Quality of Air Means Quality of Life

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AirCompare - How to Interpret the Results

For those unfamiliar with stacked bar charts, the results might be confusing. This page provides information on how to interpret the results of your comparison.

On each bar chart, the height of each bar equals the total number of unhealthy days. Three categories of unhealthy days from the Air Quality Index are possible: orange days (unhealthy for sensitive groups), red days (unhealthy for everyone), and purple days (very unhealthy). If a bar is made up of more than one color, you can see the proportion of orange days, red days, and/or purple days that add up to the total number of unhealthy days. In general, a shorter bar reflects fewer unhealthy days than a taller bar, though some people might also want to take into consideration how much red and/or purple a bar contains.

Example 1 - Monthly Average Number of Unhealthy Days

In the first example below, the height of each bar equals the total number of unhealthy days averaged over the last 5 years for each month. On average, there were 2.5 unhealthy days in February over the last 5 years, while there were 17 unhealthy days in July. All of the unhealthy days in February were orange. In July, about 10 of the unhealthy days were orange, about 4 of the unhealthy days were red, and about 3 of the unhealthy days were purple, for a total of 17 unhealthy days.

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Example 2 - Number of Unhealthy Days in Recent Years

In the second example below, the height of each bar equals the total number of unhealthy days for each year over the last several years. This chart uses the height of the bars to show how the total number of unhealthy days has changed in recent years based on the health concern you select (in this example, asthma or other lung disease).  It uses up to three colors in each bar to show how the number of orange, red, and/or purple days has changed over the years. There were fewer unhealthy days in 2006 than there were in any of the last several years and 2006 had the fewest purple days. The year 2003 had about 75 orange days, 25 red days, and 12 purple days, for a total of 112 unhealthy days.

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AIRNow is a government-backed program. Through AIRNow, EPA, NOAA, NPS, news media, tribal, state, and local agencies work together to report conditions for ozone and particle pollution. State, Local and Tribal Partners.
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