Impacts of emissions and meteorological changes on China's ozone pollution in the warm seasons of 2013 and 2017

We have quantified the impacts of anthropogenic emissions reductions caused by the Air Pollution Control Action Plan and changes in meteorological fields between 2013 and 2017 on the warm-season O-3 concentration in China using a regional 3D chemical transport model. We found that the impact on daily maximum eight-hour (MDA8) O-3 concentration by the meteorological variation that mostly increased O-3 was greater than that from emission reduction, which decreased O-3. Specifically, the control measures implemented since 2013 in China have reduced SO2, NOx, PM2.5, and VOC emissions by 33%, 25%, 30%, and 4% in 2017, while NH3 emissions have increased by 7%. The changes in anthropogenic emissions lowered MDA8 O-3 by 0.4-3.7 ppb (0.8%-7.6%, varying by region and month), although MDA8 O-3 was increased slightly in some urban areas (i.e. North China) at the beginning/end of warm seasons. Relative to 2013, the average 2 m temperature in 2017 shows increments in North, North-east, East, and South China (0.34 degrees C-0.83 degrees C) and decreases in Central China (0.24 degrees C). The average solar radiation shows increments in North, North-east, and South China (7.0-9.7 w/m(2)) and decreases in Central, South-west, and North-west China (4.7-10.3 w/m(2)). The meteorological differences significantly change MDA8 O-3 by -3.5-8.5 ppb (-8.2%-18.8%) with large temporal variations. The average MDA8 O-3 was slightly increased in North, North-east, East, and South China. The response surface model suggests that the O-3 formation regime transfers from NOx-saturated in April to NOx-limited in July on average in China.