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Gavin R. McMeeking

Colorado State University
Department of Atmospheric Science
phone: (970) 491-8294
email: grm at lamar dot colostate dot edu
vitae: PDF, HTML
Research interests: aerosol effects on visibility, biomass burning emissions, light absorption by carbonaceous aerosols, size distribution measurements, aerosol-climate interactions, aerosol measurement, science communication

News

In August 2008 I begin a postdoc with Hugh Coe's group at the University of Manchster.

Kreidenweis group webpages

Check out the group activity schedule: Subscribe to this calendar:

Research Links

This section contains links to verious websites that I've found useful for aerosol research purposes.
  1. Research Organizations

  2. Data Sources

  3. Selected CSU Field Studies and Lab Experiments

  4. Other stuff
In press / in review
  • Organic and elemental carbon aerosol measurements during the FLAME biomass burning study

    Submitted to Atmsopheric Environment

    Submitted to Atmospheric Environment
2006
  • Smoke-impacted regional haze in California during the summer of 2002

    Observations of aerosol physical, chemical, and optical properties made at 38 locations in Washington, Oregon, and California are presented to show the regional-scale influence of wildfire smoke during the summer of 2002. Aerosol measurements made during an intensive field campaign conducted in July, August, and September 2002 in Yosemite National Park indicated that smoke-impacted aerosols were present at the park during frequent haze episodes. In addition, backward trajectory analyses showed that large-scale meteorological conditions during the study were dominated by transport from western and southern Oregon, a region with high fire activity during the summer of 2002. Observations of aerosol properties at the Yosemite NP site were remarkably similar, with similar temporal variations, to data from a second monitoring site at Blodgett Forest Research Station in the Sierra Nevada, approximately 150 km to the NNW. Further similarities to the temporal changes in aerosol properties as measured by monitoring networks with numerous sites in California and Oregon confirmed the regional nature of the haze, which had elevated fine aerosol particle mass concentrations compared with typical summertime average concentrations. The observations suggest that emissions from wild fires can have strong and sustained regional impacts on aerosol concentrations, air quality, and visibility.

    McMeeking G.R., S.M. Kreidenweis, M. Lunden, J. Carrillo, C.M. Carrico, T. Lee, P. Herckes, G. Engling, D.E. Day, J. Hand, N. Brown, W.C. Malm and J.L. Collett, Jr., Agric. For. Meteor. 137 (1-2), 25-42, 2006.
2005
  • Observation of smoke-influenced aerosol during the Yosemite Aerosol Characterization Study: 2. Aerosol scattering and absorbing properties

    Direct observations and size-distribution-based estimates of light-scattering coefficients (b sp ) are presented for the Yosemite Aerosol Characterization Study (YACS), which took place during the summer of 2002, an active fire year. Uncertainty in the estimates of b sp were found to be sensitive to the choice of the aerosol refractive indices, which were retrieved by aligning optical particle counter measurements to differential mobility analyzer observations and, in addition, were calculated from composition measurements. Aerosol composition during the study was dominated by organic carbon, with highest levels observed during periods impacted by biomass burning smoke influenced hazes. As a result, estimates of the aerosol refractive index from composition measurements were highly sensitive to the assumed properties of organic carbon. Retrieved and calculated refractive indices were in agreement for reasonable assumptions for properties of organic carbon. Excellent agreement (within 6%) was found between measured b sp and size-distribution derived b sp if the imaginary component of the refractive index, determined from composition measurements and assuming all species were internally mixed, was included in the Mie calculation. Under the internally mixed assumption, aerosols sampled during the study were modeled as weakly absorbing, with computed dry single scattering albedo ranging from 0.86 to 0.94. Calculated light absorption coefficients yielded a study-averaged dry aerosol mass absorption efficiency of 0.37 0.05 m2g-1.

    McMeeking G.R., S.M. Kreidenweis, C.M. Carrico, J.L. Collett, Jr., D.E. Day and W.C. Malm (2005), J. Geophys. Res., 110, D18209, doi:10.1029/2004JD005624.

