I
Potential community exposure to toxic chemicals Usirig r drtile or;qunics measiiremetits,for assessirig community uir yuulitv
By F . Scon LaGrone An issue of great concern to both industry and regulatory agencies is cbroNc community exposure to a variety of airborne chemical substances. To address this issue, the Houston Regional Monitoring Corporation (HRM), a consortium of 45 companies located in the Houston, Texas, ship channel industrial complex, recently began a voluntary measurement program to assess long-term community air quality for a target list of 150 volatile organic indicator compounds. These compounds are indicative of air emissions from industrial, mobile, vegetative, and other area sources. The current emphasis of the HRM measurement program was brought about in part by the enactment of Title 111 of the Superfund Amendment and 366 Environ. Sci. Technol.. Vol. 25, NO.3, 1991
Reauthorization Act (SARA). HRM data are being used to assess the significance of air emissions estimates reported under SARA Title 111. This is done by comparing actual air quality measurements to annual air emission estimates of those compounds reported under SARA Title 111 by Houston industries. These data also provide a baseline for assessing long-term community air quality and evaluating the effectiveness of both voluntary and mandated emission reduction strategies for airborne toxic chemicals. Results described in this program cover only the first year of indicator compound monitoring. The program has operated continuously from August 1. 1987, through today. Information from this program was submitted to appropriate state and federal government author-
ities for their use in responding to the Clean Air Act Amendment.
Study design The Houston Regional Monitoring Network consists of eight monitoring stations in the h e m of the Houston ship channel industrial complex. HRM has been in continuous operation since 1981. Seven of the eight stations are equipped to measure criteria pollutants (Le., ozone, carbon monoxide, oxides of nitrogen, sulfur dioxide, lead, and particulate matter) as well as meteorological parameters (Le., wind speed, wind direction, wind direction variance, net radiation, ambient temperature, and precipitation). The monitoring network was modified in 1987 to allow collection of 24-h time-averaged whole air samples, which were subsequently analyzed for
0013-936x19110925-366$02.50/00 1991 American Chemical Society
Discussion of results The results of the HRM Volatile Organic Indicator Study demonstrate that annual ambient concentrations of measured volatile organic compounds (VOCs) in the Houston ship channel industrial complex are present at concentrations in the low parts-per-billion range. Estimated SARA emissions are given in Table 1 for the 10 compounds having the highest emission values and for which ambient measurement values are reported as part of the HRM program. The ambient data reported in Table l represent the aggregate mean for
1
the HRM network (all sites included) over a one-year period heginning September 18, 1987, and extending through September 18, 1988. The emission totals reported in Table 1 include reported SARA emissions for both Harris and Chambers counties. These counties encompass the entire Houston shi channe1 industrial area [2350 miP (6087 km2): 1980 population, 2,428,0001. Median VOC concentration profiles (see Figure I ) for selected cities across the United States were compared to the aggregate network profile for HRM (all sites included). The compounds in the
F . Scott LaCrone
the presence of volatile organic indicator compounds. One station measures meteorological parameters only. The HRM monitoring stations were sited based on maximum impact analysis of stationary industrial source emissions. All stations are between industrial and nearby residential areas, and in some instances the monitoring stations are within 100 to loo0 feet of sensitive residential receptors. The sites are also close to major transportation arteries and thus can measure impacts from mobile as well as stationary sources. In addition to the target list of 150 volatile indicator compounds, 22 of the 34 compounds having the highest estimated SARA Title 111 emissions by industry in the Houston ship channel are reported as part of the HRM program. Many of these compounds also contribute to the secondary formation of ozone, and therefore provide valuable information regarding the speciation of reactive organic carbon compounds present in the ambient air.
TABLE 1
Ten highest SARA emissions totals for which measurement data are reported Ambient
OOncerIration’
1987 SARA data.
Rank 1
2
3 4
5 6 7 8 10 9
Emissions (TPV
Chemical
Propylene (propene) Ethvlene Toluene Siyrene Xylene (mixed isomers) Benzene Dichloromethane (methylene chlonde) Acetone Chlorobenzene Methyl 1-Butylether
2324 2148 1369 710 551 489 465 460 379 285
IncludeS aggregate emission totals lor Harris and Chambers counldes aggregate annual network mean mncentration data repoll period (1987 lo 1988)
a Represents
Sampling and analysis Twenty-four hour, time-averaged samples are collected in 15-L SUMMA passivated stainless steel canisters housed in environmentally controlled shelters. Samples are automatically collected from midnight to midnight on each designated sampling day. The samples are collected at each of seven sites once every sixth day, permitting sequential sampling through each day of the week. This sampling frequency, which corresponds with EPA’s National Sampling Day, allows assessment of variations in ambient air concentrations related to both emission source characteristics and synoptic weather patterns, The 24-h sampling interval was selected to aid in assessing long-term community exposure over a complete diurnal period. A total of 60 samples are collected at each site annually, sufficient to assess annual air quality trends and evaluate seasonal changes in pollutant composition and concentration.
