EnviroNearby

Montgomery County, Maryland air quality history

Daily Air Quality Index summaries from EPA monitors in Montgomery, Maryland, 1980–2025.

83%
Good days in 2025
39
Median daily AQI, 2025
0
Days above 100 in 2025
360
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Montgomery, Maryland on 360 days. 299 of those days (83%) were in the Good range, and the median daily AQI was 39. That median is about the same as the typical monitored county in Maryland (median 39.5 across 16 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 202 days. Across the years with fuller monitoring, the share of Good days rose: an average of 73% in 1980–1982 versus 80% 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 205 of 270 days1980: Moderate 20 of 270 days1980: Unhealthy for Sensitive Groups 27 of 270 days1980: Unhealthy 10 of 270 days1980: Very Unhealthy 8 of 270 days19801981: Good 245 of 346 days1981: Moderate 61 of 346 days1981: Unhealthy for Sensitive Groups 27 of 346 days1981: Unhealthy 10 of 346 days1981: Very Unhealthy 3 of 346 days1982: Good 238 of 331 days1982: Moderate 55 of 331 days1982: Unhealthy for Sensitive Groups 27 of 331 days1982: Unhealthy 10 of 331 days1982: Very Unhealthy 1 of 331 days1983: Good 219 of 347 days1983: Moderate 87 of 347 days1983: Unhealthy for Sensitive Groups 22 of 347 days1983: Unhealthy 17 of 347 days1983: Very Unhealthy 2 of 347 days1984: Good 213 of 360 days1984: Moderate 117 of 360 days1984: Unhealthy for Sensitive Groups 25 of 360 days1984: Unhealthy 3 of 360 days1984: Very Unhealthy 2 of 360 days1985: Good 217 of 360 days1985: Moderate 99 of 360 days1985: Unhealthy for Sensitive Groups 33 of 360 days1985: Unhealthy 10 of 360 days1985: Very Unhealthy 1 of 360 days19851986: Good 223 of 362 days1986: Moderate 94 of 362 days1986: Unhealthy for Sensitive Groups 26 of 362 days1986: Unhealthy 19 of 362 days1987: Good 274 of 365 days1987: Moderate 54 of 365 days1987: Unhealthy for Sensitive Groups 22 of 365 days1987: Unhealthy 13 of 365 days1987: Very Unhealthy 2 of 365 days1988: Good 245 of 366 days1988: Moderate 68 of 366 days1988: Unhealthy for Sensitive Groups 16 of 366 days1988: Unhealthy 23 of 366 days1988: Very Unhealthy 14 of 366 days1989: Good 275 of 365 days1989: Moderate 69 of 365 days1989: Unhealthy for Sensitive Groups 18 of 365 days1989: Unhealthy 2 of 365 days1989: Very Unhealthy 1 of 365 days1990: Good 280 of 357 days1990: Moderate 51 of 357 days1990: Unhealthy for Sensitive Groups 22 of 357 days1990: Unhealthy 4 of 357 days19901991: Good 233 of 344 days1991: Moderate 62 of 344 days1991: Unhealthy for Sensitive Groups 34 of 344 days1991: Unhealthy 14 of 344 days1991: Very Unhealthy 1 of 344 days1992: Good 309 of 363 days1992: Moderate 37 of 363 days1992: Unhealthy for Sensitive Groups 15 of 363 days1992: Unhealthy 2 of 363 days1993: Good 264 of 363 days1993: Moderate 60 of 363 days1993: Unhealthy for Sensitive Groups 25 of 363 days1993: Unhealthy 13 of 363 days1993: Very Unhealthy 1 of 363 days1994: Good 267 of 364 days1994: Moderate 64 of 364 days1994: Unhealthy for Sensitive Groups 26 of 364 days1994: Unhealthy 7 of 364 days1995: Good 281 of 361 days1995: Moderate 45 of 361 days1995: Unhealthy for Sensitive Groups 20 of 361 days1995: Unhealthy 13 of 361 days1995: Very Unhealthy 2 of 361 days19951996: Good 276 of 360 days1996: Moderate 55 of 360 days1996: Unhealthy for Sensitive Groups 26 of 360 days1996: Unhealthy 3 of 360 days1997: Good 210 of 299 days1997: Moderate 50 of 299 days1997: Unhealthy for Sensitive Groups 26 of 299 days1997: Unhealthy 12 of 299 days1997: Very Unhealthy 1 of 299 