Project Overview
The Alaska Department of Environmental Conservation’s (DEC) Air Monitoring and Quality Assurance program began deploying low-cost air quality sensors in communities throughout Alaska in 2023. This has allowed DEC to provide real-time air quality data to the public in more than just the communities with regulatory grade air monitoring. While the data collected from these low-cost air quality sensors does not meet rigorous regulatory requirements and should not be compared to regulatory instruments or health-based standards, the data collected by the sensors are useful for tracking real-time conditions and displaying air quality trends.
DEC currently utilizes QuantAQ Modulair sensors that measure carbon monoxide (CO), ozone (O3), nitrogen oxide (NO), nitrogen dioxide (NO2), particulate matter (PM2.5 and PM10), temperature in degrees Celsius (°C), and relative humidity (RH). Data is collected over a minute-long period and then processed into hourly and daily averages.
Sensor Overview and Results
A sensor was installed in Tok at 1314 Alaska Hwy. Tok, AK 99780 on December 2, 2024.
This data report covers air quality in Tok in Winter 2025-2026 from October 1, 2025 to March 31, 2026.
Tok’s ambient air quality for the Winter 2025-2026 season had:
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156 days in the Good air quality index (AQI) category
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7 days in the Moderate AQI
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1 days in the Unhealthy for Sensitive Groups AQI
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5 days in the Unhealthy AQI
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7 days in the Very Unhealthy AQI
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1 days in the Hazardous AQI
Sensor Performance
Tok's PM2.5 ambient air quality for the Winter 2025-2026 season fell mostly in the Good range of the Air Quality Index (AQI; more information about AQI is provided in Resources). The most severe events of the season concentrated in several distinct multi-day cold-snap windows: mid-December, the first week of January, and again in late February, with sustained Hazardous-range conditions developing during prolonged overnight stagnation. Interior Alaska experienced one of its coldest winters on record this season, with extreme temperature inversions trapping emissions near ground level during prolonged deep-cold periods. Elevated readings concentrated in evening and overnight hours and partially cleared during midday, with December producing the highest concentrations of the season.
Hourly PM2.5 Air Quality Index (AQI) for Winter 2025-2026
Median PM2.5 Concentrations for Winter 2025-2026
Summary Statistics of Air Pollutants
| Statistic | 1-hour PM2.5 | 24-hour PM2.5 | 1-hour PM10* | 24-hour PM10* | O3 | NO2 | NO | CO |
|---|---|---|---|---|---|---|---|---|
| Units | µg/m3 | µg/m3 | µg/m3 | µg/m3 | ppb | ppb | ppb | ppm |
| Minimum | 0.1 | 0.2 | 0.1 | 0.4 | -1 | 3.23 | 1.55 | 0.2 |
| Mean | 24.4 | 19.5 | 13.6 | 6.8 | 12.52 | 18.28 | 6.54 | 0.28 |
| 1st Max | 999.3 | 499.2 | 986.8 | 40.6 | 44.6 | 36.65 | 53.43 | 1 |
| 2nd Max | 998.5 | 499.2 | 977.1 | 39.4 | 44.2 | 36.18 | 53.23 | 0.9 |
Data Disclaimers
These statistics are based on preliminary data readings and are intended to provide a brief overview of sensor activity. Finalized data may be obtained upon request and through our annual statistical reports. Data from the community sensor network is non-regulatory and not comparable to the EPA’s National Ambient Air Quality Standards (NAAQS).
*PM10 particle sensors can be influenced by periods of high humidity, including fog and ice fog, due to hygroscopic interference. Essentially water particles are counted as PM10, creating false maximum values that do not necessarily pose health risks. DEC currently filters out PM10 readings that exceed 1000 µg/m3, though is working on methods to better filter out data affected by fog and ice fog.
Gaseous readings can occasionally show low negative values due to environmental factors such as low relative humidity or extreme temperature fluctuations, but can also be a sign of aging sensor technology. Negative trends are corrected through calibrations and corrections.
Community Partner
The sensor is located at and hosted by the Tok Community Library Association.
Resources
Data Access
To access historical data for your community’s sensor, please email a request to AMQA-Data-Request@alaska.gov. Data will be provided in Excel or .csv format.
Questions or Comments?
Please contact us!
Isaac Van Flein (Fairbanks): 907-451-2253 / Isaac.VanFlein@alaska.gov
Ayla Crosby (Anchorage): 907-269-7750 / Ayla.Crosby@alaska.gov
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