Gas/particle partitioning of total alkyl nitrates observed with TD-LIF in Bakersfield

TitleGas/particle partitioning of total alkyl nitrates observed with TD-LIF in Bakersfield
Publication TypeJournal Article
Year of Publication2013
AuthorsRollins A.W, Pusede S., Wooldridge P., Min K.E, Gentner D.R, Goldstein AH, Liu S, Day DA, Russell LM, Rubitschun C.L, Surratt J.D, Cohen R.C
JournalJournal of Geophysical Research-Atmospheres
Date Published2013/06
Type of ArticleArticle
ISBN Number2169-897X
Accession NumberWOS:000322129600054
Keywordsaerosols and particles; atmospheric chemistry; california; composition and chemistry; instruments and techniques; isoprene photooxidation; n-alkanes; nox-air photooxidations; organosulfates; pollution: urban and regional; secondary organic aerosol; semivolatile; soa formation; southern; troposphere:; volatility

Limitations in the chemical characterization of tropospheric organic aerosol (OA) continue to impede attempts to fully understand its chemical sources and sinks. To assess the role of organic nitrates in OA, we used a new thermal dissociation-laser induced fluorescence-based (TD-LIF) technique to obtain a high-time-resolution record of total aerosol organic nitrates (hereafter sigma ANs(aer)) at the Bakersfield, CA supersite during the 2010 CalNex campaign. The TD-LIF measurements compare well with Fourier transform infrared measurements from collocated filter samples. These measurements show that sigma ANs are a ubiquitous component of the OA with the -ONO2 subunit comprising on average 4.8% of the OA mass. Scaling this fraction by an estimate of the organic backbone mass yields an estimate that 17-23% of OA molecules contain nitrate functional groups. Measurements of both total sigma AN (gas+aerosol) and sigma AN(aer) show that on average 21% of sigma ANs are in the condensed phase, suggesting atmospheric organic nitrates have similar volatilities to analogous non-nitrate oxidized organic compounds. The fraction of sigma AN that is in the condensed phase increases with total OA concentration, providing direct evidence from the atmosphere that absorptive partitioning into OA has some control over the sigma AN phase partitioning. The specific molecular identity of the sigma AN is incompletely understood. Both biogenic hydrocarbons and long chain alkanes are calculated to be significant sources of low volatility nitrates in Bakersfield, and ultra performance liquid chromatography coupled to an electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer measurements confirm the existence of particulate nitrooxy organosulfates derived from gas-phase oxidation of both isoprene and monoterpenes.