days1998: Good 95 of 208 days1998: Moderate 55 of 208 days1998: Unhealthy for Sensitive Groups 36 of 208 days1998: Unhealthy 21 of 208 days1998: Very Unhealthy 1 of 208 days1999: Good 105 of 226 days1999: Moderate 76 of 226 days1999: Unhealthy for Sensitive Groups 31 of 226 days1999: Unhealthy 13 of 226 days1999: Very Unhealthy 1 of 226 days2000: Good 123 of 244 days2000: Moderate 104 of 244 days2000: Unhealthy for Sensitive Groups 15 of 244 days2000: Unhealthy 2 of 244 days20002001: Good 123 of 254 days2001: Moderate 95 of 254 days2001: Unhealthy for Sensitive Groups 27 of 254 days2001: Unhealthy 8 of 254 days2001: Very Unhealthy 1 of 254 days2002: Good 111 of 241 days2002: Moderate 94 of 241 days2002: Unhealthy for Sensitive Groups 25 of 241 days2002: Unhealthy 11 of 241 days2003: Good 148 of 249 days2003: Moderate 90 of 249 days2003: Unhealthy for Sensitive Groups 8 of 249 days2003: Unhealthy 2 of 249 days2003: Very Unhealthy 1 of 249 days2004: Good 145 of 262 days2004: Moderate 95 of 262 days2004: Unhealthy for Sensitive Groups 20 of 262 days2004: Unhealthy 2 of 262 days2005: Good 125 of 247 days2005: Moderate 106 of 247 days2005: Unhealthy for Sensitive Groups 14 of 247 days2005: Unhealthy 2 of 247 days20052006: Good 131 of 254 days2006: Moderate 101 of 254 days2006: Unhealthy for Sensitive Groups 18 of 254 days2006: Unhealthy 4 of 254 days2007: Good 104 of 211 days2007: Moderate 86 of 211 days2007: Unhealthy for Sensitive Groups 17 of 211 days2007: Unhealthy 4 of 211 days2008: Good 152 of 289 days2008: Moderate 118 of 289 days2008: Unhealthy for Sensitive Groups 18 of 289 days2008: Unhealthy 1 of 289 days2009: Good 158 of 358 days2009: Moderate 197 of 358 days2009: Unhealthy for Sensitive Groups 3 of 358 days2010: Good 150 of 362 days2010: Moderate 188 of 362 days2010: Unhealthy for Sensitive Groups 24 of 362 days20102011: Good 139 of 335 days2011: Moderate 182 of 335 days2011: Unhealthy for Sensitive Groups 13 of 335 days2011: Unhealthy 1 of 335 days2012: Good 162 of 360 days2012: Moderate 191 of 360 days2012: Unhealthy for Sensitive Groups 6 of 360 days2012: Unhealthy 1 of 360 days2013: Good 230 of 354 days2013: Moderate 123 of 354 days2013: Unhealthy for Sensitive Groups 1 of 354 days2014: Good 196 of 355 days2014: Moderate 159 of 355 days2015: Good 160 of 345 days2015: Moderate 180 of 345 days2015: Unhealthy for Sensitive Groups 5 of 345 days20152016: Good 248 of 345 days2016: Moderate 97 of 345 days2017: Good 268 of 359 days2017: Moderate 89 of 359 days2017: Unhealthy for Sensitive Groups 2 of 359 days2018: Good 208 of 347 days2018: Moderate 138 of 347 days2018: Unhealthy for Sensitive Groups 1 of 347 days2019: Good 284 of 361 days2019: Moderate 77 of 361 days2020: Good 310 of 355 days2020: Moderate 45 of 355 days20202021: Good 251 of 361 days2021: Moderate 107 of 361 days2021: Unhealthy for Sensitive Groups 3 of 361 days2022: Good 241 of 355 days2022: Moderate 113 of 355 days2022: Unhealthy for Sensitive Groups 1 of 355 days2023: Good 291 of 357 days2023: Moderate 61 of 357 days2023: Unhealthy for Sensitive Groups 2 of 357 days2023: Unhealthy 3 of 357 days2024: Good 271 of 356 days2024: Moderate 85 of 356 days2025: Good 299 of 360 days2025: Moderate 61 of 360 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 1331981: 90th percentile AQI 1081982: 90th percentile AQI 1011983: 90th percentile AQI 1081984: 90th percentile AQI 931985: 90th percentile AQI 1121986: 90th percentile AQI 1191987: 90th percentile AQI 1011988: 90th percentile AQI 1541989: 90th percentile AQI 801990: 90th percentile AQI 901991: 90th percentile AQI 1191992: 