SmogRank / United States / Washington / Mill Plain

Mill Plain, month by month

Mill Plain has a measured daily mean on 462 days since 1 January 2023. Its worst month was January 2023, at 41 US AQI (7.4 µg/m³), 799th of 1,261 cities on that month's world ranking. Its cleanest was June 2024, at 7 US AQI (1.2 µg/m³).

Every month since 2023

2026too few days for a mean (a year needs 199)0 days measured
JannoneFebnoneMarnoneAprnoneMaynoneJunnoneJulnoneAugnoneSepnoneOctnone
2025too few days for a mean (a year needs 256)0 days measured
JannoneFebnoneMarnoneAprnoneMaynoneJunnoneJulnoneAugnoneSepnoneOctnoneNovnoneDecnone
2024too few days for a mean (a year needs 257)174 days measured
Jan17#2,349Feb17#2,430Mar13#1,673Apr9#2,511May7#2,675Jun7#2,560JulnoneAugnoneSepnoneOctnoneNovnoneDecnone
202325 for the year288 days measured1,295th of 1,355 in the world
Jan41#799Feb1 dayMar11 daysApr13#1,602May20#1,551Jun13#1,588Jul24#1,304Aug39#1,289Sep16#2,163Oct17 daysNov37#1,540Dec23#2,117
Each square is a month's mean PM2.5 in US AQI from Mill Plain'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 Mill Plain 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

31 months
MonthWhy
Oct 2026No day measured.
Sep 2026No day measured.
Aug 2026No day measured.
Jul 2026No day measured.
Jun 2026No day measured.
May 2026No day measured.
Apr 2026No day measured.
Mar 2026No day measured.
Feb 2026No day measured.
Jan 2026No day measured.
Dec 2025No day measured.
Nov 2025No day measured.
Oct 2025No day measured.
Sep 2025No day measured.
Aug 2025No day measured.
Jul 2025No day measured.
Jun 2025No day measured.
May 2025No day measured.
Apr 2025No day measured.
Mar 2025No day measured.
Feb 2025No day measured.
Jan 2025No day measured.
Dec 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Nov 2024No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Oct 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Sep 2024No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Aug 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Jul 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Oct 202317 of 31 days measured; a month needs 22. The others: 14 with under 18 hours of readings or readings that failed our checks.
Mar 202311 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive.
Feb 20231 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive, 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.

Mill Plain's worst months

MonthUS AQIDays measuredWorld rankEpisode
January 2023 417.4 µg/m³23 of 31799thof 1,261–
August 2023 397.1 µg/m³31 of 311,289thof 1,980North-western United States and Canada, August 2023
November 2023 376.6 µg/m³30 of 301,540thof 2,243–
July 2023 244.3 µg/m³28 of 311,304thof 1,432–
December 2023 234.2 µg/m³31 of 312,117thof 2,247–
May 2023 203.6 µg/m³31 of 311,551stof 1,600–

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.

Mill Plain's worst days

DayUS AQIEpisode
20 Aug 2023 13348.4 µg/m³North-western United States and Canada, August 2023
19 Jul 2023 10537.3 µg/m³–
31 Aug 2023 8828.7 µg/m³North-western United States and Canada, August 2023
1 Jan 2023 8728.2 µg/m³–
20 Jan 2023 6818.3 µg/m³–
5 Jul 2023 6617.1 µg/m³–
19 Jan 2023 6516.6 µg/m³–
17 Jan 2024 6416.3 µg/m³–
27 Aug 2023 6315.7 µg/m³North-western United States and Canada, August 2023
16 Dec 2023 6013.9 µg/m³–

Daily means, the highest since 1 Jan 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, Mill Plain, United States, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/mill-plain/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.

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

Updated 2026-10-12 17:07 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).