[rladd]

> portable masks with safe air to breath temporary when you are outside

With regard to PM2.5, that already exists and is called an N95 mask.

[cmews]

Unfortunately those masks are not protecting you against gases and vapours like sulphur dioxide, nitrogen dioxide, ozone, and carbon monoxide which do impact asthmatic people a lot or are the cause of developing asthma.

[AstralStorm]

Well, a mask with an activated carbon filter actually does, to an extent, except for carbon monoxide.

(There are other more specialized filters that are more effective against SOx and NOx too, but carbon is also good against VOC.)