Philip C. Wolf Intertech Corp. Princeton, N.J.
P
eople no longer take air for granted. Since concern over air pollution is widespread today, more accurate information on the amount, distribution, and toxic effects of pollutants is vitally needed. Carbon monoxide, a product of almost all combustion processes and one of the most widespread and toxic pollutants, cannot be detected (unfortunately) by sight or smell. The internal-combustion engine is the largest single source of carbon monoxide in ambient air. As a result, the highest concentrations are found in urban areas having dense automobile traffic. The greatest potential hazard exists, therefore, where the greatest number of people may be affected. CO effects
Carbon monoxide ( C O ) reduces the ability of the bloodstream to carry oxygen to body tissues by displacing oxygen from hemoglobin ( H b ) to form carboxyhemoglobin (COHb) . The most important factor involving carbon monoxide effects on humans is the COHb level in the blood, which is directly related to the CO concentration in the ambient air. For any given carbon monoxide concentration, the COHb level reaches equilibrium after a time period and retains this level without further increase. The effect can be reversible, however: COHb levels decrease as the concentration of CO in the ambient air decreases.
feature
It’s invisible but can be more dangerous than photochemical smog. That’s why knowing the level of carbon monoxide in densely populated areas is becoming more important as auto population continues to soar
Acute effects of relatively high concentrations of CO and levels of COHb depend on exposure time and physical activity. The length of time required for the COHb level to reach equilibrium is a function of the level of physical activity of the exposed person-i.e., the more strenuous the activity, the more rapidly equilibrium is attained. Until recently, most studies of the toxic effects of carbon monoxide dealt with acute effects of exposure to relatively high concentrations. Today, because of the widespread distribution of CO in the ambient atmosphere by the automobile, attention has turned to the chronic effects of longterm exposure to lower concentrations. The National Academy of Science ( N A S ) and the U.S. Department of Health, Education and Welfare ( H E W ) indicate that definite mental and physical impairment results from much lower levels of COHb than previously indicated. In fact, NAS states: “There is no level of CO in ambient air that is known to be without effect.” (See box.) Continuous exposure to ambient air containing 10 ppm carbon monoxide will produce a COHb equilibrium level greater than 2.0%, the point at which effects upon the nervous system become apparent. Similar exposure to concentrations of 30 ppm produces COHb levels greater than 5.0%. CO levels of 50 to 100 ppm are not uncommon in crowded center-city streets during the evening rush hour.
........
. . . . . . . .
I _
-.
~ _ _ _ - -
..
As COHb levels or duration of exposure increase, health effects become more serious COHb level, percent
Demonstrated effects
Less than 1.0 1.0 t o 2.0
No apparent effect. Some evidence of effect on behavioral performance. Central nervous system effects. Impairment of t i m e interval discrimination, visual acuity, brightness discrimination, and certain other psychomotor functions. Cardiac and pulmonary functional changes Headaches, fatigue, drowsiness, coma, respiratory failure, death.
