of Ambient Measurement for Hazardous Air Pollutants An EPA-sponsored survey points out the need for continued methods development for the Clean Air Act R . M U K U N D , THOMAS J . K E L L Y , S Y D N E Y M . GORDON M E L I N D A J . HAYS, WILLIAM A. M c C L E N N Y
he 1990 Clean Air Act Amendments (CAAA) have refocused attention on ambient air toxics. Title 111 of the CAAA seeks to reduce the public health risks from 189 hazardous air pollutants (HAPs) in ambient air through congressionally mandated riskreduction timetables and goals for HAP emission controls and other requirements (1).Health risk determination and the quantification of reductions in health risks requires knowledge of ambient HAP concentrations and, by extension, the availability of adequate ambient HAP measurement methods. However, assessments of the current database of information available on ambient concentrations and transformation products, recently reported in ES&T (z),found a paucity of data needed to conduct adequate health risk assessments for many HAPs ( 3 , 4 ) . For example, the survey showed no ambient data for 74 of the 189 HAPS. The principal reason for the absence of ambient data for many HAPS has been suggested as a lack of suitable ambient air sampling and analysis methods. Here we discuss an EPA-sponsored survey (5) of the current status of ambient measurement methods for the 189 HAPs that found 180 different candidate methods that are currently in various stages of development. This survey found that only 126 of the 189 HAPs have methods that are reasonably established for ambient air measurements, although aU of these methods are EPA-approved or well demonstrated for ambient monitoring. Of the remainder, 53 HAPs have methods that are reasonably established for nonambient air, such as for workplace or stack emissions measurements, and which could likely be developed for ambient air applications. Of the 10 remaining HAPs, six have methods that are potentially applicable to ambient air measurements following extensive further development, and four others have no methods currently in any stage of development. 0013-936W95/0929-183A$09.00/0 Q 1995 American Chemical Society
Ambient methods development research has resulted in a variety of measurement methods, particularly for volatile organics, semivolatile organics, and particulate-phase inorganics. Many of these methods, such as those in the Intersociety Committee (ISC) methods compilation (6) and the EPA's Toxic Organics (TO) compendium ( 3 ,target individual chernicals on the 189 HAPs list. However, the 189 HAPS are a varied collection of individual chemicals and generic compound groups, and include industrial chemicals, pesticides, solvents, metals, and combustion byproducts. Although some of the HAPs have long been measured in ambient air, many othersassigned to the list based on their toxicity in workplace environments-are not typically measured or even considered in ambient air. The diversity of the HAPS is a principal factor in this survey's recommendation for continued ambient measurements methods development.
Survey approach This survey differed substantially from previous reviews (8,9) of possible measurement methods for the 189 HAPs in both approach and scope. The survey initially compiled key physical and chemical properties of the HAPS. These properties were used to group the HAPs into classes of compounds and, subsequently, to conduct evaluations of the applicability of individual measurement methods. Following the division of the 189 HAPs into organic and inorganic compounds, vapor pressure (VP: mmHg at 25 C and boiling point (and/or melting point) data were compiled for all HAPS. VP data were used to categorize and rank the 189 HAPs, using quantitative (but subjective) VP criteria to define very volatile (VP > 380 mmHg) organic compounds (WOC: 15 HAPS) and very volatile inorganic compounds (VVINC: 6 HAPS);volatile (VP = 0.1-380 mmHg) organic compounds (VOC: 82 HAPS) and volatile inorganic compounds (VINC: 3 HAPS); O
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I
Format used in the HAPs methods survey report’
I
Ambient m w u m n t mlthod ColnpMlnd clma “Applicable”’ ’likely” “Potsntial’
colnpoud
CAS DO.
Acetaldehyde
75-074 WOC
Acetamide
60-355
TO-5 TO-11
R-4[141
SVOC
Limit 04 dstscticn Comr..
