Impact of spatial scales of control measures on the effectiveness of ozone pollution mitigation in eastern China.

Ozone (O) pollution is becoming the primary air pollution issue with the large decrease in fine particulate concentrations in eastern China. The development of widely recognized policies for controlling O pollution episodes is urgent. This study aims to provide actionable and comprehensive suggestions for O control policy development, with an emphasis on the precursor emission reductions. Here, we compared the impacts of different spatial scale reductions on a widespread O pollution episode in eastern China by a state-of-the-art regional air quality model. We find that region-scale joint control (in >30 cities) is much more effective than city-scale sporadic reduction in reducing O concentration. Sporadic controls only reduce the maximum daily 8-h average (MDA8) O by ∼1 μg/m in the controlled city, whereas regional controls lead to a MDA8 O decrease of ∼8 μg/m in the controlled region. In addition, the emission reduction effectiveness increased by 2.6 times from <5 cities to >30 cities. Continuous reductions have a cumulative effect on the decrease of MDA8 O, showing the strongest effects within 24 h and diminishing after 48 h, which underscores the importance of reducing emissions 24 h prior to an episode. Moreover, the effect of control measures on MDA8 O varies spatially depending on the ratio of volatile organic compounds (VOCs) to nitrogen oxides (NO) (VOCs/NO). Both the reductions of VOC and NO emissions have a positive effect on the decrease of MDA8 O in summer, but the effects of VOC reductions are 1.2 to 1.7 times higher than those of NO reductions. The residential sector, due to its high VOCs/NO emission ratio, exhibits the highest efficiency in the reduction of O concentrations. Our results highlight the importance of regional joint control and synergistic reduction of VOCs and NO in eastern China.