Abstract View
Quantifying Brown Carbon Light Absorption in Real-world Biofuel Combustion Emissions
MOHAMMAD MAKSIMUL ISLAM, Andrew Whitesell, Alyssa Sanderson, Ashley Bittner, Soroush Neyestani, Rawad Saleh, Andrew Grieshop, North Carolina State University
Abstract Number: 285
Working Group: Carbonaceous Aerosol
Abstract
Biofuel combustion is an important source of light absorbing organic carbon (OC), also known as brown carbon (BrC). In this work, we applied spectrophotometry to characterize methanol-extracted BrC from filters collected during ‘real-world’ biofuel combustion emissions tests in India and Malawi, including various wood stoves (‘traditional’, ‘improved’ and ‘chimney’) and artisanal ‘charcoal’ kilns. Extracts’ average mass absorption coefficient (MACbulk,λ) at near-ultraviolet to blue wavelengths was the highest for ‘traditional’, followed by ‘improved’, ‘chimney’, and ‘charcoal’; Absorption Angstrom Exponent (AAE) showed the opposite trend. MACbulk,λ in UV wavelengths were positively correlated with elemental carbon to organic aerosol ratio (EC/OA), although less so than in lab cookstove studies. Unlike EC/OA, modified combustion efficiency (MCE) exhibited a weak positive correlation with MACbulk, λ, indicating that EC/OA was a better indicator of combustion conditions associated with BrC production. Imaginary refractive indices of BrC at 551 nm (k551) were anti-correlated with wavelength dependence (w), suggesting that less wavelength dependent BrC has higher light absorptivity. MACbulk,λ correlated with the fraction of OC evolving at 615°C (OC3/OC) and anti-correlated with OC evolving at 310°C (OC1/OC). This association is consistent with a link between BrC absorptivity and OC volatility, and suggests that BrC absorption may be parameterized using existing OC data. EC/OA is strongly negatively correlated BrC contribution to total aerosol light absorption. BrC showed high absorption contribution ranging from 48% to 80%, on average, at 365 nm depending on mixing state assumptions. We are now estimating the direct radiative effect (DRE) of BrC from biofuel combustion over India using the BrC light-absorption properties obtained from our experiments in conjunction with MERRA reanalysis dataset.