r - changing title in multiplot ggplot2 using grid.arrange

Question

I have managed to make a 2x2 plot using grid.arrange:

library(gridExtra)
grid.arrange(p1,p3,p2,p4, ncol=2, nrow=2, top = "Daily QC: Blue")

The main title of this multiplot is very small. Is there a way to change the title text size and font.

Answer 1

main=textGrob("Daily QC: Blue",gp=gpar(fontsize=20,font=3))

Edit with v>=2.0.0 of gridExtra, main has become top (for consistency with bottom, left and right).