Responses of ozone concentrations to the synergistic control of NOx and VOCs emissions in the Chengdu metropolitan area

Abstract

Simulations of 108 emission reduction scenarios for NO x and VOCs using Comprehensive Air Quality Model with Extensions (CAMx) were conducted for eight cities in the Chengdu metropolitan area (CMA). The isopleth diagrams were drawn to explore the responses and differences of ozone (O 3 ) concentrations to NO x and VOCs emission changes under Chengdu, CMA and Sichuan Province emission reduction scenarios. The results show that the O 3 -sensitive regimes of eight cities may change under different emission reduction scenarios. Under Chengdu emission reduction scenario, the Chengdu city is in the transition regime and O 3 formation will shift from transition to VOC-limited when the VOCs emissions decreased by 50%, and the decreases in O 3 concentrations caused by VOCs emission reductions are small. For the CMA and Sichuan Province emission reduction scenarios, all cities are NO x -limited in the baseline cases and with at least a 66% and a 77% reduction in NO x emissions, respectively, the daily maximum 8-h average O 3 (MDA8) can attain the O 3 standard (160 μg m −3 ). Although reductions in VOCs emissions can also lessen the O 3 concentration, the effectiveness is relatively small. The changes in O 3 concentrations under different VOCs to NO x emission reduction ratios indicate that all cities achieve a relatively high O 3 concentration decrement with low VOCs to NO x emission reduction ratios and that the decreasing O 3 concentrations caused by non-local emission reductions are much higher than those achieved by local emission reductions. In addition, the decreases in O 3 concentrations in Chengdu are quite close when the total NO x and VOCs emissions reduction percentages are less than 30% under the CMA and Sichuan emission reduction scenarios.