Air Quality Index (Pollution Standard Index)*

Updated 10/18/19 – *Note that this measure is also an environmental determinant of health

The National Ambient Air Quality Standards (previously Pollution Standard Index) measures the region’s air quality that affects our health and outdoor lifestyle, important for tourism and attracting young professionals to the region. Federal Air Quality regulations have made a big difference in our region’s air quality and Washoe County tracks and produces a 10-year trend report for pollutants.

In the late 1980s, we had 13 and 14 days a year with unhealthful air quality, and several times, we exceeded federal pollution standards for carbon monoxide (CO) and particulate matter (PM). Today, “red” air quality days are generally linked to wild fires. But this indicator is also influenced by the following:

  • Weather (e.g., high wind blown dust)
  • Vehicle miles traveled
  • Congestion
  • Public transportation
  • Alternative transportation
  • Smoke from wild fires, controlled burns or fireplaces
  • Industries
  • How often the roads are sanded

Small particulate matter (PM) are particularly dangerous because they can enter the bloodstream by passing through the lungs. Wildfires may not smell smokey, making small PM particularly dangerous. Ozone, which especially affects people with asthma, is typically a summer phenomena from vehicle exhaust, heat, sunlight and wind-carried pollutants from other metropolitan areas.

Thunderstorms and wildfire smoke influenced summer 2018 air quality, including the highest Ozone 8-hour exceedances since 2008 wildfires. A total of nine wildfires in Nevada and California affected Washoe County in July 2017; the Detwiler Fire in Mariposa County, CA resulted in PM2.5 exceedances. Fires near Yosemite and Nappa Valley also influenced air quality into October. The Trailhead fire resulted in Ozone exceedances July 2-4, with more in mid- to late-August from California wildfires in 2016, and 2016 annual Ozone was the fourth-highest daily maximum 8-hr concentration, average in over 3 years. Large particulate (PM10) exceeded standards on January 6, 2015 due to wind blown dust from over 70 mph winds; while small particulate (PM2.5) exceeded standards in August and September 2015 due to the Valley, Butte and King fires. Unhealthy days for sensitive groups were mostly from the King Fire, September 2014; 2013 were directly influenced by wildfires in northern and central California in August and September;  2012 unhealthy days were due to dry stagnant air, high winds blowing sand, and wild fires. Unhealthy days in June-July 2008 were related to wild fires in northern California.


  • NAAQS=National Ambient Air Quality Standards
  • PM=particulate matter per micron
  • CO=Carbon Monoxide
  • 1989-1999 all unhealthy days PSI>100; 2008 days exceeding PM2.5 influenced by California wild fires; 2011 influenced by dry stagnant air, high winds and wild fires
  • The Clean Air Act requires the EPA to establish National Ambient Air Quality Standards (NAAQS) and communities with populations larger than 350,000 must report air quality to the public daily.

The County Health Rankings measure the average daily density of fine particulate matter (PM2.5) in micrograms per cubic meter using data provided by the Environmental Public Health Tracking (EPHT) Network starting 2017 and data provided by the NASA Applied Sciences Program, which used a similar methodology in prior years.

County Health Rankings notes:

  • 2019 rankings used 2014 data
  • 2017-18 rankings used 2012 data
  • 2015-16 used 2011 data


Washoe County Health District;

Robert Wood Johnson, County Health Rankings

Thank you to our Indicator Partner


Download the data

TMT members can download the data files used to monitor indicators.