As part of the Polar Sunrise Experiments (PSE) 1995, we report our results
on measurement of non-methane hydrocarbons (NMHC) collected at Alert, North
west Territories, Canada (82.5 degrees N, 62.3 degrees W) from Julian days
57 to 113, 1995 along with our data on continuous methane and ozone measure
ments during the same period. The concentration of NMHCs such as alkanes co
rrelated well with that of methane during the dark period before polar sunr
ise. However, no correlation was observed after the sunrise. Several ozone
depletion events and concurrent decreases in hydrocarbon concentrations rel
ative to their background levels were observed. In all ozone depletion peri
ods, concentration changes of alkanes and toluene were consistent with the
occurrence of Cl-atom reactions. The characteristics of alkane isomer conce
ntration changes suggest the dominance of HO chemistry prior to, and a swit
ch to CI chemistry after, the polar sunrise (during the ozone depletion eve
nts). The changes in ethyne concentration from their background level were
in excess of those expected from Cl-atom kinetics alone and are attributed
to additional Br-atom reactions. The time integral for Br mixing ratios is
a few orders of magnitudes higher than that for Cl-atoms, suggesting much h
igher Br-atom concentrations compared to Cl-atom concentrations, if they ar
e present simultaneously. (C) 1999 Elsevier Science Ltd. All rights reserve
d.