This article was downloaded by: [University of Liverpool] On: 06 October 2014, At: 04:30 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of the Air Pollution Control Association Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uawm16
A Microprocessor-Based Air Quality Monitoring System a
William W. Moyer & Fred P. Osman a
b
The Pennsylvania State University
b
Department of Environmental Resources , Pennsylvania , USA Published online: 13 Mar 2012.
To cite this article: William W. Moyer & Fred P. Osman (1975) A Microprocessor-Based Air Quality Monitoring System, Journal of the Air Pollution Control Association, 25:11, 1155-1157, DOI: 10.1080/00022470.1975.10470193 To link to this article: http://dx.doi.org/10.1080/00022470.1975.10470193
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
The standard deviation is the square root of the variance. The relative standard deviation is the standard deviation divided by the mean, c, which becomes ac _ [I/No + l/iV]1/2 (ID c ' In (No/N) under our assumptions. This expression for the relative standard deviation can be re-written as (12) No] In (No/N) Previous analyses obtained analogous expressions except that the errors in No were neglected and thus the No term in brackets in Equations (9) to (12) did not appear. As No and N become nearly equal (e.g., low mass concentrations) the relative standard deviation differs from former estimates by the factor \/2. If the No and N counts were obtained for different durations, to and t, then Equation (1) should be cast into the rate form:
Downloaded by [University of Liverpool] at 04:30 06 October 2014
c = k [In (iVoAo) ~ In (Wt)] The error expression becomes
(13)
and if the time error terms in Equation (14) are small compared with the counting error terms, the formula for the standard deviation ac becomes just what was obtained pre-
viously; Equations (9) and (12) remain unchanged. If the timing errors are not negligible and if to and t are different but dto « to and dt « t, then the expression for the standard deviation of the concentration becomes JV2
to2
(15)
This analysis is not limited to the beta absorption context but is applicable to other penetration or transmission mechanisms governed by equations of the form: N/No = e~c/k
(16)
where c is sought, k is known, and N and iVo are governed by Poisson statistics. References
1. P. Lilienfeld, "A New Ambient Participate Mass Monitor Using Beta Attenuation," 68th Annual Meeting of the Air Pollution Control Association, Boston, Mass., June 1975. 2. R. B. Husar, "Atmospheric particulate mass monitoring with a /8 radiation detector," Atmos. Environ. 8:183 (1974). 3. P. Lilienfeld and J. Dulchinos, "Portable instantaneous mass monitor for coal mine dust," Amer. Indus. Hyg. Assoc. J. 33: 136 (1972). 4. V. H. Dresia, P. Fischotter, and G. Felden, "Kontinuierliches Messen des Staubgehaltes in Luft und Abgasen mit Betastrahlen," VDI-Z, 106:1191 (1964). 5. W. Horn, "Process for continuous gravimetric determination of the concentration of dustlike emissions," Staub (English), 28 (9): 20 (1968).
A Microprocessor-Based Air Quality Monitoring System
William W. Moyer The Pennsylvania State University
Fred P. Osman Pennsylvania Department of Environmental Resources
Portable air quality monitoring systems may be required to supplement fixed installations or to provide for quick response to a transient situation, possibly at a remote location. A microprocessor-based monitoring unit has been developed for use with existing sensors. The unit is portable and its operational sequence can be programmed to adapt it to any unique requirements existing at the deployment site. Selectable on-site calculations are performed on raw data, and a hard copy or tape record of results can be produced. November 1975
Volume 25, No. 11
System Description
A block diagram of the microcomputer unit, implemented for collection of data on concentrations of eight pollutants monitored by the statewide Pennsylvania network,1 is provided as Figure 1. Sensor outputs in analog form are scaled to a common voltage range by individually adjusted amplification stages. When a set of samples is to be taken, the signal multiplexer, under control of a counter driven by the microprocessor, passes each signal in turn to the sample-hold circuit.
