Primary aerosol emissions from lignocellulosic biomass and major constituents under well-defined pyrolysis conditions

Abstract

Near-source aerosol emissions from biomass burning are challenging to model and predict because of the complexity of the feedstocks and the evolved species, as well as the potential variability in local conditions. This study investigated and characterized near-source emissions from biomass and biomass constituent pyrolysis under well-defined conditions, providing data for validation of aerosol formation models and sub-models, and tested a hypothesis that near-source aerosol emissions from biomass can be predicted through a summative model approach based on constituent emissions and lignocellulosic biomass composition. Aerosol emission factors, concentrations, sizes, and volatility were assessed during highly repeatable lignocellulosic biomass and constituent pyrolysis experiments using a macro-TGA. Lignin and cellulose were found to produce significantly more and larger pyrolysis aerosol emissions than hemicellulose, and lignin produced aerosols with lower volatility than those from hemicellulose and cellulose. Lignocellulosic composition was investigated for its influence on primary aerosol emissions from biomass pyrolysis, including contributions to aerosol quantity, size, and volatility, through two approaches. First, the superposition model was tested using experimental aerosol measurements from individual constituents. Second, a simulated pine sample was produced by mixing constituents in the proportions in which they are present in pine, and aerosol emissions from pyrolysis of this sample were experimentally measured. Simulated aerosol emissions from superposition modeling and mixed-constituent-derived “pine” were compared to elucidate synergistic constituent influences on aerosol formation, and both results were found to predict pinewood aerosol emissions well. Conclusions regarding the successes and failures of the superposition model in predicting primary biomass aerosol emissions under similar conditions were drawn. Lastly, the influence of combustion on the biomass aerosol emissions under the conditions studied in this work was characterized to highlight the applicability and limitations of the pyrolysis results presented in this work to near-source aerosols formed under oxidative conditions.