Each plot includes an R script and a PNG output. Data can be found here

plot1: Have total emissions from fine particulate matter decreased in the United States from 1999 to 2008? Answer: Yes!

plot2: Have total emissions from fine particulate matter decreased in the Baltimore City, Maryland from 1999 to 2008? Answer: Yes!

plot3: Of the four types of sources variable, which of these four sources have seen decreases in emissions from 1999–2008 for Baltimore City? Which have seen increases in emissions from 1999–2008? Answer: Point mixed, rest down

plot4: Across the United States, how have emissions from coal combustion-related sources changed from 1999–2008? Answer: They're sort of falling...

plot5: How have emissions from motor vehicle sources changed from 1999–2008 in Baltimore City? Answer: They fell, then leveled out

plot6: Compare emissions from motor vehicle sources in Baltimore City with emissions from motor vehicle sources in Los Angeles County, California. Which city has seen greater changes over time in motor vehicle emissions? Answer: LA has the greatest fluctuations, Baltimore has the most consistent decline