Each analog sample is converted to digital form and admitted to the microcomputer memory. Whenever any data sample is entered, a binary status word defining the operational condition of the sensor producing the data is passed through the digital multiplexer and also placed in microcomputer memory. The status words are tested and serve to prevent the inclusion of invalid data in statistical calculations. The status words can also be used to identify recurring sensor malfunctions. Timing circuitry operates from the 1155
APCA NOTE-BOOK Countdown Circuit
0Hz.
S0 2 Sensor
Scale Adjust
READY
Time-Date Circuitry
Digital Status Word Multiplexer
Restart Instruction
H2S
Sensor
l \ J J>
RST Four Stage Control Counter
N0 2 Sensor
INCR
Microcomputer (Intel 8080 CPU)
Downloaded by [University of Liverpool] at 04:30 06 October 2014
03 Sensor CH 4 Sensor
Analog Signal Multiplexer (Data)
HC Sensor
SampleHold Circuit
AnalogDigital Converter ParallelSerial Converter
CO Sensor Soiling Sensor Figure 1.
Scale Adjust
Teletypewriter
Block diagram of monitoring system.
standard ac supply line to generate a regular sequence of READY pulses, each of which initiates a sampling cycle controlled by the microcomputer. The READY pulses are also used to advance the time-date circuitry, which is initialized when the monitoring unit is first placed in operation. The time-date circuitry provides the information needed for time identification of taped or printed records. The microcomputer is designed around the Intel 8080 eight-bit central processor unit (CPU) chip. Operation of the CPU is directed by a sequence of instructions stored in units of reprogrammable read-only memory. This type of memory provides nonvolatile storage for the program but the instruction sequence can be readily erased and rewritten if program changes become necessary. Raw and smoothed data and other calculation results are stored in random-access memory. Input, interrupt, and output ports comprise the other major elements of the microcomputer. In addition to controlling of the input (sampling) and output operations, the microcomputer is employed to determine selected statistical properties of the data assembled. Although all data words are eight bits in length, bit 1156
HOLD
weights are varied to provide the different desired ranges of pollutant concentrations. Calculation and Output Operations
The calculation and output processes are customized to meet the requirements of the application. A program was written to perform a number of the single-site calculations executed by the central station of the Pennsylvania monitoring network. One hour blocks of raw data are assembled. The one hour average concentration, peak detected concentration, and time of peak observation (minute of the hour) are ascertained for each pollutant except soiling (average hour accumulation only). Those 4, 6, 8, and 24 hour averages involved in determination of the occurrence of an air pollution episode, as defined in Pennsylvania law,2 are also calculated. Each of these longer term averages is maintained on a running basis and, when updated, is compared to the relevant minimum episode threshold level. An average exceeding an episode threshold is flagged for special attention in the output operation. Calculation of any average is permitted only if a test of the associated status words indicates
that an acceptable percentage of the assembled data is valid, and only the valid words are used in the computation. Upon completion of the hourly calculations, the results are printed out or written on magnetic tape. The teletypewriter printout operation involves the transfer of an ordered sequence of fixed alphanumeric characters, stored in read-only memory, and the digits resulting from the calculations, stored in random-access memory. Each character or digit is retrieved from memory in turn and loaded into the parallelto-serial converter, which produces the serial ASCII-coded characters accepted by the teletypewriter. While the conversion and serial shift of a character is being completed, a HOLD signal is applied to the microprocessor to halt the printout operation until the next character can be accepted. The form of the printout produced hourly by the teletypewriter is illustrated in Table I. A time and Julian date are applied for purposes of identification. The 1 hr calculation results and the revised values of the longer term averages are tabulated. Any average exceeding the legislated episode concentration level is flagged as illustrated for the 6 hr SO2 average. If an
Journal of the Air Pollution Control Association
Downloaded by [University of Liverpool] at 04:30 06 October 2014
