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

White, William M.; Trzepla, Krystyna; Hyslop, N. P.; Schichtel, B. A.

doi:10.1080/02786826.2016.1211615

Cited by 24 publications

(23 citation statements)

References 130 publications

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“…Teflon filters are routinely used for gravimetric and elemental analysis across monitoring networks (Chow et al, 2010;Snider et al, 2015;Solomon et al, 2014), as well as in field and laboratory source characterization studies. In many measurement systems, such as the Hybrid Integrating Plate and Sphere (HIPS) method (Bond et al, 1999) used by the IMPROVE network, transmittance and reflectance are measured on the clean side of the filter and the optical depth OD c is calculated (Campbell et al, 1995;White et al, 2016). The relationship between aerosol optical depth, τ a, s , and OD c showed a larger variability across varying SSA than that between τ a, s and OD s .…”

Section: Discussionmentioning

confidence: 99%

“…Here, R b is the reflectance of the blank. An alternate measure of filter-aerosol optical depth utilizes transmittance and reflectance of the clean face of the filter (Campbell et al, 1995;White et al, 2016). This reflectance measurement R c can be assumed to be approximately equal to R b .…”

Section: Two-stream Radiative Transfer Modelmentioning

confidence: 99%

“…Instruments based on this technique, including the aethalometer (Hansen et al, 1984) and the Particle Soot Absorption Photometer or PSAP (Virkkula et al, 2005), facilitate semi-continuous sampling of particles and produce time-averaged bulk absorption measurements. Particles may also be collected on a filter substrate and analyzed for their absorption using stand-alone spectrophotometers (Martins et al, 2009;Pandey et al, 2016;White et al, 2016;Zhong and Jang, 2011).…”

mentioning

confidence: 99%

“…A previous study on the artifacts associated with this filter type used a reference material and provided a constant multiple scattering correction factor for optical loadings smaller than a certain threshold (Zhong and Jang, 2011). Another recent study (White et al, 2016) proposed a theory-based model to calibrate attenuation measurements for Teflon filter samples and applied this new model to a historical dataset from the IMPROVE network. They found that the reevaluated absorption values for the PTFE samples were well correlated with thermo-optical elemental carbon (EC) measurements for co-located quartz fiber filters.…”

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confidence: 99%

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Aerosol light absorption from optical measurements of PTFE membrane filter samples: sensitivity analysis of optical depth measures

2019

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Mass absorption cross section (MAC) measurements of atmospherically relevant aerosols are required to quantify their effect on Earth's radiative budget. Estimating aerosol light absorption from transmittance and/or reflectance measurements through filter deposits is an attractive option because of their ease of deployment in field settings, low cost, and the ability to revisit previously analyzed samples. These measurements suffer from artifacts that depend on a given filter measurement system and aerosol optics. Empirical correction algorithms are available for commercial instruments equipped with optically thick fiber filters, but optically thin filter media have not been characterized in detail. Here, we present empirical relationships between particle light absorption optical depth -measured using multiwavelength integrated photoacoustic spectrometers -and filter optical depth measurements for polytetrafluoroethylene (PTFE) membrane filter samples of carbonaceous aerosols generated from combustion of diverse biomass fuels and kerosene (surrogate for fossil fuel combustion). Through radiative transfer modeling, we assessed the suitability of three measures of filter-based optical depth for robustly describing particulate-phase light absorption over a range of single scattering albedo (SSA) values: (1) OD s -a measure of transmission of the fraction of incident radiation that is not backscattered by the filter system -which utilizes transmittance and reflectance of the sample side of the filter; (2) the commonly used OD c , which uses transmittance and reflectance of the clean side of the filter; and (3) ATN or the Beer-Lambert attenuation. Modeling results were also validated experimentally, with OD s showing the least vari-ability around the mean in this multidimensional parameter space. We establish a simple, wavelength-independent formulation for calculating aerosol MAC and absorption coefficients from measurements of OD s . We find the ratio between in situ particulate absorption optical depth and OD s to be inversely proportional to aerosol SSA. Our findings underscore that OD s is a better optical depth measure than OD c for applying appropriate correction factors when estimating particle-phase light absorption from filter-based techniques.

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Section: Discussionmentioning

confidence: 99%

Section: Two-stream Radiative Transfer Modelmentioning

confidence: 99%

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Aerosol light absorption from optical measurements of PTFE membrane filter samples: sensitivity analysis of optical depth measures

2019

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“…• In North America the number of σap datasets is much lower than the number of σsp datasets (IMPROVE sites do measure aerosol absorption, but with a different instrumental setup (White et al, 2016) • In the southwest Pacific, the high altitude station of MLO has a ss decreasing trend, whereas the coastal station of CGO in Australia exhibits not ss σap trends.…”

Section: Absorption Coefficientmentioning

confidence: 99%

Multidecadal trend analysis of aerosol radiative properties at a global scale

Coen¹,

Andrews²,

Alastuey³

et al. 2020

Preprint

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Abstract. In order to assess the global evolution of aerosol parameters affecting climate change, a long-term trend analyses of aerosol optical properties were performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption &#197;ngstr&#246;m exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann&#8211;Kendall (MK) statistical test associated with several prewhitening methods and with the Sen's slope were used as main trend analysis methods. Comparisons with General Least Mean Square associated with Autoregressive Bootstrap (GLS/ARB) and with standard Least Mean Square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficients trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficients time series also exhibit primarily decreasing trends. For single scattering albedo, 52&#8201;% of the sites exhibit statistically significant positive trends, mostly in Asia, Eastern/Northern Europe and Arctic, 18&#8201;% of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 30&#8201;% of sites have trends, which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10 year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10 year trends are primarily found for earlier periods (10 year trends ending in 2010&#8211;2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10 year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10 year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10 year trends of the scattering coefficient &#8211; there is a shift to statistically significant negative trends in 2010&#8211;2011 for all stations in the eastern and central US. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage enables a better global view of potential aerosol effects on climate changes.

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