National Air quality Characteristics Sample Clauses

National Air quality Characteristics. 3.1.1 Base year air quality Three existing emission inventories were used to simulate the ambient air quality in base year 2008. Figures 4-a and 4-b illustrate the spatial distribution of simulated PM2.5 and O3 burden in January and July in the base year using three different present emission scenarios (XXXX, XXXXX, and MEIC). Table 5-a summarizes the mean, median and the standard deviation of the simulation results for both PM2.5 and O3. Standard deviations are 100-120% of the average for PM2.5, and 19-25% of the average for O3, which indicates a high variability for PM2.5 concentrations in the nation, compared to the lower variability for O3. Meteorology, simulated in the air quality model (WRF-Chem) together with transport and chemistry, explains higher PM2.5 concentrations in January and increased O3 concentrations in July. Wet deposition, which occurs less in January, is the major route to remove fine and coarse PM and solar ultraviolet radiation, which peaks in July, is critical for O3 formation. Among the simulations using the three different emission inventories, the one using XXXXX (WRF-Chem-XXXXX) produced a 32-40% lower PM2.5 in both January and July, and 3-10% lower O3 in July compared to simulation results using REAS (WRF- Chem-REAS) and MEIC (WRF-Chem-MEIC) (Table 5-a). This result consents to the previous study, which found a 40-70% higher surface PM10, and a 16–20% higher surface O3 in North China in July comparing between WRF-Chem-REAS and WRF-Chem- XXXXX in 2007 (Zhong et al. 2015). We find different spatial patterns of PM2.5 and O3 distribution. In particular, in January, taking WRF-Chem-REAS as an example, the highest PM2.5 concentrations were observed in Southwest (207± 25 μg/m3) and Central China (231 ± 24 μg/m3), followed by 171 ± 29 μg/m3 concentrations in the North China. PM2.5 concentrations in the rest of the areas were 40% lower compared to the high-pollution areas. This trend assents to the finding of Cao et al. (2012) that mentioned measured winter and summer PM2.5 values in 14 Chinese cities located in northern and southern China. They found highest average winter PM2.5 in Xi’an (356 μg/m3), a city in central China, and higher at inland cities compared to the coastal cities. The lowest concentrations among the 14 major cities were observed in Xiamen (74 μg/m3) in South China. Compared with January, the simulated PM2.5 concentrations experienced a pronounced overall decrease (over 50%) in the Mainland China in July. Cao et al....