EnviroNearby

Mercer County, New Jersey air quality history

Daily Air Quality Index summaries from EPA monitors in Mercer, New Jersey, 1980–2025.

70%
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 Mercer, New Jersey on 365 days. 255 of those days (70%) were in the Good range, and the median daily AQI was 43. That median is higher than the typical monitored county in New Jersey (median 40 across 15 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 218 days. Across the years with fuller monitoring, the share of Good days fell: an average of 74% in 1980–1982 versus 63% 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 226 of 343 days1980: Moderate 48 of 343 days1980: Unhealthy for Sensitive Groups 27 of 343 days1980: Unhealthy 30 of 343 days1980: Very Unhealthy 12 of 343 days19801981: Good 283 of 347 days1981: Moderate 25 of 347 days1981: Unhealthy for Sensitive Groups 21 of 347 days1981: Unhealthy 14 of 347 days1981: Very Unhealthy 4 of 347 days1982: Good 256 of 343 days1982: Moderate 41 of 343 days1982: Unhealthy for Sensitive Groups 30 of 343 days1982: Unhealthy 12 of 343 days1982: Very Unhealthy 4 of 343 days1983: Good 245 of 344 days1983: Moderate 39 of 344 days1983: Unhealthy for Sensitive Groups 25 of 344 days1983: Unhealthy 23 of 344 days1983: Very Unhealthy 12 of 344 days1984: Good 224 of 366 days1984: Moderate 95 of 366 days1984: Unhealthy for Sensitive Groups 26 of 366 days1984: Unhealthy 16 of 366 days1984: Very Unhealthy 5 of 366 days1985: Good 248 of 365 days1985: Moderate 63 of 365 days1985: Unhealthy for Sensitive Groups 28 of 365 days1985: Unhealthy 18 of 365 days1985: Very Unhealthy 8 of 365 days19851986: Good 250 of 365 days1986: Moderate 61 of 365 days1986: Unhealthy for Sensitive Groups 31 of 365 days1986: Unhealthy 19 of 365 days1986: Very Unhealthy 4 of 365 days1987: Good 256 of 355 days1987: Moderate 44 of 355 days1987: Unhealthy for Sensitive Groups 19 of 355 days1987: Unhealthy 20 of 355 days1987: Very Unhealthy 16 of 355 days1988: Good 273 of 366 days1988: Moderate 38 of 366 days1988: Unhealthy for Sensitive Groups 15 of 366 days1988: Unhealthy 20 of 366 days1988: Very Unhealthy 20 of 366 days1989: Good 280 of 365 days1989: Moderate 47 of 365 days1989: Unhealthy for Sensitive Groups 21 of 365 days1989: Unhealthy 13 of 365 days1989: Very Unhealthy 4 of 365 days1990: Good 261 of 365 days1990: Moderate 56 of 365 days1990: Unhealthy for Sensitive Groups 27 of 365 days1990: Unhealthy 16 of 365 days1990: Very Unhealthy 5 of 365 days19901991: Good 242 of 365 days1991: Moderate 45 of 365 days1991: Unhealthy for Sensitive Groups 32 of 365 days1991: Unhealthy 29 of 365 days1991: Very Unhealthy 17 of 365 days1992: Good 282 of 366 days1992: Moderate 45 of 366 days1992: Unhealthy for Sensitive Groups 21 of 366 days1992: Unhealthy 14 of 366 days1992: Very Unhealthy 4 of 366 days1993: Good 258 of 365 days1993: Moderate 45 of 365 days1993: Unhealthy for Sensitive Groups 33 of 365 days1993: Unhealthy 26 of 365 days1993: Very Unhealthy 3 of 365 days1994: Good 263 of 365 days1994: Moderate 51 of 365 days1994: Unhealthy for Sensitive Groups 33 of 365 days1994: Unhealthy 16 of 365 days1994: Very Unhealthy 2 of 365 days1995: Good 260 of 365 days1995: Moderate 55 of 365 days1995: Unhealthy for Sensitive Groups 30 of 365 days1995: Unhealthy 14 of 365 days1995: Very Unhealthy 6 of 365 days19951996: Good 258 of 364 days1996: Moderate 70 of 364 days1996: Unhealthy for Sensitive Groups 26 of 364 days1996: Unhealthy 10 of 364 days1997: Good 280 of 365 days1997: Moderate 48 of 365 days1997: Unhealthy for Sensitive Groups 21 of 365 days1997: Unhealthy 12 of 365 days1997: Very Unhealthy 4 of 365 days1998: Good 252 of 365 days1998: Moderate 58 of 365 days1998: Unhealthy for Sensitive Groups 