A used Flo Mask Pro filter, visibly darkened by air pollution.
https://cdn.masto.host/federatesocial/media_attachments/files/110/527/936/722/618/297/original/bf60ef07dc581822.jpeg
Here’s the filter after a few hours of use in 200+ AQI. Original color is the white border visible around the edge (where the filter is pinched in place by the holder).
(Back of the filter wasn't discolored at all.)
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.