library(twitteR)

n <- 27
feed <- userTimeline("BeijingAir", n = n)
sfeed <- lapply(feed, function(x) strsplit(x$getText(), "; ", fixed = TRUE))
times <- vector("list", length = n)
pm25 <- numeric(n)
times <- sapply(sfeed, function(x) {
        paste(x[[1]][1:2], collapse = " ")
})
times <- strptime(times, "%m-%d-%Y %H:%M")
pm25 <- sapply(sfeed, function(x) {
        x <- x[[1]]
        if(length(grep("^Past", x[3])) > 0)
                return(NA)
        as.numeric(x[4])
})
u <- !is.na(pm25)
times <- times[u]
pm25 <- pm25[u]

png(file = "beijing24.png", width = 700, height = 480)
par(mar = c(2, 4.5, 2, 1) + .1)
plot(times, pm25, main = expression(PM[2.5] * " in Beijing"),
     xlab = "", ylab = expression(PM[2.5] * " (" * mu * g/m^3 * ")"),
     pch = 19, type = "b")
dev.off()