insufficient amount of valid data exists for the calculation of any parameter, the letter "X" is placed where the digits of that result would normally appear in the printout. The same output information could be placed on magnetic tape if a cassette recorder were used in place of the teletypewriter. The tape unit would accept parallel words and thereby speed the output process, and would result in a more portable system, but the on-site printout capability would be lost. The set of calculations described is executed in less than 0.5 sec. However, the teletypewriter requires about 70 sec for a complete printout. With the selected sampling interval of 1 min, the printout length dictates utilization of the interrupt structure provided by the microprocessor temporarily to halt the printout and allow a set of samples to be placed in microcomputer memory. The restart instruction effects the interrupt, and can be activated as often as necessitated by the length of the computation and output processes. The interrupted operation is resumed after a sample set is taken. Conclusions
Although the preceding description dealt with a specific system and a specific program, the system configuration is general and the instruction sequence can be readily altered or com-
pletely rewritten. With the CPU idle most of the time, unused computational capacity is available. Determinations of standard deviations and concentration ranges are feasible. The programmable input sampling schedule allows application of the system to a situation where a single pollutant is of interest. Hand reduction of strip chart data can be eliminated. Table I. Printout format (example). START HOUR REPORT 1900 HRS, JULIAN 029 SO2: HR AVG 0.288PPM PEAK 0.536PPM, MIN 21 H2S: HR AVG 0.048PPM PEAK 0.092PPM, MIN 05 O3: HR AVG X.XXXPPM PEAK X.XXXPPM, MIN XX NO2: HR AVG 0.032PPM PEAK 0.080PPM, MIN 46 CO:HRAVG 12.5PPM PEAK 21.0PPM, MIN 44 CH4: HR AVG 2.125PPM PEAK 3.250PPM, MIN 37 HC:HRAVG3.125PPM PEAK 4.375PPM, MIN 16 SOIL: HR AVG 4.625COHS SO2: 6-HR AVG 0.408PPM * * * * * 24-HR AVG 0.112PPM SOIL: 6-HR AVG 0.625COHS 24-HR AVG XX.XXXCOHS SO2*SOIL: 24-HR AVG X.XXX CO: 8-HR AVG 7.5PPM O3: 4-HR AVG 0.056PPM NO2: 24-HR AVG 0.032PPM END HOUR REPORT
The system1 described can be built economically and occupies a volume of about 0.5 ft3, exclusive of sensors and output device. When used with a cassette recorder, it can be rapidly put into operation at sites where the nature of the problem, the nature of the location, or simple economic considerations make construction of a more permanent station impractical. The capability provided for effecting customization of system operation by programming alterations rather than by hardware changes facilitates application of the microprocessor-based system to a wide variety of specialized monitoring tasks. References 1. B. A. Brodovicz, Jr., G. B. Murdock, and V. H. Sussman, "Pennsylvania's computerized air monitoring system," J. Air Poll. Control Assoc. 19: 484 (1969). 2. Pennsylvania P. L. 2119, Title 25, Part I, Subpart C, Article III, Chapter 135; enacted January 8, 1960, revised January 27,1972.
Mr. Moyer is a development engineer in the Applied Research Laboratory, The Pennsylvania State University, P.O. Box 30, State College, PA 16801. Mr. Osman is an air pollution control engineer with the Pennsylvania Department of Environmental Resources, Harrisburg, PA.
Progress Toward A Uniform Air Pollution Index
Gary C. Thorn Consultant, Council on Environmental Quality
Wayne R. OH U. S. Environmental Protection Agency
Recently, various authors1"4 have indicated that a need exists to establish a uniform air pollution index for communities throughout the nation. Although the literature reveals several attempts to develop air pollution indices,5"7 none of these indices has reNovember 1975
Volume 25, No. 11
ceived widespread acceptance by state and local air pollution control agencies, probably because none has received the active support or endorsement of the federal government. We now wish to report that significant progress has been made at the federal
level toward the goal of a recommended national air pollution index. During late 1974 and early 1975, an extensive national survey of air pollution indices currently in use was conducted as a joint study by the U. S. Environmental Protection Agency 1157
Journal of the Air Pollution Control Association Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uawm16
A Microprocessor-Based Air Quality Monitoring System a
William W. Moyer & Fred P. Osman a
b
The Pennsylvania State University
b
Department of Environmental Resources , Pennsylvania , USA Published online: 13 Mar 2012.
