Contribution of organic carbon to wood smoke particulate matter absorption of solar radiation

Abstract

Abstract.A spectroscopic analysis of 115 wintertime particulate matter samples collected in rural California shows that wood smoke absorbs solar radiation with a strong spectral selectivity. This is consistent with prior work that has demonstrated that organic carbon (OC), in addition to black carbon (BC), appreciably absorbs solar radiation in the visible and ultraviolet spectral regions. We apportion light absorption to OC and BC and find that the absorptionÅngström exponent of the light-absorbing OC in these samples ranges from 3.0 to 7.4 and averages 5.0. Further, we calculate that OC would account for 14 % and BC would account for 86 % of solar radiation absorbed by the wood smoke in the atmosphere (integrated over the solar spectrum from 300 to 2500 nm). OC would contribute 49 % of the wood smoke particulate matter absorption of ultraviolet solar radiation at wavelengths below 400 nm and, therefore, may affect tropospheric photochemistry. These results illustrate that BC is the dominant light-absorbing particulate matter species in atmospheres burdened with residential wood smoke and OC absorption is secondary but not insignificant. Further, these results add to the growing body of evidence that lightabsorbing OC is ubiquitous in atmospheres influenced by biomass burning and may be important to include when considering particulate matter effects on climate.

Brown carbon absorption in the red and near-infrared spectral region

“…Light-absorbing organic aerosols are also known as brown carbon (BrC) since they absorb blue light significantly but have practically zero absorption in the red band, yielding brownish colours . The distinction between the light absorption by BC and BrC in field and laboratory studies has relied on the explicit assumption that no carbonaceous particle type except BC absorbs solar radiation at a wavelength of ∼ 700 nm or larger (Bahadur et al, 2012;Kirchstetter and Thatcher, 2012;Lu et al, 2015;Drinovec et al, 2017). This common assumption has been used in spite of the finding by Alexander et al (2008), who showed a sizable absorption by a specific class of BrC at longer wavelengths.…”

“…The determination of the contribution of BrC to aerosol absorption (Bahadur et al, 2012;Kirchstetter and Thatcher, 2012;Lu et al, 2015) has been based on the explicit assumption that BrC has zero absorption at a wavelength of 700 nm or larger. The findings of the present study strongly challenge this common assumption.…”

Carbonaceous aerosols recorded in a southeastern Tibetan glacier: analysis of temporal variations and model estimates of sources and radiative forcing

“…brown carbon) and its radiative effect in both the atmosphere and snow. A growing number of studies (e.g., Kirchstetter et al, 2004;Andreae and Gelencsér, 2006;Hoffer et al, 2006;Yang et al, 2009;Kirchstetter and Thatcher, 2012) have reported that airborne brown carbon can contribute significantly to aerosol light absorption in the atmosphere, although there are still substantial uncertainties in quantifying optical properties of brown carbon, which makes the model estimation of OC radiative forcing difficult. Similarly, the importance of OC absorption in snow has been recognized and suggested for inclusion in modeling aerosol snow-albedo effects (e.g., Flanner et al, 2009;Aoki et al, 2011).…”

Light Absorbing Properties of Brown Carbon Generated from Pyrolytic Combustion of Household Biofuels

“…It must be noted here that to truly relate the notion of BrC to absorption spectra it is necessary to identify the OC components or group of components that cause increase in light absorption at shorter wavelengths. The bulk OC absorption spectra having enhanced absorption in UV visible range (Angstrom exponent > 2) are usually related to presence of BrC (Kirchstetter and Thatcher, 2012;Feng et al, 2013).…”