SmogRank / United States / Colorado / Windsor

Windsor, month by month

Windsor, Colorado has a measured daily mean on 605 days since 28 January 2025. Its worst month was August 2026, at 52 US AQI (9.6 µg/m³), 997th of 2,896 cities on that month's world ranking. Its cleanest was May 2026, at 22 US AQI (3.9 µg/m³).

Every month since 2025

202630 so far274 days measured2,589th of 2,791 in the world
Jan22#2,493Feb22#2,737Mar34#2,509Apr22#2,713May22#2,666Jun31#2,013Jul41#2,069Aug52#997Sep22#2,736Oct28#2,123
202531 for the year331 days measured2,438th of 2,681 in the world
Jan2 daysFeb34#2,067Mar24#2,611Apr27#2,583May25#2,464Jun33#2,174Jul39#2,005Aug43#1,882Sep38#1,725Oct27#2,137Nov27#2,433Dec24#2,809
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. A dashed square is the running month, so far.
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

1 month
MonthWhy
Jan 20252 of 31 days measured; a month needs 22. The others: 2 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.

Windsor's worst months

MonthUS AQIDays measuredWorld rankEpisode
August 2026 529.6 µg/m³31 of 31997thof 2,896North-western United States and Canada, July and August 2026
August 2025 437.8 µg/m³31 of 311,882ndof 2,901–
July 2026 417.3 µg/m³31 of 312,069thof 2,784North-western United States and Canada, July and August 2026
July 2025 397.0 µg/m³28 of 312,005thof 2,889–
September 2025 386.9 µg/m³30 of 301,725thof 3,104Colorado and Wyoming, United States, September 2025
February 2025 346.2 µg/m³28 of 282,067thof 2,633–

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 AQIEpisode
13 Mar 2026 16676.2 µg/m³–
6 Aug 2025 10235.9 µg/m³–
4 Aug 2026 8828.8 µg/m³North-western United States and Canada, July and August 2026
4 Sept 2025 8728.6 µg/m³Colorado and Wyoming, United States, September 2025
3 Aug 2026 8527.5 µg/m³North-western United States and Canada, July and August 2026
5 Aug 2026 7622.7 µg/m³–
7 Aug 2026 7622.4 µg/m³–
6 Sept 2025 7220.3 µg/m³–
5 Sept 2025 7120.0 µg/m³–
6 Aug 2026 7119.8 µg/m³–

Daily means, the highest since 28 Jan 2025; 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, Colorado, United States, 28 Jan 2025 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/windsor/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 18:07 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).