  • Hygroscopic properties of an organic-laden aerosol

    Observation and appreciation of scenic landscape features, airport runway visibility, and the earth's radiation balance are all dependent on the radiative properties of the atmosphere, which in turn are dependent on the scattering and absorption characteristics of ambient aerosols. Atmospheric scattering and, to a lesser degree, absorption characteristics are highly dependent on the amount of water vapor absorbed by aerosols under ambient relative humidity (RH) conditions. Water vapor absorptive properties of inorganic aerosols have been extensively measured and modeled; however, hygroscopic properties of organic aerosols are less understood, especially as they occur in the ambient atmosphere. Therefore, an aerosol characterization study was conceived and implemented at Yosemite National Park, which is highly impacted by carbonaceous aerosols. The overall objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient aerosol. The study was conducted during July, August, and the first week of September at Turtleback Dome on the south rim of the entrance to Yosemite Valley. The ratio of the scattering coefficient at some RH divided by the scattering coefficient at some minimum RH (f(RH)=bscat(RH)/bscat(RHmin)) was measured over a wide range of RHs. f(85-RH-90) decreased from about 2.0 to 1.2 as the organic carbon mass (OMC/(NH4)2(SO4)) ratio increased from a low of 0.57 to 11.15, implying that the f(RH) associated with organics is small, possibly on the order of 1.1 or less. Furthermore, modeling f(RH) as a function of RH suggested that ambient organic mass aerosols may be weakly hygroscopic with an f(RH) at RH=8590% of about 1.1.

    Malm W.C., D.E. Day, S.M. Kreidenweis, J.L. Collett, Jr., C. Carrico, G. McMeeking and T. Lee, Atmos. Env. 39(27), 4969-4982, 2005.

  • Intercomparison and closure calculations using measurements of aerosol species and optical properties during the Yosemite Aerosol Characterization Study

    Physical and optical properties of inorganic aerosols have been extensively studied, but less is known about carbonaceous aerosols, especially as they relate to the non-urban settings such as our nation's national parks and wilderness areas. Therefore an aerosol characterization study was conceived and implemented at one national park that is highly impacted by carbonaceous aerosols, Yosemite. The primary objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient aerosol, while a secondary objective was to evaluate a variety of semi-continuous monitoring systems. Inorganic ions were characterized using 24-hour samples that were collected using the URG and Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring systems, the micro-orifice uniform deposit impactor (MOUDI) cascade impactor, as well as the semi-continuous particle-into-liquid sampler (PILS) technology. Likewise, carbonaceous material was collected over 24-hour periods using IMPROVE technology along with the thermal optical reflectance (TOR) analysis, while semi-continuous total carbon concentrations were measured using the Rupprecht and Patashnick (R&P) instrument. Dry aerosol number size distributions were measured using a differential mobility analyzer (DMA) and optical particle counter, scattering coefficients at near-ambient conditions were measured with nephelometers fitted with PM10 and PM2.5 inlets, and dry PM2.5 scattering was measured after passing ambient air through Perma Pure Nafion dryers. In general, the 24-hour bulk measurements of various aerosol species compared more favorably with each other than with the semi-continuous data. Semi-continuous sulfate measurements correlated well with the 24-hour measurements, but were biased low by about 0.15 ug/m3. Semi-continuous carbon concentrations did not compare favorably with 24-hour measurements. Fine mass closure calculations suggested that the factor for estimating organic mass from measurements of carbon was approximately 1.8. Furthermore, fine scattering closure calculations showed that the use of 4.0 m2/g for the fine organic mass scattering coefficient was an underestimate by at least 30% for periods with high organic mass concentrations.

    Malm W.C., D.E. Day, C. Carrico, S.M. Kreidenweis, J.L. Collett, Jr., G. McMeeking, T. Lee, J. Carrillo and B. Schichtel (2005), J. Geophys. Res., 110, D14302, doi:10.1029/2004JD005494

  • Observations of smoke-influenced aerosol during the Yosemite Aerosol Characterization Study: Size distributions and chemical composition

    The Yosemite Aerosol Characterization Study (YACS) took place in Yosemite National Park from 15 July to 5 September 2002, during which time air masses arriving at the site were believed to have been influenced by smoke from numerous wildfires active in the western United States. Physical, optical, and chemical aerosol measurements were made to characterize visibility and to help define aerosol sources contributing to haze in the park, with a particular emphasis on the role of prescribed and wild fires. Measurements of dry aerosol size distributions were made with a differential mobility analyzer (DMA) and an optical particle counter (OPC). An iterative alignment method assuming a range of refractive indices was applied to OPC size distributions to match them to DMA size distributions, returning the real refractive index that yielded the best fit and generating a complete size distribution for 0.04 < Dp < 2 μm. Retrieved dry aerosol real refractive indices generally ranged from 1.56 to 1.59 and were comparable to values estimated from composition measurements. Organic carbon was the dominant aerosol species during the study, particularly during periods identified as smoke impacted. Mie theory was used to determine mass scattering efficiencies (λ = 530 nm) from measured dry size distributions using retrieved refractive indices. These ranged from 3 to 6 m² g-1, with the highest values occurring during smoke-impacted episodes.

