Instrumentation
Minicomputer Data Processing System for Air Monitoring Studies S. Ο. Farwell,1 H. H. Westberg, K. J. Allwine, and Ν. Κ. Shrauger 2 Air Pollution Research, Department of Chemical Engineering, Washington State University, Pullman, Wash. 99164
T h e collection of air quality infor mation during field monitoring pro grams produces huge quantities of an alytical and meteorological data. For example, a well-equipped, groundlevel sampling station continuously records ambient concentrations of ozone, oxides of nitrogen, hydrocar bons, carbon monoxide, halocarbons, gaseous sulfur species, particulate loadings, plus numerous meteorologi cal parameters such as wind speed and direction, turbulence, temperature, dew point, and solar radiation. As a supplement to these ground opera tions, the use of an instrumented air craft has increasingly become a neces sity in comprehensive field monitoring programs (1). T h e instrumented air craft, of course, greatly augments the amount of data collected since, in ad dition to recording pollutant and me teorological parameters, it is desirable to obtain a continuous record of navi gational information including dis tance and direction from a fixed ground point (direction measuring equipment or D M E and V H F omnidi rectional range or VOR, respectively), altitude, and air speed. Therefore, a computer-based data handling system is essential in processing the data ob tained in a combined aircraft/ground station monitoring network.
23-ft mobile trailer); thus, data pro cessing is performed at the actual field site. This on-site processing permits field personnel to examine a complete data set each day, which is very ad vantageous from the standpoint of recognizing instrumental malfunctions as well as short-term pollutant rela tionships t h a t warrant further study. An additional benefit of on-site data reduction is t h a t the same researchers who have collected the data are also responsible for the processing. Conse quently, any questions concerning d a t a anomalies due to instrument range changes, zero checks, and cali bration periods can be quickly re solved.
General Description of Data System A Hewlett-Packard 2100A mini computer, which was originally ob tained in the purchase of a " t u r n k e y " H - P 3352B chromatographic data sys tem (2), serves as the basic component of our system. Data are collected on identical 4-track magnetic tape re cording devices in our instrumented aircraft and ground laboratory. T h e voltage data on the tapes are then read into the minicomputer where they are converted to scientific units, time-averaged, and subsequently out put in a hard copy tabulation. Figure 1 provides a block diagram illustrating
T h e purpose of this paper is to de scribe the minicomputer-based data processing system we use in air moni toring studies. T h e computer plus all peripheral I n p u t / O u t p u t (I/O) devices are housed in our field laboratory (a
' To whom correspondence should be ad dressed. '-'• Permanent address, Electronic Re search Laboratory, Montana State Univer sity, Bozeman, Mont. 59715.
Figure 1. Basic system configuration ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977 · 357 A
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the steps from data collection to final reduction. T h e software programs developed to convert the recorded voltages to the desired physical and engineering units are very flexible with regard to both configuration and operation. During the initial dialog used to prepare a specific processing program, the operator can input a report title, date, and location; assign any of the available peripheral devices to any computer channel; specify either a raw data dump, a "converted" data d u m p of any selected scan(s), or the number of data scans to be used in an average value calculation; and, thus, define the exact format of the final report. T h e operational flexibility of the software programs includes the option to examine the event code channel of the aircraft data for any coded range change information and to include automatically this new attenuation into the corresponding calculations. Finally, the computer-operator dialog has been patterned after the conversational symbolism of a commercial chromatographic data system. Thus, an analyst who understands the symbolic language of this particular chromatographic data system can readily employ the described computing facility. This latter feature was designed to simplify the man-computer interface and thereby encourage the air pollution scientist to take further advantage of the minicomputer's capabilities in his work. Equipment Mobile Ground Laboratory. A 23-ft, custom-built travel trailer serves as our field headquarters. This laboratory contains 52 ft of bench and rack space for accommodation of the monitoring instruments, meteorological sensors, and data acquisition and processing system. Table I lists the various measurements performed at the ground monitoring station. Most of the equipment is permanently mounted in the trailer for easy transport from site to site. T h e temperature within the trailer is maintained at 75 ± 5 °F by two large air conditioners mounted on the roof. Ambient air is brought into the trailer through a 4-in. stainless steel pipe. This air sample line runs the full interior length of the trailer and serves as a manifold for supplying outside air to the continuous monitoring instruments. Aircraft. A twin-engine Cessna 336 Skymaster serves as the air sampling platform from which real-time analysis is performed (/ ). This aircraft is capable of carrying the pilot, an instrument operator, about 400 lb of instrumentation, and enough fuel for 3 h of survey work. Table II lists the common measurements performed by the
CIRCLE 107 ON READER SERVICE CARD 358 A · ANALYTICAL CHEMISTRY, VOL . 49, NO. 3, MARCH
1977
Table 1. Typical Ground-Level Monitoring Measurements Ozone Nitrogen oxides (NO-N0 2 -NO x ) Total hydrocarbons Methane Carbon monoxide Individual C 2 -C 1 0 hydrocarbons Halocarbons Sulfur dioxide Particulate sulfate
Wind speed Wind direction Turbulence Dew point Solar radiation Air temperature Vertical temperature discontinuity (acoustic radar)
instrumented aircraft. Air for the aircraft sampling instruments is brought in through a 4-in. diameter air scoop extending out approximately 10 in. from the fuselage and by the connecting 4-in. Plexiglas pipe inside the airplane cabin. Data Loggers. Both the aircraft and ground-based data are recorded on separate Metrodata DL-620 data loggers which use a '/i-in. 4-track, 20channel magnetic tape cartridge. T h e analog input data to the data logger are multiplexed by a programmable clock-controlled scanner, and the data are subsequently digitized and formatted for recording. In the airplane the data logger operates in the continuous scanning mode where it records 2'/j scans of data per second (one scan is one record of the 20 channels of data). T h e ground-based recording system records at a rate of 2 data scans per minute. In this latter intermittent scan mode, two data scans are recorded for redundancy. T h e data for each channel are recorded as a sign character and three 4-bit BCD characters. In the sign position, a plus is represented by X'A' and a minus by a X'B'. Time is automatically recorded as 6 BCD digits in channels 1 and 2, whereas channels 3-20 are the data channels. The data records are completed by recording a preparity and a parity character, and a gap is then generated between records. T h e standard bit packing density is 67 cpi. Data System Hardware. As shown
Table II. Typical Aircraft Monitoring Measurements Ozone Nitrogen oxides
