A Method for the Measurement of Atmospheric HONO Based on DNPH Derivatization and HPLC Analysis

A simple measurement technique was developed for atmospheric HONO based on aqueous scrubbing using a coil sampler followed by 2,4-dinitrophenylhydrazine (DNPH) derivatization and high-performance liquid chromatographic (HPLC) analysis. Quantitative sampling efficiency was obtained using a 1 mM phosphate buffer, pH 7.0, as the scrubbing solution at a gas sampling flow rate of 2 L min - 1 and a liquid flow rate of 0.24 mL min - 1 . Derivatization of the scrubbed nitrous acid by DNPH was fast and was completed within 5 min in a derivatization medium containing 300 μM DNPH and 8 mM HCl at 45 °C. The azide derivative was separated from DNPH reagent and carbonyl derivatives by reverse-phase HPLC and was detected with an UV detector at 309 nm. The detection limit is ≤5 pptv and may be lowered to 1 pptv with further DNPH purification. Interferences from NO, NO 2, PAN, O 3, HNO 3, and HCHO were studied and found to be negligible. Ambient HONO concentration was measured simultaneously in downtown Albany, NY, by this method and by an ion chromatographic technique after sampling using a fritted bubbler. The results, from 70 pptv during the day to 1.7 ppbv in the early morning, were in very good agreement from the two techniques, within ± 20%.