Effects of chemical and meteorological data assimilation on air-quality and meteorological forecasts in the Korean Peninsula

Abstract

Data assimilation (DA) can be used to reduce initial condition uncertainties, thereby enhancing air-quality forecasts in coupled chemistry-meteorology models. In the Korean Peninsula, complex meteorological conditions influence high concentrations of fine particulate matter (PM); hence, improving both air-quality and meteorological forecasts is important for enhancing PM forecasts. In this study, the effects of chemical and meteorological DA on air-quality and meteorological forecasts were evaluated for a high PM case occurred in the Korean Peninsula. Verified by observations, both air-quality and meteorological forecasts were the most improved in the experiment where chemical and meteorological DA were performed simultaneously. Chemical DA primarily improved the accuracy of air-quality forecasts, whereas meteorological DA played a key role in improving meteorological forecasts. With respect to the forecasts without DA, the effects of chemical and meteorological DA on the air-quality and meteorological forecasts were also evaluated in the DA cycling and non-cycling processes. In terms of the root-mean-square difference between forecasts with and without DA, the effects of chemical and meteorological DA on air-quality forecasts were similar in both cycling and non-cycling DA processes. The effects of chemical and meteorological DA were complementary in the simultaneous chemical–meteorological DA experiment. In the cycling DA process, chemical (meteorological) DA affected meteorological (air-quality) forecasts, owing to the cumulative DA effect. Chemical DA improved the absolute quantity of PM in the forecast, whereas meteorological DA enhanced the accuracy of the spatiotemporal distribution of PM by improving the transport processes. Therefore, simultaneous chemical–meteorological DA was most effective in changing air-quality and meteorological forecasts and could greatly improve air-quality and meteorological forecasts in the Korean Peninsula.