Abstract View
Quantifying Brown Carbon Measured in Real-world Biofuel Combustion Emissions
MOHAMMAD MAKSIMUL ISLAM, Alyssa Sanderson, Andrew Whitesell, Ashley Bittner, Rawad Saleh, Andrew Grieshop, North Carolina State University
Abstract Number: 518
Working Group: Aerosol Physics
Abstract
Biomass burning is considered an important source of light-absorbing organic carbon (OC), also known as brown carbon (BrC). Although BrC affects earth’s radiative balance, its absorption properties remain uncertain for many sources. In this work, we used methanol (ME) to extract organic carbon from ~60 filters collected during ‘real-world’ biofuel combustion in India and Malawi from emissions tests of various wood stoves (traditional, rocket, gasifiers and chimney) and artisanal charcoal kilns. We then used a spectrophotometer to collect the absorption spectra (239 to 800 nm wavelengths) to characterize BrC absorption.
Mass absorption coefficients (MACλ-ME) of extracted OC from chimney stoves and charcoal kilns are significantly lower than those of traditional and improved non-chimney stoves at near-ultraviolet to blue wavelengths. Traditional and chimney stove emissions have the lowest and highest absorption angstrom exponent (AAEME), respectively. MACλ-ME in the UV wavelengths shows positive correlation with elemental-to-organic carbon ratio (EC/OC), although weaker than that observed in lab cookstove studies. Unlike EC/OC, modified combustion efficiency (MCE) exhibits weak positive correlation with MACλ-ME, showing that EC/OC is a better indicator of combustion conditions associated with brown carbon production. At near-ultraviolet to blue wavelengths, imaginary refractive indices of BrC (KBrC-ME) are anti-correlated with wavelength dependence, w (≈AAE-1), suggesting that less wavelength-dependent BrC has higher light absorptivity. MACλ-ME correlated with the fraction of OC evolving at 615°C (OC3/OC; r = 0.54 at 500 nm) and anti-correlated with OC evolving at 310°C (OC1/OC; r = 0.49 at 500 nm). This association is consistent with a link between absorptivity of brown carbon and OC volatility, and hence, suggests that BrC absorption may be parameterized by using existing OC data. We apply a simple radiative forcing model to provide an estimate of BrC’s climate impacts relative to co-emitted black carbon.