Characterization of carbonaceous aerosols from biofuel combustion: emissions and climate relevant properties

Carbonaceous aerosols;optical properties;absorption;organic carbon;black carbon;biofuel combustion;cookstove;emission

Chen, Yanju

关键词: Carbonaceous aerosols;    optical properties;    absorption;    organic carbon;    black carbon;    biofuel combustion;    cookstove;    emission;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/29520/Chen_Yanju.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Aerosol direct radiative forcing on climate is significant but highly uncertain. Carbonaceous aerosols, composed of black carbon (BC) and organic carbon (OC), are important to understand aerosol radiative forcing due to their prevalence in the atmosphere. Biofuel combustion is responsible for nearly 20% of primary BC and OC emissions, but this source is relatively unstudied. Both emissions and optical properties (especially absorption) of carbonaceous aerosols from biofuel combustion need to be better characterized to estimate climate impact of biofuel combustion in models.An experimental method was developed to examine light absorption by primary OC emitted from wood combustion and to provide realistic imaginary refractive indices to radiative-transfer models. Water-soluble OC contributed to light absorption at both ultraviolet and visible wavelengths. However, a larger portion of the absorption came from OC that is not extractable by water but by methanol. Higher wood temperature is the main factor creating OC with higher absorption when compared to wood size and type. Mass absorption cross-section (MAC) of BC is an essential variable in climate models. MAC for ambient BC from literature is 10.3±4.2 m2/g. Filter-based absorption methods provide more variant and higher MAC than in-situ absorption measurement. Semi-continuous mass analyzers measure higher MAC than sample-integrated mass measurements. Thermal transmittance method measures higher MAC than the methods which remove OC prior to mass analysis. BC MAC reduces by 13-40 percent when OC is removed by a thermal denuder upstream of the BC measurement. Biofuel combustion is a highly variable source. Emission fingerprint approach was developed and used to compare emissions from different combustion activities. Improved cookstoves reduce emissions by eliminating formation of OC with high SSA, which occurs at low combustion efficiency. In the laboratory a large part of emission is missing for particles with greater SSA which generally produces under low combustion efficiency and we should seek for a way to add this part in the future cookstove testing.I also established the groundwork of data processing for the newly developed cookstove sampling system and interpreted the emission data obtained from in-field cookstove tests in Africa and South Asia. Results show that improved cookstoves may be more fuel efficient, but combustion still needs to be cleaner. Gasifier stoves in India have the lowest PM emission factors of 1 g/kg fuel.