ong-term monitoring of ammonia concentration and other trace gases was made at hourly intervals along with meteorological parameters in Seoul, Korea for a one-year period (1 September 2010-23 August 2011). The mean ammonia concentrations measured at two sites (Gwang-Jin (GJ) and Gang-Seo (GS) districts) were 10.9 +/- 4.25 and 12.3 +/- 4.23 ppb, respectively. A comparison of the seasonal data shows its relative dominance at both GJ and GS sites during the warm period (summer and spring) over the cool period (winter and fall). Likewise, over the diurnal scale, relative dominance during daytime was also apparent