FTIR Spectroscopy Measurements of Organic Functional Groups in Atmospheric Particles.

Improving our technological and analytical approaches to studying organic functional groups has proven to be increasingly important in our understanding of aerosol composition and behavior, and thus in assessing our global climate and air quality issues. There are a large variety of compounds that can make up the organic fraction of particles that affect the hygroscropicity of aerosol particles and therefore their size, residence time, and optical properties. One such method to identify and quantify the components of the organic fraction of aerosols, beyond characterizing the hygroscopicity of the components, is Fourier Transform Infrared (FTIR) spectroscopy. This technique estimates bulk organic carbon from the number of carbon bonds present in functional groups and subsequentyly organic mass from the molecular weight of each functional group associated with the measured bond type. The use of FTIR spectroscopy with X-ray fluorescence (XRF) measurements and size distributions can provide a full picture with reduced uncertainty of organic mass (OM) composition, aerosol source type, and scavenging coefficients. The following articles are case studies and products of this technique in the field of organic aerosol research.

Peer-reviewed publications on this topic:

• Uniform particle-droplet partitioning of 18 organic and elemental components measured in and below DYCOMS-II stratocumulus clouds.
  L. N. Hawkins, L. M. Russell, C. H. Twohy, J. R. Anderson



An aircraft aerosol sampling over San Diego used FTIR spectroscopy and XRF to evaluate the partitioning of 18 organic and elemental components between droplet residuals and unactivated particles in and below DYCOMS-II marine stratocumuls clouds. Filter samples were found to be dominated by internally mixed aerosols containing sea salt, ammonium, sulfate, and organic compounds, and a uniformity among scavenging coefficients was found to be consistent with aged or processed internal mixtures of these components.

• Regional variation of organic functional groups in aerosol particles on four US east coast platforms during the International Consortium for Atmospheric Research on Transport and Transformation 2004 campaign
  S. Gilardoni, L. M. Russell, A. Sorooshian, R. C. Flagan, J. H. Seinfield, T. S. Bates, P. K. Quinn, J. D. Allan, B. Williams, A. H. Goldstein, T. B. Onasch, and D. R. Worsnop



FTIR spectroscopy was used in ground & aircraft-based measurements of four east coast platforms. Samples from the Twin Otter, OH had the lowest OM-to-OC ratio (1.4) while the ratio measured at coastal platforms were between 1.5 and 1.6. Comparable results suggest that approximately 9% of the carbonyl groups at Twin Otter, OH are typically associated with low molecular weight carboxylic acids.

• Organic and Inorganic Aerosol Below-Cloud Scavenging by Suburban New Jersey Precipitation
  Steven F. Maria, and Lynn M. Russell



A ground-based ambient aerosol study using both FTIR spectroscopy & XRF measurements in Princeton, NJ found a large alkene fraction in OM from motor vehicle emissions. Measurements before and after rain events indicated high alkane fractions in OM, this indicates that the removal rates have a weak chemical dependence.

• Aerosol Orangic-Mass-to-Organic-Carbon Ratio Measurements.
  Lynn M. Russell



The use of FTIR spectroscopy in quantifying organic functional groups in aerosols is shown to reduce uncertainty from 9% to 33% in OM-to-OC ratio measurements in an aircraft and ship-based sampling in NE Asia and the Caribbean.

• Source signatures of CO and O functional groups in Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) submicron aerosol types.
  S. F. Maria, L. M. Russell, B. J. Turpin, R. J. Porcja, T. L. Campos, R. J. Weber, and B. J. Huebert



An aircraft aerosol sampling campaign near Japan used FTIR, XRF, and comparable measurements from thermal-optical OC to identify 36% of aerosol mass, and thus carbon monoxide and organic carbon values. The measured OC/OC slope suggested that 52% of the samples were indicative of biomass combustion and that increased carbonyl carbon fractions in the air downwind of large Asian aerosol sources have clear regional composition signatures.

• FTIR measurements of functional groups and organic mass in aerosol samples over the Caribbean.
  Steven F. Maria, Lynn M. Russell, Barbara J. Turpin, Robert J. Porcja.

An aircraft-based aerosol sampling in the Caribbean used FTIR and a four-solvent rinsing procedure to separate organic functional groups, sulfate, ammonium, and silicate. The Caribbean aerosols were found to contain 60-90% hygroscopic OM in the free troposphere, while 20-50% hydrophobic OM was found in the marine boundary layer.