The Environmental Protection Agency (EPA) regulates the level of carbon dioxide (CO2) emissions. Periodically these emissions measurements are under-reported due to leakage or faulty equipment. Such problems are often detected only by an expensive test (RATA) that is typically conducted only once per year. Just recently, the EPA began applying an automated control chart methodology to detect under measurement of emissions data (EPRI CEM Users Group Conference, Nashville, TN, May 13, 2008). Each day, the EPA collects emissions data by measuring CO2 concentration for each of 6 randomly selected hours. The daily average CO2 levels for each of 30 days are shown in the table at the bottom of the page. The EPA considers these values to truly represent emissions levels because the RATA test was recently performed and showed no problems with under-reporting. The lower and upper control limits for the averages were established as LCL = 12.26 and UCL = 13.76.
a. Construct a control chart for the daily average CO2 levels.
b. Based on the control chart, describe the behavior of the measurement process.
c. The following average CO2 levels were determined for a later 10-day period: 12.7, 12.1, 12.0, 12.0, 11.8, 11.7, 11.6, 11.7, 11.8, 11.7. Make an inference about the potential under-reporting of the emissions data for this 10-day period.

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Daily Average CO, Measurements for 30 Consecutive Days 3 13.4 11 12 12.8 13 12.7 14 12.9 4 13.3 10 12.5 15 12.0 13.2 13.1 13.2 13.0 12.9 13.1 12.5 12.7 16 12.9 17 12.8 18 12.7 19 13.2 21 13.3 23 27 13.1 29 13.4 30 13.4 22 13.0 24 13.2 25 13.2 26 13.4 28 13.3 13.2 13.0