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Percentage of Good Air Quality Days (2015)

In 2015, the Tucson Metropolitan Statistical Area (MSA) ranked second out of the 12 MSAs in the percentage of good air quality days. Tucson air quality was rated “good” 78.6% of the time, while Colorado Springs ranked first with 87.4%. Phoenix was last among the 12 western metropolitan areas, with only 17.0% of days in 2015 considered “good”. Good air quality days, according to the Air Quality Index (AQI), are 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 rank when compared to other MSAs increased between 2014 and 2015. The number of good air quality days in Tucson rose by 7.9 percentage points during the last year.

Why is it important?  

Air quality is vitally important. 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, dust, smoke, and pollution from industrial factories and refineries all play a part in air quality.

How do we compare?

Tucson MSA had 100% of its days classified as good or moderate air quality in 2015, with 0% ranked unhealthy (including unhealthy for sensitive groups), and 0% very unhealthy. Only one metropolitan area, Phoenix, had any very unhealthy days in 2015. Very unhealthy days indicate a health alert in which all residents may experience serious health effects. Phoenix also had the largest percentage of unhealthy days of all 12 western metropolitan areas.

What are the key trends?

Tucson moved from a fifth place rank in the percent of good air quality days in 2014 to second place in 2015. The number of good air quality days in Tucson increased by 7.9 percentage points during this time. Colorado Springs, the top ranked MSA, increased their number of good air quality days by 2.5 percentage points. El Paso posted the largest change with a 9.6 percentage point increase, while Denver had the greatest decrease at -9.3 percentage points.

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).