spherical shape with radius $r=0.052\, \mathrm{m}$ and filter surface area $S_{\mathrm{m}}=0.02012\, \mathrm{m^{2}}$. The mask had a seal with length $L_{\mathrm{g}} \approx 1.2\, \mathrm{cm}$ and there was a gap between seal and face of average height $H_{\mathrm{g}} \approx 0.26\, \mathrm{mm}$, which extended along a width of $B_{\mathrm{g}}\approx 2.5\, \mathrm{cm}$ below the left eye (cf. Fig. \[FIG3Dgeom\]).

![Top: Head (grey) with generic FFP3-type mask with filter surface (white) and seal (blue); bottom: located between nose and left eye, there is a gap with width $B_{\mathrm{g}}\approx 2.5\, \mathrm{cm}$ and height $H_{\mathrm{g}}$ between face and seal, through which air can leak[]{data-label="FIG3Dgeom"}](images/maskSide.png "fig:"){width="0.49\linewidth"} ![Top: Head (grey) with generic FFP3-type mask with filter surface (white) and seal (blue); bottom: located between nose and left eye, there is a gap with width $B_{\mathrm{g}}\approx 2.5\, \mathrm{cm}$ and height $H_{\mathrm{g}}$ between face and seal, through which air can leak[]{data-label="FIG3Dgeom"}](images/maskFront.png "fig:"){width="0.43\linewidth"}\
![Top: Head (grey) with generic FFP3-type mask with filter surface (white) and seal (blue); bottom: located between nose and left eye, there is a gap with width $B_{\mathrm{g}}\approx 2.5\, \mathrm{cm}$ and height $H_{\mathrm{g}}$ between face and seal, through which air can leak[]{data-label="FIG3Dgeom"}](images/maskGap.png "fig:"){width="\linewidth"}

The solution domain was a box with dimensions $-0.246\, \mathrm{m} \leq x \leq 0.246\, \mathrm{m}$, $-0.35\, 