ES&T
Concentrations and Transformations of Hazardous Air Pollutants
cause of the wide range in the amount of information available on the HAPs. For example, only 70 of the 189 HAPs are included in EPA's National Ambient Volatile Organic Compound (VOC) Data Base [5-7), a compilation of data on more than 300 commonly measured volatile air contaminants. Thus ambient data with w h i c h to conduct health risk assessments for many of the HAPs may be lacking. Similarly, the atmospheric reactions and products of some HAPs have been widely studied, but information on the transformations of most HAPs is scarce or nonexistent. This paper presents an overview of the ambient measurement and transformation surveys, illustrating what information is available and what is lacking for assessing the public health risks from the 189 HAPs. A survey of proven and potential ambient air sampling/analysis methods for HAPs has recently been completed (4); publication of all three EPA-sponsored surveys with full tabulations of data is planned (8).
What We Know and Don't Know About the CAAA's 189 Hazardous Air Pollutants
THOMAS J. KELLY, R. MUKUND, CHESTER W. SPICER, ALBERT J. POLLACK Battelle, Columbus, OH 43201-2693
T
he Clean Air Act Amendments of 1990 (CAAA) made a pronounced change in the regulatory approach to toxic air contaminants. Title III, Section 112 of the CAAA accelerated the pace at which air contaminants are designated and regulated by defining a list of 189 hazardous air pollutants (HAPs) (2). Title III is aimed at reducing the public health risk from exposure to HAPs in ambient air and requires regulation of routine and accidental emissions of each HAP from large industrial sources and from small commercial (i.e., "area") sources. Maximum achievable control technology emission standards are to be 378 A
developed by EPA for each of the HAPs, with the reduction of h u m a n health risks as the m a n d a t e d goal of HAPs emission control. The stated risk reduction goals of Title III include a 7 5 % reduction in cancer incidence caused by HAPs from area sources. Section 112 also specifically calls for ambient monitoring of HAPs in urban areas and for consideration of atmospheric transformations a n d other factors that can increase the health risks from HAPs (i). As initial steps t o w a r d Title III goals, EPA has sponsored surveys of the reported ambient measurements [2), a t m o s p h e r i c t r a n s f o r m a t i o n s and fate [3), a n d ambient sampling/ a n a l y s i s m e t h o d s (4) for t h e 189 HAPs. These surveys are needed be-
Environ. Sci. Technol., Vol. 28, No. 8, 1994
The HAPs list The 189 chemicals designated as HAPs are remarkably diverse, consisting of industrial chemicals and intermediates, pesticides, chlorinated and hydrocarbon solvents, metals, combustion byproducts, chemical groups such as polychlorinated biphenyls (PCBs), and mixed chemicals such as coke oven emissions. Some of the HAPs are ubiquitous ambient air contaminants, primarily VOCs. Many other HAPs were assigned to the list because of their recognized toxicity in workplace environments, but have not previously received attention as ambient air contaminants. About onethird of the HAPs are semivolatile organic compounds; that is, they may exist in both vapor and particulate phases in the atmosphere. To facilitate collection of information in the surveys described here, the 189 HAPs were organized into 10 categories of chemically similar substances. The categories include 2 to as many as 49 HAPs. The nitrogenated and oxygenated hydrocarbons categories contain the most HAPs: 49 and 40 compounds,
0013-936X/94/0927-378A$04.50/0 © 1994 American Chemical Society
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respectively. The other categories are halogenated hydrocarbons with 27 HAPs, inorganics (23), aromatics (18), pesticides (15), halogenated ar omatics (8), phthalates (4), hydro carbons (3), and sulfates (2). This classification is somewhat subjec tive, and other categorizations could be made. Several of the HAPs could reasonably be assigned to more than one chemical category. The ambient measurements survey The survey of ambient measure ments of the HAPs (2) was con ducted by computerized and man ual searches to locate ambient data. The computerized searches in cluded the Chemical Abstracts files from 1967 through November 1992, Chemical Abstracts Previews cur rent files, and National Technical Information Service files from 1964 through November 1992. Other