[R] Subscript in axis label

[pm509 at york.ac.uk]

Dear R help list members,

I am experiencing difficulty in trying to generate a subscript '2' in an 
axis label. Although I can get the '2' into a subscript using expression(), 
R then forces me to leave at least one space between the '2' and the 
following character. My label is supposed to read 'N2O concentration 
(ppm)', and the space between the '2' and the 'O' makes it look rather 
inelegant! My code is the following (the comments in it are there to stop 
me forgetting what I have done, I am new to R):

postscript(file="/Users/patrickmartin/Documents/York Innova 
Precision/N2Oinnova.eps", horizontal=FALSE, onefile=FALSE, height=4, 
width=5, pointsize=10)
> plot(n2o, lty=0, las=1, xlab="Time", ylab=expression(N[2]~"O 
> concentration (ppm)")) points(n2o, pch=16) # suppresses line but adds 
> points dev.off() # turns postscript device off again

One possibility is for me to simply leave two spaces everywhere else, but 
that looks a little strange. Does anyone know of a more elegant way of 
solving the problem?

A related query is that the journal I want to publish this figure in 
specifies that if EPS format is used, the font should be either Arial, 
Courier, Helvetica, Times or Symbol. Is one of these the default font for 
an EPS file in R, and if not, is there a possibility of changing it?

Thanks a lot in advance,
Patrick Martin