Before a route shows an AQI estimate, the air-quality signal has already passed through several steps. It may begin with a small inlet on a monitoring cabinet, a sensor in a station, or a forecast model that estimates conditions where direct observations are limited. The public number that appears later is the last step in a longer chain.
Measurement starts with pollutants
Air pollution is not one substance. Measurement systems track pollutants such as fine particles, coarse particles, ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide. Each pollutant has its own units and behavior. PM2.5 and PM10 are particle measurements. Ozone and nitrogen dioxide describe gases. Weather, sunlight, traffic, industry, fires, and regional transport can all change the picture.
Ground data needs metadata
OpenAQ aggregates public air-quality data from sources across the world. Its API documentation emphasizes that data are shared in physical units rather than as an air quality index, and that near real-time and historical readings carry metadata for context. That metadata can include where a sensor is located, which parameter is measured, and which provider supplied the reading. [1]
The same documentation also makes a boundary clear: OpenAQ does not represent all monitoring data in the world. It contains publicly available data that OpenAQ has discovered or received. Terms and licence context still matter because source providers can carry their own access and attribution conditions. For route planning, that means source coverage, permissions context, and freshness matter as much as the number itself. [2] [3]
Community monitors can add to public data
Public coverage can also grow when community monitors share outdoor readings. AirGradient describes one available path: AirGradient monitor owners can make a monitor public, add location and sensor-context details, and share outdoor air-quality data with OpenAQ. The guide also notes that OpenAQ focuses on outdoor air quality, that monitors should be placed away from very local emission sources, and that provider labeling helps explain the type of sensor behind the reading. [4]
This is a useful example, not an endorsement claim. AirGradient, OpenAQ, and Air Quality Router remain separate organizations and services. The broader lesson is that public air-quality data becomes more useful when measurements include responsible placement, coordinates, provider names, and environment notes that help people interpret what a reading represents.
Forecasts help when observations are limited
CAMS global atmospheric composition forecasts provide modeled atmospheric composition data. The dataset page describes global forecasts produced twice a day, with more than 50 chemical species, seven aerosol types, and meteorological variables. It also describes data assimilation, where current satellite observations are combined with a previous forecast to produce a globally complete estimate at the forecast start time. [5] [6]
Forecasts are useful because real monitoring coverage is uneven. A forecast can provide air-quality context where direct observations are sparse, delayed, or incomplete. It remains a model, so freshness labels, source labels, licence context, and no-endorsement boundaries should stay visible. [7] [8]
Assessment turns concentrations into AQI
Assessment is the interpretation layer. The EPA AQI technical guidance describes pollutant-specific breakpoints and reporting practices that convert concentrations into index values and categories. In AQI reporting, the critical pollutant is the pollutant with the highest AQI value for the reporting period. [9]
This is why two places with different pollutant mixtures can have similar AQI values, and why two places with the same PM2.5 reading may not tell the full story if ozone or another pollutant is driving concern nearby.
Source analysis explains where pollution comes from
Air-quality assessment can also ask where pollution originated. A 2024 Environment International study of Southeast Asia examined source emission contributions to particulate matter and ozone, including local sectors and transboundary air pollution. That kind of analysis sits upstream of daily route planning, but it explains why air pollution can be local on one day and regional on another. [10]
What a route-planning app can responsibly show
A route-planning app can compare estimated AQI, source type, freshness, forecast fallback, distance, and timing. It cannot turn a station or forecast into a personal exposure measurement. The useful product pattern is transparency: show whether the source is recent, forecast, cached, or limited, then keep the recommendation framed as planning guidance.
Sources
- OpenAQ API overview: public air-quality data, physical units, near real-time and historical readings, and metadata context.
- OpenAQ Terms of Use: authorized access and source-use boundary context.
- OpenAQ Licenses: source licence and attribution context.
- AirGradient guide to sharing data with OpenAQ: example pathway for sharing public outdoor monitor data with OpenAQ, with placement, provider-label, and privacy context. No endorsement implied.
- CAMS global atmospheric composition forecasts: forecast variables, update frequency, and data assimilation context.
- CAMS dataset DOI:
10.24381/04a0b097; dataset citation support. - Atmosphere Data Store Terms of Use: licence and service-use boundary context.
- Copernicus copyright and licences: copyright, licence, and no-endorsement boundaries.
- EPA Technical Assistance Document for AQI reporting: concentration-to-index breakpoints and critical pollutant context.
- Environment International Southeast Asia source contribution study: source-emission and transboundary pollution assessment context.
Keep source context beside each route
When comparing routes, Air Quality Router keeps estimated AQI, freshness labels, recent readings, forecast fallback, and route timing together. Download Air Quality Router from the App Store to compare walking and jogging plans with air-quality context in view.
Air Quality Router is an informational planning tool, not medical advice. Personal health decisions belong with qualified care guidance.