To cite this article: William W. Moyer & Fred P. Osman (1975) A Microprocessor-Based Air Quality Monitoring System, Journal of the Air Pollution Control Association, 25:11, 1155-1157, DOI: 10.1080/00022470.1975.10470193 To link to this article: http://dx.doi.org/10.1080/00022470.1975.10470193
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
The standard deviation is the square root of the variance. The relative standard deviation is the standard deviation divided by the mean, c, which becomes ac _ [I/No + l/iV]1/2 (ID c ' In (No/N) under our assumptions. This expression for the relative standard deviation can be re-written as (12) No] In (No/N) Previous analyses obtained analogous expressions except that the errors in No were neglected and thus the No term in brackets in Equations (9) to (12) did not appear. As No and N become nearly equal (e.g., low mass concentrations) the relative standard deviation differs from former estimates by the factor \/2. If the No and N counts were obtained for different durations, to and t, then Equation (1) should be cast into the rate form:
Downloaded by [University of Liverpool] at 04:30 06 October 2014
c = k [In (iVoAo) ~ In (Wt)] The error expression becomes
(13)
and if the time error terms in Equation (14) are small compared with the counting error terms, the formula for the standard deviation ac becomes just what was obtained pre-
viously; Equations (9) and (12) remain unchanged. If the timing errors are not negligible and if to and t are different but dto « to and dt « t, then the expression for the standard deviation of the concentration becomes JV2
to2
(15)
This analysis is not limited to the beta absorption context but is applicable to other penetration or transmission mechanisms governed by equations of the form: N/No = e~c/k
(16)
where c is sought, k is known, and N and iVo are governed by Poisson statistics. References
1. P. Lilienfeld, "A New Ambient Participate Mass Monitor Using Beta Attenuation," 68th Annual Meeting of the Air Pollution Control Association, Boston, Mass., June 1975. 2. R. B. Husar, "Atmospheric particulate mass monitoring with a /8 radiation detector," Atmos. Environ. 8:183 (1974). 3. P. Lilienfeld and J. Dulchinos, "Portable instantaneous mass monitor for coal mine dust," Amer. Indus. Hyg. Assoc. J. 33: 136 (1972). 4. V. H. Dresia, P. Fischotter, and G. Felden, "Kontinuierliches Messen des Staubgehaltes in Luft und Abgasen mit Betastrahlen," VDI-Z, 106:1191 (1964). 5. W. Horn, "Process for continuous gravimetric determination of the concentration of dustlike emissions," Staub (English), 28 (9): 20 (1968).
A Microprocessor-Based Air Quality Monitoring System
William W. Moyer The Pennsylvania State University
Fred P. Osman Pennsylvania Department of Environmental Resources
Portable air quality monitoring systems may be required to supplement fixed installations or to provide for quick response to a transient situation, possibly at a remote location. A microprocessor-based monitoring unit has been developed for use with existing sensors. The unit is portable and its operational sequence can be programmed to adapt it to any unique requirements existing at the deployment site. Selectable on-site calculations are performed on raw data, and a hard copy or tape record of results can be produced. November 1975
Volume 25, No. 11
System Description
A block diagram of the microcomputer unit, implemented for collection of data on concentrations of eight pollutants monitored by the statewide Pennsylvania network,1 is provided as Figure 1. Sensor outputs in analog form are scaled to a common voltage range by individually adjusted amplification stages. When a set of samples is to be taken, the signal multiplexer, under control of a counter driven by the microprocessor, passes each signal in turn to the sample-hold circuit.
