Measurements of OH and RO<sub>2</sub> radicals at Dome C, East Antarctica

Abstract

Abstract. Concentrations of OH radicals and the sum of peroxy radicals, RO 2 , were measured in the boundary layer for the first time on the East Antarctic Plateau at the Concordia Station (Dome C, 75.10 • S, 123.31 • E) during the austral summer 2011/2012. The median concentrations of OH and RO 2 radicals were 3.1 × 10 6 molecule cm −3 and 9.9 × 10 7 molecule cm −3 , respectively. These values are comparable to those observed at the South Pole, confirming that the elevated oxidative capacity of the Antarctic atmospheric boundary layer found at the South Pole is not restricted to the South Pole but common over the high Antarctic plateau. At Concordia, the concentration of radicals showed distinct diurnal profiles with the median maximum of 5.2 × 10 6 molecule cm −3 at 11:00 and the median minimum of 1.1 × 10 6 molecule cm −3 at 01:00 for OH radicals and 1.7 × 10 8 molecule cm −3 and 2.5 × 10 7 molecule cm −3 for RO 2 radicals at 13:00 and 23:00, respectively (all times are local times). Concurrent measurements of O 3 , HONO, NO, NO 2 , HCHO and H 2 O 2 demonstrated that the major primary source of OH and RO 2 radicals at Dome C was the photolysis of HONO, HCHO and H 2 O 2 , with the photolysis of HONO contributing ∼ 75 % of total primary radical production. However, photochemical modelling with accounting for all these radical sources overestimates the concentrations of OH and RO 2 radicals by a factor of 2 compared to field observations. Neglecting the net OH production from HONO in the photochemical modelling results in an underestimation of the concentrations of OH and RO 2 radicals by a factor of 2. To explain the observations of radicals in this case an additional source of OH equivalent to about (25-35) % of measured photolysis of HONO is required. Even with a factor of 5 reduction in the concentrations of HONO, the photolysis of HONO represents the major primary radical source at Dome C. To account for a possibility of an overestimation of NO 2 observed at Dome C the calculations were also performed with NO 2 concentrations estimated by assuming steady-state NO 2 / NO ratios. In this case the net radical production from the photolysis of HONO should be reduced by a factor of 5 or completely removed based on the photochemical budget of OH or 0-D modelling, respectively. Another major factor leading to the large concentration of OH radicals measured at Dome C was large concentrations of NO molecules and fast recycling of peroxy radicals to OH radicals.

Inter-annual variability of surface ozone at coastal (Dumont d'Urville, 2004–2014) and inland (Concordia, 2007–2014) sites in East Antarctica

“…As seen in Fig. 7c and d, where the loss reactions of ozone with OH, HO 2 , and NO (neglected by Kukui et al, 2014) were considered, the ozone net production still reaches 4 ppbv per day. In the following, we examine whether such a calculated ozone production rate of a few ppbv per day is consistent with observations.…”

“…The reason for higher ozone values observed near the ground at the South Pole compared to those at Concordia is not simply related to the fact that solar radiation needed to photochemically produce ozone acts during 24 h at the South Pole and not at Concordia. Indeed, the two inland sites are expected to experience rather similar local photochemical ozone production, with 0.13-0.20 ppbv h −1 over 24 h at the South Pole and from 0.05 ppbv h −1 at midnight to 0.27 ppbv h −1 during sunlight hours at Concordia (Kukui et al, 2014; see also Fig. 7c).…”

“…Based on observed mixing ratios of NO and RO 2 at Concordia (Table 1), an integrated local ozone production from the reaction of NO with RO 2 of 4.7 ppbv per day was calculated by Kukui et al (2014). As seen in Fig.…”

Multi-year record of atmospheric mercury at Dumont d'Urville, East Antarctic coast: continental outflow and oceanic influences

“…This daily cycle atop the East Antarctic ice sheet was attributed to: (i) an intense oxidation of Hg(0) in the atmospheric boundary layer due to the high level of oxidants present there (Davis et al, 2001;Grannas et al, 2007;Eisele et al, 2008;Kukui et al, 2014), (ii) Hg(II) dry deposition onto the snowpack, and (iii) increased emission of Hg(0) from the snowpack around midday as a response to daytime heating following photoreduction of Hg(II) in the upper layers of the snowpack. Even if DDU is located on snow free bedrock for most of the summer season, the same mechanism could apply since the station is surrounded by vast snow-covered areas.…”

Chemical cycling and deposition of atmospheric mercury in polar regions: review of recent measurements and comparison with models

“…The mean summertime Hg(0) concentration is significantly (p value < 0.0001, Mann-Whitney test) lower at DC (0.78 ± 0.46 ng m −3 ) than at DDU (0.88 ± 0.32 ng m −3 ) and TR (0.89 ± 0.29 ng m −3 ), suggesting a more intense oxidation of Hg(0). The boundary layer oxidative capacity has been shown to be high in summer on the Antarctic Plateau with elevated levels of OH, O 3 , NO x , and RO 2 radicals (Davis et al, 2001;Grannas et al, 2007;Eisele et al, 2008;Kukui et al, 2014;. Angot et al (2016b) performed Hg(0) measurements in both the atmospheric boundary layer and the interstitial air of the snowpack and analyzed total mercury in surface snow samples.…”