Research Projects

A laboratory and field study was performed to construct and evaluate an automated, semi continuous monitor for ambient air concentrations of nitric acid (HN03) and ammonia (NH3) utilizing tungstic acid-coated denuder tubes. In addition, atmospheric concentrations of hydrochloric acid (HCl) were determined. Manual techniques for atmospheric NH3 measurement were also compared. Interference in HN03 measurements was determined with nitrogen dioxide, nitrous acid and particulate ammonium nitrate. Atmospheric sampling for HN03 was done in Riverside, California during September 1984 with the automated tungstic acid technique (TAT) and by the denuder difference method (DDM), considered the reference procedure for HN03. Ammonia and HCl were measured with impregnated filter methods. In addition, NH3 was measured by a denuder tube collection procedure.

Nitrous acid was the only material studied which exhibited significant interference in nitric acid response with the automated TAT. Atmospheric nitric acid levels with the automated TAT showed 1 hour average values up to 45 µg/m3 (17.5 ppb). These values yielded moderate correlation with O3 (r = 0.78) and high correlation (r = 0.94) with HN03 by the DDM. However, the HN03 values averaged about 50% higher than those by the reference procedure. Ammonia measurements with impregnated filters showed high correlation (r = 0.98) with oxalic acid-coated denuder tube collected samples, but the former averaged 12% higher. Ammonia measurements with the automated TAT were not quantitative because of difficulties in calibration. Hydrochloric acid values ranged up to 3 µg/m3 with a pronounced diurnal variation, maxima occurring during the period 0800-1200 or 1200-1600 hour. Particulate chloride levels were similar in magnitude to those for HCl and showed no correlation with HCl.