39. Air Pollution Using Deseasonalization. Air pollution control specialists in southern California monitor the amount of ozone, carbon dioxide, and nitrogen dioxide in the air on an hourly basis. The hourly time series data exhibit seasonality, with the levels of pollutants showing patterns over the hours in the day. On July 15, 16, and 17, the following levels of nitrogen dioxide were observed in the downtown area for the 12 hours from 6:00 a.m. to 6:00 p.m.

July 15: 25 28 35 50 60 60 40 35 30 25 25 20 July 16: 28 30 35 48 60 65 50 40 35 25 20 20 July 17: 35 42 45 70 72 75 60 45 40 25 25 25

a. Construct a time series plot. What type of pattern exists in the data?

b. Identify the hourly seasonal indexes for the 12 readings each day.

c. Deseasonalize the time series.

d. Using statistical software, compute the linear trend equation for the deseasonalized data.

e. Compute the deseasonalized trend forecasts for the 12 hours for July 18 and then adjust the trend forecasts using the seasonal indexes computed in part (b).