The organic functional group composition of particles produced in laboratory smog chambers were characterized by scanning transmission X-ray microscopy (STXM) with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and characteristic spectral signatures for secondary organic aerosol (SOA) were identified. The main objective of this study is to compare the single particle functional group composition of SOA formed from five precursors (glyoxal, -pinene, isoprene, 1,2,4-trimethylbenzene, and d-limonene) to the composition of ambient particles from multiple field campaigns. This has implications for understanding the potential contributions of particles similar to those produced in SOA chambers to ambient compositions during those campaigns. Glyoxal uptake studies showed absorption from mainly alkyl, carbon-nitrogen (C-N), and carboxylic carbonyl groups. The SOA formed from the photooxidation of -pinene (with and without isoprene) showed stronger absorptions for alkyl and carbonyl groups than the SOA formed from glyoxal. The mass ratio of carbonyl to acid group was larger in -pinene-only experiments relative to the mixed -pinene-isoprene experiments. Of 338 single-particle spectra available from aerosol sampling at six field campaigns, 114 particles had spectral features that were considered similar to the chamber-SOA particles: MILAGRO-2006 (9 particles), VOCALS-2008 (41 particles), Whistler-2008 (22 particles), Scripps Pier-2009 (8 particles), Bakersfield-2010 (24 particles), and Whistler-2010 (10 particles). These similarities with chamber-generated SOA provide spectroscopic evidence of chemically similar SOA products from these precursors in ambient particles. Copyright 2013 American Association for Aerosol Research