    McMeeking G.R., S.M. Kreidenweis, C.M. Carrico, T. Lee, J.L. Collett, Jr. and W.C. Malm (2005), J. Geophys. Res., 110, D09206, doi:10.1029/2004JD005389

  • Hygroscopic growth behavior of a carbon-dominated aerosol in Yosemite National Park

    The influence of particulate organic material (POM) and the contribution of biomass smoke on air quality and visibility remain a paramount issue in addressing regional haze concerns in US national parks. Measurements during the Yosemite Aerosol Characterization Study (July - September 2002) indicated an aerosol dominated by POM (not, vert, similar70% of identified species) and strongly influenced by biomass smoke. Here we report aerosol size hygroscopic growth measurements for dry (RH<5%) aerosol diameters of 100 and 200 nm as measured with a controlled relative humidity tandem differential mobility analyzer. Hygroscopic growth was found to be negligible for relative humidity (RH) 40%, particle size typically increased smoothly with RH, and overall hygroscopic growth at high RH was low to moderate in comparison to the range of values reported in the literature. For RH>80%, both monomodal and bimodal growth profiles were observed during the study, with 200 nm particles more often splitting into bimodal profiles (68% of cases), indicating some degree of external mixing. Trimodal growth profiles were observed on two occasions during periods of changing meteorology and aerosol composition. For bimodal profiles for 200 nm dry particles, particle diameter growth factors at RH=80% (D(RH=80%)/Do where Do is measured at RH<5%) were 1.110.04 and 1.290.08 for the more and less hygroscopic modes, respectively. Ensemble D/Do was calculated using a cubic-weighted sum of D/Do of individual modes. For 200 nm particles, average ensemble D(RH=80%)/Do was 1.150.05 and D(RH=90%)/Do was 1.310.06, and were slightly large for 100 nm particles. These growth factors are dramatically lower than those for typical ambient aerosol ionic components such as sulfate, nitrate and sodium salts and sulfuric acid. An inverse relationship between the POM fraction of PM2.5 and hygroscopicity was particularly evident for 200 nm particles with D(RH=80%)/Do approaching not, vert, similar1.1 as the POM/ionic mass ratio exceeded 10. Linear correlations with several measurements of POM and select biomass smoke markers were -0.74 Carrico C.M., S.M. Kreidenweis, W.C. Malm, D.E. Day, T. Lee, J. Carrillo, G.R. McMeeking and J.L. Collett, Jr., Atmos. Env. 39(8), 1393-1404, 2005.

Presentations

2007
  • NMR analysis of FLAME 1 samples
    AAAR Annual Meeting, Reno, NV

  • Carbon comparison for controlled biomass burning aerosol
    AAAR Annual meeting, Reno, NV

  • Reaction chamber poster (presenting author)
    AAAR Annual meeting, Reno, NV
  • Size distribution and refractive index measurements during a sieries of controlled biomass burning experiments
    AAAR annual meeting, Reno, NV
  • Optical and physical properties of biomass burning aerosol
    DOE GCEP End of Summer Workshop, Washington, DC
2006
  • Preliminary measurements of light attenuation by organic carbon from FLAME
    Group meeting
  • Light absorption by biomass burning aerosol
    DOE GCEP End of Summer Workshop, Washington, DC
2005
  • Regional haze in california ...
    AGU Fall Meeting, San Francisco, CA
  • Regional scale measurements of smoke-impacted haze in California, Oregon and Washington AAAR Annual Meeting, Austin, TX
  • Carbonaceous aerosols and visibility DOE GCEP End of Summer Workshop, Washington, DC
2004
  • October (talk): Dry aerosol size distributions and derived optical properties during the Yosemite Aerosol Characterization Study AWMA Visibility Specialty Conference, Asheville, NC
2003
  • October (poster): Size distribution data from the 2002 Yosemite visibility study AAAR Annual meeting, Anaheim, CA
2002
  • August (talk): Evolution of the nocturnal boundary layer over a Columbia Basin vineyard DOE GCEP End of Summer Workshop, Argonne, IL
  • May (talk): Terrain and ambient wind effects on the warming footprint of a wind machine 25th AMS Conference on Agriculture and Forest Meteorology, Norfolk, VI
  • May (talk): Leaf-air temperature difference at Blodgett Forest Berkeley Center for Atmospheric Science Seminar series, Berkeley, CA


Last modified: Thu Jan 10 16:40:50 MST 2008