Plot1 Script

Script creates a bar plot to answer:  Have total emissions from PM
decreased in the United States from 1999 to 2008? Using the baseplotting
system, make a plot showing the total PM emission from all sources for
each of the years 1999, 2002, 2005, and 2008.
Plot 1

Plot 1 created by Plot1.R script.
Plot 2

Plot 2 created by plot2.R script.
Plot 3

Plot 2 created by plot3.R script.