90th percentile AQI 641993: 90th percentile AQI 1051994: 90th percentile AQI 971995: 90th percentile AQI 971996: 90th percentile AQI 931997: 90th percentile AQI 1121998: 90th percentile AQI 1511999: 90th percentile AQI 1222000: 90th percentile AQI 932001: 90th percentile AQI 1082002: 90th percentile AQI 1122003: 90th percentile AQI 872004: 90th percentile AQI 932005: 90th percentile AQI 932006: 90th percentile AQI 1002007: 90th percentile AQI 1002008: 90th percentile AQI 872009: 90th percentile AQI 712010: 90th percentile AQI 902011: 90th percentile AQI 792012: 90th percentile AQI 762013: 90th percentile AQI 652014: 90th percentile AQI 642015: 90th percentile AQI 712016: 90th percentile AQI 602017: 90th percentile AQI 592018: 90th percentile AQI 632019: 90th percentile AQI 572020: 90th percentile AQI 522021: 90th percentile AQI 612022: 90th percentile AQI 592023: 90th percentile AQI 612024: 90th percentile AQI 612025: 90th percentile AQI 541980: Median AQI 331981: Median AQI 391982: Median AQI 371983: Median AQI 421984: Median AQI 441985: Median AQI 451986: Median AQI 441987: Median AQI 381988: Median AQI 411989: Median AQI 361990: Median AQI 361991: Median AQI 381992: Median AQI 281993: Median AQI 321994: Median AQI 331995: Median AQI 311996: Median AQI 301997: Median AQI 391998: Median AQI 581999: Median AQI 542000: Median AQI 502001: Median AQI 512002: Median AQI 532003: Median AQI 462004: Median AQI 472005: Median AQI 502006: Median AQI 502007: Median AQI 512008: Median AQI 492009: Median AQI 522010: Median AQI 532011: Median AQI 542012: Median AQI 522013: Median AQI 452014: Median AQI 482015: Median AQI 522016: Median AQI 422017: Median AQI 432018: Median AQI 462019: Median AQI 412020: Median AQI 372021: Median AQI 422022: Median AQI 432023: Median AQI 422024: Median AQI 402025: Median AQI 391980198519901995200020052010201520202025
  • 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
Ozone20256%
Fine particles (PM2.5)15844%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025360299610000395490Ozone
20243562718500004061100Ozone
20233572916123004261165Ozone
202235524111310004359119PM2.5
202136125110730004261119Ozone
2020355310450000375277PM2.5
2019361284770000415788Ozone
201834720813810004663112PM2.5
20173592688920004359105Ozone
20163452489700004260100Ozone
201534516018050005271143PM2.5
20143551961590000486490PM2.5
201335423012310004565105PM2.5
201236016219161005276154PM2.5
2011335139182131005479156PM2.5
2010362150188240005390136PM2.5
200935815819730005271112PM2.5
2008289152118181004987172Ozone
2007211104861740051100195Ozone
20062541311011840050100190Ozone
2005247125106142005093187Ozone
200426214595202004793172Ozone
20032491489082104687210Ozone
20022411119425110053112185Ozone
2001254123952781051108202Ozone
2000244123104152005093156Ozone
19992261057631131054122208Ozone
1998208955536211058151209Ozone
19972992105026121039112202Ozone
199636027655263003093169Ozone
1995361281452013203197208Ozone
199436426764267003397187Ozone
19933632646025131032105201Ozone
199236330937152002864164Ozone
19913442336234141038119208Ozone
199035728051224003690166Ozone
198936527569182103680202Ozone
198836624568162314041154221Ozone
19873652745422132038101202Ozone
19863622239426190044119195Ozone
19853602179933101045112220Ozone
1984360213117253204493240CO
19833472198722172042108214CO
19823312385527101037101201Ozone
19813462456127103039108207Ozone
19802702052027108033133232Ozone

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 Maryland with a similar median AQI in 2025

All monitored counties in Maryland

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