Below is a clear, non-technical breakdown of how Delhi’s air gets choked and why it becomes so harmful — plus what actually helps.

1) The sources (what’s being burned/emitted)

Crop-residue (stubble) burning in Punjab/Haryana — seasonal plumes blow into Delhi and add huge amounts of fine smoke. NDTV Profit
Road traffic — exhaust (PM, NO₂), tire & brake wear, and fuel evaporation from millions of vehicles create a constant background of pollution. The Times of India
Construction, demolition and road dust — coarse particles (PM10) and re-suspended dust. NDTV Profit
Industry, power plants, diesel generators — emit SO₂, NOx, particulates and volatile organic compounds (VOCs). The Times of India
Open burning and household sources — garbage burning, biomass used in some households.
Festivals & fireworks — short but intense spikes of PM and metals. NDTV Profit

2) The chemistry that makes air “toxic”

Tiny particles (PM2.5) and gases undergo chemical reactions in sunlight or with ammonia from agriculture to form secondary aerosols — small, chemically complex particles that can be more harmful than the original smoke. These include organic aerosols and ammonium salts. sciencedirect.com+1
Gases like NOx + VOCs form ozone and other reactive pollutants that irritate airways and damage cardiovascular system. The Times of India

In late autumn / winter, lower temperatures, weak winds and temperature inversions (warm air above cold air) create a shallow boundary layer so pollutants accumulate instead of dispersing. That’s why the same emissions produce far worse AQI in winter than in summer. NDTV Profit

PM2.5 is small enough to reach deep into lungs and enter the bloodstream. Short-term exposure increases asthma attacks, hospital visits, heart attacks; long-term exposure raises risk of chronic lung disease, stroke and premature death. Studies show major impacts on children, pregnant women and the elderly. SpringerLink+1

Delhi-NCR uses the Graded Response Action Plan (GRAP) — stage-wise measures (restrict construction, ban heavy diesel entry, curb burning, parking/traffic measures, odd-even or similar limits when severe) that kick in as AQI crosses thresholds. These work short-term but don’t eliminate the root causes. caqm.nic.in+1

Useful for residents:

Avoid outdoor exertion on high-AQI days; use reliable AQI apps (CPCB/aqicn/aqi.in) and plan accordingly. AQI+1
N95 / KN95 masks reduce inhaled particles — not perfect but helpful when pollution is high.
Indoor air: keep windows closed on peak days; use HEPA air purifiers if possible and reduce indoor sources (no incense/garbage burning).
Medical: people with heart/lung disease, children, pregnant women should follow clinicians’ advice and seek care for worsening symptoms. SpringerLink

For lasting improvement (policy / city scale):

Rapid action on vehicle emissions (tighter inspection, cleaner fuels, electrification + public transport). The Times of India
Stopping stubble burning via incentives/alternatives for farmers, mechanised residue management and stricter enforcement in source states. NDTV Profit
Dust control (paved roads, construction covers), stricter industrial emission limits, and reducing diesel generator use.
Regional coordination across states (Delhi, Haryana, Punjab, UP, Rajasthan) because weather carries pollution across borders. caqm.nic.in

AQI categories: “Good” (0–50) → “Moderate” (51–100) → “Poor/Unhealthy/Very Poor/Severe/Hazardous” (higher ranges). PM2.5 concentrations above 60–100 µg/m³ are commonly linked to acute health effects; in Delhi those daily values frequently exceed those levels in winter spikes. Real-time monitors show city AQI often in the “poor” to “severe” range during worst periods. AQI+1