To measure VOCs in the atmosphere we apply mass spectrometry in two forms: GC-MS, gas chromatography – Mass spectrometry; and PTR-MS, proton transfer reaction mass spectrometry. These methods are complimentary in that the former is highly specific but generally lower in measurement frequency whereas the latter is fast but less specific. Both techniques are incredibly sensitive, being able to measure VOC mixing ratios at the parts per trillion level. The group operates several GC-MS systems, some of which are laboratory based and designed to analyze samples collected in pressurized canisters or adsorbent filled tubes. Other GC-MS systems are operated in the field, on ships or even on aircraft. Likewise, our PTR-MS systems are also operated at remote stations. The fast measurement time is exploited to generate vertical profiles of VOCs on the Amazon ATTO tower. Other PTR-MS systems have been adapted to fly in the HALO aircraft or to measure OH reactivity directly.
E. Bourtsoukidis, F. Helleis, L. Tomsche, H. Fischer, R. Hofmann, J. Lelieveld, and J. Williams: An aircraft gas chromatograph-mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow, Atmos. Meas. Tech. 10, 5089-5105, 2017, https://doi.org/10.5194/amt-10-5089-2017.
N. Yassaa, T. Custer, W. Song, F. Pech, J. Kesselmeier, and J. Williams: Quantitative and enantioselective analysis of monoterpenes from plant chambers and in ambient air using SPME, Atmos. Meas. Tech., 3, 1615-1627, doi:10.5194/amt-3-1615-2010, 2010.
V. Sinha, J. Williams, J. Crowley, and J. Lelieveld. Comparative reactivity method - a new tool for measuring total OH reactivity in ambient air. Atmos. Chem. Phys., 8, 2213-2227, 2008.
J. Williams, U. Pöschl, P. J. Crutzen, A. Hansel, R. Holzinger, C. Warneke, W. Lindinger, and J. Lelieveld: An Atmospheric Chemistry Interpretation of Mass Scans obtained from a Proton Transfer Mass spectrometer flown over the Tropical Rainforest of Surinam. J. Atmospheric Chemistry, 38, 133-166, 2001.