Reframing the Organic Aerosol Debate by Reconciling Functional Group Composition in Chamber and Atmospheric Particles

LYNN RUSSELL (1), Ranjit Bahadur (1), Paul Ziemann (2)

(1) Scripps Institution of Oceanography, University of California, San Diego, (2) University of California, Riverside

     Abstract Number: 603
     Last modified: May 14, 2010

Abstract
Measurements of submicron particles by Fourier Transform Infrared (FTIR) spectroscopy in more than a dozen campaigns in North America, Asia, South America, and Europe were used to identify characteristic organic functional group compositions of fuel combustion, terrestrial plant, and ocean bubble bursting sources, each of which often accounts for more than a third of organic mass (OM). Organosulfate and organonitrate groups contribute small fractions of OM, but the majority of the OM consists of alkane, carboxylic acid, organic hydroxyl, and non-acidic carbonyl groups. The combustion and plant-derived organic functional groups are similar to the secondary products identified in chamber studies. The near-absence of carbonyl groups in the observed combustion SOA is explained by alkane rather than aromatic precursors, and the frequent absence of organonitrate groups is attributed to their hydrolysis in humid ambient conditions. The remote forest observations have ratios of carboxylic acid, organic hydroxyl, and non-acidic carbonyl groups similar to those observed for isoprene and monoterpene chamber studies, but in combustion-influenced biogenic particles the formation of oligomeric esters replaces the acid and hydroxyl groups and leaves only non-acidic carbonyl groups. The non-acidic carbonyl groups in plant SOA provides striking evidence for the mechanism of esterification in oligomerization reactions in the atmosphere. Forest fires include biogenic emissions that produce SOA with organic components similar to isoprene and monoterpene chamber studies, also resulting in non-acidic carbonyl groups in SOA.