Organic functional group and OM/OC measurements at select IMPROVE sites using Infrared Spectra: Organosulfates and amines
Ann Dillner1, Mohammed Kamruzzaman2 and Satoshi Takahama3
The Interagency Monitoring of Protected Visual Environments (IMPROVE) is a speciation particulate matter monitoring network in the U.S. located primarily in Class 1 visibility areas. Organic carbon (OC) is measured using thermal optical reflectance (TOR) on quartz filter samples and an organic matter (OM) to OC ratio (OM/OC) of 1.8 is assumed to account for the hetero-atoms attached to the carbon including oxygen, hydrogen, sulfur and nitrogen. In previous work, we developed a method using Fourier transform-infrared spectroscopy (FT-IR) and partial least squares (PLS) regression to measure the four largest organic functional groups, aliphatic C-H, alcohol/sugar OH, carbonyl and carboxylic acid OH. These functional groups are summed to estimate OM and the carbon from the functional groups is summed to estimate OC. With this method, OM/OC can be estimates for each sample rather than relying on one assumed value for all samples. More recently, we have adopted a range of strategies for PLS model development to better estimate OC from functional group measurements (as evaluated by comparison to TOR OC).
We have expanded our suite of functional groups to include organosulfates and amines. Amines are ubiquitous in the atmosphere and come from car exhaust, animal husbandry, biomass burning and vegetation among other sources. We developed a calibration for the amine functional group and applied it to samples collected throughout 2013 at 17 IMPROVE sites. Urban sites showed the highest amine concentrations due to traffic and Fresno, CA an urban site surrounded by cattle and other agriculture, had the highest amine concentration of any site due to traffic and animal husbandry. The lowest amine concentrations were found at rural sites that did not experience prescribed or forest fires in 2013. Samples collected during the Rim Fire near Yosemite National Park had the highest individual amine concentrations of all the samples. Rural sites in the Southeast and Kansas that have prescribed fires during the January to March and high biogenic emissions in the summer, had higher amine concentrations than other rural sites. The OM/OC is higher when the amine functional group is included but for most samples, the increase is small.
Organosulfates are tracers for secondary organic aerosol (SOA) in regions with high sulfate. Results from the same 17 IMPROVE sites and the impact on OM/OC will be discussed.
1University of California, Davis, firstname.lastname@example.org 2University of California, Davis, email@example.com 3Swiss Federal Institute of Technology Lausanne (EPFL), Satoshi.firstname.lastname@example.org