It has been shown that sunlit snow and ice plays an important role in processing atmospheric species. Photochemical production of a variety of chemicals has recently been reported to occur in snow/ice and the release of these photochemically generated species may significantly impact the chemistry of the overlying atmosphere. Nitrogen oxide and oxidant precursor fluxes have been measured in a number of snow covered environments, where in some cases the emissions significantly impact the overlying boundary layer. For example, photochemical ozone production (such as that occurring in polluted mid-latitudes) of 3–4 ppbv/day has been observed at South Pole, due to high OH and NO levels present in a relatively shallow boundary layer. Field and laboratory experiments have determined that the origin of the observed NOx flux is the photochemistry of nitrate within the snowpack, however some details of the mechanism have not yet been elucidated. A variety of low molecular weight organic compounds have been shown to be emitted from sunlit snowpacks, the source of which has been proposed to be either direct or indirect photo-oxidation of natural organic materials present in the snow. Although myriad studies have observed active processing of species within irradiated snowpacks, the fundamental chemistry occurring remains poorly understood. Here we consider the nature of snow at a fundamental, physical level; photochemical processes within snow and the caveats needed for comparison to atmospheric photochemistry; our current understanding of nitrogen, oxidant, halogen and organic photochemistry within snow; the current limitations faced by the field and implications for the future.

/pdf/an-overview-of-snow-photochemistry-evidence-mechanisms-and-yaeoz9jq34.pdf

An overview of snow photochemistry: evidence, mechanisms and impacts

We have examined the 532-nm aerosol backscatter coefficient measurements by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) for their use in the monitoring of stratospheric aerosol. CALIPSO makes observations that span from 82° S to 82° N each day and, for each profile, backscatter coefficient values reported up to ~40 km. The possibility of using CALIPSO for stratospheric aerosol monitoring is demonstrated by the clear observation of the 20 May 2006 eruption of Montserrat in the earliest CALIPSO data in early June as well as by observations showing the 7 October 2006 eruption of Tavurvur (Rabaul). However, the very low aerosol loading within the stratosphere makes routine observations of the stratospheric aerosol far more difficult than relatively dense volcanic plumes. Nonetheless, we found that averaging a complete days worth of nighttime-only data into 5-deg latitude by 1-km vertical bins yields a stratospheric aerosol distribution that is fairly consistent with past measurements by spaceborne instruments. Based on comparisons with 2004 data from the Stratospheric Aerosol and Gas Experiment, the derived values are close to expectation except in the tropics where they are larger by about a factor of 2. The cause of the difference in the tropics is not readily apparent but is most likely related to difficulties in the lidar calibration process currently found in the CALIOP data at tropical latitudes.

pdf/calipso-observations-of-stratospheric-aerosols-a-preliminary-ypzh0ura94.pdf

CALIPSO observations of stratospheric aerosols: a preliminary assessment

Throughout the year 2001, aerosol samples were collected continuously for 10 to 15 days at the French Antarctic Station Dumont d'Urville (DDU) (66°40' S, l40°0' E, 40 m above mean sea level). The nitrogen and oxygen isotopic ratios of particulate nitrate at DDU exhibit seasonal variations that are among the most extreme observed for nitrate on Earth. In association with concentration measurements, the isotope ratios delineate four distinct periods, broadly consistent with previous studies on Antarctic coastal areas. During austral autumn and early winter (March to mid-July), nitrate concentrations attain a minimum between 10 and 30 ng m −3 (referred to as Period 2). Two local maxima in August (55 ng m −3 ) and November/December (165 ng m −3 ) are used to assign Period 3 (mid-July to September) and Period 4 (October to December). Period 1 (January to March) is a transition period between the maximum concentration of Period 4 and the background concentration of Period 2. These seasonal changes are reflected in changes of the nitrogen and oxygen isotope ratios. During Period 2, which is characterized by background concentrations, the isotope ratios are in the range of previous measurements at mid-latitudes: δ 18 O vsmow =(77.2±8.6)‰; Δ 17 O=(29.8±4.4)‰; δ 15 N air =(−4.4±5.4)‰ (mean ± one standard deviation). Period 3 is accompanied by a significant increase of the oxygen isotope ratios and a small increase of the nitrogen isotope ratio to δ 18 O vsmow =(98.8±13.9)‰; Δ 17 O=(38.8±4.7)‰ and δ 15 N air =(4.3±8.20‰). Period 4 is characterized by a minimum 15 N/ 14 N ratio, only matched by one prior study of Antarctic aerosols, and oxygen isotope ratios similar to Period 2: δ 18 O vsmow =(77.2±7.7)‰; Δ 17 O=(31.1±3.2)‰; δ 15 N air =(−32.7±8.4)‰. Finally, during Period 1, isotope ratios reach minimum values for oxygen and intermediate values for nitrogen: δ 18 O vsmow =63.2±2.5‰; Δ 17 O=24.0±1.1‰; δ 15 N air =−17.9±4.0‰). Based on the measured isotopic composition, known atmospheric transport patterns and the current understanding of kinetics and isotope effects of relevant atmospheric chemical processes, we suggest that elevated tropospheric nitrate levels during Period 3 are most likely the result of nitrate sedimentation from polar stratospheric clouds (PSCs), whereas elevated nitrate levels during Period 4 are likely to result from snow re-emission of nitrogen oxide species. We are unable to attribute the source of the nitrate during periods 1 and 2 to local production or long-range transport, but note that the oxygen isotopic composition is in agreement with day and night time nitrate chemistry driven by the diurnal solar cycle. A precise quantification is difficult, due to our insufficient knowledge of isotope fractionation during the reactions leading to nitrate formation, among other reasons.

/pdf/nitrogen-and-oxygen-isotopic-constraints-on-the-origin-of-3dqeipvher.pdf

Nitrogen and oxygen isotopic constraints on the origin of atmospheric nitrate in coastal Antarctica

The uptake of acidic gases on ice.

Sea spray aerosol in central Antarctica. Present atmospheric behaviour and implications for paleoclimatic reconstructions

https://escholarship.org/content/qt7jf6d7w3/qt7jf6d7w3.pdf?t=q54si4

An overview of ISCAT 2000

Major ions and radionuclides in aerosol particles from the South Pole during ISCAT-2000

Lead and mercury in aerosol particles collected over the South Pole during ISCAT-2000

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An overview of ISCAT 2000

Major ions and radionuclides in aerosol particles from the South Pole during ISCAT-2000

Lead and mercury in aerosol particles collected over the South Pole during ISCAT-2000