A study of CO emission adjustment and its implication in Taiwan using WRF-CMAQ model

The concentrations of air pollutants are mainly controlled by local emissions, physical processes, and chemical reactions. Emissions provide the primary pollutants or the precursors, while physical processes affect the concentration through transport or deposition, and chemical processes cause the production and loss of pollutants. Evaluation of emission inventories plays a crucial role in understanding the local pollutant concentration variation. In this study, we focus on carbon monoxide (CO), which is a low-reactivity species with a lifetime of 2 months. It can act as a pollutant tracer for a regional condition. Our earlier simulation of Taiwan CO based on Taiwan Emission Data System 9.0 (TEDS 9.0), shows that CO is underestimated compared with observation roughly by a factor of 3, whereas nitrogen oxide (NO_X) and ozone (O₃) have slight differences. Thus, we apply Community Multiscale Air Quality (CMAQ) model with Weather Research and Forecasting (WRF) model to re-evaluate the required emission adjustment and investigate the possible influence on other chemical species. With the minimum root mean square error (RMSE) between simulation and observation, the optimal emission correction factors are estimated as 2, 4, and 3.6 for northern, central, and southern Taiwan, respectively. The simulation result of applying emission factor adjustment shows significant improvement of simulated CO concentration, both on values and patterns. The underestimation of current emission inventories might indicate possible uncertainties in emission sources. The considerable adjustment in CO might modify the impact on climate (completing OH radicals with CH₄ and forming CO₂) and could further influence NO_X, O₃, and particle-phase nitrate, which will be discussed in this presentation.