~90%
Americans spend about 90% of their time indoors, where air can be 2-5x more polluted than outdoors.
Indoor Air: A National Imperative
Indoor Air Quality (IAQ) profoundly impacts public health, productivity, and well-being. Understanding and improving the air we breathe inside is critical for a healthier nation.
Outdoor Air's Influence on Indoor Air Quality (IAQ)
While this report focuses on indoor air, it's crucial to recognize that outdoor air quality significantly impacts indoor environments. Pollutants from outdoors, such as ozone and particulate matter from traffic, industry, and wildfires, infiltrate our buildings. The American Lung Association's 2025 "State of the Air" report indicates approximately 156 million people (46% of the U.S. population) reside in areas with unhealthy outdoor air, a major concern for indoor infiltration.
Outdoor Pollutants Affecting Indoor Air (2021-2023 Data)
Millions are exposed to outdoor pollutants that can seep indoors. Data from ALA's 2025 Report. [Table 1]
+24.6 Million
Increase in people in areas with unhealthy outdoor ozone (can react indoors) vs. prior ALA report. [Table 1]
Only 2 Cities
Cleanest outdoor air (Bangor, ME & San Juan, PR) means less infiltration risk for those areas.
Worsening outdoor particle pollution in various regions due to events like wildfire smoke transport directly translates to higher risks for indoor air quality.
Wildfires & Extreme Heat: Impact on US Indoor Air Quality
Wildfires and extreme heat, intensified by climate change, are major threats to indoor air quality. Wildfire smoke readily infiltrates buildings, and heat can increase off-gassing from indoor materials.
>86M
People exposed to outdoor PM2.5 from Canadian wildfires (June 2023), much of which entered homes & buildings.
Wildfire Smoke's Indoor Intrusion
Wildfire smoke is a primary source of indoor PM2.5 during smoke events, often making indoor air as hazardous as outdoor air without proper filtration.
Illustrative: Wildfire smoke can contribute up to 50% of ambient PM2.5, which then infiltrates indoors.
This highlights the need for robust indoor air protection strategies during such events, including high-efficiency filtration and creating clean air rooms.
The Health Burden of Indoor Air Pollutants: 2025 US Data
While outdoor air pollution is a known risk, indoor air pollutants contribute significantly to the overall health burden. Many pollutants are generated indoors or become concentrated within enclosed spaces.
Key Health Impacts Linked to IAQ
- 🌬️Respiratory Diseases: Asthma triggers, COPD, allergies, infections from mold, dust mites, VOCs, PM2.5.
- ❤️Cardiovascular Diseases: Indoor PM2.5 (e.g., from cooking, smoking) linked to heart issues.
- 🦀Cancer: Radon (lung cancer), formaldehyde, benzene from indoor sources.
- 🧠Neurological Impacts: VOCs, poor ventilation ($CO_2$) linked to cognitive decline, headaches.
- 👶Developmental Effects: Exposure to certain indoor pollutants can impact child development.
Indoor Air Disparities
Lower-income households and communities of color often experience poorer IAQ due to housing conditions, proximity to outdoor pollution, and fewer resources for mitigation.
Vulnerable groups (children, elderly, those with chronic illness) are especially susceptible to indoor pollutants.
US Indoor Air Quality (IAQ) 2025: The Unseen Threat Within Buildings
>100x
Indoor pollutant concentrations can sometimes be over 100 times higher than typical outdoor levels. [1, 30]
With Americans spending ~90% of their time indoors, IAQ is critical. Pollutants infiltrate from outdoors (e.g., wildfire smoke) and are generated indoors (cooking, cleaning products, building materials).
Common Indoor Pollutants & Sources
| Pollutant | Common Indoor Sources |
|---|---|
| Particulate Matter (PM2.5/PM10) | Cooking, smoking, candles, dust, pet dander, outdoor infiltration. |
| VOCs (e.g., Formaldehyde, Benzene) | Paints, cleaning supplies, furniture, air fresheners, gas stoves. |
| Carbon Monoxide (CO) | Malfunctioning fuel-burning appliances (furnaces, gas stoves), attached garages. |
| Nitrogen Dioxide (NO2) | Gas stoves/ovens, unvented gas heaters. |
| Radon | Seepage from soil and rock. |
| Mold & Biological Agents | Damp areas, leaks, high humidity. |
Source: Adapted from various EPA, CDC, and research reports.
