Temporally-resolved sectoral and regional contributions to air pollution in Beijing: Informing short-term emission controls

Abstract

Abstract. We investigate the contributions of local and regional emission sources to air quality in Beijing to inform the design of short-term emission control strategies for mitigating major pollution episodes. We use a well-evaluated version of the WRF-Chem model at 3 km horizontal resolution to determine the daily accumulation of pollution over Beijing from local and regional sources in October 2014 under a range of meteorological conditions. Considering feasible emission reductions across residential, transport, power and industrial sectors, we find that one-day controls on local emissions have an immediate effect on PM2.5 concentrations on the same day, but can have lingering effects as much as five days later under stagnant conditions. One-day controls in surrounding provinces have the greatest effect in Beijing on the day following the controls, but may have negligible effects under northwesterly winds when local emissions dominate. To explore the contribution of different emission sectors and regions, we perform simulations with each source removed in turn. We find that residential and industrial sectors from neighbouring provinces dominate PM2.5 levels in Beijing during major pollution episodes, but that local residential emissions and industrial/residential emissions from more distant provinces can also contribute significantly during some episodes. We then perform a structured set of perturbed emission simulations to allow us to build statistical emulators that represent the relationships between emission sources and air pollution in Beijing over the period. We use these computationally fast emulators to determine the sensitivity of PM2.5 concentrations to different emission sources and the interactions between them, including for secondary PM, and to create pollutant response surfaces for daily average PM2.5 concentrations in Beijing. We use these surfaces to identify the short-term emission controls needed to meet the national air quality target of daily average PM2.5 less than 75 μg m−3 for pollution episodes of different intensities. We find that for heavily polluted days with daily mean PM2.5 higher than 225 μg m−3, even emission reductions of 90 % across all sectors over Beijing and surrounding provinces may be insufficient to meet the national air quality standards. These results highlight the regional nature of PM pollution and the challenges of tackling it during major pollution episodes.

Temporal Source Apportionment of PM2.5 Over the Pearl River Delta Region in Southern China

“…Compared with the zero‐out method used by Ansari et al. (2021), our method avoided a large number of sensitivity experiments, and thus the computation costs were lower. If the contributions of emission from 6 source areas and 5 source time periods to the sulfate in D3 are tracked, the zero‐out method will take approximately 217 min to finish all experiments, while the temporal source apportionment method only needs about 14 min (Table S2 in Supporting Information ).…”

“…Ansari et al. (2021) conducted multiple simulation experiments to investigate the temporal contributions of different emission sectors and regions. Zhang et al.…”