TO-51 ppbv; TO-ll:l ppbv; 1141: 30 ppmv OSHA CIM
lA6251;R - 3 ; R-47
R-l:l
R-1, CLP-lA,
R3 pplieable“ inemodfor a specfic HAP does not neceaaarilv mrdihaIw
semivolatile (W= lO-’-O.l mmHg) organic compounds (SVOC: 64 HAPs) and semivolatile inorganic compounds (SVINC 2 HAPS);and nonvolatile (W mmHg) organic (NVOC 5 HAPS) and nonvolatile inorganic compounds (NVINC 12 HAPs). Nineteen of the H A P s are listed simply as compound groups (e.g., PCBs). Based on which compounds in each of these groups are most likely to be present in ambient air, these compound group H A P s were classified in multiple volatility classes. For the purposes of the above count of HAPS in each volatility class, compound group HAPs were categorized on the basis of the most volatile species in each group likely to be present in ambient air. For the volatile and very volatile HAPS, additional properties covering electmnic polarizability,water solubility, aqueous reactivity, and estimated atmospheric lifetime were compiled. The project report presents extensive tabular summaries of the property data (5).
Categorizing measurement methods
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A wide range of measurement methods were reviewed for each W including EPA SourceTest Methods, EPA Contract Laboratory Program (CLP) and TO Compendium methods, as well as standard methods designated by the ISC. the National Institute of Occupational Safety and Health (NIOSH),the Occupational Safety and Health Administration (OSHA), and the American Society for Testing and Materials L4STM). Novel methods reported in the scientific literature also were reviewed, including those in the literature citations of the S U N ~ Son ambient concentrations and atmospheric hansformations of the “6 (3.4).In addition, reports, journal articles, and meeting proceedings known to contain information on ambient measurement methods for HAPs were reviewed. Techniques such as multi-stage mass spectrometry (MS/MS),optical remote sensing, and specialized instruments currently unsuited for use in a widespread HAPs monitoring network were not included in the survey We briefly discuss the potential of such techniques later in this article. The survey also evaluated the state of develop-
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n or app
ment for individual HAPSmeasurement methods, distinguishing workplace, laboratory, or stack emission methods from methods actually tested in ambient air. The measurement methods identified for the 189 HAPs were then organized into three categories: “applicable,”“likely,”and “potential.” Methods that are reasonably established and documented for measurement of the target HAP in ambient air were termed “applicable,” but not necessarily with the implication of approval or certification by EPA for measuring that particular HAP in ambient air. In most cases, methods ideniitied as “applicable” have actually been used for ambient measurements. In other cases, methods were identified as “applicable”for a specific HAP because of the degree of associated documentation, even though no ambient data were found. “Likely” methods most commonly were those clearly established and used for the target HAP in nonambient air, such as OSHA or NIOSH methods for HAPS in workplace air. Methods identified as “applicable” for one HAP, and consequently inferred for another HAP based on close similarity of chemical and physical properties, were also included within the “likely” category. ‘“Potential”methods were those judged to need extensive further development before their application to ambient air measurements could be justified. Many ‘“potential”methods were evaluated for the w e t HAP in sample matrices other than air (e.g., water and soil). “Potential“ methods also were inferred for some HAPs,based on “applicable”or “likely” methods found for other HAPs of somewhat similar chemical and physical properties. For HAPs for which no “applicable” or “likely” methods were found, further searches were conducted beyond the reviews outlined above. Detailed literature searches were conducted using the computer database files of Chemical Abstracts Service (CAS) and the National Technical Information Service (NTIS), without restriction to Englishlanguage publications. Methods identified through such searches were then subjected to the same evaluation and categorization standards.
The results of the method survey are presented in the project report in the form of a comprehensive table that presents the 189 HAPs in the same order as they appear in the CAAA (5). Compound class HAPs were addressed by identifymg methods for the most and least volatile species of each class likely to be present in ambient air. Table 1 shows the format and content of the results table in the project report (5). For each HAP, identified methods are listed in successive columns for “applicable,”“likely,”and “potential” methods, using standard method designations (e.g.,TO-5, CLP-2, NIOSH 55141, or by citations to the pertinent literature (e.g., R-1, R-2, etc.). The limits of detection or ranges of measured concentrations for selected methods are provided as reported in the literature, along with supporting information. Citations of all the methods identified were compiled in a reference list following the complete methods table (5).Although no effort was made to compile all possible information on each method, the citations were aimed at providing sufficient information to review the basics of the identified method and to locate further information.
