Haziest Day in Tucson

Pima County experienced an increase in ozone levels in summer 2017. Ozone measurements reached 77 parts per billion in June. Federal standards set by the Environmental Protection Agency (EPA) state that levels should not top 70 ppb.

To date, the highest levels of particulate matter (PM10) ever monitored in Pima County occurred on July 22, 2009. The PM10 reading at the Pima Department of Environmental Quality’s (PDEQ) Orange Grove monitoring site was 270 micrograms/cubic meter of air. The EPA’s health standard of 150 micrograms/cubic meter.

In 2008, 96 percent of the time levels of PM10 were in the healthy range in Pima County. Unhealthy levels of particulates in our air typically occur in Pima County when there are high winds and/or forest fires.

Exposure to particulate matter has been linked to increased respiratory symptoms, such as:

  • irritation of the airways
  • coughing, or difficulty breathing
  • decreased lung function
  • aggravated asthma
  • irregular heartbea
  • nonfatal heart attacks
  • premature death in people with heart or lung disease

Pima County Department of Environmental Quality (PDEQ) monitors local air quality and provides information about current air quality readings at Air Monitoring, opens a new window. PDEQ can be reached by phone at 520-724-7400.

Another source for air quality information is the EPA's AirNow Interactive Map, opens a new window.


“Hazy Wednesday last week set record of particulate level.” Arizona Daily Star. July 30, 2009. Page A13.

Davis, Tony. "Tucson-area air quality the worst in five years., opens a new window" Arizona Daily Star. June 22, 2017.

Find the information you need by calling the library's Infoline at 520-791-4010 or by sending your question to Ask a Librarian.