Fig. 2. Comparisons of δ15N-NH4+ with NH4+ concentration and atmospheric parameters in Zhanjiang. Monthly (a) sunshine duration, (b) temperature, (c) SO2 and NO2 concentration, (d) δ15N-NH4+ and (e) rainfall and NH4+ concentration. The lack of NH4+ concentrations and δ15N-NH4+ in Feb 16, Dec 16, Jan 17 and Dec 17 is because very little (< 0.5 mm) or no rainfall occurred during these periods.