Ambient aerosol composition by infrared spectroscopy and partial least-squares in the chemical speciation network: Organic carbon with functional group identification

Andrew T Weakley,Satoshi Takahama,Ann M Dillner

doi:10.1080/02786826.2016.1217389

Abstract

ABSTRACTThe Fourier-transform infrared (FT-IR) spectra of ambient fine aerosols were used with partial least-squares (PLS) regression to accurately, inexpensively, and nondestructively predict organic carbon (OC) on polytetrafluoroethylene (PTFE) filters in the U.S. Environmental Protection Agencies' Chemical Speciation Network (CSN). Recently, a similar FT-IR method was used for OC determination in the rural United States Interagency Monitoring of PROtected Visual Environments network, with the present work extending the method to urban aerosols with low mass loadings. In the present study, FT-IR spectra were calibrated to collocated thermal/optical reflectance (TOR) OC measurements following numerical processing with a second derivative filter, backward Monte Carlo unimportant variable elimination, and a quadratic discriminant analysis-PLS vapor correction routine. After processing and vapor correcting spectra, the number of model components (latent variables) were reduced from thirty-five to three with...

Highlights

In the United States, the Chemical Speciation Network (CSN) collects, analyzes, and speciates particulate matter (PM) from urban and suburban sites while the Interagency Monitoring to PROtect Visual Environments network (IMRPOVE) monitors PM at rural sites (Malm et al 2011; Solomon et al 2014)
The CSN and IMPROVE networks analyze PM to determine the mass of inorganic ions including sulfate (SO42¡) and nitrate (NO3¡), elements related to soil, sea salt, and anthropogenic sources as well as organic and elemental carbon (OC and EC)
Rather than extrapolate existing IMPROVE calibrations to CSN samples—a process known as calibration transfer (Feudale et al 2002; Chen et al 2011)—the present study develops new calibrations to determine organic carbon (OC)

Summary

Introduction

In the United States, the Chemical Speciation Network (CSN) collects, analyzes, and speciates particulate matter (PM) from urban and suburban sites while the Interagency Monitoring to PROtect Visual Environments network (IMRPOVE) monitors PM at rural sites (Malm et al 2011; Solomon et al 2014). The CSN and IMPROVE networks analyze PM to determine the mass of inorganic ions including sulfate (SO42¡) and nitrate (NO3¡), elements related to soil, sea salt, and anthropogenic sources as well as organic and elemental carbon (OC and EC). Both networks measure OC and EC using the thermal optical reflectance (TOR) method (Chow et al 1993; Chow et al 2007). The IMPROVE_A TOR protocol operationally defines OC as the total fraction of carbonaceous material volatilized from a quartz fiber filter below 580C in the absence of oxygen. While the TOR method reliably fractionates carbonaceous material by exploiting the volatility and oxidation of condensed phase aerosols, the method is time consuming, costly, and destroys the aerosol

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Conclusion