SmogRank / United States / California / Windsor

Windsor, month by month

Windsor, California has a measured daily mean on 410 days since 13 November 2024. Its worst month was December 2025, at 38 US AQI (6.9 µg/m³), 2,179th of 3,006 cities on that month's world ranking. Its cleanest was March 2025, at 19 US AQI (3.5 µg/m³).

Every month since 2024

2026too few days for a mean (a year needs 199)128 days measured
Jan33#2,149Feb24#2,669Mar24#2,770Apr3 daysMay7 daysJun5 daysJul6 daysAug8 daysSep28#2,284Oct7 days
2025too few days for a mean (a year needs 256)233 days measured
Jan19 daysFeb20#2,561Mar19#2,742Apr23#2,759May6 daysJun5 daysJul28#2,611Aug29#2,665Sep36#1,887Oct21 daysNov27#2,447Dec38#2,179
2024too few days for a mean (a year needs 257)49 days measured
JanFebMarAprMayJunJulAugSepOctNov18 daysDec36#1,931
Each square is a month's mean PM2.5 in US AQI from Windsor's measured days, with its place on that month's world ranking under it. A month has a mean once 70% of its days are measured, the rule the monthly rankings use; under that, the square gives the days measured. Each square opens that month's ranking with Windsor marked; each year, the year's.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

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

11 months
MonthWhy
Oct 20267 of 11 days measured; a month needs 8. The others: 4 with readings for part of the day (a day needs 18 hours).
Aug 20268 of 31 days measured; a month needs 22. The others: 23 with under 18 hours of readings or readings that failed our checks.
Jul 20266 of 31 days measured; a month needs 22. The others: 25 with under 18 hours of readings or readings that failed our checks.
Jun 20265 of 30 days measured; a month needs 21. The others: 25 with under 18 hours of readings or readings that failed our checks.
May 20267 of 31 days measured; a month needs 22. The others: 24 with under 18 hours of readings or readings that failed our checks.
Apr 20263 of 30 days measured; a month needs 21. The others: 27 with under 18 hours of readings or readings that failed our checks.
Oct 202521 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks.
Jun 20255 of 30 days measured; a month needs 21. The others: 25 with under 18 hours of readings or readings that failed our checks.
May 20256 of 31 days measured; a month needs 22. The others: 25 with under 18 hours of readings or readings that failed our checks.
Jan 202519 of 31 days measured; a month needs 22. The others: 12 with under 18 hours of readings or readings that failed our checks.
Nov 202418 of 30 days measured; a month needs 21.

A day counts once 18 hours of it are measured; a month needs 70% of its days.

Windsor's worst months

MonthUS AQIDays measuredWorld rank
December 2025 386.9 µg/m³22 of 312,179thof 3,006
September 2025 366.5 µg/m³26 of 301,887thof 3,104
December 2024 366.4 µg/m³31 of 311,931stof 2,616
January 2026 335.9 µg/m³26 of 312,149thof 2,617
August 2025 295.2 µg/m³27 of 312,665thof 2,901
September 2026 285.1 µg/m³24 of 302,284thof 2,981

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.

Windsor's worst days

DayUS AQI
11 Dec 2024 7321.1 µg/m³
28 Sept 2025 7119.9 µg/m³
5 Dec 2025 6516.6 µg/m³
6 Dec 2025 6516.4 µg/m³
30 Jan 2025 6215.0 µg/m³
27 Sept 2025 6114.5 µg/m³
21 Jan 2026 5913.5 µg/m³
10 Dec 2024 5812.8 µg/m³
16 Dec 2025 5812.8 µg/m³
20 Jan 2026 5812.8 µg/m³

Daily means, the highest since 13 Nov 2024; 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, Windsor, California, United States, 13 Nov 2024 – 11 Oct 2026. Monitor data from Clarity via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/us/windsor-california/history (accessed 12 Oct 2026).

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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.

Windsor now: the last 24 hours, its ranks today and the last 12 months day by day.

Updated 2026-10-12 20:07 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).