Modeling the transport of very short-lived substances into the tropical upper troposphere and lower stratosphere

Abstract

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.

Deriving an atmospheric budget of total organic bromine using airborne in situ measurements from the western Pacific area during SHIVA

“…Aschmann et al, 2009;Hossaini et al, 2010;Liang et al, 2010;Tegtmeier et al, 2012). In contrast to longer-lived source gases, measurements of these VSLS from the planetary boundary layer can therefore not be used to constrain the amount of halogen input into the stratosphere.…”

Finding the missing stratospheric Br<sub>y</sub>: a global modeling study of CHBr<sub>3</sub> and CH<sub>2</sub>Br<sub>2</sub>

“…Earlier studies by Dvortsov et al (1999) and Nielsen and Douglass (2001) calculated a maximum of 1.8 pptv and 1.1 pptv Br y , respectively, in the stratosphere from bromoform (CHBr 3 ). More recent modeling studies by Kerkweg et al (2008), Gettelman et al (2009), Aschmann et al (2009) and Hossaini et al (2010) suggested that CHBr 3 and CH 2 Br 2 contribute significant amounts of reactive bromine to the lower stratosphere, with the calculated contribution varying between ∼2-3 pptv among individual studies. One exception is the modeling study by Warwick et al (2006) which presented a detailed emissionbased modeling analysis of all five major VSL oceanic bromocarbons, including CHBr 3 , dibromomethane (CH 2 Br 2 ), bromodichloromethane (CHBrCl 2 ), dibromochloromethane (CHBr 2 Cl), and bromochloromethane (CH 2 BrCl).…”

“…The broad spatial and temporal coverage of these measurements lends more confidence in the robustness of our derived results. Secondly, unlike many previous modeling studies that assume a constant wash-out lifetime of Br y (10-days in Dvortsov et al, 1999, Nielsen andDouglass, 2001;Warwick et al, 2006;Hossaini et al, 2010; 0 to indefinite days in Sinnhuber and Folkins, 2005) or a relative simple washout process (Aschmann et al, 2009), we implement a detailed wet deposition scheme that includes scavenging in convective updrafts and rainout/washout in large-scale precipitation. This is to assure a more realistic representation of the impact of large-scale/convective transport on the highly soluble Br y .…”

“…As a result, the rate of wet scavenging of Br y , which depends on the mechanism of dehydration, is highly uncertain. Model sensitivity studies suggest that the contribution of CHBr 3 to stratospheric bromine range from 0.5-1.6 pptv when Br y is removed completely in convective updraft to ∼3 pptv assuming no washout (Sinnhuber and Folkins, 2005;Aschmann et al, 2009).…”

Can Seaweed Farming in the Tropics Contribute to Climate Change Through Emission of Short-Lived Halocarbons?

“…It has been shown that halogens in the form of very short-lived halocarbons (VSLH) and volatile organic compounds (VOC) may affect the oxidizing capacity of the troposphere. These compounds when transported up into the troposphere and stratosphere, undergo photolysis and the halogens which are released, result in ozone depletion in the stratosphere and influence climate change (Aschmann et al, 2009). Examples are brominated and chlorinated halocarbons which indirectly affect temperature (Forster and Joshi, 2005) by ozone depletion.…”