Modelling summertime ozone in North China

Cheng, Siyu and Wild, Oliver (2020) Modelling summertime ozone in North China. Masters thesis, Lancaster University.

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Abstract

A high-resolution nested air quality model, the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem), was applied to simulate the ozone concentration in North China from 15 May 2017 to 22 June 2017 during the Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme measurement campaign and to study an ozone pollution event at the end of May 2017. The model reproduced the meteorological parameters of temperature, relative humidity, wind speed and wind direction well over the period. The key air pollutants of ozone, NOx, SO2, PM2.5 and PM10 are captured reasonable well compared with observations. Results suggest that the ozone simulation matches the observation and simulations of NO2 and SO2 are generally satisfactory using emissions scaled down based on previous studies of anthropogenic emissions changes in China. The model underestimated the peaks in ozone concentration, especially on heavily polluted days, which remain a challenge for modelling ozone and may be attributed to model weaknesses in representing the diurnal cycle of NO and the observed VOC and isoprene. We carried out sensitivity studies investigating how NOx, VOC and isoprene emissions changes affects the simulation of ozone, and improved the ozone simulation of the peaks with 50% increased VOC emissions and doubled isoprene emission. We speculate that the underestimation of VOC emissions or the reactivities of VOC in the model could be reasons for the underestimation of the peaks in ozone concentration and further investigation is needed to improve the simulation of ozone concentrations. We also note that increasing isoprene emission factors can increase the isoprene concentration and improve simulation of ozone concentration, but that simulation of isoprene can still be improved, highlighting the need for investigations of isoprene emissions and model simulation of isoprene. This study describes the effects of different emissions, analyses the weaknesses of the model in simulating ozone and proposes the need for further research on VOC and isoprene simulations.