plot1.R

# The encoding of the script is CP936
# R version 3.1.1 (2014-07-10) -- "Sock it to Me"
# Platform: i386-w64-mingw32/i386 (32-bit)
# Operating system: Windows 7 (SP1)
# 20140821 qingcheng

# Couresra-[Exploratory Data Analysis][exdata-005][Course Project 2]

# The overall goal of this assignment is to explore the National Emissions
# Inventory database and see what it say about fine particulate matter 
# pollution in the United states over the 10-year period 1999¨C2008. 

# Question 1
# Have total emissions from PM2.5 decreased in the United States from 1999 to 
# 2008? Using the base plotting system, make a plot showing the total PM2.5 
# emission from all sources for each of the years 1999, 2002, 2005, and 2008.


# see downloadData.R
# read dataset, this first line will likely take a few seconds. Be patient!
NEI <- readRDS("summarySCC_PM25.rds")
SCC <- readRDS("Source_Classification_Code.rds")


s <- tapply(NEI$Emissions, NEI$year, sum)


png("plot1.png", width=480, height=480)
plot(names(s), s, xlab="Year", type="l", main=expression(PM[2.5]),
     ylab=expression("Total " ~ PM[2.5] ~ " emissions from all sources (tons)"))
dev.off()