Date sulfate nitrate ID
1   2002-01-01      NA      NA  8
2   2002-01-02      NA      NA  8
3   2002-01-03      NA      NA  8
4   2002-01-04      NA      NA  8
5   2002-01-05      NA      NA  8
6   2002-01-06      NA      NA  8

pollutantmean <- function(directory,pollutant,id = 1:332){
        means <- c()
        for(i in id){
                x <- paste(getwd(), "/", directory, "/", sprintf("%03d", i), ".csv", sep = "")
                freem <- read.csv(x)
                inte <- freem$pollutant
                print(class(frame$pollutant))
                means[i] <- mean(inte, na.rm = TRUE)


        }
        mean(means)
}