Historical PM2.5 records
Toledo's worst air quality days
Based on the available regulatory-monitor record since 1999, July 16, 2026 provisionally ranks as Toledo's most severe daily PM2.5 day: 387.8 µg/m³ (AQI 500, hazardous), about 17.6 cigarettes in a day. The ranking updates when EPA finalizes the data.
- Daily rank
- #1 provisional
- Period of record
- Since 1999
- Peak daily PM2.5
- 387.8 µg/m³
- About
- 17.6 cigarettes
- Latest event
- 1 day, July 2026
- Status
- Preliminary
Current conditions on the smoke map → Data through Jul 20, 2026 · page built July 26, 2026
How this is measured sources, the daily measure, and what this ranking is not
Source. Daily PM2.5 from the U.S. EPA Air Quality System (AQS) , back to 1999, across 5 EPA monitors in the Toledo, OH metro area (CBSA). Days after May 1, 2026 are preliminary AirNow readings, marked provisional, and re-rank once EPA certifies them (usually the following spring).
The daily measure. "Worst area" is the metro's highest credible monitor each day, with lone bad-monitor spikes dropped (the raw single-monitor max before that filter is in the data but not charted). "Metro average" averages every monitor. The unit choice re-reads the same value as µg/m³, cigarette-equivalents (PM2.5 ÷ 22, Berkeley Earth, an illustration rather than a medical reading), or the EPA 2024 PM2.5 AQI.
Official AQI. EPA's reported metro AQI uses the single worst monitor of any pollutant, so it can run higher than the values here. The highest official daily AQI among the ranked days is 203 on June 27, 2005 (defining pollutant Ozone).
What this ranking is not. It does not attribute days to wildfire smoke: a high-PM2.5 day can be dust, fireworks, an inversion, or industry. The wildfire-smoke event ranking below arrives with a published attribution method.
Toledo's monitoring record is thinner than most, 5,289 days since 1999, with gaps between them. The ranking is real, but treat it as indicative rather than a complete accounting.
Latest major event July 2026 One ranked day, Jul 20, 2026, peaking at 51 µg/m³, #8 all-time. Provisional until EPA certifies the data. See where it ranks ↓What were Toledo's worst days?
| Rank | Date | Daily PM2.5 |
|---|---|---|
| #1 | July 16, 2026provisional2-day stretch | 387.8 µg/m³ |
| #2 | July 17, 2026provisional | 240.7 µg/m³ |
| #3 | June 29, 2023 | 99.2 µg/m³ |
| #4 | July 20, 2001 | 61.3 µg/m³ |
| #5 | August 7, 1999 | 55 µg/m³ |
| #6 | June 27, 2005 | 53.4 µg/m³ |
| #7 | June 24, 2002 | 52.5 µg/m³ |
| #8 | July 20, 2026provisional | 51 µg/m³ |
| #9 | October 24, 2000 | 50 µg/m³ |
| #10 | June 6, 2025 | 49.6 µg/m³ |
| #11 | July 15, 2025 | 49.6 µg/m³ |
| #12 | February 28, 2003 | 49.4 µg/m³ |
| #13 | February 6, 2005 | 48.3 µg/m³ |
| #14 | July 28, 2000 | 48.1 µg/m³ |
| #15 | November 14, 2001 | 47.8 µg/m³ |
Days marked provisional are preliminary AirNow readings after May 1, 2026, the latest date EPA has certified for Toledo; they may shift once finalized.
What caused Toledo's worst days?
The event catalog has named 6 episodes affecting Toledo, each resolved to a cause only where retained evidence supports it: EPA monitor qualifiers, NWS alerts, agency statements, and reporting. The ranking above stays cause-neutral; this is where the causes live.
- Wildfire smoke July 15–20, 2026 Great Lakes and eastern U.S. wildfire-smoke episode
- Wildfire smoke 2025-07-15 wildfire smoke episode affecting Toledo, OH
- Wildfire smoke June 3–6, 2025 Upper Midwest Canadian wildfire-smoke episode
- Wildfire smoke 2023 late-June Canadian wildfire-smoke episode
- Other June 27, 2005 Great Lakes regional PM episode
- Other January 31–February 6, 2005 Midwest stagnation and nitrate episode
every named episode and its evidence is in the event catalog.
How does it compare?
The current provisional record is 3.9× the previous certified record: 387.8 µg/m³ (July 16, 2026) against 99.2 µg/m³ (June 29, 2023).
How unusual is air like this?
Every measured day near Toledo, by daily PM2.5; the record stands far out on the right. 91 days at "unhealthy for sensitive groups" or worse, 4 at "unhealthy", 2 at "very unhealthy" (2024 EPA thresholds, across 5,289 measured days).
Year by year (1999–2026)
Worst single day each year, by the selected measure.
Why did reported numbers differ?
During a major event, AirNow, weather apps, news reports, and neighborhood monitors can all show different figures at the same moment. All of them can be right:
- Concentration vs AQI. µg/m³ is the measurement; AQI is a 0 to 500 index derived from it. "330 µg/m³" and "AQI 500" can describe the same air.
- Hourly vs NowCast vs daily. An hourly peak, the NowCast rolling estimate apps display, and the full-day average answer different questions; this page ranks full days.
- One monitor vs a composite. A single sensor can read far above or below a citywide figure. The measure toggle above shows both framings.
- Live vs certified. Real-time feeds get corrected when EPA certifies data months later, which is why recent days here carry a provisional label.
What about indoors?
Citywide monitors can tell you what happened outside. They cannot tell you what happened inside a particular home, school, or facility: filtration, ventilation, and building operation decide that. During and after days like the ones above, outdoor particles become an indoor load question.
Check current conditions and the next clean-air window → Estimate recent filter load where you are →
Common questions
- What was the worst air-quality day in Toledo?
- July 16, 2026 (provisional), when daily PM2.5 reached 387.8 µg/m³ (AQI 500), about 17.6 cigarette-equivalents. It ranks first of 5,289 monitored days since 1999.
- What is the highest AQI recorded in Toledo?
- On the worst day, the daily PM2.5 AQI reached 500 (Hazardous). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 203 on June 27, 2005.
- Is the July 2026 ranking final?
- No. Days after May 1, 2026 are preliminary AirNow readings. They rank now so a current event is visible, and they may shift once EPA certifies the data, usually the following spring.
- Were these days caused by wildfire smoke?
- This page ranks measured PM2.5 without assigning a cause: a high day can be smoke, fireworks, dust, an inversion, or industry. A separate wildfire-smoke event ranking, using a published attribution method with its version disclosed, is the next layer of this catalog.
- How often does Toledo get air this bad?
- Rarely. The record sits at the far end of 5,289 measured days; Toledo averages about one "unhealthy" day every 7 years.
- Why did different apps show different numbers that day?
- Concentration (µg/m³) and AQI are different scales; hourly, NowCast, and daily values answer different questions; a single monitor differs from a citywide composite; and live feeds get revised when EPA certifies data. This page uses the certified daily record, with the provisional tail labeled.
Data and citation
Ranked days for both measures are downloadable, with units and status flags: toledo.csv. Source: U.S. EPA Air Quality System (AQS) daily PM2.5, with preliminary AirNow readings for the uncertified tail. Cite as:
IAQng Air Records: Toledo, OH. iaqng.com/records/toledo. Data: U.S. EPA AQS and AirNow. Accessed July 26, 2026.