We estimate the mass loss rates of photoevaporative winds launched from the outer edge of protoplanetary discs impinged by an ambient radiation field .
We focus on mild/moderate environments ( the number of stars in the group/cluster is N \gtrsim 50 ) , and explore disc sizes ranging between 20 and 250 AU .
We evaluate the steady-state structures of the photoevaporative winds by coupling temperature estimates obtained with a PDR code with 1D radial hydrodynamical equations .
We also consider the impact of dust dragging and grain growth on the final mass loss rates .
We find that these winds are much more significant than have been appreciated hitherto when grain growth is included in the modelling : in particular , mass loss rates \gtrsim 10 ^ { -8 } M _ { \odot } / yr are predicted even for modest background field strengths ( \gtrsim 30 G _ { 0 } ) in the case of discs that extend to R > 150 AU .
Grain growth significantly affects the final mass loss rates by reducing the average cross section at FUV wavelengths , and thus allowing a much more vigorous flow .
The radial profiles of observable quantities ( in particular surface density , temperature and velocity patterns ) indicate that these winds have characteristic features that are now potentially observable with ALMA .
In particular , such discs should have extended gaseous emission that is dust depleted in the outer regions , characterised by a non-Keplerian rotation curve , and with a radially increasing temperature gradient .