Light absorption properties and molecular compositions of water-soluble and methanol-soluble organic carbon emitted from wood pyrolysis and combustion

Primary organic aerosol (POA) is produced by combustion and pyrolysis of fir wood in a tube furnace under different heating atmospheres and temperatures. Dissolved organic carbon was obtained by extracting POA with methanol and pure water. The absorption spectra, functional groups, and molecular composition of the dissolved organic carbon were measured and analyzed. The results found that dissolved organic carbon under nitrogen conditions had higher light absorption properties than dissolved organic carbon under air conditions and that methanol-soluble organic carbon had a higher light absorption capacity than water-soluble organic carbon. These results are attributed to the higher molecular weight, unsaturation, and modified aromaticity of methanol-soluble organic carbon compared to water-soluble organic carbon; and dissolved organic carbon under nitrogen has a higher molecular weight, unsaturation, and modified aromaticity than that under air. By the correlation between the mass absorption efficiency values at 365 nm and the molecular properties, the positive and negative correlation between the absorption properties of dissolved organic carbon and its molecular properties was established, which is helpful to understand the essential reasons for the changes in the absorption properties of POA at the molecular level.