An Evaluation of Mass Absorption Cross-Section for Optical Carbon Analysis on Teflon Filter Media
Creators: name: Presler-Jur, Paige
name: Doraiswamy, Prakash
name: Oki Hammond
name: Rice, Joann
Publisher: name: Taylor & Francis
Year: 2017
Subjects: subject: Space Science
subject: Physiology
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: Biotechnology
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences
subject: Ecology
subject: 69999 Biological Sciences not elsewhere classified
subject: Cancer
subject: Inorganic Chemistry
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Science Policy

description: Black carbon (BC) or elemental carbon (EC) is a by-product of incomplete fuel combustion, and contributes adversely to human health, visibility, and climate impacts. Previous studies have examined non-destructive techniques for particle light attenuation measurements on Teflon<sup>®</sup> filters to estimate BC. The incorporation of an inline Magee Scientific OT21 Transmissometer into the MTL AH-225 robotic weighing system provides the opportunity to perform optical transmission measurements on Teflon<sup>®</sup> filters at the same time as the gravimetric mass measurement. In this study, we characterize the performance of the inline OT21, and apply it to determine the mass absorption cross-section (MAC) of PM<sub>2.5</sub> BC across the U.S. We analyzed 5393 archived Teflon<sup>®</sup> filters from the Chemical Speciation Network (CSN) collected during 2010-2011 and determined MAC by comparing light attenuation on Teflon<sup>®</sup> filters to corresponding thermal EC on quartz-fiber filters. Results demonstrated the importance of the initial transmission (I<sub>0</sub>) value used in light attenuation calculations. While light transmission varied greatly within filter lots, the average I<sub>0</sub> of filter blanks during from the sampling period provided an estimate for archived filters. For newly collected samples, it is recommended that filter-specific I<sub>0</sub> measurements be made (i.e., same filter before sample collection). The estimated MAC ranged from 6.9 to 9.4 m<sup>2</sup>/g that varied by region and season across the U.S., indicating that using a default value may lead to under- or over-estimated BC concentrations. An analysis of the chemical composition of these samples indicated good correlation with EC for samples with higher EC content as a fraction of total PM<sub>2.5</sub> mass, while the presence of light scattering species such as crustal elements impacted the correlation affecting the MAC estimate. Overall, the method is demonstrated to be a quick, cost-effective approach to estimate BC from archived and newly sampled Teflon<sup>®</sup> filters by combining both gravimetric and BC measurements. Implications Robotic optical analysis is a valid, cost-effective means to obtain a vast amount of BC data from archived and current routine filters. A tailored mass absorption cross-section by region and season is necessary for a more representative estimate of BC. Initial light transmission measurements play an important role due to the variability in blank filter transmission. Combining gravimetric mass and BC analysis on a single Teflon<sup>®</sup> filter reduces costs for monitoring agencies as well as maximizes data collection.