Evidence-based reference
Air Quality Reference Library
Clear, sourced explanations of the measurements, pollutants and standards behind the live air-quality information on AQI.news.
AQI fundamentals
What is AQI?AQI converts pollutant measurements into a color-coded health scale. Learn what the number means, how it is calculated, and why AQI systems differ.AQI scaleUnderstand the US AQI scale from Good to Hazardous, including category ranges, colors, health meaning and practical precautions.PM2.5 vs PM10Compare PM2.5 and PM10 by particle size, sources, health relevance, guideline values and what each reading means.
Air-quality tools
Pollutants
PM2.5Learn what PM2.5 is, where fine particles come from, how they affect health, and the WHO guideline values for annual and daily exposure.PM10Learn what PM10 is, how it differs from PM2.5, common dust and combustion sources, health effects, and WHO guideline values.Ground-level ozoneUnderstand how ground-level ozone forms, why it differs from the protective ozone layer, its health effects and WHO guideline values.Nitrogen dioxide (NO₂)Learn where nitrogen dioxide comes from, how it affects breathing, how it contributes to ozone and particles, and how NO₂ is used in AQI.Sulfur dioxide (SO₂)Understand sulfur dioxide sources, respiratory effects, particle formation and how SO₂ readings relate to air-quality indexes.Carbon monoxide (CO)Learn why carbon monoxide is dangerous, common indoor and outdoor sources, warning symptoms and how CO is represented in AQI.
Standards and guidelines
WHO air quality guidelinesReference the WHO 2021 guideline levels for PM2.5, PM10, ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide.India air quality standardsUnderstand India’s National Ambient Air Quality Standards and CPCB AQI categories for PM2.5, PM10, ozone, gases and health communication.
Occupational dust and fumes
Construction dustA practical reference to construction dust sources, silica risks, wet methods, local exhaust and respiratory-protection limits.Cement dustLearn how cement dust affects eyes, skin and breathing, how silica can change the risk, and which controls reduce exposure.Textile dustUnderstand cotton and textile dust exposure, byssinosis, endotoxin concerns, ventilation and workplace respiratory protection.Mining dustLearn about respirable coal, silica and mineral dust, black lung and silicosis, and the controls used in mines and tunnels.Welding fumesUnderstand what welding fumes contain, how metal and process change the risk, and why local exhaust is central to exposure control.Silica dustA sourced guide to respirable crystalline silica, silicosis, lung cancer risk, high-dust tasks and effective engineering controls.
Respirator guides
N95 respiratorsLearn what N95 means, which particles it can filter, why fit matters, and where an N95 does not provide protection.N99 respiratorsUnderstand the N99 rating, its filtration difference from N95, oil limitation, fit requirements and breathing-resistance tradeoffs.FFP2 respiratorsLearn what the European FFP2 class means, how it differs from N95, why certification and fit matter, and what it cannot filter.FFP3 respiratorsUnderstand the European FFP3 class, when higher particle protection may be selected, and the fit and hazard limits that still apply.P100 respiratorsLearn what P100 means, its 99.97% minimum test efficiency, oil resistance, common formats and important limitations.Reusable respiratorsA guide to elastomeric half- and full-face respirators, particle filters, chemical cartridges, fit testing and maintenance.