2.0 t o 5.0
Greater than 5.0 10.0 to 80.0
Source National Academy of Science and National Academy of Engineering _
3000 ppm 2000 ppm
1000 ppm
_
_
_
750 ppm Death
Loss of consciousness
Observable effects
,
10
5
‘
‘
,
,
At rest
I
20
15
Heavy work
0
1
2
3
4
5
6
7
Duration of exposure, hours
Acute effects. COHb levels i n the blood depend upon t h e amount of CO i n t h e atmosphere, duration of exposure, and type of physical activity
Volume 5, Number 3, March 1971 213
_
I
All . ..infrared analyzers operate essentially in tne same manner indicating meter-
-
I
Amplifier
I I Chopper
1 1
Detector chamber (Measuring beam) Detector
Inductive pick up
Detector chamber (reference beam)
-
lexibie
membrane
Principle. The gas to be analyzed passes through the analysis chamber in the measuring beam path. The reference chamber in the second beam path is filled with nitrogen, which does not absorb any infrared energy. The difference between the radiation emanating from the measuring and reference chambers (which depends upon the absorption in the measuring chamber) results in differential heating and therefore a pressure difference between the two detector chambers. The pressure difference causes the membrane to deflect, and t h i s movement is measured by a n inductive picku p producing a n amplified electrical signal
Amplifier and power supply
Instrument. Disassembled components of the Uras 2 infrared analyzer point out the modular construction which simplifies service and maintenance
214 Environmental Science & Technology
Fortunately, at the present time, these levels are generally not of long duration. Levels of carbon monoxide in parking garages and tunnels are usually much higher and more persistent. These conditions show that carbon monoxide pollution of the atmosphere obviously presents a serious potential health hazard. Steps have been taken to alleviate this problem, and many more are being considered. Chief among these are standards for the concentration of CO in ambient air and for automobile exhaust emissions. Extensive, continuous measurement of CO levels in ambient air is essential to the establishment and enforcement of these standards. Measurement requirements include: Defining the problem. Developing logical air quality and emission standards. Measuring progress or lack of it. Measurement
There are several methods for measuring CO concentrations. The mass spectrometer and the gas chromatograph are useful laboratory instruments, but both are too slow, too expensive, and too complex for continuous, “real-time” monitoring systems. Furthermore, their operation requires technically trained personnel. Oxidation techniques are inexpensive, but they are unreliable at and insensitive to low concentrations. The most practical device for accurately measuring CO concentrations in the atmosphere is the infrared nondispersive analyzer, which can be built to be rugged while retaining sensitivity and accuracy. Technically trained personnel are not required for operation, and, with proper accessories, it can operate continuously, unattended, and with little maintenance. Unlike some instruments, infrared analyzers are not sensitive to flow rate over a considerable range. All infrared analyzers employ the same measurement principle (see box), but there are significant differences in design among specific units. I n the Uras 2 infrared analyzer (Intertech Corp., Princeton, N.J.), the specific radiation absorption of polyatomic, nonelementary gases in the infrared spectral range is used as the measuring effect. The absorption is measured in an alternating light photometer with two parallel beam paths
(measuring and reference) and a radiation detector. The detector has two chambers separated by a flexible membrane. Each is filled with the gas component to be analyzed-here, CO. One major difference among infrared analyzers is the length of the measuring cell. For carbon monoxide, this may vary from a few inches to several feet. Instruments that require long measuring cells are usually less stable over extended periods. It is important, therefore, to use the shortest possible length for the measuring cell consistent with sensitivity requirements. Because heat energy is the basic effect being measured, the analysis portion of the analyzer must be maintained at a constant temperature. This condition can be met more easily with a compact instrument and favors those with short beam paths. Essential components of a Uras 2 infrared analyzer include modular construction, which simplifies service and maintenance. An important factor in servicing this type of equipment is the ease, or lack of it, by which the separate measuring system elements can be disassembled and reassembled for proper alignment. In this dust- and splash-proof unit, the separate components are precisely located on a precision alignment bench and simply bolted together. Electronic components are mounted on the upper door for easy access and service. Infrared analyzers are calibrated for the appropriate measuring range with the minimum range depending upon the sensitivity of the instrument. F o r measuring the carbon monoxide content of ambient air, the Uras 2 can provide a low range of 0 to 25 ppm. Other measuring ranges used to monitor C O in ambient air are 0 to 50 and 0 to 100 ppm. A single instrument can be manually changed to provide several measuring ranges, or the unit can be equipped to switch automatically from one range to another. Since analog devices are subject to drift, and the infrared analyzer is no exception, periodic recalibration is required. Tests by independent investigators show the Uras 2 instrument to have a drift of less than 2% of zero and measuring span per week-an exceptionally low drift rate for this type of instrument. Recalibration is done manually or automatically by comparing the output of the instrument when measuring a “zero” gas containing n o
