Observed arrival · 2026-10-27
Air Data turns county air-quality records into plain files
A public dataset and API for daily and yearly air-quality figures in US counties with EPA monitors.
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- Researchers and developers working with US county air-quality data
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- For preliminary days, county AQI is calculated from the highest site AQI reported to AirNow in that county; those rows cover four pollutants.
Field notes
The yearly summary breaks county AQI history into counts of days in each category, plus maximum, 90th-percentile, and median daily AQI. For the daily series, Air Data says recent AirNow readings are preliminary and limited to four pollutants; the county figure is derived from the highest reported site AQI. The page also describes validation checks that keep the last good version live if an update fails.
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