The search results provide information on air quality in different contexts. Here are some key takeaways:

• The Air Quality Index (AQI) is a measure of how clean or polluted outdoor air is and the associated health effects that may be of concern. AQI values range from 0 to 500, with higher values indicating greater levels of pollution and associated health risks.
• The AQI is calculated based on the concentrations of five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide.
• Wildfires can produce a range of harmful air pollutants, including particulate matter, which can aggravate existing health problems and increase the risk of heart attack or stroke.
• The AirNow website provides daily AQI values for different areas in the US, including California. AQI values for ozone, PM2.5, and PM10 are reported, with higher values indicating greater levels of pollution and associated health risks.
• The EPA defines exceptional events as unusual or naturally-occurring events that affect air quality but are not reasonably controllable using techniques that tribal, state, or local air agencies may implement.

Overall, the search results suggest that air quality can vary depending on location and time, and that wildfires can have a significant impact on air quality. It is important to monitor AQI values and take appropriate precautions to protect ones health during periods of high pollution.