HR: 11:20h
AN: A12B-04    [Abstracts]
TI: Spatial Gradients in Halogen Oxides Across the North Slope of Alaska Indicate That Halogen Activated Airmasses are Spatially Large
AU: * Simpson, W R
EM: ffwrs@uaf.edu
AF: University of Alaska Fairbanks Geophysical Inst. and Chem. Department, University of Alaska Fairbanks 900 Yukon Drive, Fairbanks, AK 99775-6160 United States
AU: * Simpson, W R
EM: ffwrs@uaf.edu
AF: Institute of Environmental Physics, Im Neuenheimer Feld 229, Heidelberg, BW 69120 Germany
AU: Hoenninger, G S
A12B-04 AF: University of Alaska Fairbanks Geophysical Inst. and Chem. Department, University of Alaska Fairbanks 900 Yukon Drive, Fairbanks, AK 99775-6160 United States
AU: Hoenninger, G S
A12B-04 AF: Institute of Environmental Physics, Im Neuenheimer Feld 229, Heidelberg, BW 69120 Germany
AU: Platt, U
EM: ulrich.platt@iup.uni-heidelber.de
AF: Institute of Environmental Physics, Im Neuenheimer Feld 229, Heidelberg, BW 69120 Germany
AB: Reactive halogens are important oxidizers in the polar atmosphere during springtime. They deplete tropospheric ozone, oxidize hydrocarbons, and oxidize gas-phase mercury, causing it to deposit to the snow pack. We want to understand the mechanism by which halides in on snow/ice crystals and/or in aerosol particles are converted to reactive halogen species. This understanding can assist in prediction of mercury deposition and how that deposition depends on environmental variables like sea-ice extent and temperature. This mechanistic knowledge is particularly important in the context of a changing Arctic system. To study halogen activation, we are working in the Studies of the Northern Alaskan Coastal System (SNACS) project and here show results from 2005 including the LEADX experiment. A number of studies have implicated leads (cracks in the sea ice) as a source of halogen activation, but it is unclear if halogens are directly activated on ice surfaces at the lead (e.g. frost flowers) or if the lead is less directly involved. To address the role of leads in halogen activation, we measured bromine monoxide (BrO) using Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at Barrow and Atqasuk, Alaska over a four-month period. The locations of these sites, either on the coast near a recurring lead in the case of Barrow, or 100km inland in the case of Atqasuk provides an ability to measure spatial gradients on the 100km length scale. In addition, the Barrow instrument was the first implementation of fully automated two dimensional MAX-DOAS where both elevation and azimuth were scanned. Because the MAX-DOAS method typically detects path-averaged BrO amounts between the instrument and a range of approximately 10km, differences in BrO between viewing azimuths allows us to determine short-length scale BrO gradients. From the 2-D MAX-DOAS observations at Barrow, we find that there are very small if any spatial gradients on the 10km length scale. From the differences in BrO between Barrow and Atqasuk, we find that, on average, the BrO is nearly the equal at Barrow and Atqasuk. Cases occur where the gradient shows less BrO at Atqasuk than Barrow, but it is nearly equally likely to have more BrO at Atqasuk than Barrow. In the great majority of cases, the BrO at one site is within a factor of two of the other site. These relatively weak gradients may be associated with moving weather systems. If the lead were directly sourcing BrO, one would expect a consistent gradient with more BrO at the coast (Barrow) than inland (Atqasuk), which is not observed. Therefore, our data set argues that halogen oxide activation is not highly localized to the lead and is of widespread nature.
UR: http://www.uaf.edu/chem/simpson
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0736 Snow (1827, 1863)
DE: 0750 Sea ice (4540)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005