EnviroNearby

Seneca County, Ohio air quality history

Daily Air Quality Index summaries from EPA monitors in Seneca, Ohio, 1991–2004.

99%
Good days in 2004
16
Median daily AQI, 2004
0
Days above 100 in 2004
177
Days with an AQI in 2004 (of 366)

In 2004, EPA reported a daily Air Quality Index (AQI) for Seneca, Ohio on 177 days. 176 of those days (99%) were in the Good range, and the median daily AQI was 16. That median is lower than the typical monitored county in Ohio (median 43.5 across 38 counties), and lower than the typical monitored U.S. county (42). The main pollutant was coarse particles (PM10) on 177 days. Across the years with fuller monitoring, the share of Good days rose: an average of 92% in 1993–1995 versus 99% in 2002–2004.

EPA did not report an AQI for every day of 2004 here (177 of 366 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

The most recent year with data for this county is 2004; EPA's files for 2005–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (1991, 1992, 1996) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1991: Good 23 of 24 days1991: Moderate 1 of 24 days19911992: Good 101 of 108 days1992: Moderate 7 of 108 days19921993: Good 145 of 155 days1993: Moderate 10 of 155 days19931994: Good 146 of 161 days1994: Moderate 15 of 161 days19941995: Good 130 of 141 days1995: Moderate 11 of 141 days19951996: Good 103 of 106 days1996: Moderate 3 of 106 days19961997: Good 160 of 165 days1997: Moderate 5 of 165 days19971998: Good 139 of 142 days1998: Moderate 3 of 142 days19981999: Good 124 of 136 days1999: Moderate 11 of 136 days1999: Unhealthy for Sensitive Groups 1 of 136 days19992000: Good 177 of 181 days2000: Moderate 4 of 181 days20002001: Good 170 of 174 days2001: Moderate 4 of 174 days20012002: Good 172 of 174 days2002: Moderate 2 of 174 days20022003: Good 164 of 166 days2003: Moderate 2 of 166 days20032004: Good 176 of 177 days2004: Moderate 1 of 177 days2004
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001991: 90th percentile AQI 381992: 90th percentile AQI 341993: 90th percentile AQI 451994: 90th percentile AQI 451995: 90th percentile AQI 471996: 90th percentile AQI 371997: 90th percentile AQI 361998: 90th percentile AQI 391999: 90th percentile AQI 482000: 90th percentile AQI 312001: 90th percentile AQI 352002: 90th percentile AQI 352003: 90th percentile AQI 302004: 90th percentile AQI 281991: Median AQI 211992: Median AQI 181993: Median AQI 201994: Median AQI 231995: Median AQI 201996: Median AQI 191997: Median AQI 211998: Median AQI 221999: Median AQI 222000: Median AQI 182001: Median AQI 182002: Median AQI 172003: Median AQI 152004: Median AQI 1619911992199319941995199619971998199920002001200220032004
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2004

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Coarse particles (PM10)177100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
200417717610000162852PM10
200316616420000153053PM10
200217417220000173554PM10
200117417040000183556PM10
200018117740000183177PM10
19991361241110002248108PM10
199814213930000223953PM10
199716516050000213654PM10
199610610330000193753PM10
1995141130110000204780PM10
1994161146150000234582PM10
1993155145100000204583PM10
199210810170000183486PM10
1991242310000213876PM10

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

All monitored counties in Ohio

Source: U.S. EPA AirData, “Annual AQI by County” files for 1991–2004 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem