Papers by Robert Yokelson
ORNL Distributed Active Archive Center Datasets, 2004
Handbook of Vibrational Spectroscopy, 2006
Vibrational Spectroscopy, 2010
We report the construction of a database of infrared spectra aimed at detecting the gases emitted... more We report the construction of a database of infrared spectra aimed at detecting the gases emitted by biomass burning. The project uses many of the methods of the Pacific Northwest National Laboratory (PNNL) infrared database, but the selection of the species and special experimental considerations are optimized. Each spectrum is a weighted average derived from 10 or more individual measurements. Each composite has a spectral range from ≤600 to ≥6500 cm −1 with an instrumental apodized resolution of 0.11 cm −1 . The resolution was chosen to bring out all spectral features, but recognizing that pressure broadening at 760 Torr results in essentially all ro-vibrational lines having these or greater linewidths.
Journal of Geophysical Research, 2003
We examined how adsorption and desorption of gases from inlets and a cell could affect the accura... more We examined how adsorption and desorption of gases from inlets and a cell could affect the accuracy of closed-cell FTIR measurements of carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nitric oxide (NO), nitrogen dioxide (NO2), methanol (CH3OH), acetic acid (CH3COOH), and ammonia (NH3). When standards were delivered to the cell through a stainless steel inlet, temporarily reduced transmission was
Atmospheric Chemistry and Physics, 2015
ABSTRACT The current understanding of secondary organic aerosol (SOA) formation within biomass bu... more ABSTRACT The current understanding of secondary organic aerosol (SOA) formation within biomass burning (BB) plumes is limited by the incomplete identification and quantification of the non-methane organic compounds (NMOCs) emitted from such fires. Gaseous organic compounds were collected on sorbent cartridges during laboratory burns as part of the fourth Fire Lab at Missoula Experiment (FLAME-4) and analyzed by two-dimensional gas chromatography-time-of-flight mass spectrometry (GC x GC-ToFMS). The sensitivity and resolving power of GC x GC-ToFMS allowed the acquisition of the most extensive data set of BB NMOCs to date, with measurements for 708 positively or tentatively identified compounds. Estimated emission factors (EFs) are presented for these compounds for burns of six different vegetative fuels, including conifer branches, grasses, agricultural residue, and peat. The number of compounds meeting the peak selection criteria ranged from 129 to 474 among individual burns, and included extensive isomer groups. For example, 38 monoterpene isomers were observed in the emissions from coniferous fuels; the isomeric ratios were found to be consistent with those reported in relevant essential oils, suggesting that the composition of such oils may be very useful when predicting fuel-dependent terpene emissions. Further, 11 sesquiterpenes were detected and tentatively identified, providing the first reported speciation of sesquiterpenes in gas-phase BB emissions. The calculated EFs for all measured compounds are compared and discussed in the context of potential SOA formation.
Aerosol Science and Technology, 2014
Ice nucleating particles (INP) initiate heterogeneous ice nucleation in mixed-phase clouds, influ... more Ice nucleating particles (INP) initiate heterogeneous ice nucleation in mixed-phase clouds, influencing cloud phase and onset temperatures for ice formation. Determination of particle types contributing to atmospheric INP populations requires isolation of the relatively rare INP from a total particle sample, typically followed by time-consuming single-particle characterization. We propose a method to estimate the contributions of light-absorbing, primarily refractory black carbon (rBC), particles to INP populations by selectively removing them prior to determination of INP concentrations. Absorbing particles are heated to their vaporization temperature using laser induced incandescence in a single particle soot photometer (SP2) and the change in INP number concentrations, compared to unheated samples, is assessed downstream in the CSU Continuous Flow Diffusion Chamber (CFDC). We tested this approach in the laboratory using stronglyabsorbing and nonabsorbing aerosol types to confirm effective removal of rBC INP and to explore the impact of the processing on non-light-absorbing INP. An INP-active rBC particle type was efficiently removed, while nonabsorbing kaolinite and a soil-based INP were not affected by laser exposure. Results for the products of wiregrass combustion indicated that absorbing particles, primarily rBC, accounted for about 40% of all INP, consistent with electron microscopy of INP emitted during prescribed burns of this fuel type. However, kaolinite internally mixed with rBC exhibited reduced activity after passing through the SP2, suggesting that the validity of the method for realistic internal mixtures needs additional research. The sensitivity of the CFDC presently limits applicability of the method to relatively high INP number concentration samples.
The Journal of Physical Chemistry, 1993
... James B. Burkholder,' R. L. Mauldin 111, RJ Yokelson, S. Solomon, an... more ... James B. Burkholder,' R. L. Mauldin 111, RJ Yokelson, S. Solomon, and A. R. Ravishankarat Aeronomy Laboratory, NOAA, 325 Broadway, Boulder, Colorado 80303, and The Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder ...
The Journal of Physical Chemistry, 1994
The temperature dependence of the NO3 absorption spectrum was measured over the wavelength range ... more The temperature dependence of the NO3 absorption spectrum was measured over the wavelength range 440-720 nm and temperature range 298-200 K using a diode array spectrometer. The NO3 absorption cross section at 662 nm, the peak of the 0-0 transition, was measured using time resolved tunable diode laser absorption following 351 nm laser photolysis of a CldClONO:! mixture. The NO3 absorption cross section at 662 nm was (2.23 f 0.22) x cm2 at 298 K and increased 36% in going from 298 to 200 K (20 error limits including estimated systematic errors). measurements.
The Journal of Physical Chemistry, 1995
The rate coefficient for reaction 1, C1 + ClON02 -. products was measured between 195 and 354 K. ... more The rate coefficient for reaction 1, C1 + ClON02 -. products was measured between 195 and 354 K. C1 atoms were generated by pulsed laser photolysis of Clz in an excess of ClON02. The temporal profiles of C1 atom loss and NO3 product formation were monitored using resonance fluorescence and tunable diode laser absorption at 662 nm, respectively. The long path absorption system was used to measure kl between 200 and 298 K while the resonance fluorescence system was employed between 195 and 354 K. Thermal decomposition of CION02 prevented measurements at temperatures greater than 354 K. The two techniques yielded rate coefficients which are in excellent agreement. An Arrhenius rate coefficient expression of kl = (6.0 f 0.4) x exp[(l40 f 30)/T] cm3 molecule-' s-' and room temperature rate constant of kl(298 K) = (9.6 f 1.0) x lo-'* cm3 molecule-' s-' were derived from data at T I 298 K. The quoted error limits are 2 0 and include estimated systematic errors. Our results are compared with previous measurements, and values of kl for atmospheric modeling are recommended. @ Abstract published in Advance ACS Abstracts, September 1, 1995.
ABSTRACT The University of Montana/Forest Service airborne FTIR (AFTIR) was installed on the Univ... more ABSTRACT The University of Montana/Forest Service airborne FTIR (AFTIR) was installed on the University of Washington Convair-580 for 19 flights between 14 August and 14 September 2000. We quantified the major trace gases in minutes-old biomass burning smoke (namely CO2, CO, CH4, C2H4, C2H2, CH2O, CH3OH, CH3COOH, HCOOH, NH3, NO, NO2, and HCN) from 9 fires in both arid and humid, wooded savannas where most global biomass burning occurs. Several of these measurements coincided with TERRA/ER2 overpasses. The AFTIR fire measurements confirmed the importance of oxygenated organic compounds in tropical smoke and provided an emission factor for HCN (a potential biomass burning tracer) that is 20 times higher than previously thought. AFTIR also documented some rapid post-emission chemical transformations in smoke. We measured actual formation rates for ozone and acetic acid in smoke downwind from two savanna fires. The ratio of excess ozone to excess CO reached 9% after a few hours of photochemical processing. The similar ratio for acetic acid increased from 1.4 to approximately 5% over the same time period. We observed cloud scavenging of methanol, ammonia, and acetic acid from smoke and a simultaneous, cloud-related source of formaldehyde in the plumes from two other savanna fires. To our knowledge, the SAFARI-2000 flights provided the first comprehensive characterization of savanna fire smoke samples with explicitly known smoke ages and post-emission processing scenarios. We also measured vertical profiles for CO2, CO, CH4, and H2O under TERRA/ER2 at 5 locations in the southern African gyre, one location in the continental outflow over the Atlantic, and one location in the inflow adjacent to the Indian Ocean. During a 3-aircraft intercomparison we observed trace gas enhancement in the free troposphere due to deep cumulus convection. Finally, we measured high NOx emission factors for ships off Namibia. Taken together, our FTIR-based measurements of the emissions from ships, savanna fires, the production and use of biofuels, and the related structure of the African, dry-season troposphere could contribute substantially to global atmospheric chemistry models.
ABSTRACT Biomass burning is one of the most important influences on the global atmosphere. Field ... more ABSTRACT Biomass burning is one of the most important influences on the global atmosphere. Field experiments have yielded much useful knowledge about fires, but are often limited by lower S/N, lack of fuels data, and the challenges imposed by operating in remote tropical locations. In large-scale laboratory experiments at the U. S. Forest Service (USFS) Fire Sciences Laboratory we captured and measured all the emissions produced by 54 separate fires in 16 fuel types from southern Africa, Indonesia, Canada, the U. S., and Germany. Fuels included Dambo grass, Miombo litter, and Indonesian rice straw and peat. The fires were carefully simulated to match (as closely as possible) actual fires observed primarily during SAFARI-2000 and in Indonesia. Fuel C:H:N content was measured and fuel mass loss was continuously monitored. Total pressure, temperature, and flow of trace gases was monitored at the sampling platform in the stack above the fires. Trace gases were speciated by an impressive array of instrumentation. Both a closed cell and open-path FTIR were deployed by the UM group to quantify CO2, CO, CH4, NMHCs, oxygenated VOCs, NOx, HCN, and NH3 above ppb levels yielding a broad overview of the major smoke constituents. A proton-transfer reaction mass spectrometer (PTR-MS) from MPI was used to measure VOCs at ppt levels. NDIR instruments independently measured CO2 and CO. Canister sampling with GC analysis by MPI, USFS, and UC Irvine also measured CO2 and CO as well as hydrocarbons and halogenated hydrocarbons. Particles were sampled on quartz and Teflon filters to measure the emission factors for PM2.5 and elemental and organic carbon. These results constitute the most comprehensive measurements of fire emissions to date and also the first intercomparison between FTIR and PTR-MS. PTR-MS can quantify the total VOC (with proton affinity higher than water) present at each mass up to 200 a.m.u. at ppt levels. At ppb levels most molecules have multiple IR peaks so FTIR is ideally suited for compound identification. The combination of these two techniques is very powerful. Results include confirmation of the high emissions of oxygenated organic compounds and the relatively low emissions of ammonia by African fires suggested by our airborne FTIR measurements during SAFARI-2000. In addition, numerous compounds were quantified that were below our detection limit in the field campaign thus providing a more complete understanding of these important types of biomass fires.
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Papers by Robert Yokelson