Trends of halon gases in polar firn air: implications for their emission distributions

[摘要] Four halons (H-1301, H-1211, H-2402 and H-1202) have been measured in airsamples collected from polar firn from Dome Concordia (Dome C), Antarctica,from Devon Island, Canada and the North Greenland Ice Core Project (NGRIP)site, Greenland. H-2402 and H-1202 are reported for the first time in firnair. The depth profiles show the concentrations of all four halons to beclose to zero (i.e. below the detection limit of 0.001 ppt) at the base of the firnthus demonstrating their entirely anthropogenicorigin. This is the first evidence of this for H-2402 and H-1202. A 2-Datmospheric model was run with emissions previously derived usingarchive air measurements from the southern hemisphere mid-latitudes toproduce historical trends in atmospheric concentrations at the firn sites,which were then input into a firn diffusion model to produce concentration depthprofiles for comparison with the firn measurements.This comparison provides an evaluation of the model-derivedatmospheric concentration histories in both hemispheres and thus an indirectevaluation of the emission rates and distributions used in theatmospheric model.Atmospheric concentration trends produced usingglobal emissions previously determined from measurements at Cape Grim are foundto be consistent with the firn data from the southern hemisphere.Further emissions of H-1202 in recent years (late 1980s onwards) are likelyto have come from latitudes mostly south of 40° N, but emissions prior tothat may have come from further north. Emissions of H-1211 may also haveshifted to latitudes south of 40° N during the late 1980s. Followingcomparison of the atmospheric model output with the firn data, modelledatmospheric trends of total organic bromine in the form ofhalons were derived for both polar regions.

[学科分类] 大气科学