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 (HO2NO2; PNA). A dynamic calibration source for HO2NO2, HO2, and HONO was developed and calibrated using a novel total NOy 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 HO2NO2. Ambient observations of HO2NO2 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 HO2NO2 as high as 1.5 ppbv during the 2013 study. A comparison of HO2NO2 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 HO2NO2 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 HO2NO2 depending on the time of day. Sensitivity tests using a chemical box model indicate that the lifetime of HO2NO2 with respect to deposition has a non-negligible impact on ozone production rates on the order of 10 %.
Highlights
Hydrogen oxides (HOx = HO2+ OH) and nitrogen oxides (NOx = NO2+ NO) play central roles in atmospheric photochemistry
The iodide ion chemical ionization mass spectrometry (I− CIMS) instrument consists of an ion flow tube coupled to a quadrupole mass spectrometer
The I− CIMS instrument was deployed during the 2013 and 2014 Uintah Basin Wintertime Ozone Study (UBWOS) field studies conducted in the Uintah Basin, UT
Summary
Peroxynitric acid (often referred to as PNA, HO2NO2, or HNO4) plays an important role in the coupling of atmospheric HOx and NOx cycles (Niki et al, 1977), especially at low temperatures. Observations of PNA are generally limited in scope with most measurements focusing on polar regions (Slusher et al, 2002, 2010; Huey et al, 2004), the free troposphere (Murphy et al, 2004; Singh et al, 2006, 2007; Keim et al, 2008; Kim et al, 2007), and the stratosphere (Rinsland et al, 1996, 1986; Sen et al, 1998). We show applicability of this technique for the detection of both HO2 and HONO, atmospheric species that are integral to HOx and NOx cycles These results were necessary in order to rule out potential mass overlap or PNA interferences from the sampling of HO2 and HONO. The impact of PNA on HOx and NOx budgets, as it relates to the photochemical production of ozone, will be discussed
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