This project involves deployment of a High-Resolution Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (HR-PTR-ToF MS) during the August 2010 BEACHON-ROCS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen - Rocky Mountain Organic Carbon Study) field campaign in the Manitou Forest, Colorado. This will be the first deployment of this type of novel, commercially available instrument in a field campaign. During ROCS a similar HR-PTR-ToF MS will be on site and operated by the developers of the commercial instrument. In addition, various other organic trace gas analyzers will be in place, constituting a comprehensive VOC intercomparison study that will allow detailed evaluation of the operation characteristics of the HR-PTR-ToF MS technology under real field conditions. The instrument's fast response time and very low detection limit makes it very suitable for the kinds of VOC flux measurements that will be conducted during BEACHON-ROCS yielding potentially significant insights into biogenic VOC emissions and their subsequent atmospheric chemistry in a sparse forest environment. Measurement of the fluxes of oxygenated VOCs from the forest using HR-PTR-ToF MS will be attempted for the first time.
This HR-PTR-ToF MS deployment will allow evaluation of the performance of this new investigative tool and inaugurate its application in atmospheric chemistry field research. Close interaction with the manufacturer will ensure the optimal advancement of this novel technology with regard to the hardware, software, and data analytical aspects. Broader impacts also will include the exposure of a graduate student and a technician to a large field campaign for the first time. They will work with scientists from different fields and institutions as well as the developers of the HR-PTR-ToF MS. This acquired expertise will tremendously benefit their scientific and academic career development.
This grant supported the first employment of a novel instrumentation, a commercialized high resolution-proton transfer-time of flight-mass spectrometer (HR-PTR-ToF-MS), in the field during the BEACHON-ROCS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen – Rocky Mountain Organic Carbon Study) and BEACHON-RoMBAS (Rocky Mountain Biogenic Aerosol Study) intensive campaigns in the Manitou Forest, Colorado, to determine biogenic emissions of volatile organic compounds (VOCs). Knowledge of the atmospheric VOC budget is crucial to understand atmospheric oxidation capacity including ozone concentration and formation of secondary organic aerosol both affecting air quality and climate. The HR-PTR-ToF-MS possess unique and superior features compared to previously employed instrumentation such as fast response time (<100 ms), high mass resolution (>4000 m/Δm), and very low detection limit (< 10 pptv at 1 min integration, <100 pptv at 1 sec integration) which makes it very suitable for online VOC measurements in the field. Under this proposal the HR-PTR-ToF-MS was successfully operated continuously 24/7 for about 25 and 27 days during the BEACHON-ROCS and BEACHON-RoMBAS campaign, respectively. BVOCs (from a ponderosa pine ecosystem) were continuously measured from 6 different heights above ground (1.8 m, 5.0 m, 8.5 m, 12.0 m, 17.7 m, and 25.3 m) at the Manito Forest Observatory Chemistry Tower. During BEACHON-ROCS we found that 1-methanol and acetone show relatively high mixing ratios (mean values > 1.00 ppbv), followed by acetaldehyde and 2-methyl-3-buten-2-ol (MBO) (0.50-1.00 ppbv) and monoterpenes (MT). The mixing ratios of methyl vinyl ketone (MVK), methyl ethyl ketone (MEK), and toluene are similar in magnitude. Acetonitrile and benzene have the lowest mixing ratios throughout the sampling period. During BEACHON-RoMBAS a total of 9 VOC species were quantified by using a standard gas calibration system. Similar to the previous campaign, methanol and acetone exhibit relatively higher mixing ratios (> 1.00 ppbv) than the rest of the VOC species. 2-methyl-3-buten-2-ol (MBO) and monoterpenes (MT) are the two major primary BVOC species, with mean mixing ratios of about 1.00 ppbv and 0.50 ppbv, respectively. The mean mixing ratio of acetaldehyde falls between MT and MBO. Acetonitrile, MVK, MEK and toluene show relatively low and similar mixing ratios (0.10-0.20 ppbv). Our measurements allowed us to infer the typical spatial and temporal variations of MBO and MT in comparison with ozone. These VOC measurements allowed for intercomparison with previously established instrumentation such as Proton Transfer Reaction Quadrupole Mass Spectrometer (PTR-MS), a Fast Online Gas-Chromatograph coupled to a Mass Spectrometer (TOGA), a Thermal Dissociation Chemical Ionization Mass Spectrometer (PAN-CIMS) and a Fiber Laser-Induced Fluorescence Instrument (FILIF).
