Light‐absorbing properties of ambient black carbon and brown carbon from fossil fuel and biomass burning sources

Abstract

The optical properties of ambient black carbon-containing particles and the composition of their associated coatings were investigated at a downtown site in Toronto, Canada, for 2 weeks in June 2013. The objective was to assess the relationship between black carbon (BC) coating composition/thickness and absorption. The site was influenced by emissions from local vehicular traffic, wildfires in Quebec, and transboundary fossil fuel combustion emissions in the United States. Mass concentrations of BC and associated nonrefractory coatings were measured using a soot particle-aerosol mass spectrometer (SP-AMS), while aerosol absorption and scattering were measured using a photoacoustic soot spectrometer (PASS). Absorption enhancement was investigated both by comparing ambient and thermally denuded PASS absorption data and by relating absorption data to BC mass concentrations measured using the SP-AMS. Minimal absorption enhancement attributable to lensing at 781 nm was observed for BC using both approaches. However, brown carbon was detected when the site was influenced by wildfire emissions originating in Quebec. BC coating to core mass ratios were highest during this period (~7), and while direct absorption by brown carbon resulted in an absorption enhancement at 405 nm (>2.0), no enhancement attributable to lensing at 781 nm was observed. The efficiency of BC coating removal in the denuder decreased substantially when wildfire-related organics were present and may represent an obstacle for future similar studies. These findings indicate that BC absorption enhancement due to lensing is minimal for downtown Toronto, and potentially other urban locations, even when impacted by long-range transport events.

Light absorption of brown carbon in eastern China based on 3-year multi-wavelength aerosol optical property observations and an improved absorption Ångström exponent segregation method

“…It is a group of species with specific physical properties but detailed chemical components that are difficult to characterize. BrC can be produced not only from primary emissions relating to biomass burning (BB) and fuel combustion, but also from secondary organic aerosol (SOA) formation through the oxidation of volatile organic compounds (VOCs) (Andreae and Gelencsér, 2006;Saleh et al, 2014;Chen and Bond, 2010;Lack et al, 2012;Laskin et al, 2015;Healy et al, 2015). Some studies reported that vehicle and ship emissions may also be sources of BrC (Stone et al, 2009;Cavalli et al, 2004).…”

“…Based on the difference of wavelength dependence for BC and BrC, previous studies segregated light absorption of BrC from multi-wavelength optical measurements (Lack and Langridge, 2013;Mohr et al, 2013;Shen et al, 2017), which is called the AAE method. Earlier, the similar concept was used to segregate carbonaceous aerosol fractions from different emission sources based on their difference in AAE value (e.g., wood burning and traffic emission) (Sandradewi et al, 2008;Healy et al, 2012). Usually, the AAE of BC (AAE BC ) was set to be 1.0 based on the properties of bulk BC by many previous studies, assuming the unity of AAE BC between any two wavelengths within the UV to the near-infrared (IR) range (Shen et al, 2017;Olson et al, 2015;Lack and Langridge, 2013).…”

Quantifying black carbon light absorption enhancement with a novel statistical approach

“…If the temperature is too low, the coating cannot be fully removed, and charring can occur if the TD temperature is too high, leading to biased results. For example, a soot particle aerosol mass spectrometer (SP-AMS) study in Toronto found that the efficiency of BC coating removal by TD decreased substantially for wildfire-influenced samples (Healy et al, 2015). Another issue is particle loss due to TD, which can be ∼ 20 % and needs to be taken into account (Ueda et al, 2016).…”

Source Apportionment of Urban Particulate Matter using Hourly Resolved Trace Metals, Organics, and Inorganic Aerosol Components

“…Over the past years, source apportionment using high time resolution OA mass spectra measured by an aerosol mass spectrometer (AMS) or an aerosol chemical speciation monitor (ACSM) has been a useful approach to reduce the dimensionality of complex organic 15 fractions into more easily interpretable OA factors (e.g. Ulbrich et al, 2009;He et al, 2010;Ng et al, 2011;Crippa et al, 2013;Bougiatioti et al, 2014;Lee et al, 2015). Three primary factors: hydrocarbon-like organic aerosol (HOA), cooking organic aerosol (COA), and biomass burning organic aerosol (BBOA), are commonly identified in many locations.…”