EnviroNearby

Howard County, Maryland air quality history

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

80%
Good days in 2025
33
Median daily AQI, 2025
0
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 Howard, Maryland on 365 days. 293 of those days (80%) were in the Good range, and the median daily AQI was 33. That median is lower than the typical monitored county in Maryland (median 39.5 across 16 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 292 days. Across the years with fuller monitoring, the share of Good days rose: an average of 76% in 1981–1983 versus 79% in 2023–2025.

Years with fewer than 120 monitored days (1980, 1985) 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%1980: Good 88 of 102 days1980: Moderate 6 of 102 days1980: Unhealthy for Sensitive Groups 5 of 102 days1980: Unhealthy 3 of 102 days19801981: Good 238 of 300 days1981: Moderate 35 of 300 days1981: Unhealthy for Sensitive Groups 15 of 300 days1981: Unhealthy 10 of 300 days1981: Very Unhealthy 2 of 300 days1982: Good 240 of 321 days1982: Moderate 44 of 321 days1982: Unhealthy for Sensitive Groups 21 of 321 days1982: Unhealthy 15 of 321 days1982: Very Unhealthy 1 of 321 days19821983: Good 205 of 281 days1983: Moderate 30 of 281 days1983: Unhealthy for Sensitive Groups 18 of 281 days1983: Unhealthy 21 of 281 days1983: Very Unhealthy 7 of 281 days1984: Good 249 of 310 days1984: Moderate 32 of 310 days1984: Unhealthy for Sensitive Groups 21 of 310 days1984: Unhealthy 6 of 310 days1984: Very Unhealthy 2 of 310 days19841985: Good 91 of 107 days1985: Moderate 7 of 107 days1985: Unhealthy for Sensitive Groups 6 of 107 days1985: Unhealthy 3 of 107 days2014: Good 76 of 275 days2014: Moderate 199 of 275 days20142015: Good 231 of 365 days2015: Moderate 134 of 365 days2016: Good 194 of 366 days2016: Moderate 172 of 366 days20162017: Good 234 of 365 days2017: Moderate 131 of 365 days2018: Good 205 of 365 days2018: Moderate 160 of 365 days20182019: Good 267 of 365 days2019: Moderate 98 of 365 days2020: Good 297 of 364 days2020: Moderate 67 of 364 days20202021: Good 284 of 365 days2021: Moderate 81 of 365 days2022: Good 290 of 365 days2022: Moderate 75 of 365 days20222023: Good 268 of 365 days2023: Moderate 93 of 365 days2023: Unhealthy for Sensitive Groups 1 of 365 days2023: Unhealthy 3 of 365 days2024: Good 307 of 366 days2024: Moderate 59 of 366 days20242025: Good 293 of 365 days2025: Moderate 72 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 year0501001501980: 90th percentile AQI 711981: 90th percentile AQI 971982: 90th percentile AQI 1051983: 90th percentile AQI 1471984: 90th percentile AQI 971985: 90th percentile AQI 872014: 90th percentile AQI 672015: 90th percentile AQI 652016: 90th percentile AQI 612017: 90th percentile AQI 582018: 90th percentile AQI 612019: 90th percentile AQI 582020: 90th percentile AQI 542021: 90th percentile AQI 552022: 90th percentile AQI 542023: 90th percentile AQI 592024: 90th percentile AQI 542025: 90th percentile AQI 541980: Median AQI 271981: Median AQI 321982: Median AQI 371983: Median AQI 331984: Median AQI 311985: Median AQI 352014: Median AQI 552015: Median AQI 412016: Median AQI 482017: Median AQI 422018: Median AQI 472019: Median AQI 392020: Median AQI 372021: Median AQI 362022: Median AQI 372023: Median AQI 382024: Median AQI 322025: Median AQI 331980198219842014201620182020202220242025
  • 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
Fine particles (PM2.5)29280%
Nitrogen dioxide (NO₂)7119%
Carbon monoxide (CO)21%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365293720000335478PM2.5
2024366307590000325475PM2.5
20233652689313003859188PM2.5
2022365290750000375470PM2.5
2021365284810000365583PM2.5
2020364297670000375471PM2.5
2019365267980000395881PM2.5
20183652051600000476178PM2.5
20173652341310000425876PM2.5
20163661941720000486187PM2.5
20153652311340000416593PM2.5
2014275761990000556782PM2.5
198510791763003587164Ozone
198431024932216203197203Ozone
19832812053018217033147222Ozone
19823212404421151037105202Ozone
1981300238351510203297209Ozone
198010288653002771185Ozone

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