Emissions and Partitioning of Intermediate-Volatility and Semi-Volatile Polar Organic Compounds (I/SV-POCs) During Laboratory Combustion of Boreal and Sub-Tropical Peat

Abstract

Burning of peatlands is estimated to be a large source of gas-phase non-methane organic compounds and organic aerosol to the atmosphere. However, little is known about the chemical characteristics of intermediate-volatility and semi-volatile organic compounds (I/SVOC) emitted from peat combustion. Quantifying I/SVOC emissions and their subsequent transformation to secondary organic aerosol (SOA) is critical for elucidating biomass-burning (BB) SOA contributions to ambient aerosol concentrations and reducing uncertainties in aerosol radiative forcing from local to global scales. In this study, we provide one of the first estimates of the emissions of eighty-seven different polar I/SVOCs (I/SV-POCs) in both gas- and particle-phases from the laboratory combustion of peat from Alaska and Florida, USA and Pskov region of Russia. The measured I/SV-POCs include alkanoic, alkenoic, alkanedioic, substituted benzoic, resin, methoxy, and aromatic dicarboxylic acids, methoxy phenols, and anhydrous sugars. To understand the phase-partitioning behavior of the I/SV-POCs, the data is presented in two-dimensional volatility-oxidation state, volatility-solubility, and chemical partitioning space diagrams. For all fuels, methoxy phenols and C$_{6}$–C$_{10}$ alkanoic acids have the highest gas-phase mass emissions factors. Levoglucosan, a commonly used organic marker for BB, is the most abundant particle-phase I/SV-POC by mass. Alkanoic acids (C$_{10}$–C$_{20})$, alkanedioic acids with carbon number <7, and aromatic dicarboxylic acids (phthalic and isophthalic acids) are distributed between gas and particle-phases. For Alaskan and Russian peat fuels, more than 80% of I/SV-POC mass resides in the particle-phase while emissions from Florida peat are more evenly distributed between the two phases (particle-phase $\sim$60% of mass).