Ozone-driven daytime formation of secondary organic aerosol containing carboxylic acid groups and alkane groups 1Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
16 Aug 2011
*now at: Cooperative Institute for Research in the Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Received: 18 Feb 2011 – Published in Atmos. Chem. Phys. Discuss.: 02 Mar 2011Abstract. Carboxylic acids are present in substantial quantities in atmospheric
particles, and they play an important role in the physical and chemical
properties of aerosol particles. During measurements in coastal California in
the summer of 2009, carboxylic acid functional groups were exclusively
associated with a fossil fuel combustion factor derived from factor analysis
of Fourier transform infrared spectroscopic measurements and closely
correlated with oxygenated organic factors from aerosol mass spectrometry
measurements. The high fraction of acid groups and the high ratio of oxygen
to carbon in this factor suggest that this factor is composed of secondary
organic aerosol (SOA) products of combustion emissions from the upwind
industrial region (the ports of Los Angeles and Long Beach). Another
indication of the photochemically-driven secondary formation of this
combustion-emitted organic mass (OM) was the daytime increase in the
concentrations of acid groups and the combustion factors. This daytime
increase closely tracked the O3 mixing ratio with a correlation
coefficient of 0.7, indicating O3 was closely associated with the SOA
maximum and thus likely the oxidant that resulted in acid group formation.
Using a pseudo-Lagrangian framework to interpret this daytime increase of
carboxylic acid groups and the combustion factors, we estimate that the
carboxylic acid groups formed in a 12-h daytime period of one day ("Today's
SOA") accounted for 25–33 % of the measured carboxylic acid group mass,
while the remaining 67–75 % (of the carboxylic acid group mass) was likely
formed 1–3 days previously (the "Background SOA"). A similar estimate of
the daytime increase in the combustion factors suggests that "Today's SOA"
and the "Background SOA" respectively contributed 25–50 % and 50–75 %
of the combustion factor (the "Total SOA"), for a "Total SOA"
contribution to the OM of 60 % for the project average. Further,
size-resolved spectrometric and spectroscopic characterization of the
particle OM indicate that the majority of the OM formed by condensation of
gas-phase oxidation products. This unique set of measurements and methods to
quantify and characterize photochemically and ozone-linked carboxylic acid
group formation provide independent and consistent assessments of the
secondary fraction of OM, which could result from second generation products
of the oxidation of gas-phase alkane (molecules).
Revised: 29 Jun 2011 – Accepted: 09 Aug 2011 – Published: 16 Aug 2011
Citation: Liu, S., Day, D. A., Shields, J. E., and Russell, L. M.: Ozone-driven daytime formation of secondary organic aerosol containing carboxylic acid groups and alkane groups, Atmos. Chem. Phys., 11, 8321-8341, doi:10.5194/acp-11-8321-2011, 2011.