Investigations on direct and indirect effect of nitrate on temperature and precipitation in China using a regional climate chemistry modeling system

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Abstract

[1] The tropospheric atmosphere chemistry model (TACM), including a condensed gaseous chemical mechanism and an inorganic aerosol thermodynamic equilibrium submodel, was coupled with the regional climate model (RegCM3) to build a Regional Climate Chemistry Modeling System (RegCCMS), which was applied to investigate the spatial and temporal distribution of anthropogenic nitrate aerosol, radiative forcing, and also its climatic effect over China. Modeling results show that the annual average surface concentration and column burden of nitrate are 2.19 μg/m3 and 5.05 mg/m2, respectively. The countrywide annual average direct radiative forcing, first indirect radiative forcing, and total radiative forcing at the top of atmosphere induced by nitrate are −0.88 W/m2, −2.47 W/m2, and −2.52 W/m2, respectively. Numerical experiments indicate that surface air temperature decreases and precipitation reduces when nitrate aerosol is included in the coupled modeling system. Changes in annual surface air temperature due to direct effect, first indirect effect, second indirect effect, and combined effect are −0.04°C, −0.11°C, −0.68°C and −0.78°C, respectively. The corresponding precipitation reduction is −0.05 mm/d, −0.10 mm/d, −0.42 mm/d, and −0.52 mm/d. Variations of surface temperature and precipitation due to the combined effect are less than the sum of individual direct, first indirect, and second indirect effect, showing a strong nonlinearity between radiative forcing and climate change. The indirect effect of nitrate is stronger than its direct effect. These preliminary results suggest that nitrate aerosol has unignorable effect on regional climate in China compared to sulfate and carbonaceous aerosols.

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