Annotating subscript in R plots

I have to annotate one in every of my determine like this:

(b) PM<sub>2.5


And this can be a method to do it in R with ggplot2 package deal:

b ->
annotate("textual content", x=-three.5, y=zero.12, label=deparse(b),parse=TRUE)

Unsure concerning the particulars behind all of the parameters although. Because of BondedDust for answering this query.</sub>