Formation and emission characteristics of intermediate volatile organic compounds (IVOCs) from the combustion of biomass and their cellulose, hemicellulose, and lignin

Abstract

Biomass combustion is an important source of intermediate volatile organic compounds (IVOCs), which are important precursors of secondary organic aerosols. To understand how fuel types and combustion conditions affect the formation and emission characteristics of IVOCs, three biomass materials (rice straw, pine, and poplar) and their three extracted components (cellulose, hemicellulose, and lignin) were burned separately in a quartz tube furnace at different temperatures between 300 and 900 °C and with oxygen supplies (20% and 10%). The results show that 1) the emission factors of IVOCs (EFIVOC) from biomass combustion exhibit a bimodal distribution with an increase in temperature, and are more abundant during low-temperature combustion (300–500 °C). The unresolved complex mixture (UCM) accounts for more than 50% of the total IVOCs for all the biomass material. Among the identifiable compounds, methoxyphenols were the most abundant species and account for 20–30% of the total IVOCs during low-temperature combustion. The proportion of polycyclic aromatic hydrocarbons (PAHs) gradually increased to 30–50% with an increase in temperature from 700 to 900 °C, which indicates that methoxyphenols and PAHs have different formation pathways. 2) The average EFIVOC from cellulose, hemicellulose, and lignin combustion were in the order lignin > hemicellulose > cellulose. Methoxyphenols are primarily derived from lignin at low combustion temperatures. The highest proportions of methoxyphenols in lignin from rice straw and pine were more than 2 and 5 times that of cellulose and hemicellulose, respectively. PAHs are mainly derived from the combustion of cellulose and lignin at high temperatures. 3) A large amount of indene (96.4 mg/kg) is detected in lignin combustion, and indene is believed to be one of the most important precursors of PAHs in resonantly stabilized radical pathways. Indene was hardly observed in cellulose combustion, indicating that PAHs were more inclined to form via H-abstraction acetylene addition pathways. 4) The oxygen supply is also an important factor for EFIVOC during biomass burning. At 10% oxygen supply, most of the EFIVOC were higher than that for the 20% oxygen supply conditions for biomass material and the three components.