What is the air quality trend in St. Charles?

Over the past 14 days, St. Charles had an average AQI of 78 based on station measurements. The worst day was 2026-07-17 with AQI 225.

How is St. Charles air quality measured?

Air quality in St. Charles is measured by ground-level monitoring stations that report PM2.5 and PM10 concentrations hourly. CERNS.IO aggregates readings from nearby stations and converts PM2.5 to the US EPA Air Quality Index (AQI) scale.

Air Quality History for St. Charles, United States

Name: St. Charles Air Quality History
Creator: CERNS.IO
License: https://creativecommons.org/licenses/by/4.0/

Historical PM2.5 and AQI trend from monitoring stations near St. Charles, United States.

Current AQI
Good Station

48 Hours 7 Days 14 Days 20 Days

CSV JSON

Air Quality Index Station

335h

PM2.5 Station

335h · 7 stations

Temperature GFS model

55pt

Precipitation GFS model

mm/day

Daily Summary Station

Date	AQI	Range	PM2.5 avg	Hours	Stations
2026-07-21	60	31–96	17.5 µg/m³	24h	97
2026-07-20	98	55–106	34.0 µg/m³	24h	98
2026-07-19	109	60–160	39.9 µg/m³	24h	103
2026-07-18	51	32–88	13.2 µg/m³	24h	102
2026-07-17	225	67–344	170.2 µg/m³	24h	108
2026-07-16	152	49–320	98.1 µg/m³	24h	99
2026-07-15	52	40–59	12.6 µg/m³	24h	102
2026-07-14	58	27–66	15.9 µg/m³	24h	99
2026-07-13	61	38–65	16.9 µg/m³	24h	101
2026-07-12	50	33–56	12.4 µg/m³	24h	96
2026-07-11	37	26–46	8.8 µg/m³	24h	80
2026-07-10	35	27–49	8.3 µg/m³	24h	97
2026-07-09	50	31–53	12.1 µg/m³	24h	103
2026-07-08	56	49–62	14.3 µg/m³	23h	107

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