Table 1.

Studies evaluating the contribution of aromatic hydrocarbons to SOA

Reference	Description	Source apportionment	Concentrations (μg/m3)
[20]	Contribution of primary and secondary sources of OC to PM2.5 in a small subset of Southeastern Aerosol Research and Characterization (SEARCH) network samples	(2,3-hydroxy-4-oxopentanoic acid used as a chemical tracer for aromatic SOA	0.10 to 0.45 across 4 sampling locations
[21]	Contribution of primary and secondary sources of OC to PM2.5 in five midwestern United States cities year–round: East St. Louis, IL Detroit, MI Cincinnati, OH Bondville, IL and Northbrook, IL	2,3-hydroxy-4-oxopentanoic acid used as a chemical tracer for aromatic SOA	Bondville: 0.09 - 0.25; Northbrook: 0.06 - 0.21; Cincinnati: 0.02 - 0.29; Detroit: 0.07 - 0.33; East St. Louis: 0.06 - 0.26
[22]	Contribution of primary and secondary sources of OC to PM2.5 in 2006 in Research Triangle Park, NC over the course of a year	2,3-hydroxy-4-oxopentanoic acid used as a chemical tracer for aromatic SOA	average = 0.1, stdev = 0.09, min = 0.02, max = 0.36, n = 33
[33]	Positive matrix factorization of organic marker measurements to estimate primary and secondary components of organic aerosol	SOA from motor vehicles contribute 11% of total organic aerosols	method is not quantitative
[23]	Contribution of primary and secondary sources of OC to PM2.5 in July-August 2007 in Cleveland, OH, Detroit, MI and LA, CA	2,3-hydroxy-4-oxopentanoic acid used as a chemical marker for aromatic SOA, using a different analytical method than [20-22]	0.05 - 1.1 in the midwest; 0.95 - 1.61 in CA