1 research outputs found
OH-Initiated Heterogeneous Oxidation of Internally-Mixed Squalane and Secondary Organic Aerosol
Recent work has established that
secondary organic aerosol (SOA)
can exist as an amorphous solid, leading to various suggestions that
the addition of SOA coatings to existing particles will decrease the
reactivity of those particles toward common atmospheric oxidants.
Experimental evidence suggests that O<sub>3</sub> is unable to physically
diffuse through an exterior semisolid or solid layer thus inhibiting
reaction with the core. The extent to which this suppression in reactivity
occurs for OH has not been established, nor has this been demonstrated
specifically for SOA. Here, measurements of the influence of adding
a coating of α-pinene+O<sub>3</sub> SOA onto squalane particles
on the OH-initiated heterogeneous oxidation rate are reported. The
chemical composition of the oxidized internally mixed particles was
monitored online using a vacuum ultraviolet-aerosol mass spectrometer.
Variations in the squalane oxidation rate with particle composition
were quantified by measurement of the effective uptake coefficient,
γ<sub>eff</sub>, which is the loss rate of a species relative
to the oxidant-particle collision rate. Instead of decreasing, the
measured γ<sub>eff</sub> increased continuously as the SOA coating
thickness increased, by a factor of ∼2 for a SOA coating thickness
of 42 nm (corresponding to ca. two-thirds of the particle mass). These
results indicate that heterogeneous oxidation of ambient aerosol by
OH radicals is not inhibited by SOA coatings, and further that condensed
phase chemical pathways and rates in organic particles depend importantly
on composition