 33.8% increments over a domainwide scale in December 2019. The meteorology-induced changes also contributed to a 35% increment in AQI in downtown Harbin. The case study showed that the AQI was reduced by 20 over downtown Harbin in December 2019 based on the CHB control plan of 2020; accordingly, the number of days when AQI was above the standard dropped by seven. This study quantitatively addresses the role played by meteorology in haze events and validates the positive effect of CHB control in Harbin during haze episodes.