AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Chemical Characteristics of Haze Particles Generated from the VUV Photolysis of C2 Hydrocarbons Under Oxygen-Free Conditions
JONATHAN FRANKLIN, Jesse Kroll, MIT
Abstract Number: 201 Working Group: Extraterrestrial Aerosols: from Mars to Titan and Beyond
Abstract The atmospheres of some planetary bodies (such as Saturn’s moon Titan) are characterized by the presence of organic haze particles, formed by irradiation of simple organic species in the absence of oxygen. In this study, simple organic haze particles were generated in the laboratory from the photolysis of a series of C2 hydrocarbons and chemically characterized using an Aerodyne High-Resolution Time-of-Flight Soot-Particle Aerosol Mass Spectrometer (SP-AMS). Particles were formed via photolysis of ethane (C2H6), ethylene (C2H4), or acetylene (C2H2) with vacuum ultraviolet (VUV) light. The particles formed from ethane and ethane have similar mass spectra with aliphatic characteristics and an H:C ratio of ~1.9. Particles formed from the photolysis of acetylene produce mass spectra characteristic of more aromatic compounds. Consequently, the H:C ratio of these particles was much lower, ~1.3. Previous studies of laboratory analogs of haze particles produced via UV photolysis of methane show an N:C of 0.18, while particles formed in these experiments show no N incorporation. The particles from this study lack strong IR absorption, suggesting that soot or graphene-like structures are not formed. The chemistry of particles formed from photolysis of these species provides insight into the mechanisms by which small organic radicals undergo “molecular weight growth” under oxygen-free conditions, ultimately leading to the formation of high-MW, low-volatility haze particle components.