MEASUREMENTS OF C-2-C-6 HYDROCARBONS DURING THE POLAR SUNRISE 1992 EXPERIMENT - EVIDENCE FOR CL ATOM AND BR ATOM CHEMISTRY

Grab samples for nonmethane hydrocarbons (NMHCs) were collected from t hree sites: daily at Alert, Northwest Territories (82.5 degrees N, 62. 3 degrees W) from January 21 to April 19, daily at an ice floe 150 km north of Alert from April 9 to 25, and on an aerial survey conducted i n April over the Arctic archipelago. Insitu measurements of n-butane a nd i-pentane were also made hourly at Alert from April 2 to April 15. During the dark period (January to March), C-2-C-6 hydrocarbon concent rations correlated with those of methane. Concentrations declined grad ually from January to April, consistent with removal by HO radicals. O n the other hand, during low-ozone periods in April an additional decr ease in NMHC concentrations and change in distribution were observed. Concentration changes of alkanes were correlated to Cl atom reaction r ate constants. Acetylene displayed a greater change in concentration t han predicted from chlorine kinetics, possibly indicating additional r emoval by Br atoms. The Br atom concentration derived from the depleti on of acetylene can account for the low-ozone concentrations periodica lly observed at Alert. The estimated Cl atom concentration is too smal l to be a significant loss mechanism for ozone. Thus the data from Ale rt and the ice floe site provide evidence for Cl and Br atom chemistry during the ozone depletion episodes observed at polar sunrise.