ORGANIC AND INORGANIC BROMINE COMPOUNDS AND THEIR COMPOSITION IN THE ARCTIC TROPOSPHERE DURING POLAR SUNRISE

Particle and gas phase inorganic bromine, total organic bromine, and s everal individual organic bromine species were measured in the troposp here during the Polar Sunrise Experiment at Alert, Northwest Territori es, Canada, during January 18 to April 21, 1992. The measurements reve aled the following: (1) Particle bromide increased gradually from abou t 10 ng(Br) m(-3) during the dark period to >20 ng(Br) m(-3) during th e light period, with a marked peak of 120 ng(Br) m(-3) corresponding t o a strong O-3 depletion event. (2) Inorganic gaseous bromine (InorgBr ) was about 60 ng(Br) m(-3) during the dark period and relatively cons tant. A major peak, up to 280 ng(Br) m(-3), before sunrise accompanied a similar peak in the total organic bromine. These episodes originate d in the free troposphere over Greenland. After sunrise the peaks in I norgBr corresponded to O-3 depletion periods. InorgBr appeared to be t he sum of HBr, HOBr, and Br-2. (3) Total organic bromine was relativel y constant before sunrise at 100 ng(Br) m(-3) but more variable afterw ard, up to 280 ng(Br) m(-3). Individual species include CHBr3 with lev els of 7-60 ng(Br) m(-3). CH2Br2, CH2ClBr, CHClBr2, and CHCl2Br levels were lower at 0.5-7.5 ng(Br) m(-3). CHBr3 was the largest contributor to total organic bromine of the five species, on average accounting f or 23%, while the other four species amounted to less than 5% on avera ge. CH3Br (not measured) should contribute 44% of total organic bromin e assuming a concentration of 40 ng(Br) m(-3) (11 parts per trillion b y volume). The remaining contribution was probably from ''missing'' sp ecies which were episodically dominant after sunrise with concentratio ns up to 240 ng(Br) m(-3) and may include some inorganic species. All the peaks in the organic bromines after sunrise corresponded to the O- 3 depletion events. (4) CHBr3, CHClBr2, and CHCl2Br were significantly correlated. The ratio CHClBr2/CHBr3 decreased linearly with increasin g ln(CHBr3), with a steeper decrease after sunrise than before. The de creases suggest different rates of destruction with CHBr3 having a lar ger rate constant than CHClBr2. A similar relationship existed between the ratio CHCl2Br/CHClBr2 and the ln(CHClBr2), but the dark period sl ope was near zero, indicating a greater difference in rates in the two species in the light period.