SmogRank / United States / Oregon / Hillsboro
Hillsboro, month by month
Hillsboro has a measured daily mean on 1,264 days since 11 January 2023. Its worst month was November 2023, at 54 US AQI (10.8 µg/m³), 462nd of 2,243 cities on that month's world ranking. Its cleanest was May 2025, at 14 US AQI (2.5 µg/m³). 2025 averaged 29 US AQI (5.3 µg/m³), against 27 US AQI (4.9 µg/m³) in 2024.
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
3 months
| Month | Why |
|---|---|
| Apr 2023 | 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 2023 | 20 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks. |
| Jan 2023 | 7 of 31 days measured; a month needs 22. The others: 14 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.
Hillsboro's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| November 2023 | 5410.8 µg/m³ | 462ndof 2,243 | – |
| January 2026 | 5410.8 µg/m³ | 1,007thof 2,617 | Washington and Oregon, United States, January 2026 |
| August 2026 | 529.6 µg/m³ | 997thof 2,896 | North-western United States and Canada, 4 to 22 August 2026 |
| January 2025 | 519.1 µg/m³ | 1,158thof 2,474 | Western United States and Mexico, January and February 2025 |
| February 2023 | 478.5 µg/m³ | 772ndof 1,129 | – |
| November 2025 | 478.4 µg/m³ | 1,422ndof 2,715 | – |
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.
Hillsboro's worst days
| Day | US AQI | Episode |
|---|---|---|
| 5 Aug 2026 | 13950.8 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 4 Aug 2026 | 13147.7 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 20 Aug 2023 | 11240.0 µg/m³ | North-western United States and Canada, August 2023 |
| 2 Feb 2023 | 9934.8 µg/m³ | – |
| 6 Aug 2026 | 9231.1 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 9 Nov 2024 | 8829.1 µg/m³ | North-western United States and Canada, November 2024 |
| 26 Jan 2026 | 8426.9 µg/m³ | Washington and Oregon, United States, January 2026 |
| 30 Jan 2025 | 8426.7 µg/m³ | Western United States and Mexico, January and February 2025 |
| 10 Nov 2024 | 8326.1 µg/m³ | North-western United States and Canada, November 2024 |
| 6 Sept 2024 | 8024.7 µg/m³ | – |
Daily means, the highest since 11 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, Hillsboro, United States, 11 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/hillsboro/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.
Hillsboro now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 03:07 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).