Nitric acid measurement methods: An intercomparison☆

Abstract An interlaboratory comparison of methods to measure gaseous nitric acid is described. Field experiments were conducted in Claremont, CA in late August and early September of 1979. Ten nitric acid measurement methods were compared during the 8 day field experiment. Six different research groups participated in the nitric acid measurements. The methods compared include 2 which employed chemiluminescence principles, 1 infrared, 2 diffusion denuder and 5 filtration techniques. The 8 study days were divided into 32 sampling intervals of 3, 6 and 12 h. Based on the median of the 10 methods, the nitric acid concentration ranged from 1.85 to 37.05μ gm −3 . The nitric acid concentration was highly correlated with other photochemical pollutants such as O 3 and PAN, and all three were strongly correlated with temperature and solar intensity. On the average, gaseous nitric acid and paniculate nitrate contributed equally to the total inorganic nitrate burden at the site. Of the 10 methods investigated, 5 exhibited excellent agreement with the median nitric acid concentration, 2 yielded slopes significantly exceeding 1.0 and 3 suffered from problems which resulted in relatively poor agreement with nitric acid concentration. A great many chemical and meteorological variables were measured during the study, and the effects of these ancillary variables on the nitric acid measurement methods are discussed.