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 several individual organic bromine species were measured in the troposphere during the Polar Sunrise Experiment at Alert, Northwest Territories, Canada, during January 18 to April 21, 1992. The measurements revealed the following: (1) Particle bromide increased gradually from about 10 ng (Br) m −3 during the dark period to >20 ng(Br) m −3 during the light period, with a marked peak of 120 ng(Br) m −3 corresponding to a strong O 3 depletion event. (2) Inorganic gaseous bromine (InorgBr) was about 60 ng(Br) m −3 during the dark period and relatively constant. A major peak, up to 280 ng(Br) m −3 , before sunrise accompanied a similar peak in the total organic bromine. These episodes originated in the free troposphere over Greenland. After sunrise the peaks in InorgBr corresponded to O 3 depletion periods. InorgBr appeared to be the sum of HBr, HOBr, and Br 2 . (3) Total organic bromine was relatively constant before sunrise at 100 ng(Br) m −3 but more variable afterward, up to 280 ng(Br) m −3 . Individual species include CHBr 3 with levels of 7–60 ng(Br) m −3 . CH 2 Br 2 , CH 2 ClBr, CHClBr 2 , and CHCl 2 Br levels were lower at 0.5–7.5 ng(Br) m −3 . CHBr 3 was the largest contributor to total organic bromine of the five species, on average accounting for 23%, while the other four species amounted to less than 5% on average. CH 3 Br (not measured) should contribute 44% of total organic bromine assuming a concentration of 40 ng(Br) m −3 (11 parts per trillion by volume). The remaining contribution was probably from ”missing„ species which were episodically dominant after sunrise with concentrations 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) CHBr 3 , CHClBr 2 , and CHCl 2 Br were significantly correlated. The ratio CHClBr 2 /CHBr 3 decreased linearly with increasing In(CHBr 3 ), with a steeper decrease after sunrise than before. The decreases suggest different rates of destruction with CHBr 3 having a larger rate constant than CHClBr 2 . A similar relationship existed between the ratio CHCl 2 Br/CHClBr 2 and the In(CHClBr 2 ), but the dark period slope was near zero, indicating a greater difference in rates in the two species in the light period.