A reassessment of Antarctic plateau reactive nitrogen based on ANTCI 2003 airborne and ground based measurements

Abstract

The first airborne measurements of nitric oxide (NO) on the Antarctic plateau have demonstrated that the previously reported elevated levels of this species extend well beyond the immediate vicinity of South Pole. Although the current database is still relatively weak and critical laboratory experiments are still needed, the findings here suggest that the chemical uniqueness of the plateau may be substantially greater than first reported. For example, South Pole ground-based findings have provided new evidence showing that the dominant process driving the release of nitrogen from the snowpack during the spring/summer season (post-depositional loss) is photochemical in nature with evaporative processes playing a lesser role. There is also new evidence suggesting that nitrogen, in the form of nitrate, may undergo multiple recycling within a given photochemical season. Speculation here is that this may be a unique property of the plateau and much related to its having persistent cold temperatures even during summer. These conditions promote the efficient adsorption of molecules like HNO 3 (and very likely HO 2 NO 2) onto snow-pack surface ice where we have hypothesized enhanced photochemical processing can occur, leading to the efficient release of NO x to the atmosphere. In addition, to these process-oriented tentative conclusions, the findings from the airborne studies, in conjunction with modeling exercises suggest a new paradigm for the plateau atmosphere. The near-surface atmosphere over this massive region can be viewed as serving as much more than a temporary reservoir or holding tank for imported chemical species. It defines an immense atmospheric chemical reactor which is capable of modifying the chemical characteristics of select atmospheric constituents. This reactor has most likely been in place over geological time, and may have led to the chemical modulation of some trace

The adsorption of peroxynitric acid on ice between 230 K and 253 K

“…For example, field measurements have shown gas phase concentrations of up to 3 × 10 10 molecules cm −3 in Antarctica (Slusher et al, 2002(Slusher et al, , 2010 and 6 × 10 8 molecules cm −3 in the upper troposphere (Kim et al, 2007). Field data further indicate a strong chemical coupling of HO 2 NO 2 and NO (Davis et al, 2008;Slusher et al, 2010) and formation and deposition of HO 2 NO 2 has been suggested to contribute to the reduction of OH at increasing NO levels (Grannas et al, 2007).…”

Overview of mercury measurements in the Antarctic troposphere

“…It indicates a delay between the reemerging sunlight and the Hg(0) transport, and the oxidizing canopy that likely drives the atmospheric chemical production of oxidized mercury species. This peak Hg oxidation period (January-February) roughly corresponds to the annual photochemical peak cycles of nitrogen oxides, OH and HO 2 (Mauldin III et al, 2004;Davis et al, 2008). Another recent study at Concordia (Courteaud et al, 2010) showed that Hg(0) ground levels were both affected by the snowpack recycling and the variations of the boundary layer height.…”

Year-round records of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 1: Fractionation of sea-salt particles

“…The vast increase in nitrate concentration in Dome C ice in cold periods, extremely well-correlated with calcium (e.g., Legrand et al, 2000;Wolff et al, 2010), at least suggests the possibility that nitrate may have been mainly attached to dust aerosol, with an absence of nitric acid over the polar plateau. This is difficult to assess because much of the nitrate over the plateau today is secondary, created by photochemistry occurring in the snowpack (Savarino et al, 2007;Davis et al, 2008), and it is not known whether such photochemistry occurred or not during the LGM. A partial neutralization of acidic sulfur aerosol by dust could also be envisaged.…”