DETERMINATION OF NITRATE IN DEPOSITED AEROSOL-PARTICLES BY THERMAL-DECOMPOSITION AND CHEMILUMINESCENCE

Thermal decomposition-chemiluminescenee was developed to determine nanogram quantities of aerosol nitrate rapidly. Standard nitrates placed on a stainless steel strip were decomposed by resistance heating of the strip and converted to NOx, which was measured with a chemiluminescent NOx analyzer. By adding 1 mu L of 0.1 N NaOH and 0.1 mol/L CrO3 prior to heating, ammonium interference was eliminated and about 97-99% NOx conversion from nitrate was achieved. For standard NaNO3 and NH4NO3, a determination range of 5-2000 ng and a detection limit of 1.1 ng of nitrate were obtained. Interferences from the particle nitrite and the gaseous HNO3, HNO2, NO, and NO2 in sampling process were almost negligible. Other inorganic nitrates such as KNO3, Ca(NO3)(2), and Fe(NO3)(3) were examined. Among aqueous extracts of atmospheric aerosols, the nitrates quantified using this method agreed well with the results obtained by means of ion chromatography. The method is effective for measuring the size distribution of a nitrate aerosol in ambient air, when air volumes as small as 30 L are sampled.