US EPA PM2.5 data from the AirData map

This just scratches the surface of the US EPA data offerings.  I was mainly interested in seeing whether there was downloadable realtime data from sensors near Ottawa.  The short answer is there is downloadable data but in an awkward format and delayed by a month or more.

If you want real-time PM2.5 data from New York State, see my blog post Daily PM2.5 data from the New York State Department of Environmental Conservation Air Monitoring website.

The US EPA has a separate set of mapped sensors from the US AirNow site.

This link will give you a raw map:

https://epa.maps.arcgis.com/apps/webappviewer/index.html?id=5f239fd3e72f424f98ef3d5def547eb5&extent=-146.2334,13.1913,-46.3896,56.5319

You need to select layers (the stack in the upper right) and then PM2.5 - Active to see the active PM2.5 sensors.  Unlike AirNow, the EPA sensors are USA only.

The closest active PM2.5 sensor I can find to Ottawa is Whiteface Base (Whiteface Mountain, New York), AQS Site ID 36-031-0003.

As you can see, there are links to downloadable data in the popup information box you get when you click on an air sensor icon.

Here's the Whiteface Base daily data download for 2023.  (You can see you could construct this query for any site by just changing the site= at the end.)

https://www3.epa.gov/cgi-bin/broker?_service=data&_program=dataprog.Daily.sas&check=void&polname=PM2.5%20-%20NAAQS/AQI&debug=0&year=2023&site=36-031-0003

The link will give you a CSV file. 
The format is hard to parse, with row-based blocks of data and changing measurement types. Plus which the latest measurement for this site is from April 2023, it's not up-to-date.

Note however you can get real-time PM2.5 data for Whiteface Base by going directly to the New York State air quality data site.

Most of the nearby sites don't have measurements in 2023 at all.

The next closest one I could find with 2023 PM2.5 measurements was Rumford Avenue Parking Lot (RAP) in the very small town of Rumford, Maine, AQS Site ID 23-017-2011.

The daily data download link is

https://www3.epa.gov/cgi-bin/broker?_service=data&_program=dataprog.Daily.sas&check=void&polname=PM2.5%20-%20NAAQS/AQI&debug=0&year=2023&site=23-017-2011

Its daily data only runs to May 2023 though. Still no data for June.

So no luck with finding recent downloadable EPA PM2.5 near Ottawa through their map interface.

Open Data website

The EPA has much richer data than I explored, you could start at

EPA Environmental Dataset Gateway (EDG)

and then search e.g. air quality.