EnviroNearby

Saint Louis County, Missouri air quality history

Daily Air Quality Index summaries from EPA monitors in Saint Louis, Missouri, 1980–2025.

73%
Good days in 2025
43
Median daily AQI, 2025
6
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Saint Louis, Missouri on 365 days. 268 of those days (73%) were in the Good range, and the median daily AQI was 43. That median is about the same as the typical monitored county in Missouri (median 41 across 19 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 191 days. Across the years with fuller monitoring, the share of Good days rose: an average of 45% in 1980–1982 versus 69% in 2023–2025.

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%1980: Good 129 of 358 days1980: Moderate 129 of 358 days1980: Unhealthy for Sensitive Groups 55 of 358 days1980: Unhealthy 32 of 358 days1980: Very Unhealthy 13 of 358 days19801981: Good 167 of 365 days1981: Moderate 151 of 365 days1981: Unhealthy for Sensitive Groups 35 of 365 days1981: Unhealthy 9 of 365 days1981: Very Unhealthy 3 of 365 days1982: Good 196 of 365 days1982: Moderate 120 of 365 days1982: Unhealthy for Sensitive Groups 37 of 365 days1982: Unhealthy 9 of 365 days1982: Very Unhealthy 3 of 365 days1983: Good 188 of 365 days1983: Moderate 96 of 365 days1983: Unhealthy for Sensitive Groups 40 of 365 days1983: Unhealthy 23 of 365 days1983: Very Unhealthy 18 of 365 days1984: Good 213 of 366 days1984: Moderate 87 of 366 days1984: Unhealthy for Sensitive Groups 38 of 366 days1984: Unhealthy 18 of 366 days1984: Very Unhealthy 10 of 366 days1985: Good 222 of 365 days1985: Moderate 99 of 365 days1985: Unhealthy for Sensitive Groups 29 of 365 days1985: Unhealthy 10 of 365 days1985: Very Unhealthy 5 of 365 days19851986: Good 212 of 365 days1986: Moderate 104 of 365 days1986: Unhealthy for Sensitive Groups 32 of 365 days1986: Unhealthy 12 of 365 days1986: Very Unhealthy 5 of 365 days1987: Good 183 of 365 days1987: Moderate 116 of 365 days1987: Unhealthy for Sensitive Groups 36 of 365 days1987: Unhealthy 20 of 365 days1987: Very Unhealthy 10 of 365 days1988: Good 200 of 366 days1988: Moderate 92 of 366 days1988: Unhealthy for Sensitive Groups 43 of 366 days1988: Unhealthy 19 of 366 days1988: Very Unhealthy 12 of 366 days1989: Good 204 of 365 days1989: Moderate 116 of 365 days1989: Unhealthy for Sensitive Groups 28 of 365 days1989: Unhealthy 15 of 365 days1989: Very Unhealthy 2 of 365 days1990: Good 235 of 365 days1990: Moderate 92 of 365 days1990: Unhealthy for Sensitive Groups 24 of 365 days1990: Unhealthy 13 of 365 days1990: Very Unhealthy 1 of 365 days19901991: Good 229 of 365 days1991: Moderate 83 of 365 days1991: Unhealthy for Sensitive Groups 27 of 365 days1991: Unhealthy 23 of 365 days1991: Very Unhealthy 3 of 365 days1992: Good 232 of 366 days1992: Moderate 103 of 366 days1992: Unhealthy for Sensitive Groups 21 of 366 days1992: Unhealthy 9 of 366 days1992: Very Unhealthy 1 of 366 days1993: Good 245 of 365 days1993: Moderate 97 of 365 days1993: Unhealthy for Sensitive Groups 21 of 365 days1993: Very Unhealthy 2 of 365 days1994: Good 211 of 365 days1994: Moderate 102 of 365 days1994: Unhealthy for Sensitive Groups 32 of 365 days1994: Unhealthy 15 of 365 days1994: Very Unhealthy 5 of 365 days1995: Good 239 of 365 days1995: Moderate 78 of 365 days1995: Unhealthy for Sensitive Groups 23 of 365 days1995: Unhealthy 24 of 365 days1995: Very Unhealthy 1 of 365 days19951996: Good 268 of 366 days1996: Moderate 63 of 366 days1996: Unhealthy for Sensitive Groups 29 of 366 days1996: Unhealthy 5 of 366 days1996: Very Unhealthy 1 of 366 days1997: Good 260 of 365 days1997: Moderate 77 of 365 days1997: Unhealthy for Sensitive Groups 22 of 365 days1997: Unhealthy 6 of 365 days1998: Good 254 of 365 days1998: Moderate 68 of 365 days1998: Unhealthy for Sensitive Groups 35 of 365 days1998: Unhealthy 7 of 365 days1998: Very Unhealthy 1 of 365 days1999: Good 180 of 365 days1999: Moderate 144 of 365 days1999: Unhealthy for Sensitive Groups 27 of 365 days1999: Unhealthy 13 of 365 days1999: Very Unhealthy 1 of 365 days2000: Good 192 of 366 days2000: Moderate 147 of 366 days2000: Unhealthy for Sensitive Groups 21 of 366 days2000: Unhealthy 6 of 366 days20002001: Good 203 of 365 days2001: Moderate 128 of 365 days2001: Unhealthy for Sensitive Groups 27 of 365 days2001: Unhealthy 7 of 365 days2002: Good 153 of 365 days2002: Moderate 169 of 365 days2002: Unhealthy for Sensitive Groups 21 of 365 days2002: Unhealthy 19 of 365 days2002: Very Unhealthy 3 of 365 days2003: Good 104 of 365 days2003: Moderate 226 of 365 days2003: Unhealthy for Sensitive Groups 29 of 365 days2003: Unhealthy 3 of 365 days2003: Very Unhealthy 3 of 365 days2004: Good 114 of 366 days2004: Moderate 248 of 366 days2004: Unhealthy for Sensitive Groups 4 of 366 days2005: Good 168 of 365 