Because functional groups have more chemical specificity than that in ion mass fragments or atomic oxygen-to-carbon (O/C) ratios, their relative contributions are valuable information to assess the possible SOA formation pathways in the atmosphere. We propose to compare the measured organic functional group composition of atmospheric aerosols to those estimated from chamber studies to assess the extent to which their chemical similarity establishes the applicability of chamber measurements for predicting atmospheric SOA formation. To overcome this disconnect, models can adjust yields to match observations. Definitions of modeled and measured POA and SOA are different, with models using inventories and yields based on controlled conditions and measurements using composition and correlations to infer a distinction. Similarly, the discrepancies between modeled and measured OM are difficult to resolve by comparisons of global budgets ( 5) without first verifying that the SOA formation pathways and yields employed in the global models are reflective of the real atmosphere. ( 6) note that the traditional distinction between the directly emitted “primary” OA (POA) and the atmospherically formed SOA is difficult to define in atmospheric measurements. There has been significant progress in quantifying organic mass (OM, the particle-phase components of OA) from the fragments produced by online mass spectrometry of particles, with recent promulgation of techniques to quantify the resulting mixtures by two to four fragment-based positive matrix factorization (PMF) factors: two types of oxidized, hydrocarbon-like, and biomass-burning OA. Forest fires include biogenic emissions that produce SOA with organic components similar to isoprene and monoterpene chamber studies, also resulting in nonacid carbonyl groups in SOA. The carbonyl groups in SOA associated with vegetation emissions provides striking evidence for the mechanism of esterification as the pathway for possible oligomerization reactions in the atmosphere. The remote forest observations have ratios of carboxylic acid, organic hydroxyl, and nonacid carbonyl groups similar to those observed for isoprene and monoterpene chamber studies, but in biogenic aerosols transported downwind of urban areas the formation of esters replaces the acid and hydroxyl groups and leaves only nonacid carbonyl groups.

The near absence of carbonyl groups in the observed SOA associated with combustion is consistent with alkane rather than aromatic precursors, and the absence of organonitrate groups can be explained by their hydrolysis in humid ambient conditions. The organic functional groups formed from combustion and vegetation emissions are similar to the secondary products identified in chamber studies. The majority of the OM consists of alkane, carboxylic acid, hydroxyl, and carbonyl groups. Measurements of submicron particles by Fourier transform infrared spectroscopy in 14 campaigns in North America, Asia, South America, and Europe were used to identify characteristic organic functional group compositions of fuel combustion, terrestrial vegetation, and ocean bubble bursting sources, each of which often accounts for more than a third of organic mass (OM), and some of which is secondary organic aerosol (SOA) from gas-phase precursors.

Alkane functional group