Strategies for Eliminating Heavy Air Pollution in the Beijing–Tianjin–Hebei Region: Insights from Joint Practices during the 2022 Olympic and Paralympic Winter Games

The 2022 Olympic Winter Games (OWG) and Paralympic Winter Games (PWG) marked the first time the Beijing–Tianjin–Hebei (BTH) region implemented joint air pollution prevention and control measures for a winter mega-event. Notably, while Beijing maintained clean air (daily PM2.5 concentration ≤ 75 μg/m3, according to the Ambient Air Quality Standards in effect at the time) during the OWG, a heavy-pollution episode occurred during the PWG, with the 24-h average PM2.5 concentration peaking at 155 μg/m3. Combining field observations, dynamic emission characterization, and The Comprehensive Air quality Model with extensions (CAMx) simulations, we conducted a closed-loop study to investigate the underlying causes of this episode. Results show that while the industrial sector effectively regulated emissions, the mobile-source activity levels recovered rapidly after the Chinese New Year, outweighing the control measures implemented for mobile sources. This recovery increased total NOx emissions by 13% in the BTH region, driving nitrate-dominated PM2.5 pollution. During the study period, the PM2.5 nitrate concentration (normalized by the carbon monoxide concentration) was found to increase by 3 × 10–4 and 1 × 10–5 for each one-ton increase in NOx emissions in Beijing and the BTH region, respectively. To eliminate heavy PM2.5 pollution under the meteorological conditions observed during the PWG, NOx emissions would need to be further reduced by ≥1% in Beijing and ≥7% in the BTH region. This work underscores the urgent need to mitigate emissions from diesel trucks and nonroad machinery, especially under extremely adverse meteorological conditions in the BTH region.