Modeling of spatial and temporal variations of ozone-NOx-VOC sensitivity based on photochemical indicators in China.

Comprehensive air quality model with extensions (CAMx)-decoupled direct method (DDM) was used to simulate ozone-NOx-VOCs sensitivity of for May-November in 2016-2018 in China. Based on the relationship between the simulated ozone (O3) sensitivity values and the ratio of formaldehyde (HCHO) to NO2 (FNR) and the ratio of production rate of hydrogen peroxide (H2O2) to production rate of nitric acid (HNO3) ( [Formula: see text] ), the localized range of FNR and [Formula: see text] thresholds in different regions in China were obtained. The overall simulated FNR values are about 1.640-2.520, and [Formula: see text] values are about 0.540-0.830 for the transition regime. Model simulated O3 sensitivities or region specific FNR or [Formula: see text] thresholds should be applied to ensure the accurate local O3 sensitivity regimes. Using the tropospheric column FNR values from ozone monitoring instrument (OMI) satellite data as an indicator with the simulated threshold values, the spatial distributions of O3 formation regimes in China are determined. The O3 sensitivity regimes from eastern to central China are gradually from VOC-limited, transition to NOx-limited spatially, and moving toward to transition or NOx-limited regime from 2005 to 2019 temporally.

Understanding the underlying mechanisms governing the linkage between atmospheric oxidative capacity and ozone precursor sensitivity in the Yangtze River Delta, China: A multi-tool ensemble analysis.

Continued exacerbation of ozone (O3) pollution in China has driven the urgent need for an emission control strategy that efficiently reduces O3 levels. Determining O3 precursor sensitivity (OPS) and its driving factors is a prerequisite for formulating effective O3 control strategies. In this study, we proposed an atmospheric oxidative capacity-based indicator, HO2/OH, and demonstrated its effectiveness in indicating OPS over the Yangtze River Delta (YRD) of China by applying a localized comprehensive air quality model with extensions (CAMx) coupled with the Weather Research and Forecasting (WRF) model. A strong correlation was discovered between HO2/OH and OPS, and HO2/OH showed the best performance in separating NOx- and VOC-limited regimes in comparison with other commonly used indicators. A comprehensive analysis with ensemble diagnostic tools revealed the spatial heterogeneity of NOx and VOC emissions and the impact of regional transport controlling the relationship between OPS variations and the HO2/OH indicator over the YRD. The process analysis results show that days with higher contributions from horizontal advection favored OPS transitions in Shanghai, Nanjing, Hefei, Suzhou, and Wuhu, while vertical advection caused OPS transitions in Hangzhou and Ningbo. O3 source apportionment technology analysis indicated that the regional contributions from Zhejiang and Jiangsu/Anhui corresponded well to the NOx-limited and VOC-limited regimes, respectively. Our results provide a better understanding of the underlying mechanisms of the relationship between OPS and the HO2/OH indicator and can help guide contingency control measures for O3 despiking over the YRD and other photochemically active regions worldwide.

[Applying Photochemical Indicators to Analyze Ozone Sensitivity in Handan].

Ozone pollution in Handan has become severe in recent years and in the summer of 2018, the average maximum daily 8-hour average ozone concentration in Handan was 175 µg·m-3 with a maximum of 257 µg·m-3. Ozone concentrations exceeded the National Air Quality Grade Ⅱ Standard in 59% of cases. In this study, the H2O2/HNO3 indicator was applied to analyze summertime ozone sensitivity in Handan using the WRF-CMAQ modeling system. The results showed that H2O2/HNO3 was more appropriate than other ozone indicators, both theoretically and based on simulation outputs. The good simulation effect of CMAQ on H2O2 and HNO3 was attributed to fine emission inventory and grid resolution. The H2O2/HNO3 simulation results showed that the relative importance of a VOCs-limited regime decreased month by month; a VOCs-NOx-mixed-limited regime was dominant in June; and a NOx-limited regime was more dominant in July and August than in June. The remarkable spatial difference in VOCs and NOx emission ratios among the counties of Handan led to differences in ozone sensitivity. The VOCs-limited regime was concentrated in counties where VOCs/NOx emission ratios were lower than 1.7. Southern counties had a NOx-limited regime, where VOCs/NOx emission ratios were higher than 6.9. Counties with VOCs/NOx emission ratios varying from 1.7 to 6.9 were more susceptible to both VOCs and NOx. According to these results, the transition range of HCHO/NO2, O3/HNO3, and O3/NOx ratios were adjusted to 0.35-0.6, 20-35, and 10-25 respectively. Adjusting the transition range of H2O2/(O3+NO2) was not effective, indicating that this indicator may not be applicable to Handan.