Each analog sample is converted to digital form and admitted to the microcomputer memory. Whenever any data sample is entered, a binary status word defining the operational condition of the sensor producing the data is passed through the digital multiplexer and also placed in microcomputer memory. The status words are tested and serve to prevent the inclusion of invalid data in statistical calculations. The status words can also be used to identify recurring sensor malfunctions. Timing circuitry operates from the 1155
APCA NOTE-BOOK Countdown Circuit
0Hz.
S0 2 Sensor
Scale Adjust
READY
Time-Date Circuitry
Digital Status Word Multiplexer
Restart Instruction
H2S
Sensor
l \ J J>
RST Four Stage Control Counter
N0 2 Sensor
INCR
Microcomputer (Intel 8080 CPU)
Downloaded by [University of Liverpool] at 04:30 06 October 2014
03 Sensor CH 4 Sensor
Analog Signal Multiplexer (Data)
HC Sensor
SampleHold Circuit
AnalogDigital Converter ParallelSerial Converter
CO Sensor Soiling Sensor Figure 1.
Scale Adjust
Teletypewriter
Block diagram of monitoring system.
standard ac supply line to generate a regular sequence of READY pulses, each of which initiates a sampling cycle controlled by the microcomputer. The READY pulses are also used to advance the time-date circuitry, which is initialized when the monitoring unit is first placed in operation. The time-date circuitry provides the information needed for time identification of taped or printed records. The microcomputer is designed around the Intel 8080 eight-bit central processor unit (CPU) chip. Operation of the CPU is directed by a sequence of instructions stored in units of reprogrammable read-only memory. This type of memory provides nonvolatile storage for the program but the instruction sequence can be readily erased and rewritten if program changes become necessary. Raw and smoothed data and other calculation results are stored in random-access memory. Input, interrupt, and output ports comprise the other major elements of the microcomputer. In addition to controlling of the input (sampling) and output operations, the microcomputer is employed to determine selected statistical properties of the data assembled. Although all data words are eight bits in length, bit 1156
HOLD
weights are varied to provide the different desired ranges of pollutant concentrations. Calculation and Output Operations
The calculation and output processes are customized to meet the requirements of the application. A program was written to perform a number of the single-site calculations executed by the central station of the Pennsylvania monitoring network. One hour blocks of raw data are assembled. The one hour average concentration, peak detected concentration, and time of peak observation (minute of the hour) are ascertained for each pollutant except soiling (average hour accumulation only). Those 4, 6, 8, and 24 hour averages involved in determination of the occurrence of an air pollution episode, as defined in Pennsylvania law,2 are also calculated. Each of these longer term averages is maintained on a running basis and, when updated, is compared to the relevant minimum episode threshold level. An average exceeding an episode threshold is flagged for special attention in the output operation. Calculation of any average is permitted only if a test of the associated status words indicates
that an acceptable percentage of the assembled data is valid, and only the valid words are used in the computation. Upon completion of the hourly calculations, the results are printed out or written on magnetic tape. The teletypewriter printout operation involves the transfer of an ordered sequence of fixed alphanumeric characters, stored in read-only memory, and the digits resulting from the calculations, stored in random-access memory. Each character or digit is retrieved from memory in turn and loaded into the parallelto-serial converter, which produces the serial ASCII-coded characters accepted by the teletypewriter. While the conversion and serial shift of a character is being completed, a HOLD signal is applied to the microprocessor to halt the printout operation until the next character can be accepted. The form of the printout produced hourly by the teletypewriter is illustrated in Table I. A time and Julian date are applied for purposes of identification. The 1 hr calculation results and the revised values of the longer term averages are tabulated. Any average exceeding the legislated episode concentration level is flagged as illustrated for the 6 hr SO2 average. If an
