Airnow.gov, located at http://airnow.gov is a website run by the the United States Environmental Protection Agency, showing a realtime map of air pollution across the United States (and also showing at least some of Canada and Mexico). The map currently tracks two pollutants: PM 2.5 (Particulate matter of a specific size) and Ozone. Particulates are usually associated with wildfire smoke, while Ozone is usually related to industrial pollution.
The map is shown as a contour map, much like a temperature map, showing concentrations from Green ("Healthy") through Maroon ("Hazardous"). Site users can also search by zip code. The site shows both current conditions, and a forecast of what air pollution conditions are likely to be like. As with all weather forecasting, this can sometimes be inaccurate, but in general, it is good information. The site also links to other information, including a real time wildfire map.
One thing that I've learned over multiple fire seasons is that it is not always easy to perceive how bad smoke is. Over the course of a few days, a light haze on the horizon that is doing nothing but making pretty sunsets might morph into a thick life choking haze that leaves me with a bad headache, an itchy throat, and a weird sense of fatigue and confusion...and then I check and see we are well into the Red ("Unhealthy") or Purple ("Very Unhealthy", where we were today) and it makes sense. So in part, I like the site because it gives me validation...and justification! Official scientific reasons for not leaving the house!
As mentioned, the site currently only tracks two pollutants. Other pollutants, like carbon monoxide, sulfur dioxide and nitrogen dioxide, are not currently tracked. The pollutants that are tracked are often markers for other pollutants, so a user of the site can generally guess about other pollutants. Additionally, in the future, the site may add specific data for other pollutants.
I've been checking this site every day. Hopefully I won't have to soon.