Performance and application of air quality models on ozone simulation in China - A review

China has experienced increasingly severe O3 pollution in recent years and air quality models (AQMs) have been widely used to understand it and to explore the possible solutions for it. Based on a thorough literature search, this review selected and investigated 212 AQM studies on Chinese O3 since 2010, with different models and spatial scales. We evaluated the model performance of O3 simulation and analyzed the main factors influencing the simulation. The correlation coefficients between simulation and observation were larger than 0.5 and the mean normalized biases (NMB) were within +/- 30% for nearly 80% of the cases collected from AQM studies. GEOS-Chem and CAMx commonly overestimated the ambient O3 concentration, while the biases for CMAQ, WRF-Chem and NAQPMS were less conclusive. More applications and better model performances were found for the Yangtze River Delta and Pearl River Delta regions. Single-domain simulation provided the best model per-formance at a horizontal resolution of 12-30 km, and the performance would improve further at 5-10 km with the use of nested-domain and refined local emission inventory. Effective efforts for improvement of the O3 simulation included incorporating chloride reactions with reactive nitrogen species, better considering the interaction with aerosols, and optimizing the parameterization schemes in meteorological processes and the land-use data. AQMs have been mainly applied in interpreting major driving forces and factors influencing O3 level, understanding its source-receptor relationship, and evaluating its environmental impacts and policy effectiveness. Based on the diagnosis and detection of various AQM methods, meteorology seemed to always play a positive and, since the implementation of emission control strategy, increasingly important role on the growth of O3 concentration, and thus should be taken more seriously in the future along with global warming. Source apportionment studies revealed that industry, transport and biogenic sources contributed almost 80% of O3 in China while only around 30% could be attributed to local contribution during O3 episodes in megacities. NOX- focused control measures led to a growth of O3 in urban areas with VOC-limited regime, as well as a shift from VOC-limited to transitional regime in heavily polluted areas of eastern China. VOCs emission control in areas with VOC-limited regime and the negative effect of global warming should be of great concerns on O3 pollution reduction in the future.