A comparison of filter, denuder, and real-time chemiluminescence techniques for nitric acid determination in ambient air

Abstract Measurements of gas-phase nitric acid were made by four separate techniques during a 7-day summertime period at a near-coastal site on Long Island, NY. Results from methods intercomparison data for HNO 3 , and their relationship to particulate NO 3 − and other odd N and oxidant species show the following: (a) high-volume filter pack HNO 3 concentrations are well correlated with diffusion denuder difference (DD) results, except for small absolute losses with the former; (b) daytime real-time two-channel chemiluminescence HNO 3 levels correlated well with DD results, but were higher during night-time periods; (c) results by a new Al 2 (SO 4 ) 3 denuder/thermal evolution technique were not in agreement with other techniques. Based on HNO 3 and paniculate NO 3 results reported herein, it appears that negative errors in HNO 3 filter-sampling techniques resulting from HNO 3 loss by sorption generally exceed positive errors NH 4 NO 3 volatilization at this site.