An annular denuder filter pack sampling system (ADS) was used to collect acidic air pollutants in Pusan. During the study period (from June 1995 to November 1995), forty eight samples were collected every 12 hours starting from 6:00 in the morning. These samples were devided into two sets of data for day (6:00 a.m.-6:00 p.m.) and night (6:00 p.m.-6:00 a.m.). The chemical species were analyzed for HN $O_3$, HN $O_2$, S $O_2$ and N $H_3$ in the gas Phase, and N $O_3$$^{[-10]}$ , S $O_4$$^{2-}$ and N $H_4$$^{+}$ in the particulate phase. The mean concentrations measured from this study were 0.24, 1.91, 30.07 and 4.24 $mu extrm{g}$/㎥ for HN $O_3$, HN $O_2$, S $O_2$ and N $H_3$, respectively. The mean concentrations of N $O_3$$^{[-10]}$ , S $O_4$$^{2-}$ and N $H_4$$^+{ulcorner}$ were 1.95, 7.36 and 3.48 $mu extrm{g}$/㎥, respectively. The mean concentrations of gaseous species except for HN $O_2$ were higher in daytime than in nighttime, but the reverse was true in the particulates except for N $H_4$$^{+}$. +/..