One great addition to my life is the Flow - a small, portable, nice looking air quality sensor. I use it already for more than a year, and I'm honestly super happy with that product.
This works absolutely seamlessly with iPhone and exports all data (metrics, locations) in usable CSV file format, and also includes the KML format (Google Earth). There is a quite impressive accuracy. Included metrics: PM-10, PM-2.5, NO2, and VOC.
Google Earth view of imported KML file...
I bought it because of my often business trips and quite frankly speaking I was concern about my health - especially under heavy jet lags. It gave me some insight into the environment quality across the cities, airports, and hotels.
I had a chance to use it in LA, London, Warsaw, Kyiv, Beijing, and other destinations in USA, Europe and China. In general, the air quality is not great, but I cannot say it's horrible - it really depends on many factors like weather or season!