1. A face mask comprising a device for removal of solid particulates from a gas, the
device comprising:
an inlet for receiving a flow of gas; an outlet from which the flow of gas can be expelled; and a labyrinthine path extending between the inlet and the outlet for passage of the flow of gas;
wherein the labyrinthine path is arranged to steer the flow of gas such that particulates in the gas will impact on adsorption surfaces of the labyrinthine path arranged for adsorption of impacted particulates such that particulates in the gas are removed from the gas by impaction on the adsorption surfaces as the gas flows from the inlet to the outlet.
2. A face mask according to claim 1, wherein in use, the volume of air in the device with a velocity magnitude below 1ms"1 is greater than 4% of the total volume of air in the device.
3. A face mask according to claim 1 or 2, wherein in use, the pressure drop between the inlet and outlet is less than 10mb.
4. A facemask according to claim 1, 2 or 3, wherein the walls of the labyrinthine path consist of non-porous and/or non-absorptive materials.
5. A face mask according to any preceding claim, wherein the device has a continuous gas path from the inlet to the outlet.
6. A face mask according to any preceding claim, wherein the labyrinthine path is arranged to steer the flow of gas through and/or past multiple turns and/or branches with changes in the flow direction of at least 90 degrees.
7. A face mask according to any preceding claim, wherein the wails of the labyrinthine path include surfaces extending along the principal flow direction and surfaces that are at least 90 degrees relative to the flow of gas, such that particulates in the flow of gas impact on the walls of the labyrinthine path.

8. A face mask according to any preceding claim, wherein, in use, the gas does not pass through a fluid.
9. A face mask according to any preceding claim, wherein the face mask does not comprise a filter.
10. A face mask according to any preceding claim, wherein the path comprises branches that are for the capture of particulates rather than for through-fiow of the gas.
11. A face mask according to any preceding claim, wherein the device comprises baffles.
12. A face mask according to claim 11, wherein each baffle has an area that is between 10% and 90% of the cross sectional area of the path cross sectional area.
13. A face mask according to claim 11 or 12, wherein the baffles are located such that a clear line is present along at least part of all edges of the path until there is a turn in the path.
14. A face mask according to claim 11, 12 or 13, wherein the baffles are suspended in the middle of the path by members that each have a width that is less than 20% of the width of the channel.
15. A face mask according to any of claims 11 to 14, wherein the spacing between each baffle is between 50% and 300% of the cross sectional diameter of the path.
16. A face mask according to any of claims 11 to 15, wherein the baffles are shaped between concave and convex, such that the centre of each baffle is deflected by no more than +/- 75% of the width of the baffle from its edges.
17. A face mask according to any preceding claim, wherein the gas flow path of the face mask includes a bend of between 90-180 degrees after the labyrinthine path.

18. A face mask according to any preceding ciaim, wherein the face mask comprises bristles that are located across the path at, or near, the iniet of the device.
19. A face mask according to any preceding ciaim, wherein the waifs of the gas flow path are made of acryionitrile butadiene styrene (ABS).
20. A face mask according to any preceding claim, wherein the device has a removable cover to aid cleaning of the labyrinthine path.
21. A face mask according to any preceding claim, wherein the device has dimensions of 5 to 15 cm, by 5 to 15 cm, by 0.5 to 5cm.
22. A face mask according to any preceding claim , wherein the face mask comprises a second device for removal of solid particulates from a gas, the second device comprising: an inlet for receiving a flow of gas; an outlet from which the flow of gas can be expelled; and a labyrinthine path extending between the iniet and the outlet for passage of the flow of gas; wherein the labyrinthine path is arranged to steer the flow of gas such that particulates in the gas will impact on adsorption surfaces of the labyrinthine path arranged for adsorption of impacted particulates such that particulates in the gas are removed from the gas by impaction on the adsorption surfaces as the gas flows from the inlet to the outlet, wherein one device is placed, in use, on either side of the mouth of the user, adjacent the user's cheeks.
23. A method of removing particulates from a gas, the method comprising:
providing a face mask comprising a device for removal of solid particulates from a gas, the device comprising:
an iniet for receiving a flow of gas; an outlet from which the flow of gas can be expelled; and a labyrinthine path extending between the iniet and the outlet for passage of the gas;
passing a flow of gas through the device from the inlet to the outlet, wherein the labyrinthine path steers the flow of gas such that particulates in the gas impact on adsorption surfaces of the labyrinthine path arranged for adsorption of

