Peroxynitric acid (HO<sub>2</sub>NO<sub>2</sub>) measurements during the UBWOS 2013 and 2014 studies using iodide ion chemical ionization mass spectrometry

Abstract

Abstract. In this paper laboratory work is documented establishing iodide ion chemical ionization mass spectrometry (I − CIMS) as a sensitive method for the unambiguous detection of peroxynitric acid (HO 2 NO 2 ; PNA). A dynamic calibration source for HO 2 NO 2 , HO 2 , and HONO was developed and calibrated using a novel total NO y cavity ring-down spectroscopy (CaRDS) detector. Photochemical sources of these species were used for the calibration and validation of the I − CIMS instrument for detection of HO 2 NO 2 . Ambient observations of HO 2 NO 2 using I − CIMS during the 2013 and 2014 Uintah Basin Wintertime Ozone Study (UBWOS) are presented. Strong inversions leading to a build-up of many primary and secondary pollutants as well as low temperatures drove daytime HO 2 NO 2 as high as 1.5 ppbv during the 2013 study. A comparison of HO 2 NO 2 observations to mixing ratios predicted using a chemical box model describing an ozone formation event observed during the 2013 wintertime shows agreement in the daily maxima HO 2 NO 2 mixing ratio, but a differences of several hours in the timing of the observed maxima. Observations of vertical gradients suggest that the ground snow surface potentially serves as both a net sink and source of HO 2 NO 2 depending on the time of day. Sensitivity tests using a chemical box model indicate that the lifetime of HO 2 NO 2 with respect to deposition has a nonnegligible impact on ozone production rates on the order of 10 %.

Reactive nitrogen partitioning and its relationship to winter ozone events in Utah

“…It showed very large signals at the mass normally interpreted as HONO with a distinct, daytime maximum. As described in Veres et al (2015), HO 2 NO 2 mixing ratios were observed to reach an average daytime maximum of approximately 4 % of NO z . Unpublished laboratory results suggest that a large fraction of the HO 2 NO 2 is detected as HONO using the acid CIMS, resulting in a positive daytime bias in the 2013 measurements.…”

Measurements of hydroperoxy radicals (HO<sub>2</sub>) at atmospheric concentrations using bromide chemical ionisation mass spectrometry

“…Laser-induced fluorescence (LIF) is a sensitive technique for OH radical measurements and it is used for the indirect detection of HO 2 by its conversion into OH after reaction with NO. The concurrent conversion of some specific RO 2 radicals can contribute to the HO 2 signal (Fuchs et al, 2011;Whalley et al, 2013;Lew et al, 2018). This can be minimised by reducing the NO concentration added to the sampled air for the conversion of HO 2 to OH, but at the cost of a reduced sensitivity.…”

Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer

“…Gas flows containing low and reproducible concentrations of PNA were generated dynamically in a similar fashion 180 to the method described by Veres et al (2015) by combining the output of a HO2 photochemical source with NO2.…”