Observations of nitrous acid (HONO) and peroxynitric acid (HO2NO2) made during the 2013 and 2014 Uintah Basin Winter Ozone Study (UBWOS)
Monday, 15 December 2014
HONO is frequently observed to be the main OH source in the early morning, with more recent urban measurements showing significant rates of daytime production. Quantifying the impact of HONO as a source of daytime oxidant is crucial to forming a more explicit understanding of tropospheric ozone formation. In this work, ambient observations of HONO were made during the 2013 and 2014 Uintah Basin Wintertime Ozone Study (UBWOS) at a field site in Utah using various analytical techniques including chemical ionization mass spectrometry (CIMS), differential optical absorption spectroscopy (DOAS), cavity enhanced absorption spectroscopy (CEAS), and long path absorption photometry (LOPAP). Observations of HONO and HO2NO2 will be presented and compared to model results using a chemical box model applying explicit MCM chemistry to describe an ozone formation event observed during the 2013 wintertime season. Strong inversions leading to a build-up of many primary and secondary pollutants as well as low temperatures drove daytime HO2NO2 observations as high as 1.5 ppbv during the 2013 study. The potential of these high HO2NO2 concentrations as an interference to the various HONO measurements techniques will be discussed. Daytime HONO observations will be presented and analyzed with respect to coinciding vertical gradients, sampling artifacts, and potential instrumental interferences.