How Air Pollution Gets Inside Your Home

The Myth of the Indoor Safe Haven

Many people assume that closing windows keeps pollution out. The reality is more complex. Studies by IIT Delhi and IIT Kanpur show that indoor PM2.5 levels in Indian homes are typically 60–80% of outdoor levels, even with windows closed.

Pathway 1: Infiltration Through Gaps

The biggest pathway is infiltration — air seeping through cracks, gaps around windows and doors, and electrical outlets. Even a well-sealed home exchanges air with the outside several times per hour.

What to do: Use weatherstripping around doors and windows. Apply sealant around window frames. Use door sweeps at the bottom of exterior doors.

Pathway 2: Natural Ventilation

Opening windows and doors for ventilation is essential for removing indoor CO2 and VOCs, but it also lets outdoor pollution in. During high-pollution hours (early morning and evening), this trade-off is particularly problematic.

What to do: Ventilate during low-pollution periods (afternoon, post-monsoon). Use cross-ventilation for shorter, more effective air exchange. Consider a mechanical ventilation system with filters.

Pathway 3: Cooking and Combustion

Indoor sources add to the pollution load. Cooking on gas stoves generates NO2, CO, and PM2.5. Burning incense, candles, or mosquito coils adds PM2.5 directly indoors. In Indian kitchens, the combination of outdoor infiltration and indoor cooking emissions can double indoor PM2.5 levels during meal times.

What to do: Always use a chimney or exhaust fan while cooking. Avoid burning incense or candles indoors. Use electric appliances instead of gas where possible.

Pathway 4: Tracked-In Dust and Particles

You bring outdoor pollution indoors on your shoes, clothes, and skin. Soil, road dust, and settled PM10 particles are carried into the home and become resuspended in the air when disturbed.

What to do: Remove shoes at the entrance. Use high-quality doormats (both outside and inside). Vacuum frequently with a HEPA-filter vacuum.

Pathway 5: HVAC and Air Conditioning

Window AC units and split ACs draw air from outside but typically have only basic mesh filters that catch large dust — not PM2.5. Ducted systems can also accumulate mould and dust inside the ducts.

What to do: Clean AC filters monthly. Use standalone HEPA air purifiers alongside AC. Consider upgrading to ACs with PM2.5 filters.

Pathway 6: Indoor Sources

VOCs from paints, furniture, cleaning products, and air fresheners accumulate indoors. New furniture, especially plywood and MDF, off-gases formaldehyde. Together with outdoor pollution, these create a combined exposure that is often worse than being outside.

What to do: Choose low-VOC paints and furniture. Avoid synthetic air fresheners. Maintain good cross-ventilation after introducing new furniture.

Measuring Indoor Air Quality

Use a PM2.5 monitor to measure actual indoor levels. Many affordable monitors (under ₹10,000) give real-time readings. Place the monitor in the room where you spend the most time — typically the bedroom or living room.

Key Takeaways

• Indoor PM2.5 levels in Indian homes are typically 60–80% of outdoor levels
• Infiltration through gaps is the largest pathway for outdoor pollution
• Cooking and indoor combustion add significantly to indoor pollution
• Remove shoes at the door and use HEPA-filter vacuums
• Use a PM2.5 monitor to understand your actual indoor exposure