Air Quality

How are we doing?

Percentage of Good Air Quality Days (2018)

In 2018, Tucson’s air quality was rated “good” 53.7% of the time. This ranked the Tucson Metropolitan Statistical Area (MSA) fifth out of 12 western MSAs in the percent of good air quality days. Portland ranked first with 76.4%, while Phoenix ranked last with only 11.5% of days considered “good”. According to the Air Quality Index (AQI), good air quality days occur when air quality is satisfactory and air pollution poses little or no threat. The AQI has six rankings:  good, moderate, unhealthy for sensitive groups, unhealthy, very unhealthy, and hazardous. Tucson’s percentage of good air quality days in 2018 was a substantial improvement from last year’s 39.7%, which was the lowest rate reported by the AQI in the past 18 years.

Why is it important?  

Air quality is vitally important to the well-being of a region’s residents. It is a particularly important health concern to those who have sensitivity to air pollution due to respiratory or other conditions. Air pollution can cause loss of productivity due to illness, as well as damage to buildings and crops, making it a hazard not only to the environment, but also to the economy. Traffic congestion, smoke, and pollution from industrial factories and refineries all play a part in air quality.

How do we compare?

The Tucson MSA posted 97.0% of days classified as good or moderate air quality in 2018, with 3.0% ranked unhealthy for sensitive groups, and 0% very unhealthy. Of the western MSAs, only Phoenix reported very unhealthy days in 2018 with 3.3%. Very unhealthy days indicate a health alert in which all residents may experience serious health effects.

What are the key trends?

The percentage of air quality days rated “good” for the Tucson MSA has been volatile in recent years, reaching a peak of 67.4% in 2015 then sharply decreasing to an 18 year low of 39.7% in 2017. The percentage of good air quality days showed improvement in 2018, increasing to 53.7%. Tucson moved from a seventh place rank among the 12 western MSAs in 2017 to fifth place in 2018. Phoenix retained its last place ranking in the percentage of good air quality days in 2018, but has made steady improvements since 2006.

How is it measured?

Air quality data come from the U.S. Environmental Protection Agency’s Air Quality Index Report, which is an annual summary of AQI values for four major air pollutants, though many areas do not have monitoring stations for all pollutants. The AQI has a range of 0-500 broken down into six levels: good (0-50), moderate (51-100), unhealthy for sensitive groups (101-150), unhealthy (151-200), very unhealthy (201-300), and hazardous (301-500).  The AQI for ozone were updated by the EPA in 2016, this update applied to all historical data.