Air Quality Grade
AirHistory's proprietary A-F scoring system that rates cities based on average AQI, trend direction, unhealthy days, and dominant pollutant.
Detailed Explanation
The Air Quality Grade is AirHistory's proprietary scoring system that distills 10 years of EPA monitoring data into a single letter grade from A (best) to F (worst). The grade is calculated from a 0-100 numerical score based on four weighted factors: 5-year average AQI (40% weight), trend direction, whether air quality is improving or worsening over the full decade (30% weight), average number of unhealthy days per year (20% weight), and the dominant pollutant type (10% weight, with more toxic pollutants like PM2.5 scoring lower than less harmful ones). The grading scale follows standard academic conventions: A is 90-100, B is 80-89, C is 70-79, D is 60-69, and F is below 60. Unlike the raw AQI, which provides a snapshot of air quality conditions on a given day, the Air Quality Grade captures the full picture, both average conditions and whether the trajectory is positive or negative. A city with a moderate AQI but a strong improving trend may earn a higher grade than a city with a slightly lower AQI that is getting worse. This makes the grade particularly useful for relocation decisions, real estate research, and long-term health planning. AirHistory publishes grades for over 1,000 US cities, updated annually when new EPA data becomes available.
Related Terms
Air Quality Index (AQI)
A standardized EPA scale from 0 to 500 that communicates daily air quality and associated health risks.
Unhealthy Air Days
Days when the AQI exceeds 100, meaning air quality may pose health risks for sensitive groups or the general population.
Good Air Quality
Air quality conditions with an AQI of 0-50, posing little or no health risk for any population group.
EPA Air Quality System (AQS)
The EPA's national database of ambient air quality data collected from monitoring stations across the United States.
Frequently Asked Questions
AirHistory's proprietary A-F scoring system that rates cities based on average AQI, trend direction, unhealthy days, and dominant pollutant.
The Air Quality Grade is AirHistory's proprietary scoring system that distills 10 years of EPA monitoring data into a single letter grade from A (best) to F (worst). The grade is calculated from a 0-100 numerical score based on four weighted factors: 5-year average AQI (40% weight), trend direction, whether air quality is improving or worsening over the full decade (30% weight), average number of unhealthy days per year (20% weight), and the dominant pollutant type (10% weight, with more toxic pollutants like PM2.5 scoring lower than less harmful ones). The grading scale follows standard academic conventions: A is 90-100, B is 80-89, C is 70-79, D is 60-69, and F is below 60.
this entity is one of the U.S. air quality and pollution monitoring concepts that recurs across this site. The definition above is the technical answer; the paragraphs below add the practical context for how the concept connects to the the EPA Air Quality System (AQS) data behind every per-entity page on the site.
In the the EPA Air Quality System (AQS) data, this concept shapes one or more of the fields that drive the per-entity grades and rankings on this site. The methodology page describes which fields feed into which output; this glossary entry documents the underlying term.