HO 2 NO 2 and HNO 3 in the coastal Antarctic winter night: a "lab-in-the-field" experiment

• Published in: Atmospheric Chemistry and Physics
• Main Authors: A. E. Jones, N. Brough, P. S. Anderson, E. W. Wolff
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/acp-14-11843-2014; https://doaj.org/article/42fe8d5bc29a44338fc6e17d4c442240

Observations of peroxynitric acid (HO 2 NO 2 ) and nitric acid (HNO 3 ) were made during a 4 month period of Antarctic winter darkness at the coastal Antarctic research station, Halley. Mixing ratios of HNO 3 ranged from instrumental detection limits to ~8 parts per trillion by volume (pptv), and of HO 2 NO 2 from detection limits to ~5 pptv; the average ratio of HNO 3 : HO 2 NO 2 was 2.0(± 0.6) : 1, with HNO 3 always present at greater mixing ratios than HO 2 NO 2 during the winter darkness. An extremely strong association existed for the entire measurement period between mixing ratios of the respective trace gases and temperature: for HO 2 NO 2 , R 2 = 0.72, and for HNO 3 , R 2 = 0.70. We focus on three cases with considerable variation in temperature, where wind speeds were low and constant, such that, with the lack of photochemistry, changes in mixing ratio were likely to be driven by physical mechanisms alone. We derived enthalpies of adsorption (Δ H ads ) for these three cases. The average Δ H ads for HNO 3 was −42 ± 2 kJ mol −1 and for HO 2 NO 2 was −56 ± 1 kJ mol −1 these values are extremely close to those derived in laboratory studies. This exercise demonstrates (i) that adsorption to/desorption from the snow pack should be taken into account when addressing budgets of boundary layer HO 2 NO 2 and HNO 3 at any snow-covered site, and (ii) that Antarctic winter can be used as a natural "laboratory in the field" for testing data on physical exchange mechanisms.