Correlations between optical, chemical and physical properties of biomass burn aerosols

Abstract

[1] Aerosols generated from burning different plant fuels were characterized to determine relationships between chemical, optical and physical properties. Single scattering albedo (w) and Angstrom absorption coefficients (a ap ) were measured using a photoacoustic technique combined with a reciprocal nephelometer. Carbon-to-oxygen atomic ratios, sp 2 hybridization, elemental composition and morphology of individual particles were measured using scanning transmission X-ray microscopy coupled with near-edge X-ray absorption fine structure spectroscopy (STXM/ NEXAFS) and scanning electron microscopy with energy dispersion of X-rays (SEM/EDX). Particles were grouped into three categories based on sp 2 hybridization and chemical composition. Measured w (0.4 À 1.0 at 405 nm) and a ap (1.0 À 3.5) values displayed a fuel dependence. The category with sp 2 hybridization >80% had values of w (<0.5) and a ap ($1.25) characteristic of light absorbing soot. Other categories with lower sp 2 hybridization (20 to 60%) exhibited higher w (>0.8) and a ap (1.0 to 3.5) values, indicating increased absorption spectral selectivity.

Reduction in biomass burning aerosol light absorption upon humidification: roles of inorganically-induced hygroscopicity, particle collapse, and photoacoustic heat and mass transfer

“…Variations in chemical composition for ponderosa pine, chamise, and palmetto wood smokes, as determined by AMS measurements, are consistent with a classification proposed by Hopkins et al (2007a) based on X-ray and electron microscopy measurements. That work reported three major particle-type categories based on chemical and optical properties: (1) materials composed of liquid/oily organic carbon (OC) and BC with no inorganic inclusions (e.g., ponderosa pine combustion particles), (2) non-homogenous mixture of carbonaceous and inorganic materials (e.g., palmetto combustion particles), and (3) BC material with fractal morphology typical of soot containing inorganic inclusions (e.g., chamise combustion particles).…”

“…The individual particles are composed of non-homogeneously mixed carbonaceous and inorganic materials. Chamise smoke particles are more fractal-like in nature, resembling the morphology typical for BC, diesel, or methane soot, while palmetto smoke particles are dominated by OC and inorganic species (Hopkins et al, 2007a). The particles are aggregates of the mixed materials, so that the exposed surface is composed of inorganic inclusions alongside carbonaceous species, as evident from the microscopy images of chamise combustion particles in Fig.…”

“…The fraction of sp 2 hybridization reveals the graphitic nature of the material: 100% sp 2 hybridization is consistent with strongly aligned pyrolytic graphite. The three groups of combustion products were increasingly graphitic in nature, such that the mean sp 2 hybridization of the category 1, 2, and 3 fuels was 34%, 53%, and 83%, respectively (Hopkins et al, 2007a).…”

Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in Central Himalayan aerosols

“…Saarikoski et al (2008) observed an OC/EC ratio of 6.6 for biomass burning and 0.71 for vehicular emissions, whereas Sandradewi et al (2008) found values of 7.3 and 1.1 for these two sources, respectively. Hopkins et al (2007) studied the particles emitted during combustion of several plant fuels at different temperatures and suggested that flaming conditions produce more EC and less OC while smoldering fires result in higher OC content. Regional air quality over the northwestern part of India during winter season is considerably influenced by the annual practice of crop harvesting.…”

Airborne soil organic particles generated by precipitation

“…The SOM-derived composition of ASOP implies their inherent relevance to atmospheric brown carbon and their plausible contribution to the absorption and scattering of solar and terrestrial radiation 19 . Estimates of ASOP optical properties based on reported correlations 20 with the O/C ratio and the sp 2 hybridization suggest values of single scattering albedo of 0.8-1.0 and Ångström absorption coefficients of 1.5-3.5-characteristic of brown carbon, respectively. Dynamic environmental SEM imaging of hydrating ASOP ( Supplementary Fig.…”