Path of coordinated control of PM<sub>2.5</sub> and ozone in China

Abstract

Listen

Translate article

<p indent="0mm">Since the <italic>Air Pollution Prevention and Control Action Plan</italic> was issued in 2013, air quality in China has significantly improved. But the concentration of fine particulate matter (PM_2.5) remains 3 times higher than the guideline value of the WHO (World Health Organization, 2015), and the rising concentration of ozone (O₃) that has caused premature death and economic losses neutralized the environmental benefits brought in by partial reductions of PM_2.5. The coordinated control of PM_2.5 and O₃, hence, has been put at the top of the agenda for China’s air pollution prevention and control. Given nitrogen oxides (NO_{<italic>x</italic>}) and volatile organic compounds (VOCs) are major precursors of both PM_2.5 and O₃, reducing the emissions of NO_{<italic>x</italic>} and VOCs is considered as the key to the coordinated control of PM_2.5 and O₃. Focused on the common precursors of PM_2.5 and O₃, our research conducted qualitative analysis of the effects of reduced emissions of NO_{<italic>x</italic>} and VOCs, and suggested China’s path to coordinated control of PM_2.5 and O₃. The results are expected to be adopted as scientific bases by administrative authorities for relevant policy-making. Our research was based on the WRF-CAMx model and scenario analysis was used. Different scenarios where NO_{<italic>x</italic>}<italic> </italic>and VOCs emissions were reduced to different degrees were set to simulate the changes of concentrations of PM_2.5 and O₃ across China and in key areas. The indicator of sensitivity was introduced to quantitively evaluate the responsiveness of PM_2.5 and O₃ concentrations to the reduced emissions of NO_{<italic>x</italic>} and VOCs. The effects of reduced emissions of NO_{<italic>x</italic>} and VOCs on the concentrations of PM_2.5 and O₃ were revealed directly in the research. As suggested by simulation results, the reduction of NO_{<italic>x</italic>} or VOCs emission can contribute to the decrease of the concentration of PM_2.5 nationwide and in key areas. If at the same ratio of reduction, the reduction of NO_{<italic>x</italic>} emission can lead to a larger decrease of PM_2.5 concentration. The change of O₃ concentration nationwide or in key areas varies under different NO_{<italic>x</italic>} and VOCs emission reduction scenarios. From the perspective of the whole country, a small ratio of NO_{<italic>x</italic>}<italic> </italic>emission reduction may lead to the rise of O₃ concentration in some areas, but the O₃ concentration declines on the whole, and the rate of decline rises with the further reduction of NO_{<italic>x</italic>} emission. The reduction of VOCs emission can decrease the O₃ concentration nationwide, but the effect is less obvious than the reduction of NO_{<italic>x</italic>} emission. For the Pearl River Delta area, the reduced emission of VOCs is more effective for the decrease of O₃ concentration. For the “2+26” cities, the Yangtze River Delta, and the Fenwei Plain, if on a small scale, the reduction of VOCs is more effective for the decrease of O₃ concentration than that of NO_{<italic>x</italic>}. But due to the existence of natural VOCs, the proportion of artificial VOCs to the total emission of VOCs reduces as the artificial VOCs continues to decline, and hence, the benefit of the reduction of VOCs becomes less obvious than that of NO_{<italic>x</italic>}. Sensitivity results were in agreement with the concentration changes. Based on the abovementioned results, to realize the balance of the benefits of NO_{<italic>x</italic>} and VOCs emissions reduction between the local and global and between the short term and the long term, we suggest that the continuous reduction of NO_{<italic>x</italic>} emission should be regarded as the focus of coordinated control of PM_2.5 and O₃ in terms of both the whole country and key areas and the reduction of VOCs emission is the key to the improvement of O₃ pollutions in key areas in the short term, which should be incorporated in the medium-to-long-term design of China’s path to coordinated control of air pollutions.