A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer K. Toyota1,*, Y. Kanaya1, M. Takahashi1,2, and H. Akimoto1 1Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 3713-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan 2Center for Climate System Research, The University of Tokyo, Tokyo 153-8904, Japan *now at: Dept. of Earth and Space Science and Engineering, York Univ., 4700 Keele Street, Toronto, Ontario M3J 1P3 Canada
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 description 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,
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 forming 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 a 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.
The reaction between Br atoms and C2H2
is shown to be unimportant for determining the degree of bromine activation
in the remote MBL.
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.
Citation: Toyota, K., Kanaya, Y., Takahashi, M., and Akimoto, H.: A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer, Atmos. Chem. Phys., 4, 1961-1987, doi:10.5194/acp-4-1961-2004, 2004.