AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Real-time Measurements of Gas Phase Organic Acids Using SF6- Chemical Ionization Mass Spectrometry
THEODORA NAH, David Tanner, Hongyu Guo, Yi Ji, Rodney J. Weber, Greg Huey, Georgia Institute of Technology
Abstract Number: 192 Working Group: Instrumentation and Methods
Abstract Organic acids play important roles in many atmospheric processes such as secondary organic aerosol formation, precipitation chemistry and acidity. The sources and atmospheric chemistry of gas-phase organic acids remain poorly understood due to the limited range of measurement techniques available. At present, research on gas-phase organic acids has focused primarily on formic and acetic acids. This is due to the analytical difficulties in measuring gas phase > C2 organic acids in real time. In this work, we demonstrate the capabilities of SF6- chemical ionization mass spectrometry (CIMS) for the measurement of gas-phase inorganic and organic acids. Its in-field performance is illustrated using ambient measurements conducted in a mixed forest-agricultural area in Yorkville, Georgia from September to October 2016. Gas-phase organic acids as large as C5 are detected at the site. Our measurements showed that ion-molecule reactions between SF6- and organic acids proceeded through charge transfer and fluorine abduct formation. Ambient concentrations of organic acids ranged from a few parts per trillion by volume (ppt) to several parts per billion by volume (ppb), with the largest concentrations observed for formic acid. All the organic acids displayed similar strong diurnal behaviors, reaching maximum concentrations between 5 and 7 pm local time. The organic acids generally showed strong correlations with temperature, but weak correlations with nitric acid and carbon monoxide. Our analysis suggested that biogenic emissions may be an important source of gas-phase organic acids in this rural environment. The combination of high sensitivities, low detection limits and fast response time of SF6- CIMS indicates that it is a promising technique for real-time measurements of atmospheric gas-phase organic acids.