sources of information included re view articles, reference books, tech nical journals, proceedings of air quality conferences, unpublished data sets from recent urban air mon itoring studies, and the National Ambient VOC Data Base (5, 6). The recent revision of the National VOC Data Base (7) was in progress at the time of this survey; as a result, this survey included data from the pre vious version of that database [5, 6), that is, through about 1988. How ever, many of the additional data now included in the updated Na tional VOC Data Base were also inde pendently included in the present survey. In keeping with the aim of provid ing data for health risk assessment, the focus of this survey was on ambi ent data in populated areas of the United States. Data from remote sites and data indicating direct source im pacts were excluded. For frequently measured HAPs, the intent of this re view was not to catalog every data point or sample, as attempted in the National VOC Data Base [5-7), but to characterize the typical range of con centrations of HAPs and the loca tions and relative numbers of mea surements made of the various HAPs. For HAPs that have rarely been measured in ambient air, an at tempt was made to locate all reported ambient measurements. All individ ual ambient measurements were weighted equally as samples in this survey; that is, no distinction was made on the basis of the duration of each sample. The 189 HAPs include some re dundant compounds, in the form of chemical groups (e.g., xylenes and 380 A
cresols) and their respective indi vidual isomers. Searches were per formed for both the individual iso mers and the groups, but ambient data were found only for individual isomers. The HAP denoted as polycyclic organic matter (POM) is com posed of numerous individual com pounds, and the POM compounds measured are not always clearly de fined in reports of ambient mea surements. To focus on potential health risks from POM, this survey addressed eight POM compounds identified as possible or probable human carcinogens (9, 10). Ambi ent data were compiled for the sum of those eight compounds. The product of this survey is an ex tensive table that lists for each HAP the locations, dates, number of sam ples, means (and/or medians), and ranges of ambient measurements, along with citations to the pertinent literature (2). Comments on the sam pling and the number of nondetects reported in ambient samples are also included in the table (2). Atmospheric transformations survey The survey of atmospheric trans formations of the HAPs (3) was con ducted in much the same manner as the survey of ambient concentra tions, by a combination of computer and manual searches. The computer databases used i n c l u d e d those noted above for the concentration survey. Two further valuable re sources were the ABIOTIKx data base (11) and a recently published Handbook of Environmental Degra dation Rates (12). ABIOTIKx pro vides the measured rate constants for the abiotic degradation of or ganic compounds in the atmos phere and includes the published rate constants for several possible atmospheric reactions for the hun dreds of chemicals listed, along with the pertinent literature cita tions. The handbook reports biotic and abiotic degradation rates for 331 chemicals in air, water, and soil. In this study the rate data were used to estimate atmospheric life times and identify significant trans formation processes for the HAPs, and the literature cited was re viewed for product information. The atmospheric lifetimes of HAPs are important as indicators of the rates at which those compounds are removed from the atmosphere and at which hazardous products may be formed. For some HAPs, es timates of the atmospheric lifetime have been reported in the literature.
Environ. Sci. Technol., Vol. 28, No. 8, 1994
In other cases we used reported rate constants, or estimated rate con stants based on structure—reactivity relationships, along with assumed values of atmospheric reactants to estimate an atmospheric lifetime. The following reactant concentra tions were used to represent the ur ban a t m o s p h e r e : ozone ( 0 3 ) , 1.5 χ 10 12 molecules/cm 3 (i.e., 60 ppbv); OH radical, 3.0 χ 10 e mole cules/cm 3 ; hydroperoxy radical ( H 0 2 ) , 1.0 χ 10° molecules/cm 3 ; and nitrogen trioxide radical (NO.,·), 2.5 χ 10 9 molecules/cm 3 . Transfor mation of HAPs by photolysis, by reactions with liquid water, and re moval from the atmosphere by dry and wet deposition were also in cluded