Mean
PPaV
’
’
I Benzene I Toluene
0m + p Xylene
Envlmn. %I.
Technol., Vol. 25. No. 3, 1991 367
I
,
I Benzene I Toluene I Fhyl enzene
Expert Systems for Environmental Applications on T1 VOC profiles include: benzene, toluene, ethylbenzene, m + p-xylene, and o-xylene. These compounds are representative of emissions from both mobile and stationary point sources. The VOC profiles for each city in Figure 1 were summarized in part from EPA's National Ambient Volatile Organic Compound Data Base ( I ) . Included in this data base are median ambient concentration values reported from multiple sites within a particular city. The VOC profiles also include data that were collected as part of EPA's Toxic Air Monitoring System (TAMS) network (2). The TAMS data shown in Figure 2 were collected at a single site near the Houston ship channel industrial complex using similar sampling techniques (Le,, 24-h whole air integrated canister samples). Conclusions, observations There is increasing public concern over potential exposure to airborne chemical substances from all sources. Industries in Houston have cooperated to implement a comprehensive regional monitoring program to address the issue of long-term community exposure to toxic airborne chemicals. The initial results from the HRM Volatile Organic Indicator Compound Study have been used effectively to address public concerns regarding the air quality impact of a i r h o m e ~ t o x i c ~ e m ~ reported ~ ~ t ~ ~ n under s Section 313 of SARA Titk 111 The data from the HRM study are comparable with air quality data from other urban industrial areas in the United States. This fact is somewhat surpris358 Environ. Sci. Technol.. Vol. 25, NO.3, 1991
ing given the high concentration of petroleum refining and petrochemical manufacturing plants in the Houston ship channel area, and further demonstrates that regional air quality trends are strongly influenced by site specific factors (Le., terrain and geographical features, atmospheric dispersion, source characteristics, chemical fate, and meteorology). Finally it should be noted that longterm air quality monitoring programs (such as the HRM program) help establish a baseline for measuring the effectiveness of future emission control strategies, and are an effective tool for addressing public concerns about exposure t o airborne chemicals.
he only book expert systems devoted solelv to environmental aodications. this comjrereistre reme8 d ;c.sses tne stale )f the an in aeieoping expen s)stemr IC ,o ve en.i'onmentd p'ooerns Coierinq mcre tian 65 oentfied nstems ths uorn ncl-des nan, systems n e v i oefore pub ished Beginn :g MaIoroac A o!ervien. l h s 16 :hapier text describes the process of expert ystems development and all stages in their ife cycles. These include chapters on verificaSon and validation of systems; neural netmrk. systems to support environmental smpling, analysis, and data validation; and the future of evert systems in the Environmental Protection Agency. Gther chapters focus on applications areas for expert systems. Each system is described and emphasis is placed on problems encountered during development and how they were solved. The final chapter defines the needs identified Mthin EPA for expert systems and i w k at areas of future environmental expert system development. Contents
References
Shah. J . 1.; Hegerdahl, E. R. "National Ambient Volatile Organic Compound (VOCs) Data Base Update"; U S . Environmental Protection Agency: Washington, DC. 1988; EPA 600/3-88/010a-h. (2) Edgertan, S. A. et al. JAPCA 1989,39(5),
(1)
729-32.
Own.
Judith M. Hurhon. Editor. Roy F. Weston. Inc. Deveioped from a symposium sponsored by the Divlsion of Chemical Informationof the American Chemi~ tal k i e t y
F. Scott LaCrone is a senior vice president at Rudian Corp., Austin, Tx.As a founder and principal, Mr. LaCrone has been responsible for dura analysis and computer technology applications over the p u t 20 years at Rudian. His work emphizes data analysis and field measurements of toxic compounds, both domesrically and internationally. He received his B.S. and M.S. degrees inphysicsfiom the University of Texas at Austin.
ACS Symposium Series No. 431 232 pages (1990) Clothbound ISBN 0-8412-1814-5 LC 90-37399 SdP 9s
