I've been using three PMS5003 for years. It is sensitive to minute deviations in PM concentrations. Since I live in a very polluted area, I try to stay within one room as much as possible with a purifier running on full blast. Opening an inside door for a second lets a small amount of pollution in, which the sensor notices right away (it may be only half a microgram per m³, but it always goes up reliably).
I manage to keep indoor PM2.5 levels within 1% of what's happening outside, which the sensor also tracks as expected (so if outside it's 100 µg/m³, the indoor sensor shows 0-1 µg/m³, when the outside level rises to 250, my sensor starts showing 2-2.5 µg, and so on).
I manage to keep indoor PM2.5 levels within 1% of what's happening outside, which the sensor also tracks as expected (so if outside it's 100 µg/m³, the indoor sensor shows 0-1 µg/m³, when the outside level rises to 250, my sensor starts showing 2-2.5 µg, and so on).