impacted particulates such that particulates in the gas are removed from the gas by impaction on the adsorption surfaces as the gas flows from the inlet to the outlet.
24. A method according to claim 23, wherein the face mask is a face mask according to any of claims 1 to 22.
25. A device for removal of particulates from a gas, the device comprising:
an inlet for receiving a flow of gas; an outlet from which the flow of gas can be expelled; and a labyrinthine path extending between the inlet and the outlet for passage of the flow of gas;
wherein the labyrinthine path is arranged to steer the flow of gas such that particulates in the gas will impact on adsorption surfaces of the labyrinthine path arranged for adsorption of impacted particulates such that particulates in the gas are removed from the gas by impaction on the adsorption surfaces as the gas flows from the inlet to the outlet, wherein in use, the volume of air in the device with a velocity magnitude below 1ms"1 is greater than 4% of the total volume of air in the device.
26. A device according to claim 25, wherein the pressure drop between the inlet and outlet is less than 10mbar.
27. A device according to claim 25 or 26, wherein the labyrinthine path is arranged to steer the flow of gas through and/or past multiple turns and/or branches with changes in the flow direction of at least 90 degrees.
28. A device according to claim 25, 26 or 27, wherein the walls of the labyrinthine path include surfaces extending along the principal flow direction and surfaces that are at least 90 degrees relative to the flow of gas, such that particulates in the flow of gas impact on the walls of the labyrinthine path.
29. A device according to any of claims 25 to 28, wherein the walls of the labyrinthine path consist of non-porous and/or non-absorptive materials.
30. A device according to any of claims 25 to 29, wherein, in use, the gas does not pass through a fluid.

31. A device according to any of claims 25 to 30, wherein the device does not comprise a filter.
32. A device according to any of claims 25 to 31, wherein the path comprises branches that are for the capture of particulates rather than for through-flow of the gas.
33. A device according to any of claims 25 to 32, wherein the walis of the labyrinthine path have a textured, roughened or fibrous surface.
34. A device according to any of claims 25 to 33, wherein the device comprises baffles.
35. A device according to claim 34, wherein each baffle has an area that is between 10% and 90% of the cross sectional area of the path cross sectional area.
36. A device according to claim 34 or 35, wherein the baffles are located such that a clear line is present along at least part of all four edges of the path until there is a turn in the path.
37. A device according to claim 34, 35 or 36, wherein the baffles are suspended by members that each have a width that is less than 20% of the width of the path.
38. A device according to any of claims 34 to 37, wherein the spacing between each baffle is between 50% and 300% of the cross sectional diameter of the path.
39. A device according to any of claims 34 to 38, wherein the baffles are shaped between concave and convex, such that the centre of each baffle is deflected by no more than +/- 75% of the width of the baffle from its edges.
40. A device according to any of claims 25 to 39, wherein the gas flow path of the device includes a bend of between 90-180 degrees after the labyrinthine path,
41. A device according to any of claims 25 to 40, wherein the device comprises bristles that are located across the path at, or near, the inlet of the device.

42. A device according to any of claims 25 to 41, wherein the walls of the gas flow path are made of acryionitrile butadiene styrene (ABS).
43. A device according to any of claims 25 to 42, wherein the device has a removable cover to aid cleaning of the labyrinthine path.
44. A device according to any of claims 25 to 43, wherein the device has dimensions of 5 to 15 cm, by 5 to 15 cm, by 0.5 to 5cm.
45. A device according to any of claims 25 to 44, wherein the device is arranged to aliow a peak inspiratory flow rate of up to 300 litres/minute.
46. A face mask, the face mask comprising the device of any of claims 25 to 45.
47. A face mask according to claim 46, wherein the device is an integral part of the face mask.
48. A face mask according to claim 46 or 47, wherein the inlet for the device faces rearward relative to the face of the user when the face mask is worn by a user.
49. A face mask according to claim 46, 47 or 48, wherein the face mask has an exhale valve that allows exhaled air to exit the face mask without going back through the device.
50. A face mask according to any of claims 46 to 49, wherein the outlet of the device is directed on to an internal surface of the face mask that is, in use, in front of the nose and/or mouth of the user.
51. A face mask according to any of claims 46 to 50, wherein the face mask comprises two devices according to any of claims 25 to 45, wherein one device is placed, in use, on either side of the mouth of the user, adjacent the user's cheeks.
52. A face mask according to any of claims 46 to 51, wherein the face mask is a face mask according to any of claims 1 to 22.
53. A method of removing particulates from a gas, the method comprising:

providing a device for removal of particulates from a gas, the device comprising:
an inlet for receiving a flow of gas; an outlet from which the flow of gas can be expelled; and a labyrinthine path extending between the inlet and the outlet for passage of the gas;
passing a flow of gas through the device from the inlet to the outlet, wherein the labyrinthine path steers the flow of gas such that particulates in the gas impact on adsorption surfaces of the labyrinthine path arranged for adsorption of impacted particulates such that particulates in the gas are removed from the gas by impaction on the adsorption surfaces as the gas flows from the inlet to the outlet, wherein in use, the volume of air in the device with a velocity magnitude below 1ms"1 is greater than 4% of the total volume of air in the device.
54. A method according to claim 53, wherein the device is a device according to any of claims 25 to 45.
55. A method according to claim 53 or 54, wherein the method is for cleaning air that is about to breathed in by a person.
56. A method according to claim 53 or 54, wherein the method is for cleaning air at a source where the pollutants are created to prevent them being released into the atmosphere.
57. A method of removing particulates from a gas, the method comprising:
providing the face mask of any of claims 46 to 52, and passing a gas through the device from the inlet to the outlet.