15 Jan 2021

15 Jan 2021

Review status: this preprint is currently under review for the journal AMT.

Quantifying organic matter and functional groups in particulate matter filter samples from the southeastern United States – Part 2: Spatiotemporal Trends

Alexandra J. Boris1, Satoshi Takahama2, Andrew T. Weakley1, Bruno M. Debus1, Stephanie L. Shaw3, Eric S. Edgerton4, Taekyu Joo5, Nga L. Ng5,6,7, and Ann M. Dillner1 Alexandra J. Boris et al.
  • 1Air Quality Research Center, University of California Davis, Davis, California USA
  • 2Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
  • 3Electric Power Research Institute, Palo Alto, CA, 94304, USA
  • 4Atmospheric Research & Analysis, Inc., Cary, NC 27513, USA
  • 5School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • 6School of Chemical and Bimolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • 7School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA

Abstract. Organic species within atmospheric particles vary widely in molecular structure. The variety of molecules that comprise the aerosol make it rich in information about its sources and chemical lifecycle but also make particulate organic matter (OM) difficult to characterize and quantify. In Part 1 of this pair of papers, we described a direct method for measuring the composition and concentration of OM in aerosol samples that is compatible with routine monitoring of air quality. This method uses Fourier Transform Infrared (FT-IR) spectrometry of filter-based aerosol samples to quantify bonds, or functional groups, that represent the majority of organic composition; summation of these functional groups gives OM. In this paper, functional group composition and OM concentrations are directly measured in eight years of aerosol samples collected at two rural and two urban sites in the Southeastern Aerosol Research and Characterization (SEARCH) network. FT-IR spectrometry with a multivariate calibration is used to quantify the concentrations of aliphatic C-H (aCH), carboxylic acid (COOH), oxalate (oxOCO; representing carboxylates), non-acid and non-oxalate carbonyl (naCO), and alcohol O-H (aCOH) in approximately 3500 filter samples collected every third day from 2009 through 2016. In addition, measurements are made on samples from all days in 2016.

A decline in the total OM is observed from 2011 to 2016 that is caused by decreases in the more oxygenated functional groups (carboxylic acid and oxalate) and is attributed to anthropogenic SO2 and/or volatile organic compound (VOC) emissions reductions. The trend in OM composition is consistent with those observed using more time- and labor-intensive analytical techniques. Concurrently, the fractional contributions of aCOH and naCO to OM increased, which might be linked to monoterpene-derived secondary OM, with possible influences from decreasing NOx and/or increasing O3 concentrations. In addition, this work demonstrates that OM to organic carbon (OM / OC) ratios in the Southeast U.S. (SE U.S.) did not appreciably change over the study time period, as a result of these competing functional group contributions to OM. Monthly observations support the sources suggested by these overall trends, including strong biogenic and photo-oxidation influences, while daily samples from 2016 further elucidate the consistent impact of meteorology and biomass burning events on shorter term OM variability, including prescribed burning in the winter/spring and wildfires in the autumn. These shorter-term and spatial observations thus reinforce the results of the broader dataset and serve to evaluate the applicability of FT-IR spectrometry measurement to trends analysis on various timescales relevant to routine monitoring of aerosol composition.

Alexandra J. Boris et al.

Status: open (until 12 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2020-401', Anonymous Referee #1, 28 Jan 2021 reply
  • RC2: 'Comment on amt-2020-401', Anonymous Referee #2, 19 Feb 2021 reply

Alexandra J. Boris et al.

Data sets

Organic functional group and organic matter concentrations from FT-IR measurements of particulate matter samples in the Southeastern Aerosol Research and Characterization (SEARCH) network from 2009-2016, UC Davis A. M. Dillner, A. J. Boris, S. Takahama, A. T. Weakley, B. Debus, C. D. Frederickson, M. Esparza-Sanchez, C. Burke, M. Reggente, S. L. Shaw, and E. S. Edgerton

Alexandra J. Boris et al.


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Short summary
Infrared spectrometry can be applied in routine monitoring of atmospheric particles to give comprehensive characterization of the organic material by bond rather than species. Using this technique, the concentrations of particle organic material were found to decrease 2011–2016 in the Southeastern U.S., driven by a decline in highly aged material, concurrent with declining anthropogenic emissions. However, an increase was observed in the fraction of more moderately aged organic matter.