2025 IAQ Report: Homes, Schools, & Office Indoor Air Quality
IAQ challenges and solutions differ across homes, schools, and offices, where we spend most of our indoor time.
🏡 Homes
Cooking is a major source of indoor PM2.5 (peaks >150 µg/m³ [34]). Gas stoves release NO2 and benzene. Housing disparities (multi-family, low-income) often mean higher exposure and fewer resources for mitigation.
🏫 Schools
~50% of K-12 schools lack IAQ management plans. Poor IAQ harms student health and cognitive function (good IAQ can significantly boost scores). CDC recommends ≥5 Air Changes per Hour (ACH) & MERV-13 filters. An "IAQ equity gap" exists for underserved schools.
Good IAQ boosts cognitive function.
🏢 Offices
Poor IAQ impacts productivity and health. COVID-19 and wildfires heightened IAQ awareness. MERV-13+ filtration and good ventilation (e.g., 5 ACH) are key. IAQ is now an ESG consideration.
Health Toll & Economics of Poor Indoor Air Quality
Contaminated indoor air causes short-term irritations (eyes, nose, throat, headaches) and long-term diseases (respiratory, heart, cancer). Sick Building Syndrome is often linked to poor IAQ.
Key Indoor Pollutant Health Effects
- PM2.5: Respiratory & cardiovascular problems.
- VOCs (Formaldehyde, Benzene): Irritation, organ damage, cancer.
- CO: Flu-like symptoms, confusion, potentially fatal.
- NO2 (from gas stoves): Asthma development, respiratory infections.
- Radon: Second leading cause of lung cancer.
- Mold: Allergic reactions, asthma attacks.
Economic Impacts of Poor IAQ
Poor IAQ (high CO2, VOCs, PM2.5) is linked to declines in cognitive function and productivity in offices and schools. This leads to significant economic drain from:
- Reduced productivity & absenteeism.
- Increased healthcare costs.
- Higher building energy/maintenance costs (clogged filters).
Investing in IAQ is an economic strategy, not just a health measure.
Managing Indoor Air Quality 2025: Solutions & Evolving Tech
IAQ management is transforming due to awareness, technology, and science. Key drivers include government regulations (though limited for IAQ) and consumer demand.
US IAQ Market Growth
The U.S. Indoor Air Quality Market is projected to grow, reflecting increased concern and investment.
🌬️ Air Purification Tech:
HEPA filters, MERV-13+, activated carbon. Nanotechnology emerging (e.g., Kronos Model 8 FDA cleared July 2024).
📡 IAQ Sensing & Monitoring:
Precise, compact sensors (LCS), IoT, AI/ML for real-time smart control. Challenges in accuracy and data interpretation.
💨 Ventilation Strategies:
Emphasis on ≥5 ACH (CDC May 2023 guidance). ASHRAE standards (62.1, Guideline 44-2024 for smoke).
Key IAQ Improvement Recommendations (Simplified)
Adapted from various EPA, CDC, ALA, ASHRAE guidelines.
Policy & Future Outlook for Indoor Air Quality
Top 5
EPA's Science Advisory Board consistently ranks IAQ among the top five environmental risks to public health.
Governance of IAQ needs cohesive strategies. A key federal development is H.R. 9131, the "Indoor Air Quality and Healthy Schools Act of 2024", aiming for a national program to reduce indoor air threats.
Federal agencies (EPA, CDC, CPSC) play roles, but comprehensive federal IAQ regulation for most buildings is lacking. State/local governments often lead. Much IAQ policy is "crisis-driven" (COVID-19, wildfires).
Unified Vision for Healthy Indoor Air: A 2025 Call to Action
The state of US indoor air quality is a critical challenge, directly impacting health, well-being, and productivity. Vulnerable populations bear a disproportionate burden. Achieving healthy indoor air for all requires a multi-faceted, collaborative commitment.
Key actions are needed from:
- Policymakers (stronger IAQ standards, funding for schools & vulnerable housing)
- Industry (low-emitting products, advanced IAQ tech)
- Research Community (advancing IAQ science, effective solutions)
- Healthcare Professionals (IAQ education, patient advocacy)
- Educators & School Administrators (prioritizing school IAQ actively)
- Building Owners & Managers (implementing IAQ best practices)
- Communities & Individuals (IAQ awareness, personal action, advocacy)
Healthy indoor air is fundamental. A unified vision and concerted action can create healthier indoor environments for everyone.