33 of 365 days1998: Unhealthy 22 of 365 days1999: Good 211 of 365 days1999: Moderate 104 of 365 days1999: Unhealthy for Sensitive Groups 23 of 365 days1999: Unhealthy 16 of 365 days1999: Very Unhealthy 11 of 365 days2000: Good 230 of 366 days2000: Moderate 108 of 366 days2000: Unhealthy for Sensitive Groups 16 of 366 days2000: Unhealthy 9 of 366 days2000: Very Unhealthy 3 of 366 days20002001: Good 222 of 365 days2001: Moderate 102 of 365 days2001: Unhealthy for Sensitive Groups 24 of 365 days2001: Unhealthy 15 of 365 days2001: Very Unhealthy 2 of 365 days2002: Good 223 of 365 days2002: Moderate 86 of 365 days2002: Unhealthy for Sensitive Groups 28 of 365 days2002: Unhealthy 22 of 365 days2002: Very Unhealthy 6 of 365 days2003: Good 246 of 365 days2003: Moderate 95 of 365 days2003: Unhealthy for Sensitive Groups 17 of 365 days2003: Unhealthy 5 of 365 days2003: Very Unhealthy 2 of 365 days2004: Good 249 of 366 days2004: Moderate 99 of 366 days2004: Unhealthy for Sensitive Groups 15 of 366 days2004: Unhealthy 3 of 366 days2005: Good 231 of 365 days2005: Moderate 107 of 365 days2005: Unhealthy for Sensitive Groups 19 of 365 days2005: Unhealthy 8 of 365 days20052006: Good 238 of 365 days2006: Moderate 97 of 365 days2006: Unhealthy for Sensitive Groups 24 of 365 days2006: Unhealthy 6 of 365 days2007: Good 163 of 365 days2007: Moderate 166 of 365 days2007: Unhealthy for Sensitive Groups 28 of 365 days2007: Unhealthy 7 of 365 days2007: Very Unhealthy 1 of 365 days2008: Good 172 of 366 days2008: Moderate 176 of 366 days2008: Unhealthy for Sensitive Groups 17 of 366 days2008: Unhealthy 1 of 366 days2009: Good 201 of 365 days2009: Moderate 158 of 365 days2009: Unhealthy for Sensitive Groups 6 of 365 days2010: Good 194 of 365 days2010: Moderate 138 of 365 days2010: Unhealthy for Sensitive Groups 28 of 365 days2010: Unhealthy 5 of 365 days20102011: Good 180 of 365 days2011: Moderate 172 of 365 days2011: Unhealthy for Sensitive Groups 10 of 365 days2011: Unhealthy 3 of 365 days2012: Good 206 of 366 days2012: Moderate 140 of 366 days2012: Unhealthy for Sensitive Groups 20 of 366 days2013: Good 203 of 365 days2013: Moderate 159 of 365 days2013: Unhealthy for Sensitive Groups 3 of 365 days2014: Good 179 of 365 days2014: Moderate 180 of 365 days2014: Unhealthy for Sensitive Groups 6 of 365 days2015: Good 210 of 365 days2015: Moderate 145 of 365 days2015: Unhealthy for Sensitive Groups 10 of 365 days20152016: Good 198 of 366 days2016: Moderate 155 of 366 days2016: Unhealthy for Sensitive Groups 12 of 366 days2016: Unhealthy 1 of 366 days2017: Good 225 of 365 days2017: Moderate 136 of 365 days2017: Unhealthy for Sensitive Groups 4 of 365 days2018: Good 229 of 365 days2018: Moderate 129 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days2018: Unhealthy 1 of 365 days2019: Good 232 of 365 days2019: Moderate 131 of 365 days2019: Unhealthy for Sensitive Groups 2 of 365 days2020: Good 262 of 366 days2020: Moderate 101 of 366 days2020: Unhealthy for Sensitive Groups 3 of 366 days20202021: Good 193 of 365 days2021: Moderate 165 of 365 days2021: Unhealthy for Sensitive Groups 7 of 365 days2022: Good 227 of 365 days2022: Moderate 135 of 365 days2022: Unhealthy for Sensitive Groups 3 of 365 days2023: Good 194 of 365 days2023: Moderate 160 of 365 days2023: Unhealthy for Sensitive Groups 6 of 365 days2023: Unhealthy 4 of 365 days2023: Very Unhealthy 1 of 365 days2024: Good 246 of 366 days2024: Moderate 115 of 366 days2024: Unhealthy for Sensitive Groups 5 of 366 days2025: Good 255 of 365 days2025: Moderate 104 of 365 days2025: Unhealthy for Sensitive Groups 6 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 1051982: 90th percentile AQI 1081983: 90th percentile AQI 1511984: 90th percentile AQI 1221985: 90th percentile