Indoor vs Outdoor Air Quality Comparison Tool
Compare indoor and outdoor air quality by entering pollutant concentrations. The tool calculates AQI values, identifies dominant pollutants, and provides health recommendations.
Outdoor Air Pollutants
Indoor Air Pollutants
Formulas Used
US EPA AQI Linear Interpolation (40 CFR Part 58, Appendix G):
AQI = ((AQIHi − AQILo) / (CHi − CLo)) × (C − CLo) + AQILo
Where C is the measured concentration, and CHi/CLo are the breakpoint concentrations bracketing C.
Indoor/Outdoor (I/O) PM2.5 Ratio:
I/O Ratio = Cindoor PM2.5 / Coutdoor PM2.5
Ratio > 1.5 indicates significant indoor sources; ratio < 0.5 indicates effective filtration.
CO₂ Score (ASHRAE 62.1 / RESET Air Standard):
Score = max(0, 100 − ((CO₂ − 400) / (2500 − 400)) × 100)
Indoor Wellness Score (Composite, weighted):
Score = (PM2.5_inverted × 0.30 + CO₂_score × 0.25 + VOC_score × 0.25 + Humidity_score × 0.20) / Σweights
Assumptions & References
- AQI calculations follow US EPA 40 CFR Part 58, Appendix G breakpoints (PM2.5 updated to 2024 NAAQS: 9.0 µg/m³ annual standard).
- Outdoor AQI is the maximum across all entered pollutants (EPA reporting convention).
- PM2.5 and PM10 use 24-hour average breakpoints; O₃ uses 8-hour; NO₂ and SO₂ use 1-hour; CO uses 8-hour.
- CO₂ thresholds: <800 ppm = good, 800–1000 ppm = acceptable, >1000 ppm = poor per ASHRAE 62.1-2022.
- VOC thresholds based on WHO Indoor Air Quality Guidelines and RESET Air Standard v2.0.
- Relative humidity comfort range 30–60% per ASHRAE Standard 55-2020.
- I/O ratio > 1.5 suggests indoor sources; < 0.5 suggests effective filtration (EPA Indoor Air Quality guidance).
- Indoor wellness score is a composite index for informational purposes only and is not an official standard.
- This tool does not replace professional air quality monitoring or certified laboratory analysis.