Validating a nondestructive optical method for apportioning colored particulate matter into black carbon and additional components

Abstract

Exposure of black carbon (BC) is associated with a variety of adverse health outcomes. A number of optical methods for estimating BC on Teflon filters have been adopted but most assume all light absorption is due to BC while other sources of colored particulate matter exist. Recently, a four-wavelength-optical reflectance measurement for distinguishing second hand cigarette smoke (SHS) from soot-BC was developed (Brook et al., 2010; Lawless et al., 2004). However, the method has not been validated for soot-BC nor SHS and little work has been done to look at the methodological issues of the optical reflectance measurements for samples that could have SHS, BC, and other colored particles. We refined this method using a lab-modified integrating sphere with absorption measured continuously from 350 nm to 1000 nm. Furthermore, we characterized the absorption spectrum of additional components of particulate matter (PM) on PM2.5 filters including ammonium sulfate, hematite, goethite, and magnetite. Finally, we validate this method for BC by comparison to other standard methods. Use of synthesized data indicates that it is important to optimize the choice of wavelengths to minimize computational errors as additional components (more than 2) are added to the apportionment model of colored components. We found that substantial errors are introduced when using 4 wavelengths suggested by Lawless et al. to quantify four substances, while an optimized choice of wavelengths can reduce model-derived error from over 10% to less than 2%. For environmental samples, the method was sensitive for estimating airborne levels of BC and SHS, but not mass loadings of iron oxides and sulfate. Duplicate samples collected in NYC show high reproducibility (points consistent with a 1:1 line, R2 = 0.95). BC data measured by this method were consistent with those measured by other optical methods, including Aethalometer and Smoke-stain Reflectometer (SSR); although the SSR looses sensitivity at filter loadings above 90 ng/mm2. Furthermore, positive correlations (R2 = 0.7) were observed between EC measured by NIOSH Method 5040 on quartz filters and BC measured in co-located Teflon filter samples collected from both heating and non-heating seasons. Overall, the validation data demonstrates the usefulness of this method to evaluate BC from archived Teflon filters while potentially providing additional component information.

Validation of MicroAeth® as a Black Carbon Monitor for Fixed-Site Measurement and Optimization for Personal Exposure Characterization

“…Of particular note the multi-wavelength optical measurement of BC is calibrated gravimetrically by collecting, weighing and then optically measuring PM 2.5 filters of kerosene soot and assuming that 100% of the mass is BC (Yan et al , 2011); literature values consistently show values of 95% ± 5% (Lam et al , 2012). This comparison testing was conducted from the window of a fifth floor apartment along the W168th street, NYC, which is situated at an intersection of a busy street with idling ambulances and a truck route with heavy traffic.…”

“…A multi-wavelength optical method has been established for measuring BC levels collected on PM 2.5 Teflon filters via optical equipment purchased from Ocean Optics (Dunedin, FL) including a balanced deuterium tungsten halogen light source (DH-2000-BAL), an integrating sphere (ISP-50-8-R) modified to have a reflective white bottom, a lab-made filter holder, and an Ocean Optics USB4000-VIS-NIR fiber-optic spectrometer (Yan et al , 2011). Whereas the microAeth and full size Aethalometer measures the change in light attenuation between every time stamp (e.g., each min), from which the BC air concentration is calculated for that period of time, the multi-wavelength optical reflectance method determines the total BC mass loading on filters (based on an empirical gravimetric calibration) that occurred over the entire deployment period, which was 24 hrs in this experiment.…”

A critical review of filter transmittance measurements for aerosol light absorption, and de novo calibration for a decade of monitoring on PTFE membranes

“…This focus overlooked a comparably long, if less ramified, history of filter optics studies using PTFE membranes as the collection substrate (Szkarlat and Japar 1981;Bennett and Patty, 1982;Campbell et al 1989Campbell et al , 1995Clarke et al 1996;Huffman 1996;Chow et al 2000;Taha et al 2007). Optical transmittance measurements are sometimes added to PTFE measurement suites as a proxy determination for "black carbon" (Cahill et al 1984;Nejedly et al 2003;Cuccia et al 2010;Barraza-Villarreal et al 2011) and, with sufficient spectral resolution, environmental tobacco smoke (Lawless et al 2004;Yan et al 2011). Massabo et al (2013) recently developed a multi-wavelength and multiangle optical system to make off-line MAAP-like absorption measurements on PTFE as well as quartz fiber filters.…”

Real-time diesel particulate monitor for underground mines

“…However, researchers have reported filter-based methods using multiwavelength light extinction to determine cigarette smoke and some dusts concentrations in the presence of black carbon in atmospheric samples. [28][29][30] In order to use these methods to correct for interferences of DPM in occupational settings, further research and optimization would be necessary. 29 Borak et al evaluated the Aethalometer for determining realtime DPM concentrations at three occupational settings including one underground mine.…”

“…[28][29][30] In order to use these methods to correct for interferences of DPM in occupational settings, further research and optimization would be necessary. 29 Borak et al evaluated the Aethalometer for determining realtime DPM concentrations at three occupational settings including one underground mine. 31 The Aethalometer is a filterbased method which measures real-time black carbon in the atmosphere via absorption.…”