Journal of the Air Pollution Control Association
Downloaded by [University of Liverpool] at 04:30 06 October 2014
insufficient amount of valid data exists for the calculation of any parameter, the letter "X" is placed where the digits of that result would normally appear in the printout. The same output information could be placed on magnetic tape if a cassette recorder were used in place of the teletypewriter. The tape unit would accept parallel words and thereby speed the output process, and would result in a more portable system, but the on-site printout capability would be lost. The set of calculations described is executed in less than 0.5 sec. However, the teletypewriter requires about 70 sec for a complete printout. With the selected sampling interval of 1 min, the printout length dictates utilization of the interrupt structure provided by the microprocessor temporarily to halt the printout and allow a set of samples to be placed in microcomputer memory. The restart instruction effects the interrupt, and can be activated as often as necessitated by the length of the computation and output processes. The interrupted operation is resumed after a sample set is taken. Conclusions
Although the preceding description dealt with a specific system and a specific program, the system configuration is general and the instruction sequence can be readily altered or com-
pletely rewritten. With the CPU idle most of the time, unused computational capacity is available. Determinations of standard deviations and concentration ranges are feasible. The programmable input sampling schedule allows application of the system to a situation where a single pollutant is of interest. Hand reduction of strip chart data can be eliminated. Table I. Printout format (example). START HOUR REPORT 1900 HRS, JULIAN 029 SO2: HR AVG 0.288PPM PEAK 0.536PPM, MIN 21 H2S: HR AVG 0.048PPM PEAK 0.092PPM, MIN 05 O3: HR AVG X.XXXPPM PEAK X.XXXPPM, MIN XX NO2: HR AVG 0.032PPM PEAK 0.080PPM, MIN 46 CO:HRAVG 12.5PPM PEAK 21.0PPM, MIN 44 CH4: HR AVG 2.125PPM PEAK 3.250PPM, MIN 37 HC:HRAVG3.125PPM PEAK 4.375PPM, MIN 16 SOIL: HR AVG 4.625COHS SO2: 6-HR AVG 0.408PPM * * * * * 24-HR AVG 0.112PPM SOIL: 6-HR AVG 0.625COHS 24-HR AVG XX.XXXCOHS SO2*SOIL: 24-HR AVG X.XXX CO: 8-HR AVG 7.5PPM O3: 4-HR AVG 0.056PPM NO2: 24-HR AVG 0.032PPM END HOUR REPORT
The system1 described can be built economically and occupies a volume of about 0.5 ft3, exclusive of sensors and output device. When used with a cassette recorder, it can be rapidly put into operation at sites where the nature of the problem, the nature of the location, or simple economic considerations make construction of a more permanent station impractical. The capability provided for effecting customization of system operation by programming alterations rather than by hardware changes facilitates application of the microprocessor-based system to a wide variety of specialized monitoring tasks. References 1. B. A. Brodovicz, Jr., G. B. Murdock, and V. H. Sussman, "Pennsylvania's computerized air monitoring system," J. Air Poll. Control Assoc. 19: 484 (1969). 2. Pennsylvania P. L. 2119, Title 25, Part I, Subpart C, Article III, Chapter 135; enacted January 8, 1960, revised January 27,1972.
Mr. Moyer is a development engineer in the Applied Research Laboratory, The Pennsylvania State University, P.O. Box 30, State College, PA 16801. Mr. Osman is an air pollution control engineer with the Pennsylvania Department of Environmental Resources, Harrisburg, PA.
Progress Toward A Uniform Air Pollution Index
Gary C. Thorn Consultant, Council on Environmental Quality
Wayne R. OH U. S. Environmental Protection Agency
Recently, various authors1"4 have indicated that a need exists to establish a uniform air pollution index for communities throughout the nation. Although the literature reveals several attempts to develop air pollution indices,5"7 none of these indices has reNovember 1975
Volume 25, No. 11
ceived widespread acceptance by state and local air pollution control agencies, probably because none has received the active support or endorsement of the federal government. We now wish to report that significant progress has been made at the federal
level toward the goal of a recommended national air pollution index. During late 1974 and early 1975, an extensive national survey of air pollution indices currently in use was conducted as a joint study by the U. S. Environmental Protection Agency 1157
