Google now lets users get air quality and pollution data in the search results. If you do [air quality], [air pollution] type searches, along with optional city qualifies, like [air quality in portland oregon], Google will display a rating of the air quality in that city.
See the following examples:
This feature works for both mobile and desktop versions of Google.
BreezoMeter is the source of the data. By clicking on the name of the company in the footer of the answer, it shows more details about the air quality in that location.