05 Jan 2023
05 Jan 2023
Status: this preprint is currently under review for the journal ACP.

Snowpack nitrate photolysis drives the summertime atmospheric nitrous acid (HONO) budget in coastal Antarctica

Amelia M. H. Bond1,2, Markus M. Frey1, Jan Kaiser2, Jörg Kleffmann3, Anna E. Jones1, and Freya A. Squires1 Amelia M. H. Bond et al.
  • 1British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
  • 2Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 3Department of Physical and Theoretical Chemistry, Faculty for Mathematics and Natural Sciences, University of Wuppertal, Germany

Abstract. Measurements of atmospheric nitrous acid (HONO) amount fraction and flux density above snow were carried out using a long path absorption photometer at Halley station in coastal Antarctica between 22 January and 3 February 2022. The mean±1σ HONO amount fraction was (2.1 ± 1.5) pmol mol−1 and showed a diurnal cycle (range 1.0−3.2 pmol mol−1) with a maximum at solar noon. These HONO amount fractions are generally lower than have been observed at other Antarctic locations. The flux density of HONO from the snow, measured between 31 January and 1 February 2022, was between 0.5 and 3.4 ×1012 m−2 s−1, and showed a decrease during the night. The measured flux density is at the upper limit of the calculated HONO production rate from photolysis of nitrate present in the snow. A simple box model of HONO sources and sinks showed that the flux of HONO from the snow makes a > 10 times larger contribution to the HONO budget than its formation through the reaction of OH and NO. Ratios of these HONO amount fractions to NOx measurements made in summer 2005 are low (0.15−0.35), which we take as an indication of our measurements being comparatively free from interferences. Further calculations suggest that HONO photolysis could produce up to 12 pmol mol−1 h−1 of OH, approximately half that produced by ozone photolysis, which highlights the importance of HONO snow emissions as an OH source in the atmospheric boundary layer above Antarctic snowpacks.

Amelia M. H. Bond et al.

Status: open (until 16 Feb 2023)

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Amelia M. H. Bond et al.

Amelia M. H. Bond et al.


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Short summary
Atmospheric nitrous acid (HONO) amount fractions measured at Halley Research Station, Antarctica, were found to be low. Vertical fluxes of HONO from the snow were also measured and agree with the estimated HONO production rate from photolysis of snow nitrate. In simple box model of HONO sources and sinks there was good agreement between the measured flux and amount fraction. HONO was found to be an important OH radical source at Halley.