Measurements of gas-phase inorganic and organic acids from biomass fires by negative-ion proton-transfer chemical-ionization mass spectrometry

Emissions from 34 laboratory biomass fires were investigated at the combustion facility of the U.S. Department of Agriculture Fire Sciences Laboratory in Missoula, Montana. Gas‐phase organic and inorganic acids were quantified using negative‐ion proton‐transfer chemical‐ionization mass spectrometry (NI‐PT‐CIMS), open‐path Fourier transform infrared spectroscopy (OP‐FTIR), and proton‐transfer‐reaction mass spectrometry (PTR‐MS). NI‐PT‐CIMS is a novel technique that measures the mass‐to‐charge ratio (m/z) of ions generated from reactions of acetate (CH3C(O)O−) ions with inorganic and organic acids. The emission ratios for various important reactive acids with respect to CO were determined. Emission ratios for isocyanic acid (HNCO), 1,2 and 1,3‐benzenediols (catechol, resorcinol), nitrous acid (HONO), acrylic acid, methacrylic acid, propionic acid, formic acid, pyruvic acid, and glycolic acid were measured from biomass burning. Our measurements show that there is a significant amount of HONO in fresh smoke. The NI‐PT‐CIMS measurements were validated by comparison with OP‐FTIR measurements of HONO and formic acid (HCOOH) and with PTR‐MS measurements of HCOOH.