Nitrogen isotope composition of ammonium in PM2.5 in the Xiamen, China: impact of non-agricultural ammonia. - Wu, Shui-Ping; Zhu, Heng; Liu, Zhe; Dai, Lu-Hong; Zhang, Ning; Schwab, James J.; Yuan, Chung-Shin; Yan, Jin-Pei (Environmental Science & Pollution Research, 2019)