Measurements of OH, H₂SO₄, and MSA at the South Pole during ISCAT

Abstract

The first measurements of OH, H2SO4, and MSA performed at the South Pole as part of the Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) study are presented. OH concentrations were found to be quite elevated for such a dry environment, with average values of 2x106 molecule cm−3. Model simulations suggest that much of the observed OH is a result of unexpectedly high NO concentrations. Concentrations of H2SO4 and MSA were generally low with average values of 2.5x105 and 1x105 molecule cm−3, respectively. Major variations in the concentration levels of the above species were found to have a high correlation with changes in the polar mixing layer as estimated from the measured temperature difference from 22 to 2m above the snow surface. Chemical details are discussed.

Possible contribution of triboelectricity to snow - air interactions

“…[27,28] For data obtained in 2000 at the South Pole, model predictions of OH were accurate only in a certain range of NO levels. [4,27] For data obtained at Summit, the discrepancy between model and measured values was found to depend strongly on meteorology: [6] when the wind was light (,6 m s À1 ) the measured value was twice the calculated values, whereas in high wind (.6 m s À1 ) and blowing snow the measured value was an order of magnitude higher than the calculated value. [6] Thus, the model calculations that have used only photochemical reactions have underestimated the level of OH in all cases.…”

“…Hydroxyl and superoxide radicals as well as atmospheric nitrogen oxides, carbon monoxide, methane, and hydrogen also participate in radical reaction cycles. Chemical ionisation mass-spectrometry [8] South Pole, ISCAT expedition (Investigation of Sulfur Chemistry in the Antarctic Troposphere), November1998-January 1999 2 Â 10 6 cm À3 Chemical ionisation mass-spectrometry [4] Summit (72 834 0 N, 38 829 0 W, 3250 m ASL), Greenland, 2003 6.4 Â 10 6 cm À3 Chemical ionisation mass-spectrometry [6] Halley Laser-induced fluorescence method [7] Bromine compounds, however, are considered separately because they are very effective ozone depletion catalysts. But the mechanism of bromine release to the gas phase is not fully understood, nor has it been physically interpreted yet.…”

“…[4,20] Because radicals are short-lived, their concentrations are regarded as the difference between the rate of formation and decay. Concentrations of OH measured recently at the South Pole [4] and at Summit, Greenland, [6] were found to be comparable with concentrations of this radical in the tropics ((3À6) Â 10 6 cm À3 [21] ) and 3-5 times higher than values measured at Palmer and Halley Research Stations (Table 1). It has been suggested that recorded levels of OH are a product of photochemical transformations at the snow-air interface.…”

“…Discussions about mechanisms and driving forces of snow-air interactions started with the discovery by Mauldin et al [4] of surprisingly high concentrations of some radicals and intermediates of radical reactions at the South Pole. Subsequently, it became clear that observed levels of these substances arise from chemical reactions in the snowpack and at the snow-air interface.…”

Hydroxyl concentration estimates in the sunlit snowpack at Summit, Greenland

“…Conversely, hydroxyl concentrations in Polar Regions have traditionally been expected to be much lower. However, Mauldin et al (2004) reported typical OH concentrations of (2.5-3.5) Â 10 6 molecules cm À3 above the snow at South Pole. In addition, at Summit, Greenland (72134 0 N, 38129 0 W, 3200 m elevation), the model of Yang et al (2002) predicted OH levels of more than 4 Â 10 6 molecules cm À3 .…”