Lake-atmosphere exchange impacts ozone simulation around a large shallow lake with large cities

Abstract

Weather Research and Forecast model coupled with Chemistry (WRF-Chem) coupled with CLM4.5 lake model is used to understand the impacts of lake-atmosphere exchange on ozone concentration in the Lake Taihu region during a high temperature and high ozone concentration event. About 8 °C bias in lake surface temperature simulated by different lake schemes significantly change the structure and evolution of the lake-land breeze system. As a result, the vertical and horizontal advection directly impacts distribution of ozone around and over the lake in early morning, the difference in ozone concentration is 20–60 μg m−3. Location of the lake breeze front and development of the thermal inner boundary layer around midday are also highly sensitive to the lake-atmosphere exchange. In addition, difference in the local circulation patterns leads to distinct spatial distributions of NOx, an ozone precursor, in regions downwind of their emission sources, especially along the Yangtze River. In response, ozone concentration in this region is drastically changed (about 80 μg m−3) due to the combined actions of transport and chemical reactions. Overall, this study highlights that in regions with spatially extensive shallow lakes with megacities, it is important to accurately represent the lake-atmosphere exchange for ozone pollution simulations, especially under high-temperature and light-wind conditions, in which ozone high concentration events occur frequently and effects of the local lake breeze are expected to dominate.