What Is the Air Quality in Weld, Colorado?
Weld, Colorado has an Air Quality Grade of D (poor) with a 5-year median AQI of 53. The dominant pollutant is Ground-Level Ozone, and air quality has been worsening over the past decade.
Weld, Colorado Air Quality Snapshot
| Air Quality Grade | D47/100 |
| 5-Year Median AQI | 53 (Moderate) |
| Most Recent Median AQI (2023) | 55 (Moderate) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Worsening (+0.82 AQI/yr) |
| Unhealthy Days (last 5 yr) | 76 |
| National Rank (cleanest = #1) | #978 of 1,020 (96th most polluted percentile) |
| Colorado Rank | #31 of 32 |
What Does the D Grade Mean?
Weld, Colorado earns a D — air quality falls below the U.S. average, with a 5-year median AQI of 53. Residents with asthma, COPD, heart disease, or young children should watch daily AQI forecasts and limit outdoor exertion when alerts go out.
Weld, Colorado's 5-year median AQI of 53 is 12 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Colorado, Weld, Colorado runs more polluted than the state average of 39 — local sources or geography are concentrating pollution above the state's typical reading.
For context within Colorado: Alamosa, Colorado currently holds the state's cleanest grade (A, AQI 14), while Jefferson, Colorado sits at the bottom (D, AQI 47).
What's in Weld, Colorado's Air?
The dominant pollutant in Weld, Colorado is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Ground-Level Ozone | 263 | 72% |
| Fine Particulate Matter (PM2.5) | 102 | 28% |
Is the Air Getting Better or Worse?
Air quality in Weld, Colorado has been getting worse over the past decade, with median AQI climbing by roughly 0.8 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.
In 2014, Weld, Colorado posted a median AQI of 46. By 2023 that figure was 55 — a rise of 9 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Weld, Colorado
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 46 | 239 | 4 | Ozone |
| 2015 | 47 | 224 | 9 | Ozone |
| 2016 | 49 | 201 | 3 | Ozone |
| 2017 | 51 | 173 | 8 | Ozone |
| 2018 | 54 | 138 | 10 | Ozone |
| 2019 | 53 | 152 | 8 | Ozone |
| 2020 | 52 | 166 | 13 | Ozone |
| 2021 | 54 | 156 | 40 | Ozone |
| 2022 | 51 | 170 | 10 | Ozone |
| 2023 | 55 | 146 | 5 | Ozone |
Health Context for Weld, Colorado
Across the past five years, this area has logged 76 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 15 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Treat daily AQI forecasts as essential input. On flagged days, sensitive groups (asthma, COPD, heart disease, pregnancy, young children, older adults) should limit outdoor exertion and keep windows closed. A HEPA air cleaner sized to a bedroom or family room can cut indoor PM2.5 by 80%+ during smoke or pollution events. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
Weld, Colorado has an Air Quality Grade of D (poor) with a 5-year median AQI of 53. The dominant pollutant is Ground-Level Ozone, and air quality has been worsening over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.