A simple device but why didn't I think of it before?

Pros:

• As mentioned, really good for those polluted cities.
• Keep a flow at home and monitor the PMI in the house. Pair it with motorised windows and close them when the readings get too high
• Great addition to complete the smart home innovation

Cons:

• Suggest to share data to a centralised system. A pollution map could then be created to aid future planning.