This is what outdoor air LOOKS like
We can talk about air and can see smog, but most of the pollutants and particulate matters are naked to the human eye.
This is a filter from a MVHR Heat Recovery system installed in London that has had air coming in from outside for 6 months (yes just 6 months)
We think the picture says it all.
If you've got a heat recovery ventilation system, check out our range of filters based on your Indoor Air Quality needs.