Surface formation of HONO over soil and snow during UBWS 2012, 2014

Abstract:

The release of HONO from snow in remote polar regions has been known for many years. HONO in the snow is likely formed through chemical processes initiated by the photolysis of nitrate in the snowpack. This source has recently also been invoked to explain high ozone levels observed at wintertime gas-drilling locations. The release of HONO from snowpack would be enhanced in oil and gas fields, where emissions of NOx are significant, thus serving as an important OH precursor and driver of ozone formation.

Here we present observations of gradients of HONO mixing ratios using the UCLA LP-DOAS instrument during the Uintah Basin Winter Ozone Studies (UBWOS) in 2012 and 2014. HONO levels were measured at about 25, 45, and 65 m above the ground level. The lack of snow during UBWS 2012 compared to the snowy 2014 conditions allows us to directly study the influence of snow cover on HONO chemistry. Preliminary results show that HONO mixing ratios were comparable during both years, with nighttime hourly averages ranging from 60 ppt to 120ppt and daytime hourly averages close to 50ppt. However, during the snow covered year, we observed a significant peak of HONO (up to 100 ppt in the lowest light path) around 13:00 local time. During this time, a strong HONO vertical gradient was also observed. We will discuss the possible daytime HONO sources responsible for these observations and investigate the role of snow in HONO formation in a polluted environment