"The goal of this research project is to understand the nitrous acid (HONO or HNO2) emissions from snow in Antarctica and their contributions to the oxidative capacity of the Antarctic atmosphere. Nitrous acid is an important atmospheric trace gas. Upon photo-dissociation, it forms hydroxyl radical (OH) and nitrogen monoxide (NO). It therefore enters both the HOx (OH + HO2) and NOx (NO + NO2) budgets which are key budgets when considering the oxidative capacity of the atmosphere. In Antarctica, the oxidative capacity governs for instance the oxidation of marine biogenic sulphur emissions (dimethyl sulphide, DMS) into sulphur aerosols which may cause regional climatic feedbacks via their interactions with solar radiations and cloud microphysics. Oxidation also leads to atmospheric processing and/or post-depositional processing which to date prevent from interpreting – in terms of past atmospheric changes – the nitrate, sulphur, hydrogen peroxide and formaldehyde concentrations recorded in glacial ice. The role of HONO in the HOx and NOx budgets as well as its contribution to the oxidative capacity in Polar Regions is not yet understood. In this project, HONO emissions will be measured in central Antarctica at the French-Italian research station Concordia (75°S, also know as Dome C) using – for the first time – a recently developed Long Path Absorption Photometer (LOPAP). All the parameters influencing HONO emissions will also be measured during the field campaign. These measurements as well as chemical, physical and physico-chemical processes driving HONO emissions and results of previous laboratory experiments will be subsequently gathered in a numerical “box” model. The model being able to reproduce measured HONO emissions, it will be possible to understand the role of HONO in the HOx and NOx budgets and quantify its contribution to the oxidative capacity of the Atmosphere at Dome C and by extension in Polar Regions."