PTR-MS Measurements of VOCs at Thompson Farm, NH, 2004-2006

A proton transfer reaction-mass spectrometer (PTR-MS) is being used in an ongoing study of volatile organic compounds (VOCs) at the University of New Hampshire's Observing Station at Thompson Farm (TF) in Durham, New Hampshire. Measurements were conducted during the summer of 2004, with continuous data sets available starting 1 June 2005 to the present. An overview of the results for 15 different masses corresponding to individual and groups of VOCs will be presented. Basic statistics of the measurements, e.g., means, minima, and maxima, for the overall data set will be presented along with seasonal information and diurnal patterns. Preliminary results have yielded means (10th; 90th percentiles) in ppbv for 11 compounds as follows: 0.64 (0.05; 0.21) acetonitrile; 0.50 (0.09; 0.83) acetaldehyde; 0.66 (0.09; 1.56) acetic acid; 0.32 (0.01; 0.94) isoprene; 0.34 (0.01; 1.07) methyl vinyl ketone + methacrolein; 0.20 (0.04; 0.45) methyl ethyl ketone; 0.21 (0.03; 0.21) benzene; 0.21 (0.03; 0.42) toluene; 0.14 (0.02; 0.29) C8 aromatics; 0.08 (0.02; 0.17) C9 aromatics and 0.03 (0.01; 0.07) C10 aromatics. The data will be presented within the context of local photochemistry and regional transport. Deposition velocities have been estimated for several of these compounds and are significantly higher than values used in many models. Such efficient removal may have important implications for the chemical impact of these species, at least on a regional scale. The results from Thompson Farm will be compared to similar observations made at other locations.