Secondary Organic Aerosol Yields from High-NOx Photo-oxidation of Cycloalkanes

DANIEL S. TKACIK (1), Albert A. Presto (1), Christopher J. Hennigan (1), Ngoc T. Nguyen (1), Allen L. Robinson (1)

(1) Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA

     Abstract Number: 841
     Last modified: August 9, 2010

Abstract
Atmospheric aerosols significantly affect human health and climate. The highly uncertain organic component of these particles remains a challenge in predicting their chemical activity. Recent research has shown that treating primary organic aerosol (POA) emissions as semivolatile may help explain much of the discrepancy between observed and predicted secondary organic aerosol (SOA) levels. This treatment accounts for SOA formation from intermediate-volatility organic compounds (IVOC) and semi-volatile organic compounds (SVOC). Though these lower volatility precursors are less abundant in the atmosphere than traditional volatile SOA precursors, they can have higher SOA yields. However, the mechanism to form SOA from IVOCs and SVOCs is highly uncertain because these vapors are a complex and largely unknown mixture of compounds. As such, the role of molecular structure on SOA yield remains a large question. Since organic vapor-particle equilibrium is significantly affected by organic aerosol concentrations (C$_(OA)), experiments addressing the role of molecular structure on SOA formation should be carried out under atmospherically relevant C$_(OA). Previously, we published results for linear alkanes, and in this study we present results for cyclic alkanes.

Hydroxyl radical-initiated photo-oxidation experiments were performed in an environmental chamber to investigate the formation of SOA from cycloalkanes under high-NOx conditions. SOA yields were calculated based on measurements from a scanning mobility particle sizer (SMPS) and an Aerodyne high-resolution aerosol mass spectrometer (AMS). To measure the decay of precursors we collected Tenax TA sorbent samples which were analyzed by a thermal-desorption gas chromatography mass spectrometer (GC-MS) system. These experiments illustrate the importance of molecular structure in SOA formation, and the information extracted from these results may be used in chemical transport models (CTMs).