Investigation of black and brown carbon multiple‐wavelength‐dependent light absorption from biomass and fossil fuel combustion source emissions

Abstract

Quantification of the black carbon (BC) and brown carbon (BrC) components of source emissions is critical to understanding the impact combustion aerosols have on atmospheric light absorption. Multiple-wavelength absorption was measured from fuels including wood, agricultural biomass, coals, plant matter, and petroleum distillates in controlled combustion settings. Filter-based absorption measurements were corrected and compared to photoacoustic absorption results. BC absorption was segregated from the total light extinction to estimate the BrC absorption from individual sources. Results were compared to elemental carbon (EC)/organic carbon (OC) concentrations to determine composition's impact on light absorption. Multiple-wavelength absorption coefficients, Angstrom exponent (6.9 to <1.0), mass absorption cross section (MAC), and Delta C (97 μg m À3 to~0 μg m À3) were highly variable. Sources such as incense and peat emissions showed ultraviolet wavelength (370 nm) BrC absorption over 175 and 80 times (respectively) the BC absorption but only 21 and 11 times (respectively) at 520 nm wavelength. The bulk EC MAC EC, λ (average at 520 nm = 9.0 ± 3.7 m 2 g À1; with OC fraction <0.85 =~7.5 m 2 g À1) and the BrC OC mass absorption cross sections (MAC BrC,OC,λ ) were calculated; at 370 nm ultraviolet wavelengths; the MAC BrC,OC,λ ranged from 0.8 m 2 g À1 to 2.29 m 2 g À1 (lowest peat, highest kerosene), while at 520 nm wavelength MAC BrC,OC,λ ranged from 0.07 m2 g À1 to 0.37 m 2 g À1 (lowest peat, highest kerosene/incense mixture). These MAC results show that OC content can be an important contributor to light absorption when present in significant quantities (>0.9 OC/TC), source emissions have variable absorption spectra, and nonbiomass combustion sources can be significant contributors to BrC.

Joint measurements of PM&lt;sub&gt;2. 5&lt;/sub&gt; and light-absorptive PM in woodsmoke-dominated ambient and plume environments

“…The patterns of the wavelength-dependent responses shown in Fig. 1 were consistent with the findings from several previous studies, which suggested that UV absorbing compounds are enriched in biomass-combustion PM but scarce in diesel PM (Chen et al, 2015;Olson et al, 2015) or traffic-related PM (Kirchstetter et al, 2004). Broadly, the light-absorbing organic compounds, referred to as "brown carbon" or BrC, have been shown to strongly absorb UV (Andreae and Gelencsér, 2006).…”

“…Studies show that woodsmoke enhancement peaks at ∼ 300 nm (Kirchstetter et al, 2004;Kirchstetter and Thatcher, 2012). It is possible that including shorter wavelengths in future instrumentation would improve the sensitivity to woodsmoke PM (Olson et al, 2015). Another approach taking advantage of UV enhancement (or wavelength dependence of the aerosol absorption coefficient in general), as reported by Sandradewi et al (2008a), derives light absorption Ångström exponents (AAE, or α) from multi-wavelength Aethalometer readings.…”

“…However, Harrison et al (2013) analyzed data for DC from an Aethalometer network in the UK and suggested the presence of other UV absorbing contributors (such as coal burning) to the DC signal. Laboratory experiments conducted by Olson et al (2015) showed that besides biomass burning, other sources such as uncontrolled coal (e.g., lignite) and kerosene combustion in lamps can also lead to high DC values. In addition, some secondary organic aerosol (SOA) products have also been found to result in UV Figure 1.…”

Relative importance of black carbon, brown carbon, and absorption enhancement from clear coatings in biomass burning emissions

“…Potential sources of BrC include emissions from biomass burning (Kirchstetter et al, 2004;Moosmüller et al, 2009;Chen and Bond, 2010;Lack et al, 2012a;Saleh et al, 2014;Washenfelder et al, 2015); incomplete combustion of fossil fuels, especially coal (Bond, 2001;Yang et al, 2009;Olson et al, 2015); and secondary organic aerosols (Saleh et al, 2013;Zhang et al, 2013;Lin et al, 2015). There exists significant uncertainty concerning the relative contribution of each of these source types to total BrC concentrations, but several studies have identified biomass burning as a potentially significant source (Washenfelder et al, 2015;McMeeking et al, 2014;Lack et al, 2012a).…”

The Multi-Wavelength Absorption Analyzer (MWAA) Model as a Tool for Source and Component Apportionment Based on Aerosol Absorption Properties: Application to Samples Collected in Different Environments

“…(c) the Ångström absorption exponent of BC (α BC ) is assumed a priori. In this work α BC = 1 was set according to expectancies for pure, small BC spheres (e.g., [3]) as often applied in the literature (e.g., [51]). Nevertheless, different choices can be in principle be performed due to the possible effect of BC core and coating sizes on the Ångström absorption exponent (e.g., [52]).…”