Measurements of OH and RO2 radicals at Dome C, East Antarctica

A. Kukui, M. Legrand, S. Preunkert, Markus Frey, R Loisil, Jamie Gil Roca, B jourdain, Martin King, James France, G Ancellet

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Concentrations of OH radicals and the sum of peroxy radicals, RO2, 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) dur- ing the austral summer 2011/2012. The median concentra- tions of OH and RO2 radicals were 3.1 × 106 molecule cm−3 and 9.9 × 107 molecule cm−3, respectively. These values are comparable to those observed at the South Pole, confirming that the elevated oxidative capacity of the Antarctic atmo- spheric boundary layer found at the South Pole is not re- stricted to the South Pole but common over the high Antarc- tic plateau. At Concordia, the concentration of radicals showed distinct diurnal profiles with the median maximum of 5.2 × 106 molecule cm−3 at 11:00 and the median mini- mum of 1.1 × 106 molecule cm−3 at 01:00 for OH radicals and 1.7 × 108 molecule cm−3 and 2.5 × 107 molecule cm−3 for RO2 radicals at 13:00 and 23:00, respectively (all times are local times). Concurrent measurements of O3, HONO, NO, NO2, HCHO and H2O2 demonstrated that the major pri- mary source of OH and RO2 radicals at Dome C was the pho- tolysis of HONO, HCHO and H2O2, with the photolysis of HONO contributing ∼ 75 % of total primary radical produc- tion. However, photochemical modelling with accounting for all these radical sources overestimates the concentrations of OH and RO2 radicals by a factor of 2 compared to field ob- servations. Neglecting the net OH production from HONO in
the photochemical modelling results in an underestimation of the concentrations of OH and RO2 radicals by a factor of 2. To explain the observations of radicals in this case an addi- tional source of OH equivalent to about (25–35) % of mea- sured photolysis of HONO is required. Even with a factor of 5 reduction in the concentrations of HONO, the photol- ysis of HONO represents the major primary radical source at Dome C. To account for a possibility of an overestima- tion of NO2 observed at Dome C the calculations were also performed with NO2 concentrations estimated by assuming steady-state NO2 / NO ratios. In this case the net radical pro- duction from the photolysis of HONO should be reduced by a factor of 5 or completely removed based on the photochem- ical budget of OH or 0-D modelling, respectively. Another major factor leading to the large concentration of OH rad- icals measured at Dome C was large concentrations of NO molecules and fast recycling of peroxy radicals to OH radi- cals
Original languageEnglish
Pages (from-to)12373-12392
Number of pages20
JournalAtmospheric Chemistry and Physics
Issue number22
Publication statusPublished - 26 Nov 2014

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