Organic vapors from wood, straw, cow dung, and coal burning using Vocus PTR-TOF

Abstract. Solid fuel (SF) combustions, including coal and biomass, are important sources of pollutants in the particle and gas phase and therefore have significant implications for air quality, climate, and human health. In this study, we systematically examined real-time gas-phase emissions using the Vocus proton-transfer-reaction time-of-flight mass spectrometer, from a variety of solid fuels, including beech logs, spruce and pine logs, spruce and pine branches and needles, straw, cow dung, and coal. The average emission factors (EFs) for organic gases ranged from 6.7 to 74.2 g kg^-1, depending on the combustion phases and fuel types. Despite slight differences in modified combustion efficiency (MCE) for some experiments, increasing EFs for primary organic gases were observed with lower MCE. The C_xH_yO_z family is the most abundant group, but a greater contribution of nitrogen-containing species and C_xH_y families (related to polycyclic aromatic hydrocarbons) could be found in cow dung burning and coal burning, respectively. Intermediate volatility organic compounds (IVOCs) also constituted a considerable fraction in solid-fuel combustions (from 12.6 % to 39.3 %), especially for spruce and pine branches and needles (39.3 %), and coal (31.1 %). Despite the large variability of EFs in the organic gas emissions, the relative contribution of different classes showed large similarities between the combustion phases in beech stove burning. The product from pyrolysis of coniferyl-type lignin and the extract of cedar pine needle were identified as characteristic compounds in the spruce and pine branches and needles open burning (e.g., C₁₀H₁₄O₂, C₁₁H₁₄O₂, C₁₀H₁₀O₂). The characteristic product (C₉H₁₂O) from the pyrolysis of beech lignin was identified as the characteristic compound for beech log stove burning. Many series of nitrogen-containing homologues (e.g., C₁₀H_11-21NO, C₁₂H_11-21N, C₁₁H_11-23NO and C₁₅H_15-31N) and nitrogen-containing species (e.g., acetonitrile, acrylonitrile, propanenitrile, methylpentanenitrile) were specifically identified in cow dung burning emissions. Polycyclic aromatic hydrocarbons (PAHs) with 9-12 carbons were identified with significantly higher abundance from coal burning compared to emissions from other studied fuels. The composition of these characteristic organic vapors reflects the burned fuel types and can help constrain emissions of solid fuel burning in regional models.