Context : The infrared emission ( IR ) of the interstellar dust has been claimed to be a tracer of the star formation rate .
However , the conversion of the IR emission into star formation rate can be strongly dependent on the physical properties of the dust , which are affected by the environmental conditions where the dust is embedded .

Aims : We study here the dust properties of a set of H ii  regions in the Local Group Galaxy M 33 presenting different spatial configurations between the stars , gas and dust to understand the dust evolution under different environments .

Methods : We model the SED of each region using the DustEM Â tool and obtain the mass relative to hydrogen for Very Small Grains ( Y _ { VSG } ) , Polycyclic Aromatic Hydrocarbons ( Y _ { PAH } ) and Big Grains ( Y _ { BG } ) .
We furthermore perform a pixel-by-pixel SED modelling and derive maps of relative mass of each grain type for the whole surface of the two most luminous H ii  regions in M 33 , NGC 604 and NGC 595 .

Results : The relative mass of the VSGs ( Y _ { VSG } / Y _ { TOTAL } ) changes with the morphology of the region : Y _ { VSG } / Y _ { TOTAL }  is a factor of \sim 1.7 higher for H ii  regions classified as filled and mixed than for regions presenting a shell structure .
The enhancement of VSGs within NGCÂ 604 and NGCÂ 595 is correlated to expansive gas structures with velocities \geq 50 km s ^ { -1 } .
The gas-to-dust ratio derived for the H ii  regions in our sample exhibits two regimes related to the H i - H _ { 2 } transition of the ISM .
Regions corresponding to the H i  diffuse regime present a gas-to-dust ratio compatible with the expected value if we assume that the gas-to-dust ratio scales linearly with metallicity , while regions corresponding to a H _ { 2 } molecular phase present a flatter dust-gas surface density distribution .

Conclusions : The fraction of VSGs can be affected by the conditions of the interstellar environment : strong shocks of \sim 50-90 km s ^ { -1 }  existing in the interior of the most luminous H ii  regions can lead to fragmentation of BGs into smaller ones , while the more evolved shell and clear shell objects provide a more quiescent environment where reformation of dust BG grains might occur .
The gas-to-dust variations found in this analysis might imply that grain coagulation and/or gas-phase metals incorporation to the dust mass is occurring in the interior of the H ii  regions in M 33 .