AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
The Effects of Long-Wavelength UV Light on Photochemically Generated Organic Aerosols
Iftikhar Awan, W. SEAN MCGIVERN, National Institute of Standards and Technology
Abstract Number: 514 Working Group: Aerosol Chemistry
Abstract Recent work in our group has shown that photochemistry of peroxy radicals affects product distributions in organic aerosols formed from photochemically generated alkyl radicals at 254 nm. In this study, we utilize a photochemical flow reactor to examine the effects of longer-wavelength UV light on the particles formed. The reaction is initiated with a short initial exposure of 1-iodooctane to 254 nm light in air at room temperature, which forms octyl radicals that rapidly react with ambient oxygen to form octylperoxy radicals. This short-wavelength region is followed by a long region of the cell that is either nonirradiated or irradiated with (311 ± 5) nm light. In the absence of the 311 nm light, a small number of particles are formed, but we observe a substantial increase in particle size and mass in the presence of the longer wavelength light. We utilize a previously developed derivatization methodology coupled with HPLC/UV-Vis and MS-MS to examine the changes in the functional group distributions of particles generated using the (254 nm/nonirradiated) and (254 nm/311 nm) combinations. Substantial differences in the complexity of the resulting particle compositions have been observed, which we attribute to photochemistry of the peroxy radicals at the longer wavelengths, a wavelength region for which little peroxy radical absorption data is available. Utilizing a lumped chemical kinetics model previously applied to the single wavelength system, we demonstrate how such compositional variations can be manifested and consider possible atmospheric implications of peroxy radical absorption at longer wavelengths.