plot2.R

# Have total emissions from PM2.5 decreased in the Baltimore City, Maryland (fips == "24510") 
# from 1999 to 2008? Use the base plotting system to make a plot answering this question.

NEI.file  <- "summarySCC_PM25.rds"
SCC.file  <- "Source_Classification_Code.rds"
Baltimore.fip <- "24510"

message(paste("Reading ", NEI.file, " dataset"))

NEI <- readRDS(NEI.file)

message(paste("Reading ", SCC.file, " dataset"))

SCC <- readRDS(SCC.file)

message("Extracting Baltimore data")

NEI.Baltimore <- NEI[which(NEI$fips == Baltimore.fip),]

message("Calculating yearly total emissions")

NEI.Baltimore.total  <- aggregate(list(emissions = NEI.Baltimore$Emissions), by=list(year = NEI.Baltimore$year), FUN = sum)

message("Plotting and saving file")

par(mar=c(5,5,6,3))
barplot((NEI.Baltimore.total$emissions/1000), 
        ylim=c(0, 4),
        names.arg = c(as.character(NEI.Baltimore.total$year)), 
        col="red",
        xlab = "Years", 
        ylab="PM2.5 Emissions (per 1000 tons)")
mtext(side=3, line=3, "PM2.5 Emissions in Baltimore City between 1999 and 2008", cex=1.2)
dev.copy(png, file = "plot2.png", width = 580, height = 580)
dev.off()