Relay transport of ozone due to urbanization-modified thermal circulations during tropical cyclones

Abstract

Thermal circulations are important for ozone transport and are affected by synoptic weather systems and urbanization. In this study, based on in-situ observations and numerical simulations, changes in thermal circulations induced by urbanization in Suzhou and their impacts on ozone pollution during tropical cyclone Jongdari were investigated. We found that calm weather conditions due to subsidence on the tropical cyclone periphery were conducive to the formation of sea breeze, lake breeze and ozone pollution. The sea and lake breezes had opposite directions, resulting in relay transport of ozone. When polluted air masses passed through, urban areas experienced repeated ozone pollution. Furthermore, urbanization altered the surface energy balance through increased urban land use (LU) and anthropogenic heat (AH) release, raising urban temperature and enhancing urban heat island circulation. This led to higher ozone concentrations in urban areas, especially where urban LU and AH emissions were concentrated, further exacerbating ozone pollution.