Atmospheric nitric oxide and ozone at the WAIS Divide deep coring site: a discussion of local sources and transport in West Antarctica 1Environmental Systems, University of California, Merced, California, USA
05 Sep 2013
2British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
3Sierra Nevada Research Institute, University of California, Merced, California, USA
Received: 18 December 2012 – Published in Atmos. Chem. Phys. Discuss.: 14 March 2013 Abstract. The first measurements of atmospheric nitric oxide (NO) along with
observations of ozone (O3), hydroperoxides (H2O2 and
MHP) and snow nitrate (NO3–) 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 ±1σ mixing ratios of
NO were 19 ± 31 pptv and confirmed prior model estimates
for the summer boundary layer above WAIS. Mean ±1σ mixing ratios
of O3 of 14 ± 4 ppbv were in the range of previous
measurements from overland traverses across WAIS during summer, while average
±1σ concentrations of H2O2 and MHP revealed higher
levels with mixing ratios of 743 ± 362 and
519 ± 238 pptv, respectively.
Revised: 20 June 2013 – Accepted: 18 July 2013 – Published: 05 September 2013
An upper limit for daily average NO2 and NO emission fluxes
from snow of 8.6 × 108 and
33.9 × 108 molecule cm–2 s–1, respectively, were
estimated based on photolysis of measured NO3– and nitrite
(NO2–) in the surface snowpack. The resulting high NOx
emission flux may explain the little preservation of NO3– in snow
(~ 30%) when compared to Summit, Greenland (75–93%). Assuming
rapid and complete mixing into the overlying atmosphere, and steady state of
NOx, these snow emissions are equivalent to an average (range)
production of atmospheric NOx 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 O3 production of 0.8 ppbv day–1 triggered with
NO higher than 2 pptv is too small to explain the observed
O3 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 O3 levels
were on average 13 ± 3 ppbv. The remaining 25% are katabatic
outflows from the East Antarctic Plateau above 2500 m. When
near-surface air from the East Antarctic Plateau reaches WAIS Divide through
a rapid transport of less than 3 days, O3 levels are on average
19 ± 4 ppbv with maximum mixing ratios of 30 ppbv.
Episodes of elevated ozone at WAIS Divide are therefore linked to air mass
export off the East Antarctic Plateau, demonstrating that outflows from the
highly oxidizing summer atmospheric boundary layer in the interior of the
continent can episodically raise the mixing ratios of long-lived atmospheric
chemical species such as O3 and enhance the oxidative capacity of the
atmosphere above WAIS.
Citation: Masclin, S., Frey, M. M., Rogge, W. F., and Bales, R. C.: Atmospheric nitric oxide and ozone at the WAIS Divide deep coring site: a discussion of local sources and transport in West Antarctica, Atmos. Chem. Phys., 13, 8857-8877, doi:10.5194/acp-13-8857-2013, 2013.