AQI 1261986: 90th percentile AQI 1261987: 90th percentile AQI 1511988: 90th percentile AQI 1561989: 90th percentile AQI 1011990: 90th percentile AQI 1151991: 90th percentile AQI 1611992: 90th percentile AQI 1011993: 90th percentile AQI 1361994: 90th percentile AQI 1221995: 90th percentile AQI 1261996: 90th percentile AQI 1001997: 90th percentile AQI 1011998: 90th percentile AQI 1261999: 90th percentile AQI 1222000: 90th percentile AQI 902001: 90th percentile AQI 1022002: 90th percentile AQI 1332003: 90th percentile AQI 872004: 90th percentile AQI 842005: 90th percentile AQI 872006: 90th percentile AQI 932007: 90th percentile AQI 1002008: 90th percentile AQI 852009: 90th percentile AQI 742010: 90th percentile AQI 972011: 90th percentile AQI 742012: 90th percentile AQI 792013: 90th percentile AQI 712014: 90th percentile AQI 712015: 90th percentile AQI 772016: 90th percentile AQI 672017: 90th percentile AQI 642018: 90th percentile AQI 672019: 90th percentile AQI 642020: 90th percentile AQI 582021: 90th percentile AQI 672022: 90th percentile AQI 612023: 90th percentile AQI 702024: 90th percentile AQI 712025: 90th percentile AQI 631980: Median AQI 411981: Median AQI 271982: Median AQI 361983: Median AQI 381984: Median AQI 441985: Median AQI 401986: Median AQI 381987: Median AQI 351988: Median AQI 361989: Median AQI 331990: Median AQI 371991: Median AQI 381992: Median AQI 341993: Median AQI 361994: Median AQI 401995: Median AQI 401996: Median AQI 401997: Median AQI 401998: Median AQI 401999: Median AQI 472000: Median AQI 422001: Median AQI 442002: Median AQI 432003: Median AQI 422004: Median AQI 422005: Median AQI 452006: Median AQI 422007: Median AQI 532008: Median AQI 522009: Median AQI 462010: Median AQI 482011: Median AQI 512012: Median AQI 482013: Median AQI 472014: Median AQI 512015: Median AQI 462016: Median AQI 482017: Median AQI 462018: Median AQI 432019: Median AQI 452020: Median AQI 422021: Median AQI 482022: Median AQI 462023: Median AQI 492024: 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
Ozone21860%
Fine particles (PM2.5)14740%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536525510460004363126Ozone
202436624611550004371133Ozone
202336519416064104970244PM2.5
202236522713530004661119PM2.5
202136519316570004867130PM2.5
202036626210130004258112PM2.5
201936523213120004564136Ozone
201836522912961004367187PM2.5
201736522513640004664133PM2.5
2016366198155121004867151PM2.5
2015365210145100004677147Ozone
201436517918060005171119PM2.5
201336520315930004771122PM2.5
2012366206140200004879143Ozone
2011365180172103005174159PM2.5
2010365194138285004897174Ozone
200936520115860004674108PM2.5
2008366172176171005285174PM2.5
20073651631662871053100201PM2.5
200636523897246004293195Ozone
2005365231107198004587185Ozone
200436624999153004284169Ozone
200336524695175204287204Ozone
20023652238628226043133210Ozone
200136522210224152044102209Ozone
2000366230108169304290216Ozone
1999365211104231611047122225Ozone
19983652525833220040126192Ozone
19973652804821124040101209Ozone
19963642587026100040100195Ozone
19953652605530146040126219Ozone
19943652635133162040122218Ozone
19933652584533263036136220Ozone
19923662824521144034101229Ozone
199136524245322917038161232Ozone
19903652615627165037115223Ozone
19893652804721134033101215Ozone
198836627338152020036156258Ozone
198735525644192016035151262Ozone
19863652506131194038126223Ozone
19853652486328188040126221Ozone
19843662249526165044122244Ozone
198334424539252312038151242Ozone
19823432564130124036108223Ozone
19813472832521144027105229Ozone
198034322648273012041161230Ozone

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 New Jersey with a similar median AQI in 2025

All monitored counties in New Jersey

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