Modeling Impacts of Urbanization and Urban Heat Island Mitigation on Boundary Layer Meteorology and Air Quality in Beijing Under Different Weather Conditions

Abstract

Beijing has experienced a rapid urbanization in the last few decades and has been suffering from serious air pollution during recent years. The Weather Research and Forecasting‐Chem model is used to quantify the effects of urbanization on regional climate and air quality and those of urban heat island (UHI) mitigation strategy on urban air quality in Beijing, with a special focus on the impacts under different weather conditions (heat waves in summer and polluted days in winter). The modification of rural land use into urban impervious surface significantly increases 2‐m temperature (T2) and planetary boundary layer height but decreases 2‐m relative humidity (RH2) and 10‐m wind speed (WS10) in urban Beijing, which further leads to the increases in surface‐layer O3 concentrations of 9.5 ppbv in summer and 1.8 ppbv in winter and the decreases in PM2.5 concentrations of 16.6 μg m−3 in summer and 26.2 μg m−3 in winter. Compared with normal days (clean days), the UHI intensity is enhanced by 11.1% during heat waves in summer (by 16.7% during polluted days in winter). Although increasing urban albedo is an effective mitigation strategy to decrease UHI intensity, it worsens the urban air quality. When the urban albedo increases from 0.2 to 0.85, the daily average PM2.5 concentrations are increased by 10.2 (6.1) μg m−3 in summer (in winter), and the daily maximum O3 concentrations are increased by 12.8 ppbv under heat waves in summer.

Assessing the formation and evolution mechanisms of severe haze pollution in Beijing−Tianjin−Hebei region by using process analysis

“…However, an obvious underestimation is found in Beijing from 25 to 26 December when a maximum hourly concentration of 600 µg m -3 was observed. The negative bias is also simulated by previous studies (Chen et al, 2018;Zhang et al, 2018b), and the possible reasons for the underestimation are (1) the bias in simulated meteorological conditions (e.g., underestimated RH 2 and overestimated WS 10 );…”

“…following Chen et al (2018) and Wu et al (2012). The vertical dimension is resolved by 29 full sigma levels, with 16 layers located in the lowest 2 km for finer resolution in the planetary boundary layer, and the height of the first layer averaged in BTH is about 30 m.…”

Interaction Between Planetary Boundary Layer and PM2.5 Pollution in Megacities in China: a Review

“…The UHI can also result in a local breeze between the downtown areas and surrounding rural areas [48,49], but it is usually weaker than the mountain-plain breeze and sea-land breeze in the NCP [50]. The thermodynamic perturbations and turbulent mixings induced by urbanization on surface properties can facilitate the growth of urban PBL and the dispersion of PM 2.5 [51], while the urbanization-induced increases in aerosol emissions outweigh those of land use modification, resulting in a net increase of aerosol concentration in megacities [52, 53•]. The local thermally circulations in the NCP are generally suboptimal pollution ventilators: first, the speed of these winds is usually rather low (less than 7 ms −1 ) [18]; second, they are closed circulation systems that accumulate pollutants in a limited box [45•]; and third, they exhibit a diurnal reversal in the direction of winds (e.g., upslope/inland breeze during the day and downslope/offshore breeze after sunset) that leads to a recirculation of pollutants [45•, 54].…”

MICS-Asia III: Multi-model comparison and evaluation of aerosol over East Asia

“…As is known to all, China has been experiencing air pollutions with high concentrations of fine particles, and recent studies highlight the importance of secondary aerosols in the formation of haze episodes (Liu et al, 2013;Sun et al, 2016;Chen et al, 2018). However, observed aerosol components (e.g.…”