In the isopleth map (Figure 3) the sulphur dioxide lines tend to parallel the lake e, i.e., the high population zones, indicating a slower decay of concentration toward northwest and southwest. The highest concentrations are in the Hyde Park-Kenwood , the location of station L. tfall While dustfall is not as important as either sulphur dioxide or suspended particulates, In a public health point of view, it is included here only briefly for the sake of completeness. the twenty dustfall stations that compose the network, the yearly average was 41.0 tons/ are mile/month. The dustfall concentrations follow the pattern of density of population *industrial concentration as well as reflect seasonal variation because of heating, particularly to the use of low-grade fuels. During the heating season, solubles and combustibles are ticularly high. The insolubles and non-combustibles appear to follow wind patterns, showing her concentrations in spring and summer months. (Figure 4) LOCATION OF STATIONS FOR THE CONTINUOUS AIR MONITORING PROGRAM As the Department's Five-Year Air Resource Management Program progressed, it same apparent that continuous air quality data must be available, not simply bi-weekly ri-weekly information gathered by air sampling technicians. A statistical analysis of year's of data on suspended particulates and sulphur dioxide was made to determine adequate number of stations and their location throughout the city. The stations ected had to meet two criteria: (1) they must be truly representative of the >graphical coverage of the city, and (2) they must provide an estimate of air quality significantly different from the data acquired from the twenty-station networks. The statistical analysis of the twenty stations revealed an adequate grouping of eight subsets with the stations in each subset comprising the same regional area. Moreover, the readings of pollutants were reasonably similar at the different stations located within the same subset. (Table 2) For example, stations A and C, located in the northwest protion of the city, had median concentrations of suspended particulates of 76 and 85 ug/m3 respectively. In addition, the correlation coefficient between measurements made on the same day at these stations was r=0.98, indicating nearly a one-to-one correspondence. For all practical purposes, either one of these stations could be selected to represent that general area of the city. By June of 1965 seven months of SO2 data at nineteen stations had become available. A check was made on the adequacy of the chosen sites based on the correspondence between the average SO2 concentration for these stations and that for the total network. In addition, eight stations were independently selected, using a graphic method, based on the correspondence of graphed data of individual stations with those of averages of the network. Table 3 shows the results of these checks. Though the alternate network thus obtained revealed a somewhat better correlation coefficient, it was not as adequate geographically. Thus, the original eight station choice was retained; however, station P was substituted for station Q. Finally, two additional criteria were used in selecting one station from each of the eight subsets: (1) Health studies under the direction of Dr. Mark Lepper, Chairman of Preventive Medicine, University of Illinois School of Medicine, required a broad socio-economic distribution. (2) Wide geographic distribution was desirable to obtain suitable meteorological coverage. CONTINUOUS AIR MONITORING TELEMETERED NETWORK In evaluating various approaches to a data-gathering and logging system certain ctors had to be considered: cost, reliability, simplicity for ease of maintenance, data indling, availability of service, and manufacturers with proven experience in all phases the system requirements. Specifications for the system on order were developed with ese general considerations in mind and by evaluating the technical aspects of a number of stems available. To obtain reliability of data telemetered to a central location and ease of intenance it was decided to digitize at remote sites by installing a shaft encoder on ich chemical analyzer and meteorological sensor. Solid state design electronics was ecified because of its inherent reliability in addition to lending itself to modular plugconstruction, making maintenance a matter of merely replacing a plug-in module and pairing the defective unit at a more convenient time. Teletype transmission of data to the central station offered the use of the lowest ist leased line available from the telephone company. At the central station the transmitted ita are printed on a page printer in addition to being recorded on punched paper tape for bsequent computer handling. The remote stations utilize solid state distributors in lieu the electro-mechanical units normally used for teletype transmission. They are introlled by a precision clock and should require virtually no maintenance or adjustment. stems Operation The Air Quality Monitoring System finally purchased consists of eight remote stations, ch having a sulphur dioxide analyzer and an aerovane. It is designed for recording data 15-minute intervals by transmitting sequentially from each remote station to the central station. Data gathered at each remote site include sulphur dioxide in parts per million, five-minute integrated wind direction to the nearest degree and a five-minute integrated wind speed to the nearest one-tenth knot. (Figure 5) (Figure 6) Fifteen-minute intervals were selected because of their representativeness over a 24-hour period, thereby precluding the likelihood of excessive highs and lows occurring without being detected. A new and rather unique meteorological method is employed in the recording of 15-minute intervals inasmuch as wind speed and direction are "integrated," i.e., readings on wind speed and direction are taken every five seconds and are stored in the electronic memory; the information is then averaged by the computer for 15-minute readings and recorded. The problem of eliminating ambiguity of readings of wind speed and direction was solved by suing two Selson motors counter-clockwise. At pre-slected intervals the central station clock signals the beginning of a recording cycle. The programmer starts the printer and tape punch and initiates the recording of the date-time group and parameter data which is utilized by the computer for the analysis assigned to the block of data. The programmer then interrogates the first station, and it immediately transmits its three-digit identification followed by the air quality and wind data. This is repeated for all stations with a total transmission time of 40 seconds. The central station control panel allows for automatic or manual selection of signals for zero checks, calibration checks, and changes of sampling and recording intervals. Further, it contains provisions for by-passing a station in the event of line or equipment difficulties, initiation of demand recording cycles and indicators to show functions taking place. The central console incorporates a graphic display representing the metropolitan Chicago area with indicators that illuminate each station location when the station is transmitting data. f vantages of the System The system is so constructed that expansion to twenty plus stations may be accomplished installing additional circuit modules and adding chassis by merely tying into existing nectors. Each remote station will be able to accept inputs from as many as five different quality analyzers. Encoders allow the user to utilize any of the available analyzer instruments by ng onto the shaft of the recorder which in most cases is an integral part of the analyzer. also presents linearized and scaled output and no data interpretation is required. They no errors to the analyzer accuracy. Digital transmission precludes any degradation system accuracy. Using teletype recording equipment allows the use of lowest cost ephone lines. Minimal modification is required for tying the system to an on-line computer for mplete pollution monitoring. CONCLUSION The Telemetered Air Monitoring Network information will be used to: 1. Advise the public of the air quality in the City of Chicago. 2. Provide the back-up information with which health studies will be correlated. 3. Provide the information to determine the effectiveness of the enforcement program in reducing sulphur dioxide. 4. Provide an enforcement tool to pinpoint large emittors of sulphur dioxide. 5. Provide the information to support the design and operation of a diffusion 6. Establish air quality standards as an aid to enforcement. 7. Develop an air pollution climatology for the City of Chicago. |