SmogRank / Mexico / Hidalgo / San Marcos
San Marcos, month by month
San Marcos has a measured daily mean on 571 days since 15 August 2023. Its worst month was February 2026, at 73 US AQI (20.7 µg/m³), 528th of 2,866 cities on that month's world ranking. Its cleanest was June 2025, at 54 US AQI (10.8 µg/m³).
Every month since 2023
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
Months without a mean, and why
21 months
| Month | Why |
|---|---|
| Oct 2026 | No day measured. The others: 7 with no readings from the monitor, 2 with readings for part of the day (a day needs 18 hours), 2 with readings left out by our checks. |
| Sep 2026 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Aug 2026 | 1 of 31 days measured; a month needs 22. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Dec 2025 | 21 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks. |
| Mar 2025 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Feb 2025 | No day measured. The others: 28 with under 18 hours of readings or readings that failed our checks. |
| Jan 2025 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Dec 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Nov 2024 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Oct 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Sep 2024 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Aug 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jul 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jun 2024 | 4 of 30 days measured; a month needs 21. The others: 26 with under 18 hours of readings or readings that failed our checks. |
| May 2024 | 2 of 31 days measured; a month needs 22. The others: 29 with under 18 hours of readings or readings that failed our checks. |
| Apr 2024 | 3 of 30 days measured; a month needs 21. The others: 27 with under 18 hours of readings or readings that failed our checks. |
| Mar 2024 | 1 of 31 days measured; a month needs 22. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Feb 2024 | No day measured. The others: 1 missing from OpenAQ's archive, 28 with under 18 hours of readings or readings that failed our checks. |
| Jan 2024 | 15 of 31 days measured; a month needs 22. The others: 16 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | 13 of 31 days measured; a month needs 22. The others: 18 with under 18 hours of readings or readings that failed our checks. |
| Aug 2023 | 11 of 31 days measured; a month needs 22. The others: 6 with under 18 hours of readings or readings that failed our checks. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
San Marcos's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| February 2026 | 7320.7 µg/m³ | 528thof 2,866 | – |
| January 2026 | 7120.0 µg/m³ | 426thof 2,617 | Mexico, January 2026 Southern Mexico, January 2026 |
| March 2026 | 6818.4 µg/m³ | 658thof 2,971 | – |
| May 2026 | 6818.2 µg/m³ | 328thof 2,874 | – |
| April 2025 | 6818.1 µg/m³ | 431stof 2,951 | – |
| November 2025 | 6717.6 µg/m³ | 483rdof 2,715 | Hidalgo, Puebla and Querétaro, Mexico, November 2025 |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
San Marcos's worst days
| Day | US AQI | Episode |
|---|---|---|
| 14 May 2024 | 13448.9 µg/m³ | – |
| 2 Feb 2026 | 12445.0 µg/m³ | – |
| 7 Jun 2024 | 12043.2 µg/m³ | Southern Mexico, June 2024 |
| 1 Jan 2026 | 10637.4 µg/m³ | Southern Mexico, January 2026 |
| 9 Mar 2026 | 10035.2 µg/m³ | – |
| 1 Jan 2024 | 9935.1 µg/m³ | Southern Mexico, January 2024 |
| 31 Dec 2025 | 9733.7 µg/m³ | – |
| 25 Dec 2025 | 9432.4 µg/m³ | – |
| 15 May 2024 | 9432.3 µg/m³ | – |
| 9 Jan 2026 | 9331.9 µg/m³ | Mexico, January 2026 |
Daily means, the highest since 15 Aug 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, San Marcos, Mexico, 15 Aug 2023 – 16 Aug 2026. Monitor data from Sinaica Mexico via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/mx/san-marcos-hidalgo/history (accessed 13 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
San Marcos now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 05:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).