The cyclone/annular denuder system/filter pack sampling system (ADS) was used to collect the acidic air pollutants in Chongju city. The data set was collected on fifty -eight different days with 24 hour sampling period from October 27, 1995 through August 25, 1996. The chemical species measured were HN $O_3$, HN $O_2$, S $O_2$ and N $H_3$ in the gas phase, and PM2.5( $d_{p}$ ＜2.5 ${mu}{ extrm}{m}$), S $O_4$$^{2-}$, N $O_3$$^{[-10]}$ and N $H_4$$^{+}$ in the Particulate Phase. Mean concentrations measured for this study were: 0.45 $mu extrm{g}$/㎥ for HN $O_3$, 3.39 $mu extrm{g}$/㎥ for HN $O_2$, 26.4 $mu extrm{g}$/㎥ for S $O_2$, 3.83$mu extrm{g}$/㎥ for N $H_3$, 44.2 $mu extrm{g}$/㎥ for P $M_{2.5}$, 8.22 $mu extrm{g}$/㎥ for S $O_4$$^{2-}$, 3.63 $mu extrm{g}$/㎥ for N $O_3$$^{[-10]}$ , and 2.84 $mu extrm{g}$/㎥ for N $H_4$$^{- }$. HN $O_3$ and N $H_3$ were higher during the summer. However, HN $O_2$ and S $O_2$ were higher during the fall and winter. P $M_{2.5}$ , S $O_4$/ sup 2-/ and N $H_4$$^{+}$ were not showed seasonal variations, but N $O_3$$^{[-10]}$ was higher in the winter.ter.r.