days2005: Moderate 143 of 365 days2005: Unhealthy for Sensitive Groups 43 of 365 days2005: Unhealthy 10 of 365 days2005: Very Unhealthy 1 of 365 days20052006: Good 120 of 365 days2006: Moderate 217 of 365 days2006: Unhealthy for Sensitive Groups 23 of 365 days2006: Unhealthy 5 of 365 days2007: Good 82 of 365 days2007: Moderate 245 of 365 days2007: Unhealthy for Sensitive Groups 25 of 365 days2007: Unhealthy 13 of 365 days2008: Good 77 of 366 days2008: Moderate 285 of 366 days2008: Unhealthy for Sensitive Groups 4 of 366 days2009: Good 99 of 365 days2009: Moderate 262 of 365 days2009: Unhealthy for Sensitive Groups 4 of 365 days2010: Good 113 of 365 days2010: Moderate 236 of 365 days2010: Unhealthy for Sensitive Groups 16 of 365 days20102011: Good 147 of 365 days2011: Moderate 200 of 365 days2011: Unhealthy for Sensitive Groups 15 of 365 days2011: Unhealthy 3 of 365 days2012: Good 124 of 366 days2012: Moderate 199 of 366 days2012: Unhealthy for Sensitive Groups 32 of 366 days2012: Unhealthy 11 of 366 days2013: Good 135 of 365 days2013: Moderate 226 of 365 days2013: Unhealthy for Sensitive Groups 4 of 365 days2014: Good 187 of 365 days2014: Moderate 173 of 365 days2014: Unhealthy for Sensitive Groups 5 of 365 days2015: Good 172 of 365 days2015: Moderate 188 of 365 days2015: Unhealthy for Sensitive Groups 5 of 365 days20152016: Good 205 of 366 days2016: Moderate 154 of 366 days2016: Unhealthy for Sensitive Groups 7 of 366 days2017: Good 161 of 365 days2017: Moderate 203 of 365 days2017: Unhealthy for Sensitive Groups 1 of 365 days2018: Good 178 of 365 days2018: Moderate 181 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days2019: Good 194 of 365 days2019: Moderate 168 of 365 days2019: Unhealthy for Sensitive Groups 3 of 365 days2020: Good 246 of 366 days2020: Moderate 114 of 366 days2020: Unhealthy for Sensitive Groups 6 of 366 days20202021: Good 251 of 365 days2021: Moderate 111 of 365 days2021: Unhealthy for Sensitive Groups 3 of 365 days2022: Good 263 of 365 days2022: Moderate 100 of 365 days2022: Unhealthy for Sensitive Groups 2 of 365 days2023: Good 218 of 365 days2023: Moderate 130 of 365 days2023: Unhealthy for Sensitive Groups 14 of 365 days2023: Unhealthy 3 of 365 days2024: Good 269 of 366 days2024: Moderate 95 of 366 days2024: Unhealthy for Sensitive Groups 2 of 366 days2025: Good 268 of 365 days2025: Moderate 91 of 365 days2025: Unhealthy for Sensitive Groups 5 of 365 days2025: Unhealthy 1 of 365 days2025
  • 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 year0501001502001980: 90th percentile AQI 1611981: 90th percentile AQI 1041982: 90th percentile AQI 1061983: 90th percentile AQI 1641984: 90th percentile AQI 1361985: 90th percentile AQI 1051986: 90th percentile AQI 1171987: 90th percentile AQI 1401988: 90th percentile AQI 1471989: 90th percentile AQI 1081990: 90th percentile AQI 1011991: 90th percentile AQI 1221992: 90th percentile AQI 971993: 90th percentile AQI 871994: 90th percentile AQI 1191995: 90th percentile AQI 1151996: 90th percentile AQI 971997: 90th percentile AQI 931998: 90th percentile AQI 1081999: 90th percentile AQI 1082000: 90th percentile AQI 902001: 90th percentile AQI 972002: 90th percentile AQI 1122003: 90th percentile AQI 1002004: 90th percentile AQI 782005: 90th percentile AQI 1152006: 90th percentile AQI 942007: 90th percentile AQI 1012008: 90th percentile AQI 772009: 90th percentile AQI 762010: 90th percentile AQI 842011: 90th percentile AQI 862012: 90th percentile AQI 1052013: 90th percentile AQI 722014: 90th percentile AQI 742015: 90th percentile AQI 682016: 90th percentile AQI 672017: 90th percentile AQI 672018: 90th percentile AQI 712019: 90th percentile AQI 692020: 90th percentile AQI 632021: 90th percentile AQI 612022: 90th percentile AQI 632023: 90th percentile AQI 742024: 90th percentile AQI 582025: 90th percentile AQI 611980: Median AQI 611981: Median AQI 531982: Median AQI 481983: Median AQI 491984: Median AQI 471985: Median AQI 461986: Median AQI 471987: Median AQI 501988: Median AQI 481989: Median AQI 471990: Median AQI 451991: Median AQI 461992: Median AQI 451993: Median AQI 431994: Median AQI 471995: Median AQI 441996: Median AQI 421997: Median AQI 421998: Median AQI 431999: Median AQI 512000: Median AQI 482001: Median AQI 472002: Median AQI 562003: Median AQI 582004: Median AQI 562005: Median AQI 532006: Median AQI 572007: Median AQI 622008: Median AQI 582009: Median AQI 582010: Median AQI 562011: Median AQI 542012: Median AQI 562013: Median AQI 552014: Median AQI 502015: Median AQI 522016: Median AQI 482017: Median AQI 522018: Median AQI 512019: Median AQI 492020: Median AQI 442021: Median AQI 422022: Median AQI 442023: Median AQI 462024: Median AQI 432025: Median AQI 431980198519901995200020052010201520202025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2025

