The AQI Calculator converts PM2.5 concentration (μg/m³) to the Air Quality Index using the EPA's linear interpolation formula. Returns the AQI value, color-coded health category, and sensitive group guidance — used for air quality monitoring, public health alerts, and personal exposure decisions.
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Your air quality sensor reads 35.4 μg/m³ of PM2.5. Is that safe? Should you close the windows, cancel the outdoor workout, or keep an eye on your kids playing outside? Raw concentration numbers are hard to interpret — that is why the EPA AQI system was created. The calculator for PM2.5 AQI converts the raw measurement into the standardized 0–500 scale with instantly meaningful color-coded health guidance.
The AQI is calculated by piecewise linear interpolation between EPA-defined concentration breakpoints:
AQI = [(AQI_Hi − AQI_Lo) / (BP_Hi − BP_Lo)] × (C_p − BP_Lo) + AQI_Lo
where C_p is the truncated PM2.5 concentration (μg/m³, truncated to one decimal place), and BP_Hi/BP_Lo are the breakpoint concentrations bracketing C_p. The 2024 EPA PM2.5 24-hour breakpoints are:
Note: EPA revised the PM2.5 NAAQS in 2024, tightening the annual standard from 12 to 9 μg/m³ and adjusting the AQI breakpoints accordingly. Use this online calculator with your sensor's 24-hour average PM2.5 reading for an accurate AQI result. The multi-pollutant AQI calculator handles all six EPA criteria pollutants.
The six AQI categories with recommended protective actions:
PM2.5 (fine particulate matter with diameter ≤ 2.5 micrometers) is produced by combustion, secondary atmospheric reactions, and — increasingly — wildfire smoke. During major wildfire events in the western US, Australia, and Southeast Asia, PM2.5 AQI can reach 300–500+ in downwind communities hundreds of miles from the fire. Wildfire smoke PM2.5 may carry different toxicological profiles than traffic-generated PM2.5 due to the combustion of biomass, plastics, and building materials, though current AQI health guidance applies across all PM2.5 sources. The particulate matter exposure calculator and air pollution calculators provide complementary air quality assessment tools.
Low-cost consumer air quality sensors (PurpleAir, IQAir, Awair) provide useful real-time local data but require correction factors to align with official EPA reference monitors. PurpleAir sensors using the US EPA correction factor (applied on PurpleAir's map since 2021) show good agreement with federal monitors under typical conditions, but may under- or over-read during wildfire events due to the different optical properties of smoke particles. For decision-making during extreme events, cross-reference consumer sensors with official AirNow.gov data from the nearest regulatory monitor.
The calculator applies standard scientific formulas for EPA Air Quality Index from multiple pollutant concentrations. Input parameters are processed through validated mathematical models, and results are displayed with appropriate precision. All formulas follow established methodologies from leading environmental science organizations.
Review your results in context of established benchmarks and standards. Compare values against regulatory limits, industry averages, or scientific thresholds to assess significance. Use the results to identify improvement opportunities or compliance status.
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Typical air quality index scenario with default parameters.
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Modified parameters for comparison analysis.
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There are several evidence-based strategies to improve your results. Start by focusing on the largest contributing factors identified in your calculation. Small changes in the dominant input parameters often yield the greatest improvements. Consult local environmental agencies for region-specific recommendations and incentive programs.
Air Quality Index is a quantitative measure used in environmental science and ecology. It represents key metrics that help researchers, policymakers, and individuals understand environmental impacts. The specific definition and measurement methodology are established by international scientific organizations and regulatory bodies.
How does this relate to environmental policy involves analyzing relevant parameters using established scientific methodologies. Our calculator applies peer-reviewed formulas and standard emission factors to provide accurate results. The specific approach varies by parameter but follows guidelines from organizations such as the EPA, IPCC, and relevant scientific bodies.
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