A comparison of nitric acid and particulate nitrate measurements by the penetration and denuder difference methods

Measurements of ambient nitric acid and particulate nitrates were made by the dual-filter, denuder difference and penetration methods for 53 days during the summer of 1981 in Warren, Michigan. Nitric acid average concentrations determined by the penetration method (3.71 μg m −3) and the denuder difference method (3.11 μg m −3) were significantly lower than the dual-filter measurements (4.52 μg m −3). Similarly, nonvolatile particulate nitrate averaged 0.95 μg m −3 by penetration and 1.10 μg m −3 by denuder difference compared to 1.53 μg m −3 by the dual-filter method. These comparisons indicated that the penetration and denuder difference methods achieve significant reductions in nitric acid and nonvolatile particulate nitrate interferences. Based upon its operational simplicity, the denuder difference method is recommended.