Tropospheric bromine chemistry and its impacts on ozone: A model study

Abstract

[1] An off-line three-dimensional tropospheric chemical transport model, parallelTropospheric Off-Line Model of Chemistry and Transport (p-TOMCAT), has been extended by incorporating a detailed bromine chemistry scheme that contains gas-phase reactions and heterogeneous reactions on both cloud particles and background aerosols. Bromine emission from bromocarbon photo-oxidation and from sea-salt bromine depletion and bromine removal through dry and wet deposition are included. Using this model, tropospheric bromine chemistry and ozone budgets are studied. The zonal mean of the inorganic gas-phase bromine compounds (Br x ) is calculated to be high (4-8 pptv) in the lower troposphere of the midlatitudes to high latitudes in each hemisphere, with decreasing trends with altitude (down to $2-3 pptv in the upper troposphere). The lowest Br x (<2 pptv) is over low latitudes, corresponding to small sea-salt Br emission and a high rate of precipitation scavenging. A mean lifetime of $5 days is obtained for the tropospheric Br x . Sea-salt emission plays the dominant role in total Br x in the lower troposphere while organic Br-containing compounds are important in upper layers. High daytime BrO mixing ratios (>1 pptv) are found over the high-latitude ocean surface, corresponding to high tropospheric column BrO values of up to 1.6 Â 10 13 molecules/cm 2 in the monthly mean. The addition of bromine chemistry to the model leads to a reduction in tropospheric ozone amounts by 4-6% in the Northern Hemisphere and up to $30% in the Southern Hemisphere high latitudes. The net ozone loss depends not only on total Br x , but also on solar irradiance, especially at high latitudes. The hydrolysis reaction of bromine nitrate, which occurs on cloud and aerosol surfaces (BrONO 2 + H 2 O aq ! HOBr + HNO 3 ), has a significant influence on ozone chemistry through its effect on NO x as well as on reactive BrO and Br.

Earth System Chemistry integrated Modelling (ESCiMo) with the Modular Earth Submodel System (MESSy) version 2.51

“…Following Yang et al (2005), we assume that 50 % of the bromide is released to the gas phase (leading to an additional factor of 0.5). The resulting time series of oceanic Br emissions is shown in Fig.…”

Global lifetime of elemental mercury against oxidation by atomic bromine in the free troposphere

“…Lin et al [2006] suggested that Hg-Br chemistry is also significant in the upper troposphere. We present here a quantitative analysis of the global lifetime of Hg 0 against oxidation by tropospheric Br by combining the mechanism of Goodsite et al [2004] with Br concentrations from a global 3-D simulation of tropospheric bromine chemistry [Yang et al, 2005] as well as updated kinetic data. We find that oxidation by Br in the middle and upper troposphere could be an important sink for Hg 0 , and that the mechanism yields an atmospheric lifetime of Hg 0 consistent with observational constraints.…”

“…However, oxidation by Br atoms is fast [Calvert and Lindberg, 2004;Goodsite et al, 2004]. Rapid chemical cycling between BrO and Br through BrO photolysis, selfreaction, and reaction with NO, balanced by Br oxidation by O 3 , maintains Br:BrO molar ratios of 0.01 -2 in the daytime troposphere [Platt and Janssen, 1995;Yang et al, 2005].…”

“…Balloon measurements in the northern mid-latitudes and tropics give independent evidence for 0.5-2 pptv BrO in the troposphere [Fitzenberger et al, 2000;Pundt et al, 2002;Van Roozendael et al, 2002]. Tropospheric sources include activation from sea salt; oxidation and photolysis of bromocarbons; transport from the stratosphere; and recycling from reservoir species (Br 2 , HOBr, BrNO 2 , BrONO 2 , HBr) by homogeneous and heterogeneous processes [von Glasow et al, 2002;Platt and Honninger, 2003;Yang et al, 2005;Salawitch, 2006].…”

Estimating Uncertainty in Global Mercury Emission Source and Deposition Receptor Relationships

“…As there remains some uncertainty concerning atmospheric Hg oxidation process [35][36][37], simulations were also run including an oxidation mechanism based on bromine, with oxidant fields from the p-Tomcat model [38,39].…”