Analyzer. This infared CO analysis system used in the CAMP stations includes automatic recalibration. Although not presently used, telemetry equipment can be included for direct data transmission from the analyzer to a central collection point carbon monoxide and a “span” gas having a known carbon monoxide content with the calibration curve provided with the instrument. Automatic recalibration, an essential feature for instruments that operate at unattended remote locations, has several advantages. Accurate manual recalibration requires 10 to 20 minutes, is subject to human error, and usually consumes a large quantity of the relatively expensive calibration gases. But automatic recalibration can be done in only 3 minutes. Furthermore, automatic recalibration has no limitations as in manual recalibration. Sample conditioning
To ensure that the measuring instrument will function reliably and accurately, the air sample must be properly conditioned. The typical carbon monoxide measuring system consists of a probe, refrigeration unit, filter, pump, flow meter, analyzer, and automatic calibration unit. A probe for ambient air usually can be any type of pipe or tubing. If the ambient air contains high concentrations of dust, soot, or other particulate matter, a filter should be located at the probe inlet. The refrigeration unit removes the moisture that is al-
ways present in ambient air. Since water vapor absorbs infrared radiation across almost the entire infrared spectrum, its effect must be nullified. Condensation to remove water vapor entirely, or to reduce it to a constant low level, is the best means of eliminating its effect. Although optical filters reduce the effect of water vapor, sensitivity is minimized-requiring the use of longer measuring cells, increasing the nonlinearity of the output signal, and decreasing the instrument’s stability. Membrane filters used with ambient air generally remove all particles larger than 1 , ~ .The filter protects the pump and keeps the windows in the beam path from being covered with solid particles that cause the analyzer to drift. All components of the system, including the recorder, are housed in a single, compact instrument cabinet. In addition, alarm and ventilation fan control circuits can be incorporated into the package, Multiple probes can be used in a single system with the air at each probe sampled sequentially. Restricted area monitoring
Carbon monoxide monitoring systems can be classified by their function. One type is used to monitor CO levels in restricted areas of high automobile traffic and poor ventilation, such as vehicular tunnels and parking garages, to assure that hazardous conditions do not exist. A second measures CO concentrations over broad geographic regions. A third type investigates the effect of design and location of highways and nearby structures on carbon monoxide concentration and distribution in limited areas. Carbon monoxide has been monitored in mine shafts and vehicular tunnels for many years. In older installations, catalytic/oxidation-type instruments have proved reasonably satisfactory when properly maintained. However, infrared analyzers are used today because they are more accurate, sensitive, reliable, and require less maintenance. In the Dewey Square vehicular tunnel (Boston, Mass.), infrared carbon monoxide analyzers have replaced oxidation-type instruments which were in use for over 10 years. As a result of the more accurate and reliable data provided by the new instruments, it has been possible to cut fan operation Volume 5, Number 3, March 1971 215
by more than 30%, thus reducing power costs and fan maintenance requirements while maintaining at least as high air quality standards. The Dewey Square tunnel consists of two 2400-ft tubes: one northbound, one southbound. Each tube is 2400-ft long, 40-ft wide, and 14.5-ft high. The tubes are ventilated by 22 8-ft diameter fans that are capable of changing the tunnel air every 1.5 minutes. During the tunnel’s first 10 years, the normal schedule called for 56.5 hours of fan operation per week, Fans were also operated during normally “off’ periods whenever it seemed advisable. Extra operation was based on visual observation of congestion via the tunnel’s closed-circuit television system, rather than by any precise knowledge of existing CO concentrations (because the catalytic/ oxidation devices were considered not reliable enough to use their output for passing judgment). In April 1970, an