Development and Use of Negative-Ion Proton-Transfer Chemical-Ionization Mass Spectrometry for the Measurement of Gas-Phase Acids

Many of the key processes in the atmosphere are heavily influenced by acidic trace gas. Gas phase acids, both organic and inorganic, are poorly understood largely due to the limited range of measurement techniques available. This thesis details the development and use of negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS) for the measurement of gas phase inorganic (HCl, HONO, HNO3, and HNCO) and organic acids (formic, acrylic, methacrylic, etc.). This method is based on the chemical ionization of acids via proton transfer reactions with the acetate ion (CH3COO-). This thesis discusses various laboratory experiments and field deployments of the NI-PT-CIMS instrument: (1) laboratory development and characterization including the characterization of response times and humidity dependence, (2) development of calibration systems, (3) laboratory measurement of acidic trace gas emissions from biomass fires at the Fire Sciences Laboratory in Missoula, MT, (4) measurements of organic and inorganic acids in urban air made during the CalNex 2010 field study, and (5) a discussion of a compound of emerging interest, isocyanic acid (HNCO), which is released from biomass burning and was found to be produced photo-chemically in urban air. NIPT- CIMS represents a significant advancement in gas phase acid measurement techniques allowing for measurements on a 1 sec timescale with detection limits in the parts per trillion (ppt) range