3:00 PM - 3:15 PM
[AAS21-23] Impact of oxidation processes on optical properties of isoprene SOAs
Keywords:Isoprene, Secondary organic aerosol, Aerosol optical properties, Complex refractive index, Brown carbon
The SOAs were generated in a 6 m3 Teflon coated stainless steel photochemical smog chamber. In the OH oxidation experiments, the reaction mixture of isoprene and NO in the presence or absence of SO2 (sulfuric acid precursor) was continuously irradiated by UV light after the addition of a small amount of methyl nitrite as a source of OH radicals. In the ozonolysis experiments, isoprene was reacted with O3 in the presence or absence of CO (OH scavenger) and SO2. In the NO3 oxidation experiments, ozone was added to the mixture of isoprene and NO2 in the presence of SO2. The optical properties of the SOAs were measured by two photoacoustic spectrometers (PASS-3 and PAX, absorption and scattering at 375, 405, 532, 781 nm) and a custom-built cavity ring-down spectrometer (CRDS, extinction at 532 nm). Chemical properties of aerosols were also measured by an Aerodyne aerosol mass spectrometer (ToF-AMS). The size distributions of SOAs were measured by a scanning mobility particle sizer (SMPS).
Absorption, scattering, and extinction efficiencies of SOAs are calculated by dividing the absorption, scattering, and extinction coefficients by total mobility cross sections measured with the SMPS. The RI of the SOAs is determined by comparing the size parameter dependence of extinction, scattering, and absorption efficiencies with Mie theory. The significant imaginary part values of RI at 405 and 532 nm are obtained for the SOAs generated in the OH oxidation of isoprene in the presence of SO2, while the imaginary part values are negligible for the SOAs generated in the ozonolysis (in the presence of OH scavenger) and NO3 oxidation of isoprene. In the presentation, relationship with chemical properties and the atmospheric implications of the results will also be discussed.