infrared carbon monoxide monitoring system was installed. The system consists of four probes at different locations in the tunnel, connected to a single analyzer located in the tunnel’s control room. Air from each location is sampled and analyzed every 2 minutes. When concentrations exceed 150 ppm at any one of the four locations, an alarm sounds, the operator notes the location of the excessive CO concentration, and he turns on the appropriate fans, Automatic calibration of the analyzer virtually eliminates system maintenance requirements. Data from each sampling location are also recorded. On the basis of data generated during the first few months of operation, the normal fan operating schedule has been cut to less than 39 hours a week-only 70% of the original schedule. Fan operation is based on the measured concentration of CO rather than visual observation of congestion. The 30% reduction in fan operation has substantially cut operating cost, maintenance requirements, and will undoubtedly extend fan life. The ability to obtain reliable data from essentially maintenance-free instruments increases the potential for automation of tunnel fan systems, Although Dewey Tunnel ventilation is manually controlled, it could be easily automated. Signals from individual CO analyzers can be utilized to control automatically the operation of in216 Environmental Science & Technology
dividual fans, or groups of fans, providing the proper degree of ventilation to maintain air of whatever quality might be specified. Besides eliminating a manual operation, such a system can be expected to save money through lower power consumption and to reduce wear and tear on ventilating fans, since ventilation schedules would be optimized for safe operation. Remote monitoring systems
Systems that monitor air pollutants over a broad geographic area are at the opposite end of the spectrum from a restricted-space monitoring system. Such systems sample air from numerous remote locations and feed the data to a central location. Systems of this type are used for the enforcement of air pollution regulations and gathering of data for the establishment of future air quality criteria and legislation. Ultimately, analysis of the data gathered by these regional systems should also be useful in longrange land-use planning. The Continuous Air Monitoring Project (CAMP)of the Air Pollution Control Office (formerly the National Air Pollution Control Administration), established in 1962, is one pioneer system of this type. The CAMP system operates six stations that measure eight parameters, including infrared analysis of carbon monoxide, Stations are located in center-city locations in Philadelphia, Chicago, Washington, D.C., Denver, Cincinnati, and St. Louis. The original purpose of the system was to provide concurrent data for analysis with data from studies on automobile exhaust emissions. This study is now complete with correlations between the two studies showing good statistical accuracy. Presently, the system is providing long-term data from the same sites using the same measuring procedures while also assisting local air pollution agencies, testing new measuring instruments, demonstrating the operation of air monitoring stations, and cataloging data for scientific studies. Data from CAMP stations are recorded on magnetic tapes, which are mailed weekly to a central headquarters for computer analysis. Newer systems, especially those used for the enforcement of air pollution regulations, are designed with telemetry to transmit data to the central computer in real time. The New Jersey Air Monitoring
Network is an excellent example of this type of system. Although many such systems have been planned and are in various stages of construction and trial, the New Jersey network is one of the few which is fully operational. The network began operating in October 1965 with six remote stations. By 1969, it was considerably expanded and modernized by the addition of improved telemetry and data-reduction equipment. At present, the New Jersey system measures three pollutants continuously-carbon monoxide, sulfur dioxide, and particulates (as smoke shade)-at 18 fixed locations throughout the state. In addition, three trailer laboratories capable of measuring 10 air pollution and seven meterological parameters also report into the central data center continuously. The purpose of the New Jersey Air Monitoring Network is twofold: To provide information for the enforcement of air pollution emergency regulations. To provide continuous data for study in the preparation of future air quality legislation. Air sampling stations are generally located in urban and industrial areas, where air pollution problems are expected to be greatest. Although carbon monoxide is only one of three parameters measured at the fixed stations, the desire to determine maximum CO levels dictated specific air sampling locations in most cases. Because their sources are less concentrated, sulfur dioxide and particulate matter are quite widely distributed throughout most urban areas. Carbon monoxide, on the other hand, tends to be concentrated in areas of hightraffic volume; therefore, most of the fixed stations are located in downtown areas. Although carbon monoxide concentrations are highest at street level, diminishing as it travels upwards, the remote fixed stations are located at the second-floor level for security reasons. As a result, maximum levels of carbon monoxide can be expected to be somewhat higher than those measured and recorded by the network. The importance of automatic operation at unattended remote stations cannot be minimized. Equipment must also be rugged and reliable. Minimal drift is important and automatic recalibration essential, The Uras 2 carbon monoxide analyzers used in this