Status of current methods In all, this survey identified 183 methods pertinent to ambient measurements of the 189 HAPs, comprising 15TO methods, 51 NIOSH methods, 30 OSHA methods, three EPA screening methods, four CLP methods, and 80 literature citation methods. Although the method status for each HAP cannot be presented in this paper, an overview of method status as a whole for the 189 HAPs is almost equally informative. Figure 1 summarizes the current method status for all 189 HAPs and indicates the total number of HAPs in each method development category based on the most developed method identified for each HAP. As Figure 1 reveals, “applicable” ambient measurement methods were found for 126 HAPs (twothirds of the HAPs listed): “likely” methods, but no “applicable”methods, were found for 53 HAPs. Most of these “likely” methods were specific to the HAP in question, but for seven HAPs the identification of “likely” methods was inferred based on HAP properties. For six HAPS-acetamide (SVOC), 2-acetylaminofluorene (NVOC), benzotrichloride (SVOC), chloramben (SVOC), 1,2-diphenylhydrazine (SVOC),and N-nitroso-N-methyl urea (V0C)only “potential” methods could be identified. In addition, of those, three were inferred on the basis of chemical and physical properties. For four HAPSacrylic acid (VOC),ethyl carbamate (VOC),hexamethyl phosphoramide (SVOC), and titanium tetrachloride (VINC)-no measurement methods could be identified at any level of development. The identification of 126 HAPSwith “applicable” methods is consistent with our recent HAPS concentrations survey (31,which found ambient data from urban areas in the United States available for 115 of the HAPs. This count must be qualified with several caveats to avoid an overly optimistic view of the state of HAP measurement methods, particularly with respect to the definition of an “applicable”method. ‘IApplicable” methods, though targeted for the indi-
cated HAP in ambient air and documented to a reasonable degree, may not necessarily have been actually used for ambient measurements of the indicated HAPs or have had all the related sampling and analysis difficulties resolved. Furthermore, for the 19 HAPs that are compound groups, Figure 1uses a simplified standard (discussed in the figure note), which does not consider all of the various compounds within each class that may be present in ambient air. Taken by HAP volatility class, “applicable”methods were identified for the majority of the HAPS. In total, “applicable”methods were identified for 109 of the 166 organic compounds, and for 17 of the 23 inorganic compounds. However, for the five NVOCs and two of the threeVINCs, no “applicable”methods were found. In all volatility classes, most compounds with no “applicable”methods could be associated with one or more ‘‘Likely”methods, suggesting that for most HAPS promising methods exist from which ambient methods may be developed. Of the 183 separate measurement methods identified, 54 methods were deemed to be “applicable” to one or more HAPS. Filter, sorbent, or multiple collector (e.g., filter and sorbent) sampling methods predominate among these “applicable”methods (40 of 54 methods); this is not surprising considering the number of semi- and nonvolatile compounds among the 189 HAPs. Canister and impinger-based methods (five each of the 54) are also common, a probable consequence of the number of volatile HAPs compounds. Gas chromatography (GC) dominates the analytical techniques in the 54 “applicable”methods, being cited in 36 of the 54 methods. GUMS analysis is cited in 23 methods, and GC coupled with other detection techniques in 13 methods (probably as a direct result of the high sensitivity required to detect air toxics in ambient air). Liquid and ion chromatography (LC, IC), inductively coupled plasmalatomic absorption (ICPIAA),MS, and other analysis techniques are cited in the remaining 18 ‘lapplicable” methods. A few of the “applicable” methods are individually capable of measuring many of the 189 HAPs. Table 2 is a summary of the top 10 methods “applicable” to the greatest number of HAPS. A few of these methods are by themselves capable (at least on paper, in some cases) of measuring a substantial fraction of the 189 HAPs. This result is mainly a consequence of the number of volatile and semivolatile organics among the HAPs, which may be collected by canister and sorbent-based methods developed over the past decade. Another interesting observation from Table 2 is the number of similar techniques among the top 10 applicable methods, each of which has its own definitions and target pollutants. This result points to the possibility of consolidating similar methods into more broadly capable methods. Although the various measurement methods identified in this survey were selected specificallywith a view toward their use in ambient air monitoring, it remains the responsibilityof the user to establish the worthiness of a particular candidate method in an individual application. This responsibility is of particular significance in air monitoring programs, in contrast to research-type measurements, because VOL. 29, NO. 4, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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by measurement method sta6s CategorizationIS by the most developed ambient measurement method currently identdred 'Likely" methods
"applicare" methods and the number Of HAPs measured by each method Applicable rnlthod rnlnplingand a n n ~ c atechniq l Tenax sorbent GUMS ICLP-1AI Multisorbsnt' GUFIDECD (R-31 FiherKADPUF: GCMS (CLP-21 Canister; GUECD/NPDFID [TO-14) Canister: GUMS (CLP-16) Sorbent; Auto GCECDIFID (R-6) Tenax; GUMS (TO-1) PIIF . -. ,c c m n iTn-ini ,. ._, Filter: ICP/GFAA (CLP-31 PUF: GC/ECD/MS IR-27)
__ ___ -
39 37 36 33 23
16 13
.-
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6 4
4 1
5
-A
10
10
1
'Melhod references provided in lhe project isport 171: "R-" methods are literature citation melhods; FID = flame ionizationdetector, ECO = electron caplure detector. NPD = n b g e n phosphorus detector, GFA4 = graphite furnace aomic abrorptlon 8~~clroscopy. XAD-PUF=XAO resin or poh/urethanefoam sorbents. 'Method capabili: A '"applicable"; L: "IikeV; P: "potential:
"monitoring" generally implies a routine and longterm effort with potential regulatory implications as well as cost, data quality, and legal considerations.
