Organic and inorganic bromine compounds and their composition in the Arctic troposphere during polar sunrise

Abstract

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 O3 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 O3 depletion periods. InorgBr appeared to be the sum of HBr, HOBr, and Br2. (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 CHBr3 with levels 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 for 23%, while the other four species amounted to less than 5% on average. CH3Br (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 O3 depletion events. (4) CHBr3, CHClBr2, and CHCl2Br were significantly correlated. The ratio CHClBr2/CHBr3 decreased linearly with increasing In(CHBr3), with a steeper decrease after sunrise than before. The decreases suggest different rates of destruction with CHBr3 having a larger rate constant than CHClBr2. A similar relationship existed between the ratio CHCl2Br/CHClBr2 and the In(CHClBr2), but the dark period slope was near zero, indicating a greater difference in rates in the two species in the light period.

Short-lived brominated hydrocarbons – observations in the source regions and the tropical tropopause layer

“…We find a high correlation of CHBrCl 2 to CHBr 3 (with R 2 = 0.87), while for CH 2 BrCl only a weak relationship to CHBr 3 is indicated (R 2 = 0.42). A study in the Arctic boundary layer at Alert (CAN) also revealed a significant correlation of CHBrCl 2 to CHBr 3 and CHBr 2 Cl (Li et al, 1994). Corresponding analyses of the UM data sets for CHBr 3 , CH 2 Br 2 and CHBr 2 Cl confirm the above findings of a strong linear relationship between the three species.…”

“…O'Brien et al, 2009;Yokouchi et al, 2005), indicating that these substances share the same sources. Li et al (1994) suggested the additional possibility that reactions of CHBr 3 with seawater chlorine could produce CHBr 2 Cl and thus account for the observed correlations to this compound.…”

Marine organohalogens in the atmosphere over the Atlantic and Southern Oceans

“…This approach is similar to that taken by Li et al [1994] except that it removes the need for the product (k 1 À k 2 )[X]Át to be very small. We neglect diffusion/transport in this treatment, assuming such terms would cancel if their rates were equivalent for both compounds.…”

“…The correlations have been attributed to identical or similar pathways of either biological production, that is, macroalgal metabolism, and/or of chemical production, for example, S N 2 chloride attack on CHBr 3 to form CHBr 2 Cl [Class and Ballschmiter, 1988;Moore and Tokarczyk, 1993]. Li et al [1994] used the relationships observed in air between CHBr 2 Cl, CHBrCl 2 , and CHBr 3 at Alert, Canada, to infer differences in chemical reactivity. They assumed that CHBr 3 , CHBr 2 Cl, and CHBrCl 2 reacted with a common oxidant X with rate coefficients k 1 , k 2 , and k 3 , respectively, and used a simple Lagrangian approach to show that the slope b 1 of the ratio CHBr 2 Cl/CHBr 3 versus ln [CHBr 3 ] was related to the difference in the values of k 1 and k 2 , as follows: time since leaving the source area.…”

A Study on the Production and Emission of Marine-Derived Volatile Halocarbons

“…After transport to the laboratory, the samples were analyzed using a pre-concentration/capillary gas chromatograph-mass spectrometry (GC-MS). Details of the analytical procedures are described elsewhere (Li et al 1994; Yokouchi et al 1997).…”