Derivation of Hydroperoxyl Radical Levels at an Urban Site via Measurement of Pernitric Acid by Iodide Chemical Ionization Mass Spectrometry

摘要

Hydroperoxyl radical (HO_2) is a key species to atmospheric chemistry. At warm temperatures, the HO_2 and NO_2 come to a rapid steady state with pernitric acid (HO_2NO_2). This paper presents the derivation of HO_2 from observations of HO_2NO_2 and NO_2 in metropolitan Atlanta, US, in winter 2014 and summer 2015. HO_2 was observed to have a diurnal cycle with morning concentrations suppressed by high NO from the traffic. At night, derived HO_2 levels were nonzero and exhibited correlations with O_3 and NO_3, consistent with previous studies that ozonolysis and oxidation by NO_3 are sources of nighttime HO_2. Measured and model calculated HO_2 were in reasonable agreement： Without the constraint of measured HO_2NO_2, the model reproduced HO_2 with a model-to-observed ratio (M/O) of 1.27 (r = 0.54) for winter, 2014, and 0.70 (r = 0.80) for summer, 2015. Adding measured HO_2NO_2 as a constraint, the model predicted HO-2 with M/O = 1.13 (r = 0.77) for winter 2014 and 0.90 (r = 0.97) for summer 2015. These results demonstrate the feasibility of deriving HO_2 from HO_2NO_2 measurements in warm regions where HO_2NO_2 Has a short lifetime.