> co2 and pm should both go down with windows open.
Very much depends on where you live. I have a few DIY air quality stations with data being piped to Grafana. I just looked at the latest data, the average outside PM level for the past 5 months has been around 100 µg/m³, while inside it's around 10 µg/m³.
This spring happens to be pretty windy and this skews the outside levels down, otherwise the ratio would be much worse.
Very much depends on where you live. I have a few DIY air quality stations with data being piped to Grafana. I just looked at the latest data, the average outside PM level for the past 5 months has been around 100 µg/m³, while inside it's around 10 µg/m³.
This spring happens to be pretty windy and this skews the outside levels down, otherwise the ratio would be much worse.