2.5 Sulfur dioxide is one of the major components of the AQI measure of air quality. Table 2.4 gives the sulfur dioxide estimates (in short tons) for years 1980 and 2000. (National Air Quality and Emissions Trends Report, http://www.epa.gov/

airtrends/).

a Construct a time series plot for the total emission across the years. Comment on any trend you observe.

b Construct a time series plot for each of the sources of sulfur dioxide emission across the years. Comment on any trend you observe.