EPA
FreeLiveLast verified 24 Sept 2026
US EPA Air Quality System: ambient air monitor readings by site, county, or state.
Example request
curl -s 'https://aqs.epa.gov/data/api/sampleData/bySite?email=$EMAIL&key=$API_KEY¶m=44201&state=37&county=183&site=0014&bdate=20170618&edate=20170618'
Free tier, in plain English
Entirely free after registering with an email address; no paid tiers, but requests are capped at 10 per minute.
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