Air Quality — US Air Quality Index (US AQI)

Air Quality — US Air Quality Index (US AQI)

Overview

The Air Quality — US Air Quality Index (US AQI) indicator shows the daily mean air quality index calculated according to the United States Environmental Protection Agency (EPA) methodology. The US AQI converts concentrations of six key pollutants — PM2.5, PM10, O₃ (ozone), CO (carbon monoxide), SO₂ (sulphur dioxide), and NO₂ (nitrogen dioxide) — into a unified scale from 0 to 500. The index value is determined by the pollutant with the highest sub-index on any given day.

This is a sub-type of the parent Air Quality KPI. It appears as a selectable variable within the Air Quality line chart on the Risks > Pollution tab. The US AQI is the most widely used international standard for communicating air quality to the public and enables direct comparison with US regulatory thresholds.

The EPA scale defines six health categories:

Calculation Methodology

Data come from the Open-Meteo Air Quality API, which is based on the Copernicus Atmosphere Monitoring Service (CAMS) atmospheric composition model. The variable retrieved is the composite US AQI index.

Processing steps:

1. Hourly retrieval — hourly US AQI values are fetched from the Open-Meteo Air Quality API for the site coordinates
2. Daily aggregation — for each day, the mean of the hourly values is calculated
3. Spatial interpolation — values are interpolated to the exact site position from the CAMS grid

The US AQI composite value is determined by the sub-pollutant with the highest individual AQI on any given hour, following the EPA breakpoint methodology.

Unit: dimensionless (EPA 0–500 scale).

Data Sources

What You See on the Platform

Risks > Pollution > "AQI USA" (line chart)

Line chart. A time-series line chart showing the daily mean US AQI value over the selected period, displayed within the Air Quality chart card on the Pollution tab.

Purpose: To answer the question "What is the air quality trend at this site according to the US EPA standard?" — enabling users to track pollution episodes, seasonal patterns, and long-term air quality trends.

Description: The chart card has a header row containing the title "Air Quality" with a Topic E2 badge and a pollution icon, plus a variable selector dropdown. The user selects "AQI USA" from the dropdown to display this specific variable. The chart shows a time-series line with the daily mean US AQI on the Y-axis and time on the X-axis. A resolution toggle allows switching between daily and hourly views. Threshold reference lines for PM10 and PM2.5 can be displayed when those pollutants are selected but do not apply to the composite AQI view.

How it's calculated: Each point on the line represents the daily mean of the hourly US AQI composite values retrieved from the Open-Meteo Air Quality API (CAMS model). The composite value is determined by the sub-pollutant with the highest index at each hour. No letter grade (A–E) is assigned; the raw AQI value is displayed directly.

Legend: The chart line color follows the 5-band platform quality scale mapped to the AQI range. The AQI categories and their health implications are:

Interpretation example:

If the chart shows a daily mean US AQI of 72, the air quality is in the "Moderate" category — acceptable for most people but potentially concerning for individuals with pre-existing respiratory conditions. A sustained period with values above 100 indicates recurring unhealthy episodes for sensitive groups, suggesting the site is exposed to significant pollution sources such as traffic, industry, or biomass burning.

Highlights > "Air quality" (highlights card)

Highlights card. A summary card in the highlights section of the Overview page showing the current air quality status.

Purpose: To provide a quick glance at the site's air quality conditions without navigating to the detailed Risks section.

Description: The card displays the label "Air quality" with an info icon that opens a tooltip explaining the AQI metric. The card shows the current air quality value or status derived from the parent Air Quality KPI, which includes the US AQI as one of its selectable sub-variables.

How it's calculated: The value displayed reflects the parent Air Quality KPI's overall assessment. The US AQI is one of the available variables contributing to this assessment.

Interpretation example:

If the highlights card shows a "Moderate" status with a green/yellow indicator, the site's air quality is generally acceptable but monitoring the detailed trend on the Risks > Pollution tab is recommended to identify any recurring pollution spikes.

Assessment > Sidebar > E2 Pollution > "Air quality" (assessment sidebar row)

Assessment sidebar row. A row in the Assessment sidebar under the E2 Pollution topic showing the Air Quality grade.

Purpose: To show where air quality ranks within the overall site risk assessment.

Description: The sidebar row displays "Air quality" with an associated quality grade. It appears under the E2 Pollution section alongside other pollution-related KPIs. Clicking the row navigates to the detailed Air Quality chart in the Risks > Pollution tab.

How it's calculated: The grade is derived from the parent Air Quality KPI's assessment logic. The US AQI is one of the available sub-variables within the Air Quality family.

Interpretation example:

If the sidebar row shows "Air quality" with an orange indicator, the site's air quality has been flagged as a risk factor that warrants closer investigation in the detailed pollution charts.

Bibliography

1. U.S. EPA (2024). "Technical Assistance Document for the Reporting of Daily Air Quality — the Air Quality Index (AQI)". EPA-454/B-24-002.

2. AirNow.gov. "AQI Basics". U.S. Environmental Protection Agency. Available at: https://www.airnow.gov/aqi/aqi-basics/

3. Open-Meteo (2024). "Air Quality API Documentation". Available at: https://open-meteo.com/en/docs/air-quality-api

4. Copernicus Atmosphere Monitoring Service (CAMS). "European air quality reanalysis". ECMWF.

5. WHO (2021). "WHO Global Air Quality Guidelines". World Health Organization, Geneva.

Detailed Methodology

See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.

Technical Notes

• The US AQI is a sub-type of the parent Air Quality KPI. All air quality sub-variables (PM2.5, PM10, O₃, NO₂, SO₂, CO, European AQI, US AQI, and others) share the same chart interface with a variable selector dropdown.
• Data are available from 2013 to present. The CAMS model provides global coverage at approximately 11 km spatial resolution over Europe; resolution is coarser in other regions.
• The US AQI composite value is determined by the "worst" (highest) sub-pollutant AQI at each time step. This means the composite AQI can be driven by different pollutants on different days depending on local conditions.
• Values above 300 (Hazardous) are extremely rare in European locations and are more commonly observed during severe wildfire, industrial, or dust events.
• The AQI scale used here follows the EPA 2024 revised breakpoints. Note that the EPA breakpoints differ from the European AQI (EAQI) scale, which uses different pollutant thresholds and category definitions.
• The 5-band colour scale on the platform maps the 6 EPA categories into 5 colour bands for visual consistency with other platform KPIs.
• Hourly and daily resolution views are available via the resolution toggle on the chart.
• This KPI is related to individual pollutant sub-variables (PM2.5, PM10, O₃, NO₂, SO₂, CO) which can each be selected independently from the same Air Quality chart dropdown.