Updated to use explicit reference to function argument names.
Updated to use subset() function over [,] notation.
Updated plot title to use a subtitle for location information.
Updated to use explicit reference to function argument names.
Updated to use subset() function over [,] notation.
Updated plot title to use a subtitle for location information.
Updated to use explicit reference to function argument names.
Updated to use subset() function over [,] notation.
Updated plot title to use a subtitle for location information.
Removed custom library loading function. Replaced with call to require() function instead.
Added plot and code for United States coal combustion-related source emissions trend from 1999-2008.
Added plot and code for Baltimore City motor vehicle source emissions trend from 1999-2008.
Added plot and code for comparative analysis of coal combustion-related source emissions for Baltimore City, Maryland and Los Angeles, California from 1999-2008.