Influence of Sea Ice‐Derived Halogens on Atmospheric HOx as Observed in Springtime Coastal Antarctica

• Published in: Geophysical research letters 2019-08, Vol.46 (16), p.10168-10176
• Main Authors: Brough, Neil, Jones, Anna E., Griffiths, Paul T.
• Format: Article
• Language: English
• Subjects: Air masses; Antarctica; Bromine; bromine chemistry; Chemistry; Chlorine; Crustaceans; Diurnal; Gases; Halogens; Irradiance; OH and HO2 + RO2; Organic chemistry; polar; Sea ice; sea ice zone; Snowpack; Solar irradiance; Spring; Spring (season); springtime; Surveying; Trace gases; Wind; Wind direction
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL083825

We present first observations of OH and (HO2 + RO2) carried out in Antarctica outside the summer season. Measurements were made over 23 days in spring at the coastal Antarctic station Halley. Increases in concentrations were evident during the measurement period due to rapidly increasing solar irradiance, and clear diurnal cycles were present throughout. There were also notable differences in air mass composition depending on wind direction. Air masses that had traversed the sea ice zone had both higher concentrations of OH and a larger OH:(HO2 + RO2) ratio. We use steady state kinetic arguments and a 0‐D box model to probe the chemical drivers. We find that differences in bromine chemistry, previously measured at Halley, are sufficient to account for the observed differences in OH concentration as well as the ratio. There is some evidence also that chlorine chemistry is influencing concentrations of RO2. Plain Language Summary The chemistry that goes on in the air is very sensitive to the presence of reactive trace gases, known as OH and the sum of HO2 + RO2. We have made the first measurements of these gases during the Antarctic spring, at the British Antarctic Survey station, Halley, in coastal Antarctica. We show that their concentrations vary regularly over the course of a day but generally increase over the 23 days of measurements as the Sun rises after the Antarctic winter. We also show that the concentrations of OH varied considerably from one day to the next, depending on the prevailing wind direction. At Halley, the wind tends to arrive at the station either after it has traveled over the continental snowpack (to the east of the station) or from over the sea ice zone (to the west/southwest of the station). When air has traveled over the sea ice zone, we know that it carries higher concentrations of halogen gases. We show that the higher concentrations of OH in air that has traversed the sea ice zone can be accounted for by the presence of bromine chemistry. Key Points First measurements of OH and HO2 + RO2 made in Antarctica outside of summer show dependence (concentration and ratio) on sea ice contact Using a 0‐D model, we are able to reproduce OH concentrations and HOx partitioning by including bromine chemistry This influence of sea ice‐derived halogens is another factor to be accounted for when considering impacts of changing polar sea ice