SmogRank / United States / Pennsylvania / Johnstown
Johnstown, month by month
Johnstown has a measured daily mean on 1,279 days since 1 January 2023. Its worst month was June 2023, at 76 US AQI (22.5 µg/m³), 223rd of 1,603 cities on that month's world ranking. Its cleanest was May 2026, at 21 US AQI (3.8 µg/m³). 2025 averaged 37 US AQI (6.7 µg/m³), against 37 US AQI (6.6 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 |
|---|---|
| Aug 2025 | 21 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | 4 of 31 days measured; a month needs 22. The others: 27 with under 18 hours of readings or readings that failed our checks. |
| Sep 2023 | No day measured. The others: 30 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.
Johnstown's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| June 2023 | 7622.5 µg/m³ | 223rdof 1,603 | Eastern United States and Canada, June and July 2023 United States and Canada, June 2023and 1 more |
| July 2026 | 7220.5 µg/m³ | 314thof 2,784 | Northern United States and Canada, July 2026 |
| July 2023 | 5511.1 µg/m³ | 520thof 1,432 | United States and Canada, July 2023 Eastern United States and Canada, June and July 2023 |
| February 2026 | 5410.9 µg/m³ | 1,208thof 2,866 | – |
| June 2025 | 5310.0 µg/m³ | 1,296thof 2,508 | – |
| January 2023 | 529.9 µg/m³ | 493rdof 1,261 | – |
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.
Johnstown's worst days
| Day | US AQI | Episode |
|---|---|---|
| 17 Jul 2026 | 235160.0 µg/m³ | Northern United States and Canada, July 2026 |
| 29 Jun 2023 | 195118.0 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 16 Jul 2026 | 184103.0 µg/m³ | Northern United States and Canada, July 2026 |
| 28 Jun 2023 | 17386.8 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 18 Jul 2026 | 15866.1 µg/m³ | Northern United States and Canada, July 2026 |
| 30 Jun 2023 | 15763.7 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 6 Jun 2023 | 9934.7 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 8 Jun 2023 | 9633.2 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 7 Jun 2023 | 9331.6 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 17 Jun 2023 | 8627.9 µg/m³ | United States and Canada, June 2023 |
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, Johnstown, 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/johnstown/history (accessed 12 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.
Johnstown 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).