Strong spectral variation of biomass smoke light absorption and single scattering albedo observed with a novel dual‐wavelength photoacoustic instrument

Abstract

[1] A dual-wavelength photoacoustic instrument operating at 405 and 870 nm was used during the 2006 Fire Lab at Missoula Experiment to measure light scattering and absorption by smoke from the combustion of a variety of biomass fuels. Simultaneous measurements of aerosol light scattering by reciprocal nephelometry within the instrument's acoustic resonator accompany photoacoustic aerosol light absorption measurements. Single scattering albedo values at 405 nm ranging from 0.37 to 0.95 were measured for different fuel types, and the spectral dependence of absorption was quantified using the Å ngström exponent of absorption. An absorption Å ngström exponent near unity is commonly observed for motor vehicle emission-generated black carbon aerosol. For biomass smoke, Å ngström exponents as high as 3.5 were found in association with smoke having single scattering albedo near unity. The measurements strongly suggest that light-absorbing organic material is present in wood smoke. A second singlewavelength photoacoustic instrument with reciprocal nephelometry was used to quantify aerosol scattering and absorption at 532 nm. Absorption Å ngström exponents calculated using 532 and 870 nm data were as large as 2.5 for smoke with single scattering albedos near unity. The spectral variation in optical properties provides insight into the differentiation of aerosols from mobile or industrial sources versus those from biomass burning. Optical properties of biomass smokes could be classified by general fuel type such as flowering shrubs versus pine needle litter.Citation: Lewis, K., W. P. Arnott, H. Moosmüller, and C. E. Wold (2008), Strong spectral variation of biomass smoke light absorption and single scattering albedo observed with a novel dual-wavelength photoacoustic instrument,

The Absorption Ångström Exponent of black carbon: from numerical aspects

“…However, after coating, the AAE becomes less sensitive to RI real part, but more sensitive to RI imaginary part. Considering the significant uncertainty in estimated BC RI due to 10 differences on combustion fuels and conditions as well as whether BC is fresh or aged, it is highly questionable to use a fixed AAE value as in past studies (Lack and Langridge, 2013;Lack et al, 2008;Kirchstetter et al, 2004;Lewis et al, 2008).…”

“…Furthermore, it is not clear if the real 25 BC AAE is 1.0 on the average. Despite all these uncertainties, BC AAE has been assumed to be 1.0 in many studies (Lack and Langridge, 2013;Lack et al, 2008;Kirchstetter et al, 2004;Lewis et al, 2008). Meanwhile, numerical studies on BC AAE did not show systematic nor conclusive results to improve our understanding on them (Li et al, 2016;.…”

Truncation and Angular-Scattering Corrections for Absorbing Aerosol in the TSI 3563 Nephelometer

“…Aerosol measured at or very near sources is subject to these larger errors. Examples include measurements in traffic tunnels (Ban-Weiss et al 2008) or biomass burning regions (Johnson et al 2008), laboratory and field measurements of biomass or biofuel combustion (Roden et al 2006;Lewis et al 2008), and laboratory studies of the relationship between absorption and aerosol mixing state (Schnaiter et al 2005). Figure 1 is comparable in slope and range; the dependence of C ts on size is similar regardless of refractive index.…”

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

“…Several studies have used the absorption spectral dependence to apportion the fossil fuel and BB contributions to total absorption (Favez et al, 2010;Massabò et al, 2015;Sandradewi et al, 2008). However, the å abs values do not always reflect the combustion type and using it as a source apportionment parameter could lead to erroneous results (Garg et al, 2016;Lewis et al, 2008;Wang et al, 2016b).…”