Future directions
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Although the existence of methods currently capable of ambient air measurements for 126 of the 189 HAPS is encouraging. it also points to the contin-
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fied would-be particularly valuable and costeffective. The definition of a "likely" method suggests that a reasonable degree of further development should result in a method applicable to ambient ax. Of the 53 HAPs with "likely" methods, 44 are WOCs, VOCs, or SVOCs. These three groups are the largest classes of HAPS, so further development of methods for such compounds would be particularly beneficialand potentially cost-effective.The large number of "applicable" methods already available for volatile and semivolatile organics should facilitate development of methods for additional compounds. Even for those H A P s for which "applicable" measurement methods are available, continued evaluation would be worthwhile, especially w t h the goal of consolidating the current variety of similar methads into fewer, well-characterized, and broadly applicable methods. One such noteworthy effort is the development of a "TO-15 m e t h o d ("Determination of Volatile Organic Compounds (VOCs) in Air Collected in Summa Canisters and Analyzed by Gas Chromatography/MassSpectrometry (GC/MS)";under development by U.S. EPA/Atmospheric Research and Exposure Assessment Laboratory, Research Triangle Park, NC 27711). for addition to EPNs TO compendium (7).TO-15 will modify the current TO-14, evacuated Summa canister technique (7).to apply to a larger subset of the VOCs among the 189 HAPS. In addition to such developmental efforts, further validation of HAPs methods also is needed for "applicable" methods, particularly for the identified literature citation methods. For six HAPs, existing measurement methods would require extensive further development before application to ambient air can be considered. For four HAPs, no measurement methods in any state of development were identified. Together, these 10 HAPs comprise the greatest gap in measurement capabilities for the HAPS. These 10 HAPS are relatively unusual compounds not normally regarded as ambient air contaminants, and some are highly reactive with short atmospheric lifetimes (2).Conseauentlv. it is difficult to determine whether thev or their reaction products constitute a significant health risk in ambient air. Methods development for these 10 HAPs should, therefore, be prioritized based on information for emissions, reactivity, and products of these HAPS. This approach will avoid allocating time and resources on methods development for a HAP or HAPS that are, for example, too reactive (e.g., titanium tetrachloride) or are emitted in quantities too small to be measurable in the atmosphere.This linkage of method development with other information should in general be valuable for all HAPs. As discussed previously, some techniques were specifically not included in this survey because the instrumentation involved was considered currently unsuited for application in a widespread H A P s monitoring network. Two potentially applicable methads not included are optical remote sensing systems and MS/MS systems with a direct air interface. Both methods require a significant investment in equipment, which limits current applications pri-
marily to special studies. Remote sensing techniques, particularly open-path systems, are receiving increasing attention for HAPs monitoring ( e g , 10). The techniques are appealing because they require no sampling and could provide essentiallyrealtime, multipollutant monitoring. Future enhancements and technical breakthroughs in these techniques are expected to yield practical detection limits in the low-ppbv range for many HAPS. Similarly, commercial ion-trap MS/MS systems are now becoming available for use with direct air interfaces (11). The high sensitivity,real-time response and potential applicability of MSlMS techniques to a wide spectrum of HAPs suggests that applications of such techniques could be widespread soon. Ongoing methods development efforts, either as additions to the EPA Compendium of Methods (7)or as focused research projects that support EPA Program Offices, currently address a number of the HAPs still requiring “applicable” methods. EPAs Office of Research and Development (ORD) plans to address the overall methods development needs indicated in this report through a combined in-house and extramural research program. Current EPA-ORD budgetary policy directs about one-half of extramural methods research funding into long-term research projects, many at university centers of excellence, with the grant process administered through EPAs Office of Exploratory Research. EPA expects the results of this survey to help focus the research community on EPAs specific needs for HAPs measurement methods and thereby encourage submission of pertinent research proposals. A new policy on competition for resources to allow in-house EPA experts to pursue EPA research objectives, including methods development, is being formulated. The HAPs methods survey reported here represents a snapshot of a rapidly evolving and dynamic research field. Although not intended to be necessarily all-encompassing, this survey provides guidance in prioritizing methods development and may provoke valuable commentary on new techniques as costeffective potential alternatives to current methods.
