Precipitation trend increases the contribution of dry reduced nitrogen deposition

Abstract

Given the leveling off in oxidized nitrogen emissions around the world, the atmospheric deposition of reduced nitrogen (NHx = NH3 + NH4+) has become progressively critical, especially dry deposition, which presents great threats to plant growth. A combination of historical deposition data of measured wet NHx and modeled dry NHx in China suggests that dry NHx deposition has been increasing substantially (4.50% yr−1, p < 0.05) since 1980. Here, chemical transport model (WRF-EMEP) results indicate that variation in NH3 emissions is not a dominant factor resulting in the continually increasing trends of dry NHx deposition, while climate change-induced trends in precipitation patterns with less frequent light rain and more frequent consecutive rain events (with ≥2 consecutive rainy days) contribute to the increase in dry NHx deposition. This will continue to shift NHx deposition from wet to dry form at a rate of 0.12 and 0.23% yr−1 (p < 0.05) for the period of 2030–2100 in China under the RCP4.5 and RCP8.5 scenarios, respectively. Further analysis for North America and Europe demonstrates results similar to China, with a consistent increase in the contribution of dry NHx deposition driven by changing precipitation patterns from ~30% to ~35%. Our findings, therefore, uncover the change of precipitation patterns has an increasing influence on the shifting of NHx deposition from wet to dry form in the Northern Hemisphere and highlight the need to shift from total NHx deposition-based control strategies to more stringent NH3 emission controls targeting dry NHx deposition in order to mitigate the potential negative ecological impacts.