OH-Initiated Oxidation of m-Xylene on Black Carbon Aging.
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Laboratory experiments are conducted to investigate aging of size-classified black carbon (BC) particles from OH-initiated oxidation of m-xylene. The variations in the particle size, mass, effective density, morphology, optical properties, hygroscopicity, and activation as cloud condensation nuclei (CCN) are simultaneously measured by a suite of aerosol instruments, when BC particles are exposed to the oxidation products of the OH-m-xylene reactions. The BC aging is governed by the coating thickness (rve), which is correlated to the reaction time and initial concentrations of m-xylene and NOx. For an initial diameter of 100 nm and rve = 44 nm, the particle size and mass increase by a factor of 1.5 and 10.4, respectively, and the effective density increases from 0.43 to 1.45 g cm(-3) due to organic coating and collapsing of the BC core. The BC particles are fully converted from a highly fractal to nearly spherical morphology for rve = 30 nm. The scattering, absorption, and single scattering albedo of BC particles are enhanced accordingly with organic coating. The critical supersaturation for CCN activation is reduced to 0.1% with rve = 44 nm. The results imply that the oxidation of m-xylene exhibits larger impacts in modifying the BC particle properties than those for the OH-initiated oxidation of isoprene and toluene.
