Grantee Research Project Results
Final 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 Amount: $506,742
RFA: Urban Air Toxics (1999) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The objective of this combined laboratory and pilot research project was to establish a viable means of measuring the emission rates and temporal and spatial distributions of urban air toxics and hazardous air pollutants (HAPs) using an existing, ultra-sensitive continuous emissions monitor (CEM). This research project leveraged SRI International’s development of a 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). Using this Jet-REMPI approach, detection limits in the low 20 ppt have been obtained. 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 HAPs now can be measured concurrently at levels that are of toxicological interest.
This instrument will provide direct detection and identification of most HAPs and HAP mixtures in urban air in real time (i.e., 1 to several minutes of averaging). 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 developed the capability to identify and characterize critical emission sources over a wide geographical area under a variety of ambient monitoring conditions. We used 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 was 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 and local variations in oxidizing potential, as indicated by ambient ozone levels measured independently using off-the-shelf instrumentation.
Summary/Accomplishments (Outputs/Outcomes):
We can conclude from our work that an instrument based on a jet-cooled molecular beam combined with REMPI and TOF-MS can provide the sensitivity, selectivity, and time response required for characterization of urban air toxics. We have determined that the single, critical parameter in maximizing the REMPI signal is the local gas density at the point of ionization. The lack of dependency of the internal cooling on the distance from the nozzle exit simplifies the design optimization process.
A number of significant improvements in the Jet-REMPI system were made that have enhanced both its capabilities and its ease of use. Our greatly expanded spectral library now includes more than 150 compounds, including many of the most common urban air toxics. We began a preliminary, local field study by collecting urban air samples onto sorbent tubes for off-line analyses. These analyses allowed 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. This latter data permitted us to determine that our current instrumental sensitivity is sufficient for real-time field measurements without significant further improvements being required to acquire field data.
In parallel with this effort, we performed a pseudo-field study with support from DOE. That study, performed at the U.S. Environmental Protection Agency's (EPA) National Risk Management Research Laboratory in cooperation with Dr. Brian Gullett, further demonstrated the usefulness of Jet-REMPI for rapidly detecting and identifying organic species at trace levels. Using a duplicate Jet-REMPI instrument built and delivered to EPA, we were able to identify trace organic species in the combustion exhaust stream of a nominally pure methane flame. Our collaboration with Dr. Gullett has continued to expand.
We also pursued the development of a more compact Jet-REMPI system based on a variety of commercial components, including a compact tunable UV laser system. Working in cooperation with Opotek, Inc., we have demonstrated that combining their Vibrant laser system with our Jet-REMPI apparatus resulted in a system with only slightly reduced detection capabilities. Preliminary experiments with this system proved that the xylene isomers could not only be detected in the 100 ppt range, but also with isomeric selectivity. These specifications were maintained even when other, closely related organics were present in the sample at concentrations up to 1,000 times higher.
A preliminary system design concept has been developed jointly by SRI International and Opotek, Inc., that combines an improved, ruggedized version of the Vibrant laser system with a commercial, compact TOF-MS to yield a transportable Jet-REMPI instrument capable of unprecedented sensitivity, selectivity, and analytical speed. Once developed, such a system will be very useful in field studies of urban air toxics.
Because of the unequalled temporal resolution and sensitivity of our Jet-REMPI instrument, its use in the field could provide the only reliable, real-time data set on the concentration and distribution of numerous HAPs in polluted urban air. Spatial and temporal mapping of HAP levels as a function of meteorological, seasonal, and atmospheric conditions eventually may establish a means to identify emissions trends, determine human exposure levels, and assess the increased risks associated with specific geographical areas or subpopulations. Such studies with this instrument will permit experiments to rapidly determine cause and effect relationships between HAP emissions and the operational conditions of their sources.
An important result of this effort has been 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. When performed, 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 with a fieldable system, we also plan to 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 independently measured using off-the-shelf instrumentation. We hope to continue the development of a compact, transportable Jet-REMPI system and to use it for a series of urban HAP measurements.
Journal Articles on this Report : 4 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, Volquardsen B, Crosley DR, Oser H. Development of a real-time continuous emissions monitor for hazardous aromatic air pollutants. Organohalogen Compounds 2000;45:141-144. |
R827927 (Final) |
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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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Oser H, Coggiola MJ, Young SE, Faris GW, Crosley DR. Dioxin and furan laboratory measurements using jet-REMPI. Organohalogen Compounds 2001;54:360-363. |
R827927 (Final) |
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Supplemental Keywords:
volatile organic compound, VOC, polycyclic aromatic hydrocarbon, PAH, polychlorinated biphenyl, PCB, peptide nucleic acid, PNA, dioxin, furan, environmental chemistry, physics, risk assessment, chemical transformation, epidemiology,, RFA, Air, Scientific Discipline, Toxics, chemical mixtures, Chemistry, HAPS, Environmental Chemistry, 33/50, tropospheric ozone, air toxics, hazardous air pollutants, hydrocarbons, Benzene (including benzene from gasoline), urban air, emission control strategies, urban air pollutants, hydrocarbon, stratospheric ozone, atmospheric chemistry, benzene, Cresols/Cresylic acid (isomers and mixture), chemical composition, Toluene, measure, urban air toxics, furans, air pollutants, Xylenes, ambient air quality, acute toxicityProgress 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.