PNNL

Abstract

Functional group composition of particles produced in smog chambers are examined using scanning transmission X-ray microscopy (STXM) with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in order to identify characteristic spectral signatures for secondary organic aerosol (SOA). Glyoxal uptake studies showed absorption for mainly alkyl, carbon-nitrogen (C-N), and carboxylic carbonyl groups. The SOA formed from the photooxidation of a-pinene (with and without isoprene) showed stronger absorptions for alkyl and carbonyl groups than the glyoxal studies. The mass ratio of carbonyl to acid group was larger in a-pinene-only experiments relative to the mixed a-pinene-isoprene experiments. The chamber particle spectra were compared with the ambient particle spectra from multiple field campaigns to understand the potential SOA sources. One hundred nineteen particles from six field campaigns had spectral features that were considered similar to the chamber-SOA particles: MILAGRO-2006 (9 particles), VOCALS-2008 (42 particles), Whistler-2008 (22 particles), Scripps Pier-2009 (9 particles), Bakersfield-2010 (25 particles), and Whistler-2010 (12 particles). These similarities with SOA formed from glyoxal, a-pinene (with and without isoprene), 1,2,4-trimethylbenzene, and limonene provide spectroscopic evidence of SOA products from these precursors in ambient particles.