Author:
Xu Rongshuang,Lam Hoi Ki,Wilson Kevin R.,Davies James F.,Song Mijung,Li Wentao,Tse Ying-Lung Steve,Chan Man Nin
Abstract
Abstract. The 2-methyltetrols have been widely chosen as chemical tracers for
isoprene-derived secondary organic aerosols. While they are often assumed to
be relatively unreactive, a laboratory study reported that pure erythritol
particles (an analog of 2-methyltetrols) can be heterogeneously oxidized by
gas-phase OH radicals at a significant rate. This might question the
efficacy of these compounds as tracers in aerosol source-apportionment
studies. Additional uncertainty could arise as organic compounds and
inorganic salts often coexist in atmospheric particles. To gain more
insights into the chemical stability of 2-methyltetrols in atmospheric
particles, this study investigates the heterogeneous OH oxidation of pure
erythritol particles and particles containing erythritol and ammonium
sulfate (AS) at different dry inorganic-to-organic mass ratios (IOR) in an
aerosol flow tube reactor at a high relative humidity of 85 %. The same
reaction products are formed upon heterogenous OH oxidation of erythritol
and erythritol–AS particles, suggesting that the reaction pathways are not
strongly affected by the presence and amount of AS. On the other hand, the
effective OH uptake coefficient, γeff, is found to decrease by
about a factor of ∼20 from 0.45±0.025 to 0.02±0.001 when the relative abundance of AS increases and the IOR increases from
0.0 to 5.0. One likely explanation is the presence of dissolved ions slows
down the reaction rates by decreasing the surface concentration of
erythritol and reducing the frequency of collision between erythritol and
gas-phase OH radicals at the particle surface. Hence, the heterogeneous OH
reactivity of erythritol and likely 2-methyltetrols in atmospheric particles
would be slower than previously thought when the salts are present. Given
2-methyltetrols often coexist with a significant amount of AS in many
environments, where ambient IOR can vary from ∼1.89 to
∼250, our kinetic data would suggest that 2-methyltetrols in
atmospheric particles are likely chemically stable against heterogeneous OH
oxidation under humid conditions.
Cited by
11 articles.
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