SOURCES AND SINKS OF CARBONYL-COMPOUNDS IN THE ARCTIC-OCEAN BOUNDARY-LAYER - POLAR ICE-FLOE EXPERIMENT

Measurements of HCHO, CH3CHO, and CH3C(O)CH3 were made at the Narwhal ice flee camp in the Lincoln Sea at 84 degrees N latitude from April 1 0 to 24, 1994. During the period April 13 to 18, O-3 was below the det ection limit of the measurement (i.e., <1 ppb), and the average HCHO, CH3CHO, and CH3C(O)CH3 concentrations were 193, 93, and 1730 ppt, resp ectively. A box model of the chemistry involved in the surface O-3 dep letion shows that the majority of BrOx termination reactions occur via Br atom reaction with the aldehydes. The reaction of Br atoms with CH 3CHO is shown to be very effective in removing NOx from the Arctic mar ine boundary layer (MBL), via formation of peroxyacetyl nitrate (PAN). This denitrification of the surface layer has a significant impact on the radical chemistry. In particular, the model indicates that the ob served levels of HCHO and CH3CHO cannot be reproduced if, as discussed in recent reports of Arctic ozone chemistry at sunrise, both Br atom and Cl atom chemistry occur simultaneously (at estimated concentration s of 1x10(4) and 1x10(7) atoms/cm(3), respectively). However, if only chlorine atoms are present (at 1x10(4) atoms/cm(3)), reasonable steady state CH3CHO levels (similar to 80 ppt), but rather low HCHO levels ( similar to 50 ppt) are produced. The model HCHO levels for chlorine-at om-only chemistry are as much as a factor of 10 lower than those obser ved (by these authors and others) in the Arctic MBL at sunrise. Model simulations show that the ratio CH3C(O)CH3/C2H5CHO could be a useful i ndicator of the relative importance of Br atom and Cl atom chemistry.