FY 2009
Oxygenated fraction and mass of organic aerosol from direct emission and atmospheric processing measured on the R/V Ronald Brown during TexAQS/GoMACCS 2006
Russell, L.M., S. Takahama, S. Liu, L.N. Hawkins, D.S. Covert, P.K. Quinn, and T.S. Bates
J. Geophys. Res., 114, D00F05, doi: 10.1029/2008JD011275 (2009) |
Submicron particles collected on Teflon filters aboard the R/V Ronald Brown during the Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) 2006 in
and around the port of Houston, Texas, were measured by Fourier transform infrared (FTIR) and X‐ray fluorescence for organic
functional groups and elemental composition. Organic mass (OM) concentrations (1–25 μg m−3) for ambient particle samples measured by FTIR showed good agreement with measurements made with an aerosol mass spectrometer.
The fractions of organic mass identified as alkane and carboxylic acid groups were 47% and 32%, respectively. Three different
types of air masses were identified on the basis of the air mass origin and the radon concentration, with significantly higher
carboxylic acid group mass fractions in air masses from the north (35%) than the south (29%) or Gulf of Mexico (26%). Positive
matrix factorization analysis attributed carboxylic acid fractions of 30–35% to factors with mild or strong correlations (r
> 0.5) to elemental signatures of oil combustion and 9–24% to wood smoke, indicating that part of the carboxylic acid fraction
of OM was formed by the same sources that controlled the metal emissions, namely the oil and wood combustion activities. The
implication is that a substantial part of the measured carboxylic acid contribution was formed independently of traditionally
“secondary” processes, which would be affected by atmospheric (both photochemical and meteorological) conditions and other
emission sources. The carboxylic acid group fractions in the Gulf of Mexico and south air masses (GAM and SAM, respectively)
were largely oil combustion emissions from ships as well as background marine sources, with only limited recent land influences
(based on radon concentrations). Alcohol groups accounted for 14% of OM (mostly associated with oil combustion emissions and
background sources), and amine groups accounted for 4% of OM in all air masses. Organosulfate groups were found in GAM and
SAM, accounting for 1% and 3% of OM, respectively. Two thirds of the OM and oxygen‐to‐carbon (O/C) measured could be attributed
to oil and wood combustion sources on the basis of mild or strong correlations to coemitted, nonvolatile trace metals, with
the remaining one third being associated with atmospherically processed organic aerosol. The cloud condensation nuclei (CCN)
fraction (normalized by total condensation nuclei) had weak correlations to the alcohol and amine group fractions and mild
correlation with O/C, also varying inversely with alkane group fraction. The chemical components that influenced f(RH) were
sulfate, organic, and nitrate fraction, but this contrast is consistent with the size‐distribution dependence of CCN counters
and nephelometers. |