Grantee Research Project Results
2001 Progress Report: Characterization of Urban Air Toxics Sources in Support of HAPs Emission Control Strategies
EPA Grant Number: R827927Title: Characterization of Urban Air Toxics Sources in Support of HAPs Emission Control Strategies
Investigators:
Institution: Sri International
EPA Project Officer: Chung, Serena
Project Period: December 1, 1999 through November 30, 2002
Project Period Covered by this Report: December 1, 2000 through November 30,2001
Project Amount: $506,742
RFA: Urban Air Toxics (1999) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
This research project leverages SRI's current development of a continuous emissions monitor (CEM) for dioxins and furans supported by the U.S. Department of Energy (DOE). The detector uses a pulsed nozzle gas inlet, resonance-enhanced multiphoton ionization (REMPI), and time-of-flight mass spectrometry (TOF-MS). We have obtained detection limits in the low 20 ppt, using the Jet-REMPI approach. The extreme sensitivity and chemical specificity of this instrument and the nearly universal nature of REMPI and mass spectrometry provide a new analytical capability. With a single instrument, the spatial and temporal distribution of a majority of the most toxic organic hazardous air pollutants (HAPs) can be measured concurrently at levels that are of toxicological interest.
This instrument will provide direct detection and identification of the most HAPs and HAP mixtures in urban air in real time (i.e., 1 to several minutes of averaging). The objectives of this research project are to establish a viable means of measuring the emission rates, and temporal and spatial distributions of urban air toxics and HAPs using an existing, ultra-sensitive CEM. Because our CEM is capable of directly measuring in real time the concentration of specific HAPs and urban air toxics at levels far below present analytical instruments, we will develop the capability to identify and characterize critical emission sources over a wide geographical area, under a variety of ambient monitoring conditions. We will use this capability in a pilot field study to validate our approach to measurement and characterization of urban air toxics.
An important result of this effort will be the design of a field-deployable instrument based on our approach that can be used in a subsequent comprehensive field study of urban air toxics linked to epidemiological or health effects studies. These studies will provide the scientific basis for regional or national emissions control strategies and standards. Once these exposure levels are measured using the techniques established in this effort, they will contribute to a significant improvement in the ability to link exposure and risk associated with urban air toxics.
In addition to making HAP concentration measurements, we also will study the temporal variation and interconversion of related chemical species with exposure to sunlight and other meteorological conditions. This will provide direct information on atmospheric transformations of emitted HAPs by photolytic processes. This aspect often is neglected in urban pollution studies, but is crucial to establishing the identity of those compounds actually causing toxic effects. Such transformation studies can be enhanced by correlating our real-time HAPs and transformed HAP levels with short-term, local variations in oxidizing potential as indicated by ambient ozone levels measured independently using off-the-shelf instrumentation.
Progress Summary:
Several significant improvements in the Jet-REMPI system were made during this reporting period that have enhanced both its capabilities, as well as its ease of use. Our spectral library now includes more than 120 compounds, including many of the most common urban air toxics. We have begun a preliminary, local field study by collecting urban air samples onto sorbent tubes for offline analysis. We anticipate that these analyses will allow us to not only improve the sampling and analysis protocols, but also to establish some approximate air toxics levels in the San Francisco Bay area. These latter data will permit us to determine if our current instrumental sensitivity is sufficient for real-time field measurements, or if further improvements will be required to acquire this type of field data.
As a first approach, we used standard charcoal sorbent tubes connected to portable air metering pumps. By operating the pumps at a calibrated air flow for selected periods of time, we could sample known volumes of air. We returned the sorbent tubes to the laboratory, and we recovered the adsorbed organic compounds using conventional solvent extraction methods. Because we needed to perform a chemical survey before applying Jet-REMPI, we analyzed the extracted samples using GC-MS. Once a set of target compounds had been identified by GC-MS, the same sample was examined using Jet-REMPI to confirm their presence and ascertain the signal levels available from our instrument.
To test this sampling and analysis approach, we collected samples from open containers, gasoline tank headspace, automobile exhaust, and ambient air. In ambient air, we collected samples for 3.5 hours to obtain enough material to use GC-MS as a survey tool. Only toluene shows as a small signal in the GC-MS scan. To use Jet-REMPI, we diluted the sample by a factor of 20,000 to avoid overloading the instrument. This dilution is equivalent to a direct measurement with a sampling time of about 1 second. The BTEX (benzene, toluene, ethyl benzene, and xylenes) compounds were readily seen in the Jet-REMPI instrument, and the three isomers of xylene can be individually quantified. Our preliminary study showed that many urban air pollutants, such as BTEX, can be detected quantitatively using Jet-REMPI long-term sorbent sampling. More importantly, because of the high sensitivity of REMPI, these same compounds also were detected in the field in near real-time without sampling and preconcentration.
In parallel with this effort, we already have performed a pseudo-field study with support from the DOE. That study, performed at the U.S. EPA's National Risk Management Research Laboratory (NRMRL) in cooperation with Dr. Brian Gullett, further demonstrated the usefulness of Jet-REMPI for rapidly detecting and identifying organic species at trace levels. SRI had the unique opportunity to perform these measurements without the time and expense associated with transporting the instrument to a field site. This was possible by using the REMPI apparatus that SRI built for Dr. Gullett. Because that apparatus is a duplicate of the one currently used at SRI, measurements taken with the system in conjunction with the U.S. EPA's combustion facility allowed us to make these "field-like" measurements. We expect that our collaboration with Dr. Gullett will continue and expand.
Among the most intriguing observations was the detection of several interesting species that were identified in a nominally "clean" methane flame. Benzene and phenol were both positively detected in the off-gas stream of the reactor. In addition, clear evidence also was found for aniline produced in the U.S. EPA reactor under the test conditions. For all species, the measured spectra are essentially identical to those recorded using a "clean" test gas mixture, and all were easily detected in the exhaust stream. Furthermore, their presence could be entirely attributed to the methane combustion chemistry, as the background levels were not detectable in the absence of the flame.
Future Activities:
We will continue with the limited scope field study of urban air toxics. We will complete the analysis of the initial offline samples acquired recently, while refining the sampling and analysis protocol. We plan to extend the study by acquiring additional offline samples and subjecting them to Jet-REMPI analysis.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 8 publications | 4 publications in selected types | All 4 journal articles |
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Oser H, Coggiola MJ, Faris GW, Young SE, Volquardsen B, Crosley DR. Development of a jet-REMPI (resonantly enhanced multiphoton ionization) continuous monitor for environmental applications. Applied Optics 2001;40(6):859-865. |
R827927 (2000) R827927 (2001) R827927 (Final) |
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Oser H, Copic K, Coggiola MJ, Faris GW, Crosley DR. Congener-specific detection of dioxins using jet-REMPI. Chemosphere 2001;43(4-7):469-477. |
R827927 (2001) R827927 (Final) |
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Supplemental Keywords:
VOC, PAH, PCB, PNA, dioxin, furan, environmental chemistry, physics, risk assessment, chemical transformation, epidemiology., RFA, Scientific Discipline, Air, Toxics, air toxics, Environmental Chemistry, HAPS, Chemistry, chemical mixtures, tropospheric ozone, 33/50, ambient air quality, emission control strategies, urban air toxics, urban air, stratospheric ozone, air pollutants, Toluene, hydrocarbon, Xylenes, hazardous air pollutants, benzene, chemical composition, urban air pollutants, Cresols/Cresylic acid (isomers and mixture), furans, acute toxicity, hydrocarbons, Benzene (including benzene from gasoline), Xylenes (isomers and mixture), atmospheric chemistryProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.