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
Ozone19152%
Fine particles (PM2.5)15843%
Nitrogen dioxide (NO₂)164%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652689151004361151Ozone
20243662699520004358122Ozone
2023365218130143004674166PM2.5
202236526310020004463140Ozone
202136525111130004261126PM2.5
202036624611460004463144PM2.5
201936519416830004969143PM2.5
201836517818160005171119PM2.5
201736516120310005267147PM2.5
201636620515470004867136PM2.5
201536517218850005268119PM2.5
201436518717350005074145PM2.5
201336513522640005572150PM2.5
201236612419932110056105172PM2.5
2011365147200153005486164PM2.5
2010365113236160005684133PM2.5
20093659926240005876115PM2.5
20083667728540005877126PM2.5
20073658224525130062101195PM2.5
2006365120217235005794182PM2.5
200536516814343101053115203Ozone
200436611424840005678119PM2.5
20033651042262933058100202PM2.5
200236515316921193056112209PM2.5
2001365203128277004797164Ozone
2000366192147216004890182NO2
199936518014427131051108214NO2
1998365254683571043108220NO2
199736526077226004293187NO2
199636626863295104297203NO2
19953652397823241044115208NO2
199436521110232155047119227NO2
199336524597210204387203NO2
1992366232103219104597207NO2
19913652298327233046122204NO2
19903652359224131045101202NO2
198936520411628152047108220NO2
198836620092431912048147240NO2
1987365183116362010050140259NO2
198636521210432125047117243NO2
19853652229929105046105219NO2
198436621387381810047136257NO2
198336518896402318049164268NO2
19823651961203793048106221NO2
19813651671513593053104230NO2
1980358129129553213061161242Ozone

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.

Counties in Missouri with a similar median AQI in 2025

All monitored counties in Missouri

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem