Multiyear measurements on 15N natural abundance of precipitation nitrate at a rural forested site

Abstract

Large anthropogenic NOxemissions increase atmospheric nitrate (NO3−) deposition. The China's Clean Air Action has been implemented to reduce anthropogenic NOxemissions since 2013. To examine if atmospheric NO3− deposition would decrease and its sources had changed as a result of this regulation, we collected the precipitation samples (n = 181) on a daily basis at a rural forested site in Northeast China from April 2014 to December 2017 and measured the concentrations and δ15N values of NO3−. We found annual NO3− deposition ranged from 6.5 to 7.3 kg N ha−1 yr−1 and gradually declined since 2015. The δ15N–NO3- spanned a large range from −17.4 to 13.1‰ with a mass-weighted mean of −3.5‰ during the study period. The δ15N–NO3- was higher by 10‰ in winter (3.3 ± 4.2‰) than in summer (−7.4 ± 3.9‰), which was driven by the changes of both coal combustion and soil emission. Over the study period, NOx from coal combustion, vehicle exhaust, biomass burning and soil emission contributed 28.2 ± 11.9%, 28.8 ± 16.3%, 26.9 ± 14.7%, and 16.1 ± 7.2% to precipitation NO3−, respectively. We found that relative contribution of fossil fuel combustion did not decline with the China's Clean Air Action and considerable NOxreduction at the regional scale.