Modeling Investigation of Impacts of Lake Breeze on Ozone Diffusion Around Lake Taihu

Lake Taihu basin is one of the most developed regions in China, with the development of social economy, the atmospheric environment in this region needs more research and attention. Previous studies have shown that as a large open water body, Lake Taihu has significant impacts on the surrounding thermal environment and local circulation. However, the corresponding impacts on air pollution need to be studied to better guide air pollution forecasting, as well as control and protection. Three lake schemes were used to simulate lake breeze effect on ozone diffusion around Lake Taihu by WRF-Chem model during an ozone high concentration event. Three cases were labeled Noah-lake, CLM4-lake Lake-improved respectively. It should to be noted that lake surface albedo, water surface layer thickness, extinction coefficient, water surface roughness, eddy diffusivity and other parameters were modified in Lake-improved case. Compared with Noah-lake and CLM4-lake, Lake-improved had best simulation results. The simulation of lake surface temperature improved significantly. The average root mean square errors of three cases are 6.58°C, 2.99°C and 1.06°C, respectively. The maximum difference with the value of 11.2°C between Lake-improved case and Noah-lake case appeared at 14:00 in 23^rd July. One important reason to explain the difference was that in Lake-improved case, the eddy diffusion coefficient was adjusted to a suitable value for the shallow lake. The surface temperature caused the intensity and penetration distance of the lake breeze greatly different, which changed ozone transportation and diffusion. Ozone concentration and distribution were different between Noah-lake and Lake-improved. It was about 40μg·m^-3 lower at night and 50μg·m^-3 lower during the daytime above lake surface in the simulation of Lake-improved. The diffusion condition as well as chemical reaction condition was changed after the changes in the local circulation. Results showed that the impacts of local circulation on ozone diffusion and transport dominantly, largely changing the temporal and spatial distribution of ozone in Lake Taihu region. The photolysis rate of ozone is a key parameter for characterizing changes in chemical reactions, while the difference of this parameter was not obvious in the three cases.