Atmospheric nitric oxide and ozone at the WAIS Divide deep coring site: a discussion of local sources and transport in West Antarctica

• Published in: Atmospheric Chemistry and Physics
• Main Authors: S. Masclin, M. M. Frey, W. F. Rogge, R. C. Bales
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2013
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; The Antarctic; West Antarctica; West Antarctic Ice Sheet; Greenland; Antarc*; Antarctica; Ice Sheet
• Online Access: https://doi.org/10.5194/acp-13-8857-2013; https://doaj.org/article/52f29bb1c15b422ab36650379c397541

The first measurements of atmospheric nitric oxide (NO) along with observations of ozone (O 3 ), hydroperoxides (H 2 O 2 and MHP) and snow nitrate (NO 3 – ) on the West Antarctic Ice Sheet (WAIS) were carried out at the WAIS Divide deep ice-coring site between 10 December 2008 and 11 January 2009. Average ±1 σ mixing ratios of NO were 19 ± 31 pptv and confirmed prior model estimates for the summer boundary layer above WAIS. Mean ±1 σ mixing ratios of O 3 of 14 ± 4 ppbv were in the range of previous measurements from overland traverses across WAIS during summer, while average ±1 σ concentrations of H 2 O 2 and MHP revealed higher levels with mixing ratios of 743 ± 362 and 519 ± 238 pptv, respectively. An upper limit for daily average NO 2 and NO emission fluxes from snow of 8.6 × 10 8 and 33.9 × 10 8 molecule cm –2 s –1 , respectively, were estimated based on photolysis of measured NO 3 – and nitrite (NO 2 – ) in the surface snowpack. The resulting high NO x emission flux may explain the little preservation of NO 3 – in snow (~ 30%) when compared to Summit, Greenland (75–93%). Assuming rapid and complete mixing into the overlying atmosphere, and steady state of NO x , these snow emissions are equivalent to an average (range) production of atmospheric NO x of 30 (21–566) pptv h –1 for a typical atmospheric boundary-layer depth of 250 (354–13) m. These upper bounds indicate that local emissions from the snowpack are a significant source of short-lived nitrogen oxides above the inner WAIS. The net O 3 production of 0.8 ppbv day –1 triggered with NO higher than 2 pptv is too small to explain the observed O 3 variability. Thus, the origins of the air masses reaching WAIS Divide during this campaign were investigated with a 4-day back-trajectory analysis every 4 h. The resulting 168 back trajectories revealed that in 75% of all runs air originated from the Antarctic coastal slopes (58%) and the inner WAIS (17%). For these air sources O 3 levels were on average 13 ± 3 ppbv. The remaining 25% are katabatic outflows from ...