ARB Research Seminar
This page updated July 26, 2013
Improving the Understanding and Usefulness of Thermal Optical Carbon Analyses
Kochy Fung, Ph.D., of AtmAA, Inc.; with Judith C. Chow, Sc.D, and John G. Watson, Ph.D. of the Desert Research Institute, Nevada
February 22, 2006
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA
Particulate carbon is a major component of PM2.5. Major reasons to measure particulate carbon are assessment of its impact on global climate, health, visibility, and source apportionment. Many methods were developed since the mid 1970's. Today, the thermal optical volatilization techniques are used most commonly. Examples are IMPROVE used since 1987 for the National Parks Service's visibility network and STN for the U.S. EPA's Speciation Trends Network. Both techniques use thermal volatilization with optical correction for charring. The differences in the temperature profiles (ramping rates, plateaus, and dwell times), and charring correction approaches (laser reflectance for IMPROVE and laser transmittance for STN) result in differences in evolved carbon fractions and EC. Our research has shown that aggressive temperature ramps in the OC phase in STN can result in oxidation of particulate EC by in-situ metal oxides, and that charring of the adsorbed organic vapor in the filter can influence the charring correction by transmittance. Some of these adsorbed compounds include n-alkanes (C23-C31), hopanes (C27-C31), and n-alkanoic acids (C10-C22) (Sihabut et al, 2005). As the extent of charring is affected by the nature of the compounds, their concentrations present, and the rate of heating, transmittance correction is affected by the internal charring. On the other hand, reflectance only monitors the charring due to the particles on the filter surface and thus is unaffected by the temperature profile used.
Agreement of carbon fractions from different analyzers depends on the accuracy of sample temperatures and the level of trace oxygen in the system. We developed a temperature calibration procedure to audit thermal optical carbon analyzers so that sample temperatures would be correctly indicated by the oven sensor. At ~40 ppm or higher of trace oxygen, some changes in the carbon fractions were observed, but the OC/EC split was not be affected due to charring correction.
Other applications of the analyzer include determination of carbonates (to assess the impact of yellow sand in China, for example) and water soluble organic compounds to estimate secondary organic aerosols.
Kochy Fung received his B.S. in chemistry from UCLA. and his Ph.D. in pharmaceutical chemistry from the University of Southern California. Dr. Fung has over 35 years of research experience in several fields, with the most recent 29 years in the environmental areas. After working 12 years for an environmental consulting firm (ERT, later as ENSR), he founded AtmAA, an environmental laboratory with a partner and Atmoslytic Inc. for instrumental development. He has conducted over 50 gaseous and particulate monitoring programs, participating as a principle investigator on the measurement of carbonyls and VOCs in major air quality studies in California, Houston, and Northeastern United States. As the technical director in regional acid deposition monitoring programs: EPRI's Operational Evaluation Network, and EPA's ACID MODES, and principle co-investigator in CARB's CADMP, he developed many laboratory procedures to facilitate the monitoring. Many measurement techniques he pioneered are used currently on a routine basis. Some examples are the DNPH method for carbonyls in ambient air, the TMO method for speciation of particulate organic and elemental carbon, the use of passive organic vapor badges for the assessment of short term exposures to ambient aromatic and chlorinated hydrocarbons, and the South Coast Method 25.3 adopted by the U.S. EPA as CTM Method 35 for the assessment of emissions from low VOC stationary sources such as IC engines, flares and turbines. He has authored and co-authored many papers, and conducted presentations and workshops internationally.
Judith C. Chow is a Research Professor in the Division of Atmospheric Sciences at Desert Research Institute (DRI), where she directs the Environmental Analysis Facility. Dr. Chow has more than 28 years of experience in conducting air quality studies and performing statistical data analysis. She is the principal author or co author of more than 242 peer reviewed publications, 361 presentations, and 192 technical reports. She is the chair of the Editorial Review Board for the Journal of the Air & Waste Management Association, co-editor-in-chief of Aerosol and Air Quality Research, and a member of the Editorial Review Board for TheScientificWorld. Dr. Chow's service on prominent committees includes membership on the National Academy of Sciences/National Research Council (NAS/NRC) Committee on Research Priorities for Airborne Particulate Matter. She is currently on the NRC Board of Environmental Studies and Toxicology (BEST). Her other national committee experience includes the U.S. Environmental Protection Agency (EPA) Clean Air Scientific Advisory Committee (CASAC) Ambient Air Monitoring and Methods (AAMM) Subcommittee; the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility Science Board; the National Environmental Respiratory Center (NERC) External Scientific Advisory Committee (ESAC); and the South Coast Air Quality Management District (SCAQMD) Multiple Air Toxics Exposure Study III (MATES III). Dr. Chow earned MS and Sc.D. degrees in Environmental Science from Harvard University. She has also been the principal investigator or major collaborator in more than 50 large air quality studies, including the State of Nevada Air Pollution Study (SNAPS).
John G. Watson is a Research Professor in the Division of Atmospheric Sciences at Desert Research Institute (DRI). Dr. Watson received his B.A. and M.S. in Physics and Ph.D. in Environmental Sciences from Oregon Graduate Institute. He has over 30 years of experience in planning and conducting air quality studies in the U.S. and internationally. Some of his professional activities include serving in National Research Council (NRC) Committee on The Effects of Changes in New Source Review as the Topic Leader in Programs for Stationary Sources of Air Pollutants (March 2004-February 23, 2006); Chair in National Academy of Engineering U.S. Committee on Energy Futures and Air Pollution in Urban China and the United States, January 2005 - December 2006; Journal of the Air and Waste Management Association Associate Editor (March 1, 2004-February 28, 2007) and Lecturer, Receptor Model and Data Analysis Training Workshops (various sponsors) in Portland, OR; Las Vegas, NV; San Francisco, Sacramento, Los Angeles, San Diego, and El Centro, CA; Pocatello, ID; Denver, CO; Phoenix and Tucson, AZ; Research Triangle Park, NC; Pittsburgh, PA; Austin, TX; Chicago, IL Vancouver, B.C., Canada; Santiago, Chile; Taipei, Taiwan; and Johannesburg, Cape Town; Pretoria, South Africa; and Mexico City and Cuernavaca, Mexico; A&WMA Publications Committee (chair, 1998-2001), A&WMA Critical Review Committee (member, 1982-present; chair, 1995-1998); Intersociety Committee on Methods of Air Sampling and Analysis (chair, 1995-present); and California Regional PM10/PM2.5 Regional Air Quality Study Technical Committee.