Q:

printing text in multiple lines as the title of a plot or axis WITH a subscript present in the text

I wish to print a text in the title in two lines but am not able to achieve desired output because of subscript present in the text. Following is the e.g of the text that I want in two lines. 
plot(1,main=expression(paste(CO[2]~'Flux (kg C ', m^-2,' ',s^-1,')')))

BUT using line break as in following command does not give desired result of bringing (only) the text following it in new line:
plot(1,main=expression(paste(CO[2]~'Flux \n(kg C ', m^-2,' ',s^-1,')')))

Please help me with this issue.
Thanks in advance

A:

You can do this with the atop function.
plot(1,main=expression(atop(CO[2]~'Flux', paste('(kg C ', m^-2,' ',s^-1,')'))))

Since the lheight par doesn't affect expressions, if you want tighter spacing between the lines, you can use the following.
plot(1,main=expression(textstyle(atop(CO[2]~'Flux', paste('(kg C ', m^-2,' ',s^-1,')')))), 
     cex.main=2)

