  We present a new FRIED grid of mass loss rates for externally far-ultraviolet
(FUV) irradiated protoplanetary discs. As a precursor to the new grid, we also
explore the microphysics of external photoevaporation, determining the impact
of polycyclic aromatic hydrocarbon (PAH) abundance, metallicity, coolant
depletion (via freeze out and radial drift) and grain growth (depletion of
small dust in the outer disc) on disc mass loss rates. We find that metallicity
variations typically have a small effect on the mass loss rate, since the
impact of changes in heating, cooling and optical depth to the disc
approximately cancel out. The new FRIED grid therefore focuses on i) expanding
the basic physical parameter space (disc mass, radius, UV field, stellar mass)
ii) on enabling variation of the the PAH abundance and iii) including an option
for grain growth to have occurred or not in the disc. What we suggest is the
fiducial model is comparable to the original FRIED grid. When the PAH-to-dust
ratio is lower, or the dust in the wind more abundant, the mass loss rate can
be substantially lower. We demonstrate with a small set of illustrative disc
evolutionary calculations that this in turn can have a significant impact on
the disc mass/radius/ evolution and lifetime.
