What is the air quality trend in San Marcos?

Over the past 8 days, San Marcos had an average AQI of 26 based on station measurements. The worst day was 2026-10-13 with AQI 38.

How is San Marcos air quality measured?

Air quality in San Marcos 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 San Marcos, United States

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

Historical PM2.5 and AQI trend from monitoring stations near San Marcos, United States.

Current AQI
Good Station

48 Hours 7 Days 14 Days 20 Days

CSV JSON

Air Quality Index Station

158h

PM2.5 Station

158h · 6 stations

Temperature GFS model

28pt

Precipitation GFS model

mm/day

Daily Summary Station

Date	AQI	Range	PM2.5 avg	PM10 avg	Hours	Stations
2026-10-20	34	15–80	8.5 µg/m³	23.6	18h	5
2026-10-19	25	15–39	5.9 µg/m³	19.3	24h	5
2026-10-18	22	8–75	5.5 µg/m³	10.9	23h	5
2026-10-17	17	10–38	4.0 µg/m³	11.3	22h	4
2026-10-16	23	7–65	5.6 µg/m³	19.2	23h	4
2026-10-15	31	11–68	7.7 µg/m³	22.1	23h	5
2026-10-14	24	12–51	5.9 µg/m³	19.4	23h	5
2026-10-13	38	21–56	9.7 µg/m³	23.0	2h	5

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