What does “unhealthy air quality” mean?

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When you look at the weather and it states ‘unhealthy air quality’ as the weather condition, what substances is it referring to as making the air quality unhealthy?

In: Chemistry

Never heard such a general warning, we usually get specifics in germany.

Could be a lot of things, Ozone, Pollution, Dust

It means things like emissions from cars and factories, or smoke from wildfires. Generally speaking, the air we breathe isn’t just O2, it’s a mix of other gasses like carbon monoxide, nitrogen, methane, Etc. as well as particles that occur naturally or are byproducts of human industry. To answer your question simply, it means anything in a large enough quantity to negatively impact a population’s health and well being. For example: Inhaling air that is contaminated due to a nearby forest fire can be likened to smoking X packs of cigarettes per day, depending on the concentration of smoke, and the duration of a person’s exposure to it.

Most places use either AQI or AQHI for measuring general air healthiness. Those are a combination of 3-4 things:

NO2: mostly from vehicle traffic, not super great for your lungs, can make smog, eliminated by ozone.

Ozone: mostly made by sunlight, also not great for your lungs, can be an irritant.

PM2.5: general category of dust (less than 2.5microns) thats small enough to make it past your nose and throat and make it to your lungs. Its a general collection so could be really bad, or not so bad. But like dirt in water its just generally not great for it to be there (and may or may not be poisonous depending on the dirt).

SO2: from coal power (basically does not exist if you don’t have coal power nearby or a relevant industry). Causes smog and acid rain.

If enough things are there in enough concentrations some places will issue warnings, cause its not great to breath it in and it will pass in time. (Normally PM2.5 is the big one).

If inside the U.S., you can see a map and get a more detailed breakdown of the components of your local air quality, with explanations, at airnow.gov