The seasonal and diurnal changes of concentration of various gaseous ($HNO_3, NH_3, NO_2, NO, O_3$) and particulate ($NO_3^-, SO_4^{2-}, NH_4^+$) species were monitored to examine the charateristics of total nitrate ($HNO_3/NO_3^-$) concentration in Pusan from October 1996 to August 1997. Also temperature and relative humidity in ambient air were measured. The concentrations of gaseous nitrate (HNO$_3$:4.087-0.116 ppb) were higher during summer time and daytime compared with those during winter time and night time. But the concentrations of particulate nitrate (NO$_3^-$) were 11.21~1.089 $\mu g/m^3$ and higher during winter time and night time. These phenomena may be attributable to the photochemical reactions. Conversion rates of NO$_x$ to gaseous nitrate (Fn : 11.87~0.67%) were greater in summer time and day time and conversion rates of NO$_x$ to particulate nitrate (Fn
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