The risk of corona infection is definitely greatest indoors. Virus particles can often stick to invisible particles (aerosols) for hours and be inhaled. In other words, the thicker the fabric of a mask and the more layers the mask has, the better it can reduce the spread of aerosol as far as possible.
The FFP2 mask should generally be disposed of after it has been worn for a maximum of 8 hours. However, after short and repeated use, it is also important to let it dry out in between and, if necessary, to spray it with alcohol (at least 70%) inside / outside in order to stop the supposed colonization and multiplication of germs.