We report the first measurements of both particulate and gas phase bromine in the Arctic troposphere. Data from continuous sampling of the Arctic aerosol over a period of 4 years (1976)(1977)(1978)(1979)(1980) indicate that the bromine content in the aerosol averages 6 + 4 ngBr/SCM (5 + 3 pptm Br) for 9 months of every year. During the 3-month period between February 15 and May 15, however, we observed an annual sharp maximum in particulate bromine with levels exceeding 100 ngBr/SCM (82 pptm Br). The Arctic aerosol showed no bromine enrichment relative to seawater except for this 3 month peak period. During the bromine maximum, enrichment factors reached 40 with average values near 10. Calculations of the amount of excess bromine in the Arctic aerosol showed that over 90% of the-peak bromine had an origin other than from direct bulk seawater injection. Total levels of gas phase bromine in the Arctic troposphere found during the peak aerosol period averaged 422 + 48 ngBr/SCM (118 + 14 pptv). Total bromine content during this period averaged 474 + 49 ngBr/SCM with gas-to-particle ratios ranging from 7 to 18. A measurement under nonpeak conditions showed total bromine levels at < 25 ngBr/SCM. The possibility that local contamination contributed to the seasonal development of the 3-month bromine peak was carefully considered and ruled out. Elevated particulate bromine levels, with peak values ranging from 22 to 30 ngBr/SCM, were also found at Ny-,&lesund, Spitsbergen (Norway). The apparent seasonal nature of this bromine peak suggests that the large bromine maximum observed at Barrow is not an isolated or unique phenomenon characteristic of that sampling location. The level of total bromine in the Arctic troposphere during the 3-month maximum was found to exceed all measurements made in the natural troposphere by up to an order of magnitude. When compared to the natural background levels, the results presented in this paper indicate that the bromine concentrations in the Arctic troposphere are the highest found anywhere in the world. Moyers and Duce, 1972a; Lovelock, 1975; Rahn et al., 1976; Singh et al., 1977, 1983-1. Smaller anthropogenic sources have been identified and include the production of (1) CH3Br, used as a soil fumigant; (2) tetrabromobisphenol-A, used as a flame retardant in printed circuit boards; (3) CF3Br, used as a fire retardant and refrigerant; and (4) C2H,•Br2, together with assorted brominated additives, used in automotive and other fossil fuels. The relative intensities of the various global sources of atmospheric bromine compounds, however, remain largely unknown. In addition, recent stratospheric measurements [-e.g., Sedlacek et al., 1979; Berg et al., 1980-1 have raised the possibility that one or more additional sources for atmospheric bromine near the earth's surface remain to be identified.

A large discrepancy exists among recent estimates of the primary quantum efficiencies (ϕ1) of nitrogen dioxide photodecomposition, NO2 + hν → NO + O(3P), in the wavelength range from 374 to 396 nm. To resolve this problem, quantum yields of formation of NO, O2, and NO2 loss have been measured for NO2 vapor at low pressures (0.13–0.30 torr) irradiated at selected wavelengths (334.1–404.3 nm) and temperatures (273–370 K). From these data, estimates of ϕ1 were derived which confirm the previous findings of Jones and Bayes (1973b): ϕ1 increases rapidly from near zero at 424 nm to near unity for excitation at λ < 394 nm. The temperature and wavelength dependences of ϕ1 appear to be in qualitative accord with the simple theory of Pitts et al. (1964) that the energy deficiency for photodissociation of NO2 excited at λ > 397.9 nm (λdiss) is made up in large part from the rotational and vibrational energy of the NO2 molecules. Recommended values for ϕ1 based upon a review of these data and estimates made over a period of 58 years, are given as a function of wavelength.

The photodecomposition of acrolein in dilute mixtures of synthetic air (24-760 Torr) has been studied with excitation at 313 or 334 nm. The decomposition of excited acrolein is very inefficient at high air pressures (0d =* 6.5 X 10~3 at 1 atm, 313 nm) but increases with decreasing pressures (0d =* 8.1 X 10~2 at 26 Torr). The quantum yields of acrolein loss and the observed products, C2H4, CO, C02, CH20, (HCO)2, and CH3OH, are elucidated by the primary processes I-V: CH2=CHCHO(S, or T,) -C2H4 + CO (I); -CH2=CH + HCO (II); -CH3CH(S) + CO (III); -CH3CH(T) + CO (IV); -CH2=CHCO + H (V). New evidence is given for the mechanism of the reactions of the vinyl radical with 02: CH2=CH + 02 -(CH2=CH02) -OCH2CHO; OCH2CHO -* CH20 + HCO (4); OCH2CHO + 02 -* (HCO)2 + H02 (5); the data suggest ks/k4 ^6 x 10'19 cm3 molecule'1 11. From computer simulations of the sequence of reactions describing acrolein decay, it is estimated that, at low air pressures (26 Torr), m + 0IV > 4>i> 0v -nl in 1 atm of air, 0v -> 0ii > 0m + 0iv > 0i-J values for acrolein photodecomposition in the troposphere are derived from the data.

Abstract. Measurements are reported of four gas-phase, brominated organic species found in the Arctic atmosphere during March and April 1983. Volume mixing ratios for CH3Br, CH2BrCH2Br, CHBr3, and CH2Br2 were determined by GC/MS analysis from samples taken Arctic wide, including at the geographic North Pole and during a tropopause folding event over Baffin Bay near Thule, Greenland. Methyl bromide mixing ratios were reasonably constant at 11 + 4 pptv while the other three brominated organics showed a high degree of variability. Bromoform (2 to 46 pptv) was found to be the dominant contributor to gaseous organic bromine to the Arctic troposphere at 38 + 10% followed by CH2Br2 (3 to 60 pptv) at 29 + 6%. Both CH3Br and CH2BrCH2Br (1 to 37 pptv) reservoirs contained less than 20% of the organically bound bromine. Stratospheric samples, taken during a tropopause folding event, showed mixing ratios for all four species at levels high enough to support a stratospheric total volume mixing ratio of 249 pptv Br (888 ngBr/SCM).

Recent studies of the oxidation of sulfur dioxide by hydrogen peroxide in solution indicate that this process may be the dominant mechanism for the conversion of SO2 to H2SO4 in cloud water where the typical pH is less than 5.5. In the interpretation of theoretical calculations and previous hydrogen peroxide measurements it has generally been assumed that the limiting factor in the acidification of precipitation is the amount of gas‐phase H2O2 available to the cloud‐precipitation system. Field observations of H2O2 during Acid Precipitation Experiment (APEX) missions revealed that in addition to vapor phase H2O2, there were present one or more atmospheric constituents which produced H2O2 in the aqueous phase, and there were other species which consumed the collected H2O2 vapor. We report here an investigation of these phenomena undertaken to ensure that the instrumentation was responding to H2O2 alone and to identify the species which interfered in the aqueous collection and measurement of H2O2 vapor. Our results showed that (1) the H2O2 found within the collectors frequently exceeded the amount initially present as vapor, (2) the species which produced H2O2 were relatively insoluble, (3) NO2 did not enhance H2O2 formation, (4) O3 enhanced H2O2 formation, and (5) SO2 depleted aqueous H2O2. The amount of aqueous H2O2 lost when SO2 vapor was added to ambient air was larger than expected. The results of these experiments have important implications for cloud water chemistry. If the processes occurring within the impinger can be extrapolated to droplets, the amount of H2O2 available for SO2 oxidation would not be limited by the amount of H2O2 vapor in precloud air but would also depend upon the concentration of the precursors capable of generating H2O2 in droplets.