A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

Abstract

Abstract. A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit treatment of oxidative degradation of up to C3-hydrocarbons CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in the formation of halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. On the other hand, the reaction between Br atoms and C2H2 is unimportant for determining the degree of bromine activation in the remote MBL. It is suggested that peroxyacetic acid formed via CH3CHO oxidation is one of the important chemical agents for triggering autocatalytic halogen release from sea-salt aerosols. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

Recent Trends in Stratospheric Chlorine From Very Short‐Lived Substances

“… and are not phosgene forming channels as CHCl 2 O is expected to decompose to CHClO + Cl (e.g., Catoire et al, ). The atmospheric fate of CHClO is poorly known but sinks are expected to include atmospheric removal via heterogeneous and multiphase deposition processes (e.g., Ko et al, ; Toyota et al, ).…”

Influence of nitrate radical on the oxidation of dimethyl sulfide in a polluted marine environment

“…The most important oxidants for DMS are hydroxyl (OH) and nitrate (NO 3 ) radicals. Halogen compounds, especially Cl atoms and BrO radicals, have also recently been suggested as oxidants for DMS in the marine environment [ Toyota et al , 2004; Wingenter et al , 2005; Barnes et al , 2006]. By contrast, DMS oxidation by O 3 in the gas phase is thought to be unimportant, although this conclusion is based on only a small number of laboratory studies [ Martinez and Herron , 1978].…”

“…There have been numerous laboratory and theoretical investigations of the mechanism for gas phase DMS oxidation, establishing OH and NO 3 as the main oxidants and leading to various products, which will be discussed later [ Hynes et al , 1986; Yin et al , 1990; Jensen et al , 1992; Le Bras et al , 1993; Turnipseed et al , 1996; Capaldo and Pandis , 1997; Ravishankara et al , 1997; Davis et al , 1999; Arsene et al , 2001; Williams et al , 2001; Lucas and Prinn , 2002, 2005]. Several recent studies have pointed out that Cl atoms and BrO radicals could play an important role as DMS oxidants [ Keene et al , 1996; Knipping et al , 2000; Sciare et al , 2000; Toyota et al , 2004; Dyke et al , 2005; Wingenter et al , 2005; Barnes et al , 2006]. The subsequent reactions, yields, and end products arising from each of the possible oxidants OH, NO 3 , and halogens, are important to the impact of DMS on the global source for nss aerosols.…”

Tropospheric Halogen Chemistry

“…During daytime, the cloudy part of the MBL is dynamically decoupled from the subcloud layer, which confines the active halogen chemistry to the subcloud layers. Toyota et al (2004) have suggested that organic bromine may form from inorganic bromine compounds in the MBL. The diurnal variation of gas-and aqueous-phase bromine is reversed compared to the cloud-free MBL, which might help resolve discrepancies in the diurnal variations between previous model studies and field experiments (e.g., Rancher and Kritz, 1980;Sander et al, 2003a;Pszenny et al, 2004).…”