Fragmentation vs. Functionalization: Extent of Oxidation Influence on SOA Formation

HEBER CHACON-MADRID (1), Neil Donahue (1), Albert Presto (1)

(1) Carnegie Mellon University

     Abstract Number: 695
     Last modified: May 14, 2010

Abstract
When organic compounds are oxidized in the atmosphere, they will follow one of three fundamental pathways, with profound implications for the relationship between the vapor pressure of the parent compound and the products. If the carbon backbone remains intact, we call this the functionalization pathway, and product vapor pressures are much lower than the parent. If the carbon backbone cleaves, we call this the fragmentation pathway, and the products will generally be more volatile than functionalization products. Finally if the backbone grows we call this oligomerization. Studying the role of fragmentation vs. functionalization of organic oxidation reactions in the environment is extremely important in order to understand the formation of secondary organic aerosol (SOA). However, the tens of thousands of different species encountered in the atmosphere, combined with the multiple chemical paths make this chemistry very complex. To simplify this problem, we examine SOA yields of atmospherically relevant species with different extents of oxidation and similar vapor pressures. The first sequence of chemical species, in order of oxidation state, is n-pentadecane, n-tridecanal and pinonaldehyde (saturation concentrations ~10^5 µg/m3); the second sequence is n-nonadecane, n-heptadecanal and pinonic acid (saturation concentrations ~10^3 µg/m3). The SOA yields give us an insight into chemical aging as well since the more oxidized compounds work as a proxy of older molecules. We also concentrate our efforts in studying a set of n-aldehydes (from a size of 5 to 13 carbons) because their carbon-carbon fragmentation reaction chemistry is relatively well known. n-Aldehydes give us an initial insight into fragmentation mechanisms. We use all these data together to understand how more oxidized or aged molecules contribute to SOA.