Acknowledgments The methods survey described in this paper was conducted by Battelle under the sponsorship of the U.S. Environmental Protection Agency’sAtmospheric Research and Exposure Assessment Laboratory (EPAIAREAL),under Contract No. 68DO-0007, Work Assignment 44. The views and opinions expressed in this paper do not necessarily reflect the views of the Agency, and no official endorsement should be inferred. We gratefully acknowledge the technical insights and contributions of Robert G. Lewis of EPA/AREAL, as well as those of an anonymous reviewer for the journal.
References “Clean Air Act Amendments of 1990”; Conference Report to Accompany S. 1630, Report No. 101-952;U.S.Government Printing Office: Washington, DC, 1990; pp. 13962. Kelly, T. J. et al. Environ. Sci. Technol. 1994, 28, 378A87A. Kelly, T. J. et al. “Ambient Concentration Summaries for Clean Air Act Title I11 Hazardous Air Pollutants”; Final Report to U.S. Environmental Protection Agency; Battelle Press: Columbus, OH, July 1993; EPA EPA-600/R94-090 (available NTIS). Spicer, C. W. et al. ‘ R Literature Review of Atmospheric Transformation Products of Clean Air Act Title 111 Hazardous Air Pollutants”; Final Report to US.Environmental Protection Agency; Battelle: Columbus, OH, July 1993; EPA-600/R94-088(available NTIS). Kelly, T.J. et al. “Ambient Measurement Methods and Properties of the 189 Title I11 Hazardous Air Pollutants”; Final Report to U.S. Environmental Protection Agency; Battelle Press: Columbus, OH, 1994;EPA-600/R-94-098(available NTIS: PB95-123923). Intersociety Committee. Methods ofAir Sampling andAna1ysis, third ed.; James E Lodge, Ed.; Lewis: Chelsea, MI, 1989.
Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air; US. Environmental Protection Agency:Washington, DC, June 1988; EPA-6001 4-89-017 (available NTIS). Keith, L. H.; Walker, M. M. EPA’s Clean Air Act Air Toxics Database, VolumeI: Sampling and Analysis Methods Summaries; Lewis: Boca Raton, FL, 1992. Winberry, W. T., Jr.; Environ. Lab. 1993, June/July, 46-68. (10) “Optical Sensing for Environmental Monitoring”; Proceedings of an International Specialty Conference, October 11-14, 1993,Atlanta, GA; publication SP-89,Air & Waste Management Association, Pittsburgh, PA. (11) McLucky, S. A. et al. Anal. Chim.Acta 1989,225, 25-35.
R. Mukund is a project manager at EM-Northeast (Albany, NY).His current work includes air quality regulatory compliance management and air toxics modeling and monitoring. Thomas J, Kelly is a senior research scientist in atmospheric science and applied technology at Battelle Memorial Institute (Columbus, OH). His research interests include development of measurement methods for contaminants and natural trace species in air Sydney M . Gordon is a research leader in atmosspheric science and applied technology a t Battelle Memorial Institute. His research interests include developing methods for measuring VOCs in air and human breath using ion trap technology,for application in human exposure assessment. Melinda J. Hays is a researcher in atmospheric science and applied technology at Battelle Memorial Institute, where she currently manages the Dioxin Sample Preparation Laboratory. William A. McClenny, a senior scientist with the Atmospheric Research and Exposure Assessment Laboratory, Office of Research and Development, has developed monitoring methods for EPA as a bench scientist, science managel; and supervisor
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