network recalibrate automatically every 8 hours to ensure high accuracy of incoming data. Without such automatic features, labor costs for maintaining these remote stations would be exhorbitant. The 21 stations in the New Jersey network report continuously to a central data center in Trenton via a telemetry system. Here, the analog data is recorded continuously on strip charts and converted to digital form by a Bristol PDP 8 Data Master computer. Fifteen-minute average values for each measured parameter from each location are printed out on a master log sheet. Any 15-minute average reading which is greater than that normally expected for a given parameter from a given station is automatically printed out separately. Also, instantaneous readings of any parameter can be obtained from a third peripheral device. Data are further analyzed by use of an RCA Spectra 70-45 computer. Average concentrations of any parameter over various time spans can be obtained. Such data are essential for the establishment of air quality standards. The computerized data acquisition portion of the New Jersey Air Monitoring Network has been operating for over one year. Statistical analysis indicates that the system is producing the data sought with a high degree of reliability. Field study
One goal of present air pollution studies is to provide guidance for planners in locating and designing highways and structures and in future land-use development. Data collected by systems such as the New Jersey Air Monitoring Network may provide useful data for large-scale planning in the distant future. In the more immediate future, however, planners will undoubtedly obtain guidance for specific situations from studies into the effect of the location and design of highways and structures on the distribution of air pollutants in ambient air. Numerous studies of this type are in progress, and all involve monitoring carbon monoxide as well as other pollutants. One study of this type, underway i n New York City for the past year, was recently completed. This Urban Expressway Air Pollution Study has been conducted from a mobile field laboratory designed, built, and operated by the Reentry and Environ-
mental Systems Division of the General Electric Co. under contract to the New York City Department of Air Resources. The laboratory, set u p in a large trailer, is equipped to measure carbon monoxide, nitrogen oxide, hydrocarbons, particulate matter, and meteorological conditions. Sixteen channels of carbon monoxide information are rovided by eight Uras 2 infrared
analyzers, each measuring CO concentrations at two locations sequentially. Thus, CO can be measured continuously at 16 different points. The same probes are used to provide air samples for measuring hydrocarbons and nitrogen oxide through a switching mechanism in the trailer. However, as the laboratory contains one analyzer each for hydrocarbons and nitrogen oxide, values collected
CQ concentrations peak at rush hours 90
80
70
60
50
kn i
eE
40 e
e
E
! 30
20
10
0 0400
0800
1200
1600
2000
2400
Time, hour
Peaks. CO concentrations, taken at three different levels, 75 feet inside the FDR Drive at 5 4 t h St. i n New York City show the differences i n carbon m o n oxide buildup i n completely enclosed areas versus partially open areas
Volume 5, Number 3, March 1971 217
for these parameters represent average concentrations of samples from several probes. The meteorological system provides 10 channels of information for measuring temperature, wind direction and velocity, and the like, at various points along and near the roadway. Because most carbon monoxide is emitted close to the ground and heavy emissions occur at specific locations at specific times, it is probably not as evenly distributed in the atmosphere as most other air pollutants. Therefore, a major objective of the studies conducted by the laboratory has been to investigate the distribution of carbon monoxide at various horizontal and vertical distances from the roadway proper. One-half inch plastic tubinig was extended from the trailer to var i.