Modeling dry deposition of reactive nitrogen in China with RAMS-CMAQ

Abstract

China has the world highest production of reactive nitrogen (Nr), and the Nr consumption increased sharply during the last decade. However, the potential environmental influence of dry nitrogen (N) deposition in China remains uncertain due to that the long-term measurement or remote sensing of various N species are difficult. This requires a better understanding of dry N deposition over China in its various forms and including magnitude and distribution features. Thus, the air quality modeling system RAMS-CMAQ was applied to simulate dry deposition of Nr over China from 2010 to 2014. The model results were then analyzed to investigate the long-term spatial and temporal distributions of major inorganic nitrogen (N) components (10 species) and selected organic N components (5 species). Comparisons between modeled and observed deposition rates and surface mass concentrations showed generally good agreement. Model results indicated a total dry N deposition budget of 9.31 Tg N yr−1 in China, including 4.29 Tg N yr−1 as NOy and 4.43 Tg N yr−1 as NH3. NOy was the main component of dry N deposition in the Beijing-Tianjin-Hebei area (0.31 Tg N yr−1), the Yangtze River Delta (0.29 Tg N yr−1), and the Pearl River Delta (0.09 Tg N yr−1), where the major megacity clusters of China are located. NH3 was the main component of dry N deposition in Shandong province (0.24 Tg N yr−1), Northeast China (0.46 Tg N yr−1), the Sichuan Basin (0.48 Tg N yr−1), and central China (0.95 Tg N yr−1), where the major agricultural regions are located. The highest values of the deposition flux for NH3 occurred in Shandong province (19.40 kg N ha−1 yr−1) and Beijing-Tianjin-Hebei (17.20 kg N ha−1 yr−1). The seasonal variation of total dry N deposition was obvious in the east part of China, and was higher in July and lower in January. The spatio-temporal variations and major sources of dry N deposition were strongly heterogeneous, implying that the comprehensive pollution control strategies should be implemented to reduce the risk associated with N deposition.