Observation of filterable bromine variabilities during Arctic tropospheric ozone depletion events in high (1hour) time resolution

The halogen ions Br and Cl- together with NO3-, SO4(=), MSA(-) (methane sulfonate), Na+ and NH4+ were analysed by ion chromatography in extracts of more than 800 aerosol cellulose filter samples taken at Ny (A) over circle lesund, Svarbard (79 degrees N, 12 degrees E) in spring 1996 (March 27 - May 16) within the European Union project ARCTOC (Arctic Tropospheric Ozone Chemistry). Anticorrelated variations between f-Br (filterable bromine, i.e. water soluble bromine species that can be collected by aerosol filters) and ozone within the arctic troposphere were evaluated at a resolution of 1 or 2 hours for periods with depleted ozone and 4 hours at normal ozone. A mean f-Br concentration of 11 ng m(-3) (0.14 nmol m(-3)) was observed for the whole campaign, while maximum concentrations of 80 ng m(-3) (1 nmol m(-3)) were detected during two total O-3-depletion events (O-3 drop to mixing ratios below the detection limit of < 2 ppb). Anticorrelation between f-Br and O-3 was also seen during minor O-3-depletion episodes (sudden drop in O-3 by at feast 10 ppb, but O-3 Still exceeding the detection limit) and even for ozone variations near its background level (40-50 ppb). A time lag of about 10 hours between the change of ozone and of f-Br concentrations could only be found during a total ozone depletion event, when f-Br reached its maximum values several hours after ozone was totally destroyed. Bromine oxide (BrO) concentrations, measured by DOAS (Differential Optical Absorption Spectroscopy), and f-Br showed a coincident variability during almost the entire campaign (except in the case of total O-3-loss). Frequently enhanced anthropogenic nitrate and sulphate concentrations were observed during O-3-depletion periods. At O-3 concentrations < 10 ppb sulphate and nitrate exceed their typical mean level by 54% and 77%, respectively. This may indicate a possible connection between acidity and halogen release.