A dynamic ammonia emission model and the online coupling with WRF–Chem (WRF–SoilN–Chem v1.0): development and regional evaluation in China

Abstract

The volatilization of ammonia (NH3) from fertilizer application and livestock wastes is an overwhelmingly important pathway of nitrogen losses in agricultural ecosystems and constitutes the largest source of atmospheric NH3. The volatilization of NH3 highly depends on environmental and meteorological conditions, however, this phenomenon is poorly described in current emission inventory and atmospheric models. Here, we develop a dynamic NH3 emission model capable of calculating the NH3 emission rate interactively with temporal- and spatial-varying meteorological and soil conditions. The NH3 flux parameterization relies on several meteorological factors and anthropogenic activity including fertilizer application, livestock waste, traffic, residential, and industrial sectors. The model is then embedded into a regional WRF–Chem model and is evaluated against field measurements of NH3 concentrations, emission flux, and satellite retrievals of column loading. The evaluation shows a substantial improvement in the model performance of NH3 flux and ambient concentration in China. The model represents the spatial and temporal variations of ambient NH3 concentration well, indicating the highest emission in the North China Plain (NCP) and Sichuan Basin, especially during summertime. Compared with normal simulations using fixed emission inventory input, this model features superior capability in simulating NH3 emission flux and concentration during drastic weather changes like frontal activities and precipitation. Such advances in emission quantification also improve the model performance of secondary inorganic aerosol on synoptic scales. While more laboratory and field measurements are still needed for better parameterization of NH3 volatilization, the seamless coupling of soil emission with meteorology provides a better understanding of NH3 emission evolution and its contribution to atmospheric chemistry.