Measurements of OH and RO 2 radicals at the coastal Antarctic site of Dumont d'Urville (East Antarctica) in summer 2010–2011

Measurements of OH and total peroxy RO 2 (HO 2 plus organic peroxy) radicals were conducted in December 2010/January 2011 at the coastal East Antarctic site of Dumont d'Urville (DDU, 66°40′S 140°01′E) as part of the Oxidant Production over Antarctic Land and its Export (OPALE) project. Compared to measurements carried out at the West Antarctic coast, relatively high concentrations of radicals were found with 24 h average values of 2.1 × 10 6 and 3.3 × 10 8 molecule cm −3 for OH and peroxy radicals, respectively. On the basis of the steady state calculations, the observed high concentration of peroxy radicals is in good agreement with the observed levels of O 3 and HCHO representing via their photolysis the major primary radical sources. The observed OH levels at DDU could be explained only assuming some RO 2 to OH conversion mechanism equivalent to the presence of NO in the range of 10 to 50 pptv. As neither NO nor halogen oxides were measured at DDU the mechanism of this recycling could not be explicitly identified. However, an examination of variability of radical levels as a function of the origin (oceanic versus continental) of sampled air masses suggests a more important OH production from RO 2 recycling in continental air masses.