New coaxial 'long-path-DOAS' system: first application to BrO measurement in the Arctic troposphere

摘要

Abstract: Recently episodic destruction of boundary-layer ozonehas been observed in the Arctic. Those episodes, whenozone levels drop from the normal 30 - 40 ppb tounmeasurable ($LS 3 ppb) levels, appear to beassociated with high concentrations of `filterablebromine' (bromine that can be collected on cellulosefilters). While it is not clear what the exact natureof filterable bromine is, it was hypothesized byseveral authors that the active component of filterablebromine might be BrO radicals. Several presses havebeen suggested to produce BrO radicals during Arcticspringtime conditions: (1) Photolysis of bromoform gas(CHBr$-3$/) produced biologically in the ocean fromBr-atoms. (2) Formation of BrNO or BrNO$-2$/ byreaction of NO$-2$/ or N$-2$/O$-5$/, respectively, withNaBr contained in sea salt aerosol particles. Thespecies BrNO and BrNO$-2$/ are both rapidly photolyzedto yield Br-atoms. (3) Photochemical reaction ofsea-salt Br$+$MIN$/ on the surface of aerosol particlesor snow pack to form Br$-2$/. Br$-2$/ would be rapidlyphotolyzed to form Br-atoms. Bromine atoms reactrapidly with O$-3$/ to form bromine oxide radicals. !19