as possible pathways. Life times were classified into broad ranges of 5 days, representing (in the context of an urban atmosphere) rapidly trans formed or removed, moderately per sistent, and long-lived species, re spectively. The lifetime estimates are exponential values, that is, indi cating the time required for the HAP concentration to decrease to 1/e (i.e., 37%) of its original value by chemical transformation or removal from the atmosphere. The available information on at mospheric transformations of HAPs was restricted almost entirely to re actions in the gas phase. Chemical reactions of semivolatile HAPs in the particulate phase were not ad dressed in this survey. Conse quently, the atmospheric lifetimes determined for such compounds are dominated by the gas-phase data. However, the actual atmospheric lifetimes of semivolatile HAPs will depend on the extent of their vaporparticle partitioning. HAPs for which vapor-particle partitioning may be important are appropriately indicated, and deposition of parti cle-phase material was considered as a factor in the atmospheric life times of particulate-phase HAPs, in cluding semivolatile compounds. The product of the survey of HAP transformations is a lengthy table with an associated list of more than 140 literature citations (J). For each HAP, the table includes the chemi cal formula or structure, the major removal process(es), the atmos pheric lifetime, the reported trans formation products, comments on the data, and references to the perti nent literature. Survey results A summary of the surveys on am bient measurements and atmos-
TABLE 1
Summaries of the atmospheric concentrations and transformations surveys Compound Acetaldehyde * Acetamide Acetonitrile * Acetophenone * 2-ΑθΒίνΐ3ΓηίηοίΙυθΓΒΠ6Τ Acrolein * Acrylamide Acrylic Acid Acrylonitrile * Allyl Chloride * ^Aminobipheny^ Aniline * o-Anisidine Asbestos Benzene * Benzidine^ Benzotrichloride Benzyl Chloride * Biphenyl Bis (2-ethvlhexyl) phthalate* Bis (chloromethyl) ether Bromoform * 1,3-Butadiene * Calcium Cyanamide Caprolactam Captan' Carbaryf Carbon Disulfide * Carbon Tetrachloride « Carbonyl Sulfide * Catechol Chloramben t Chlordane' Chlorine Chloroacetic Acid 2-Chloroacetophenone Chlorobenzene * Chlorobenzilate' Chloroform * Chloromethyl Methyl Ether Chloroprene * Cresols/Cresylic Acid o-Cresol * m-Cresol * p-Cresol « Cumene * 2,4-D salts & esters' DDE* Diazomethane Dibenzofurans* 1,2-Dibromo-3-Chloropropane * Dibutylphthalate' 1,4-Dichlorobenzene (p) * 3,3'-Dichlorobenzidine t Dichloroethyl Ether * 1,3-Dichloropropene Dichlorvos Diethanolamine Diethyl Sulfate * S.S'-Dimethoxybenzidine* Dimethylamino-azobenzene* Ν,Ν-Dimethylaniline 3,3'-Dimethyl Benzidine' Dimethylcarbamoyl Chloride Dimethyl Formamide 1,1-Dimethyl Hydrazine Dimethyl Phthalate
CAS no. 75-07-0 60-35-5 75-05-8 98-86-2 53-96-3 107-02-8 79-06-1 79-10-7 107-13-1 107-05-1 92-67-1 62-53-3 90-04-0 1332-21-4 71-43-2 92-87-5 98-07-7 100-44-7 92-52-4 117-81-7 542-88-1 75-25-2 106-99-0 156-62-7 105-60-2 133-06-2 63-25-2 75-15-0 56-23-5 463-58-1 120-80-9 133-90-4 57-74-9 7782-50-5 79-11-8 532-27-4 108-90-7 510-15-6 67-66-3 107-30-2 126-99-8 1319-77-3 95-48-7 108-39-4 106-44-5 98-82-8 94-75-7 3547-04-4 334-88-3 132-64-9 96-12-8 84-74-2 106-46-7 91-94-1 111-44-4 542-75-6 62-73-7 111-42-2 64-67-5 119-90-4 60-11-7 121-69-7 119-93-7 79-44-7 68-12-2 57-14-7 131-11-3
Class Oxy Org Nitro Org Nitro Org Oxy Org Nitro Org Oxy Org Nitro Org Oxy Org Nitro Org Hal Hydro Nitro Org Nitro Org Nitro Org Inorg Arom Nitro Org Hal Arom Hal Arom Arom Phthal Oxy Org Hal Hydro Hydro Inorg Oxy Org Pestic Pestic Inorg Hal Hydro Oxy Org Arom Pestic Pestic Inorg Oxy Org Oxy Org Hal Arom Pestic Hal Hydro Oxy Org Hal Hydro Arom Arom Arom Arom Arom Pestic Pestic Nitro Org Oxy Org Hal Hydro Phthal Hal Arom Nitro Org Oxy Org Hal Hydro Pestic Nitro Org Sulfat Nitro Org Nitro Org Nitro Org Nitro Org Nitro Org Nitro Org Nitro Org Phthal
Ambient concentration measurements Median or Locations Samples ranges (pg/m 3 ) 50
1178
2^7
5 2
5(5 3
ND
2
12
ND
7 6
88 >81
0v2 ND
3
4
ND
Atmospheric transformations Known Lifetime products 24
ND 1 3 - 1 6 ng/m 3 N D - 1 7 ng/m 3
17 57
423! 1168
ND 0.4
2 2 3 T3J 4
288 288 15 5739 1J3
ND ND - 11 ng/m 3 OJ 08 1^3
5 (Photol) >5 345
ND - 630 ng/m 3
5 >5 >5 5 < 1 to 1 -5 (Water) 10
>^5
>100
17
94
Atmospheric transformations
Median or ranges (pg/m3)
Lifetime -
5
ng/m3
>5 1 to 5
114-26-1
Pestic
78-87-5
Hal Hydro
Propylene Oxide *
75-56-9
O x y Org
>5
1,2-Propylenimine
75-55-8
Nitro Org
