SmogRank / United States / Montana / Helena Valley West Central
Helena Valley West Central, month by month
Helena Valley West Central has a measured daily mean on 1,213 days since 7 May 2023. Its worst month was July 2024, at 66 US AQI (17.3 µg/m³), 135th of 2,566 cities on that month's world ranking. Its cleanest was June 2026, at 17 US AQI (3.0 µg/m³). 2025 averaged 49 US AQI (8.8 µg/m³), against 54 US AQI (10.9 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
Helena Valley West Central's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2024 | 6617.3 µg/m³ | 135thof 2,566 | North-western United States and Canada, July 2024 |
| January 2024 | 6315.7 µg/m³ | 423rdof 2,385 | – |
| September 2024 | 6315.5 µg/m³ | 156thof 2,010 | North-western United States and Canada, 4 to 11 September 2024 North-western United States and Canada, 10 to 11 September 2024 |
| August 2026 | 6214.8 µg/m³ | 394thof 2,896 | North-western United States and Canada, 4 to 22 August 2026 North-western United States and Canada, July and August 2026 |
| May 2023 | 5913.4 µg/m³ | 192ndof 1,600 | North-western United States and Canada, May 2023 Northern United States and Canada, May 2023 |
| October 2024 | 5813.1 µg/m³ | 333rdof 2,020 | North-western United States, October 2024 |
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.
Helena Valley West Central's worst days
Daily means, the highest since 7 May 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, Helena Valley West Central, United States, 7 May 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/helena-valley-west-central/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.
Helena Valley West Central now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 02:07 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).