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

Abstract

Comprehensive air quality model with extensions (CAMx)-decoupled direct method (DDM) was used to simulate ozone-NO_x-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 NO_x-limited spatially, and moving toward to transition or NO_x-limited regime from 2005 to 2019 temporally.

Keywords: Formaldehyde; NO(2); Ozone monitoring instrument (OMI); Ozone sensitivity analysis; Photochemical indicator.