^ ous predetermined locations near th= highway and on and in adjacent huildings. The study consisted of measuring these parameters 24 hours a day for two weeks at each of 10 different sites, Sites were selected to represent different types of highway designs and included a ventilated tunnel, a covered roadway open at one side, a shallow cut, a short unventilated tunnel, a deep cut, a road at grade, a cantilever section, a viaduct, a typical city street, and an intermittently covered subsurface highway. Partial data obtained from one of the 10 locations have already been published and illustrate the nature of the data obtained. The location described above as a covered roadway which is open at one side is on Franklin D. Roosevelt Drive where it passes under Sutton Place at 54th Street in Manhattan. Here, an air rights structure extends over the highway bordering the East River. Carbon monoxide concentrations were measured 75 ft inside the tunnel at three elevations-3, 11, and 20 ft-above the roadway along the west wall, along the center divider, and along the open east wall of the underpass. CO concentrations were also measured 30 and 55 ft up the south wall of the overhanging apartment house and 12 and 30 ft above the sidewalk located over the underpass. Partial data developed by this study illustrate the uneven distribution of carbon monoxide with respect to both time and space (see graph). A considerable gradient exists between the closed west wall of the southbound 218
Environmental Science & Technology
roadway and the open east wall of the northbound lanes. As a result of the venting effect along the open east wall, the average peak concentration at this location, which occurs during the evening rush hour, is less than half the peak concentration during the morning rush hour at the west wall. Carbon monoxide concentration generally decreases at the higher levels above the road surface. The lowest average carbon monoxide concentrations measured occurred 55 ft above the south wall of the building. At the sidewalk, average hourly concentrations approximated 30 ppm during peak rush hour periods. This study, as one of the most complete of its kind ever undertaken. shows that there il; a direct correlation between traffic density and speed ^^1 . . . L . _ -.._._ a u L ~ L V V U muwnide concentrations near a highway, At present, the equipment has been removed from the van and is located in an apartment in a 32-story air rights structure located directly above the Manhattan approaches to the George Washington Bridge. This TransManhattan Expressway carries some 200,000 vehicles a day. The study is in-
vestigating air quality inside and outside the building at various levels. A similar study incorporating the measurement of CO and meteorological data has been conducted in Frankfurt, West Germany, by Georgie and associates (see additional reading). A major problem in carbon monoxide pollution control is that little is known about its distribution in the atmosphere. A potentially hazardous condition may exist at one location, while just a block away, concentrations may he extremely low. Such conditions should he considered when planning traffic flow in and around urban areas. Obviously, highway design, traffic patterns, location and configuration of adjacent structures, and meteorological conditions influence the concentration and distribution of carbon monoxide. How these factors interrelate to affect the distribution of CO is being studied. When this information is available, man will he better equipped to plan highway systems and to control urban development with minimization of the carbon monoxide effects on the environment. Additional reading
Air Pollution Control Program, New Jersey State Department of Health, Di-
Philip C . Wolf is president and director of Intertech Corp., a company of which he was cofounder in 1962. Dr. Wolf is a graduate of the Technical University, Munich, Germany, and has Dipl. Zng. (1942) and Dr. Ing. (1946) degrees from that institution. He has had wide engineering experience with the DeLaval Turbine Co. and with the General Electric Co. At Intertech, he has focused on gas analysis f o r the measurement of pollutants in the air and in stack gases.
vision of Clean Air and Water, "New Jersey Air Monitoring Systems and Air Quality Data, October 1965 through December 1968," Technical Bulletin A-69.1, July 1969. Cooper, A.G., "Carbon Monoxide, a Bibliography with Abstracts." Public Health Service Publication no. 1503, U.S. Department of Health, Education and Welfare, Washington, D.C., 1966. Fensterstock. J.C., Kurtzweg. J.A., Ozolins. G., "Reduction of Air Pollution Potential through Environmental Planning," presented at the Annual Meeting of the Air Pollution Control Association, June 1970. Georgie. H.W.. Busch, E., Weber, E., Untersuchungen ueber die zeitiiche und raeumliche Verteilung der lnrnissions-Konzentration des Kohlenmonoxid in Frankfurt/Main," Universitaet Frankfurt, Institut fuer Meteorlogie und Geophysik, 1967. Goldsmith, J.R., "Epidermological Bases for Possible Air Quality Criteria for Carbon Monoxide," Paper no. 69146A. Air Pollution Control Association Symposium on Toxicological and Epidermological Bases for Air Pollution Criteria, June 1969. h,.,+;..n-, .%.."A".-,, -' C^i^"^^ ""A h,* tional Academy mra"r'''y of y ' Engineering. .,L'5''r5 '"cI""''a'
"Ef-
fects of Chronic Exposure to Low Levels Of Monoxide On Hu. man Health, Behavior. and Performances," Washington, D.C.. 1969. U S . Department of Health, Education and Welfare, "Air Qualitv Criteria for Carbon Monoxide,,.Washington, D,C., March 1970. "DI-Nachrichten, "Luftverun!;einigung foerderl Arterienverkaikung. no. 22. October 21, 1970, p 27.
