Kinetics of the BrO + NO2 association reaction. Temperature and pressure dependence in the falloff regime

Thorn, R. P.; Daykin, Edward; Wine, P. H.

doi:10.1002/kin.550250703

Cited by 20 publications

(30 citation statements)

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“…Although gas-phase halogen chemistry in the Arctic has now been studied for several decades (Impey et al, 1997;Hausmann and Platt, 1994;Barrie et al, 1988), few studies have examined the effect of atmospheric NO x on these halogen chemical cycles. Model studies have shown that NO x can react with halogen radicals through several reactions (as shown in Reactions R8-R12), to produce inorganic halogen nitrates or nitryl halides, which can, in turn, activate further halogen chemistry through heterogeneous reactions (Cao et al, 2014;Toyota et al, 2013;Morin et al, 2007Morin et al, , 2012Thomas et al, 2012;Evans et al, 2003;Rossi, 1999, 2002;von Glasow et al, 2002;Thorn et al, 1993), and thereby alter gas phase halogen radical reaction pathways.…”

Section: Introductionmentioning

confidence: 99%

The NOx dependence of bromine chemistry in the Arctic atmospheric boundary layer

et al. 2015

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Abstract. Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean – Atmosphere – Sea Ice – Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase halogen radical-based depletion of ozone, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.

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Section: Introductionmentioning

confidence: 99%

The NOx dependence of bromine chemistry in the Arctic atmospheric boundary layer

et al. 2015

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“…BrO + NO 2 f BrONO 2 (7) BrONO 2 + hν f Br + NO 3 (8) NO 3 + hν f NO + O 2 (9) NO + O 3 f NO 2 + O 2 (10) net: 2O 3 f 3O 2…”

Section: Introductionunclassified

Rate Coefficients for the Thermal Decomposition of BrONO₂and the Heat of Formation of BrONO₂

and

Tyndall

1996

J. Phys. Chem.

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Rate coefficients (k -7 ) for the thermal decomposition of bromine nitrate, BrONO 2 + M f BrO + NO 2 + M, have been obtained at temperatures between 320 and 340 K and pressures between 100 and 1000 Torr. These data are combined with recommended values for the reverse reaction to obtain an equilibrium constant for the reaction pair, K P,7 ) 5.44 × 10 -9 exp(14192/T) atm -1 , and a heat of reaction for the thermal dissociation of 28.2 ( 1.5 kcal/mol at 298 K. This reaction enthalpy is used in conjunction with literature data to arrive at a consistent set of ∆H f°( 298 K) data for BrONO 2 (10.1 ( 2.0 kcal/mol), BrO (30.4 ( 2.0 kcal/mol), HOBr (-14.1 ( 2.0 kcal/mol), and Br 2 O (27.3 ( 2.0 kcal/mol). Additional measurements were made to determine the rate coefficient for Br atom reaction with BrONO 2 (k 11 ) relative to the rate coefficient for its reaction with CH 3 CHO (k 12 ) at 298 K: k 11 /k 12 ) 12.5 ( 0.6. This relative rate measurement yields a rate coefficient of (4.9 ( 1.5) × 10 -11 cm 3 molecule -1 s -1 for k 11 , using the currently recommended value for k 12 . Approximate rate constants for reaction of NO (reaction 17) and BrNO (reaction 19) with BrONO 2 were also obtained: k 17 ) 3 × 10 -19 cm 3 molecule -1 s -1 , k 19 > 1 × 10 -16 cm 3 molecule -1 s -1 . IntroductionThe role of bromine in the destruction of ozone in the earth's stratosphere is now well characterized. 1-5 Free bromine atoms are released from the destruction of source compounds such as CH 3 Br and the halons and participate in catalytic ozone depleting cycles such as the following:

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“…Because BrONO2 has a relatively short lifetime, the BrONO2 concentration responds very rapidly to any change in NO2, as occurs, for example, due to denoxification on surfaces. The rate recommended for the formation of BrONO2 by DeMote et al[1992] is based on kinetic measurements made byThorn et al [1993] andDanis et al [1990]. These measurements were made at over 260 K and so quite large temperature extrapolations are involved when considering lower stratospheric temperatures.…”

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confidence: 99%

Gas phase atmospheric bromine photochemistry

Lary¹

1996

J. Geophys. Res.

126

103

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This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate-limiting step. The chain effectiveness enables a fair comparison of different catalytic cycles involving species which have very different concentrations. This analysis clearly shows that below 25 km the BrO/C10 and BrO/HO2 cycles are among the most important ozone destruction cycles. Introduction This paper is a review of gas phase bromine photochemistry and is intended to complement the companion paper [Lary et al. this issue] which considers heterogeneous bromine photochemistry. Bromine enters the atmosphere by a variety of natural and anthropogenic processes. The three main bromine source gases that can reach the stratosphere (i.e. are not removed from the troposphere by rainout, reaction with OH or photolysis) are CH3Br, CBrC1F2 and CBrF3. The most abundant of these source gases is methyl bromide (CH3Br) whose natural source is mainly due to oceanic biological processes. In these, mainly algal, processes CH3Br is formed together with other species such as CH2Br2, CHBr3, CH2BrC1 and CHBrC12. The oceans are a significant natural source of CH3Br [Singh et al., 1983]. Measurements of larger tropospheric northern henrisphere mixing ratios suggest a large land based northern hemisphere source of CH3Br which could well be anthropogenic [Penkett et al., 1985; Reeves and Penkett, 1993]. The main industrial use of CH3Br is as a fumigant, particularly for the treatment of soils. CH3Br is also used in quarantine treatments and in insect and rodent control. The wide variety of CH3Br measurements made over the last decade in different parts of the world [Berg et al., 1984; Rasmussen and Khalil, 1984; Penkett et al., 1985; Cicerone et al., 1988; Fabian et al., 1994; Kaye et al., 1994] suggest that the natural background concentration of CH3Br in the troposphere is approximately 10 pptv. CH3Br concentrations of up to 15 pptv have also been observed; these are likely to reflect the effect of anthropogenic sources. The first study of atmospheric bromine chemistry was by Yung et al. [1980], who pointed to the general importance of atmospheric bromine chemistry and to the catalytic destruction of ozone by the C10/BrO cycle. Bromine has been shown to play a significant role (m20%) in the formation of the ozone hole in polar stratospheric regions [McElroy et al., 1986]. The contributions to ozone loss from bromine reactions are largest below about 20 km [e.g., Poulet et al., 1992; Garcia and Solomon, 1994]. Bromine plays an important role in stratospheric ozone depletion despite being much less abundant than chlorine [World Meteorological Organisation ( WMO), 1992].When atmospheric bromine chemistry is compared to chlorine chemistry, it can be seen ...

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Kinetics of the BrO + NO₂ association reaction. Temperature and pressure dependence in the falloff regime

Cited by 20 publications

References 20 publications

The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer

The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer

Rate Coefficients for the Thermal Decomposition of BrONO₂and the Heat of Formation of BrONO₂

Gas phase atmospheric bromine photochemistry

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Kinetics of the BrO + NO2 association reaction. Temperature and pressure dependence in the falloff regime

Cited by 20 publications

References 20 publications

The NO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; dependence of bromine chemistry in the Arctic atmospheric boundary layer

The NO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; dependence of bromine chemistry in the Arctic atmospheric boundary layer

Rate Coefficients for the Thermal Decomposition of BrONO2and the Heat of Formation of BrONO2

Gas phase atmospheric bromine photochemistry

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Kinetics of the BrO + NO₂ association reaction. Temperature and pressure dependence in the falloff regime

The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer

The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer

Rate Coefficients for the Thermal Decomposition of BrONO₂and the Heat of Formation of BrONO₂