Delhi Weather | Dazzling Delhi

On most days, I can run on the treadmill for 10 minutes without feeling breathless. But in the days after Diwali, when the air turns severely polluted, I find myself gasping for air in just 5 minutes. The main reasons for Delhi’s post-Diwali air pollution are stubble burning, vehicular emissions, cold weather, geography, construction activity, and burning crackers. Key solutions include curbing stubble burning, implementing the GRAP (Graded Response Action Plan), and reducing vehicular pollution. Crackers are blamed every year (and rightly so), but they’re only the tip of the iceberg. Some causes of pollution are within our control; others are beyond it. Real Causes of High Pollution Levels in Delhi After Diwali Post-Diwali, pollutant levels in the air rise sharply. A 2024 report by the Centre for Science and Environment (CSE) noted that the concentration of particulate matter 2.5 (PM2.5), which had already been climbing from October 28 to October 31, spiked by 46%. By midnight on October 31, PM2.5 peaked at 603 micrograms per cubic metre (µg/m³), around 13% higher than the Diwali peaks recorded in 2022 (October 24) and 2023 (November 12). Of the 38 air-quality monitoring stations, nine reported PM2.5 concentrations reaching 900 µg/m³ on Diwali night. In stark contrast, the World Health Organization (WHO) recommends a 24-hour average guideline value of just 15 µg/m³. Immediate impacts included visibility dropping below 500 metres, flight operations slowing, and a roughly 20% surge in respiratory complaints among residents. People reported symptoms such as wheezing, coughing, and shortness of breath, among other respiratory problems. During severe episodes, the Delhi government shut schools and advised companies to allow employees to work from home to reduce exposure. The surge in pollution cannot be blamed solely on firecrackers; several other factors are also responsible. 1. Stubble Burning According to an official Delhi government notice, the majority of Delhi’s pollution is attributed to stubble (crop-residue) burning in Punjab and Haryana. The Indian Institute of Tropical Meteorology (IITM) reported that on 1 November 2024, stubble burning accounted for more than 35% of Delhi’s air pollution. The share dipped over the next few days, then rose again to 31% on 13 November 2024. Stubble burning is a common practice used by farmers to clear fields quickly and cheaply for the next sowing season. With the rabi season running from October to December, farmers often burn residue from the previous crop cycle to prepare the fields. India generates about 500 million tonnes (MT) of crop residue annually, of which roughly 100 MT is burnt, mostly in the north-western states closer to Delhi. This contributes to sharp increases in PM2.5, with ambient levels often in the 50–200 µg/m³ range and, during severe episodes, spiking up to about 1,200 µg/m³. 2. Weather and Geography Another driver of Delhi’s high pollution levels is winter weather and local geography. Pollutants get trapped because of a process called temperature inversion. Normally, air temperature decreases with altitude. Warm air near the Earth’s surface rises, carrying pollutants upward where they can disperse. In winter, the ground cools quickly at night. The air just above it also cools, while a layer higher up stays relatively warmer. This creates a warm lid over a cold layer, trapping pollutants near the surface. The mixing height (the depth of air within which pollutants can disperse) drops sharply in winter and is much higher in summer. As a result, pollutants accumulate in this shallow layer, pushing the AQI higher. Delhi’s monsoon typically runs from July to September. In October-November, rainfall is minimal and winds are lighter, so there’s less washout and dispersion of pollutants. Delhi is landlocked, so there’s no sea breeze to flush polluted air. Topography also plays a role: the Himalayas to the north and the Aravalli hills to the southwest act as barriers, slowing the outward movement of polluted air. 3. Vehicular Pollution Vehicular pollution is the single largest contributor to Delhi’s high pollutant levels. The Centre for Science and Environment (CSE) reports that vehicular emissions account for about 51.1% of the city’s pollution. According to the Economic Survey 2023-24, Delhi has 79 lakh registered vehicles, with 6.5 lakh added in 2023-24. Around 1.1 lakh vehicles enter and leave the city each day. The number of cars and two-wheelers grows by roughly 15% annually, and vehicles are responsible for up to 81% of nitrogen oxides (NOx) emissions. As Delhi has expanded into neighbouring areas such as Gurugram and Noida, the per-capita trip rate has risen by 12.3%. 4. Construction Activities Roughly 30% of Delhi’s air pollution is attributed to construction dust and fine particles that become airborne during building and infrastructure work. According to data from the Delhi Pollution Control Committee (DPCC), existing construction-waste processing facilities can handle only about 2,600 tonnes, whereas Delhi generates up to 3,600 tonnes. This capacity gap leaves more debris and dust unmanaged, adding to the city’s particulate load. Common site activities such as excavation, cutting, drilling, material transport, loading and unloading, and mixing concrete and mortar, also contribute substantially to dust emissions. 5. Firecrackers Often cited as the most notorious cause, firecracker burning is a significant short-term driver of severe pollution episodes. Studies indicate that firecracker use can trigger sharp spikes in particulate matter. PM2.5 rises by roughly 100% and PM10 by about 55%, which amplifies an already poor baseline in Delhi’s winter air. Possible Solutions to Reduce Air Pollution Levels in Delhi After Diwali 1. Graded Response Action Plan Each year, as air quality deteriorates in Delhi-NCR, the Commission for Air Quality Management (CAQM) invokes the Graded Response Action Plan (GRAP). The plan has four stages: Stage 1 (Poor; AQI 201-300), Stage 2 (Very Poor; AQI 301-400), Stage 3 (Severe; AQI 401-450), and Stage 4 (Severe+; AQI above 450). Measures are cumulative, i.e., actions under Stage 3 or 4 apply in addition to those in Stages 1 and 2. Stage 1 typically includes proper disposal of construction dust, mechanised road sweeping, and water sprinkling at required sites. As pollution levels rise, additional measures are triggered. For example, a ban on construction and demolition activities, closure of educational institutions and offices (or a shift to online mode), restrictions on entry of inter-state vehicles running on inferior fuel, and implementation of the odd-even road-rationing scheme for private vehicles. 2. Action on Stubble Burning Since we can’t control weather or geography, we should target what we can, i.e., reducing stubble burning. The Indian Council of Agricultural Research (ICAR) has introduced bio-decomposers as a solution. One of these, the Pusa Decomposer, is a mix of microbes that break down tough plant residue. Sprayed on fields, it decomposes stubble within 20-25 days, turning it into useful manure. Instead of burning crop residue, farmers can convert it into soil nourishment. 3. Action on Vehicular Pollution The Delhi government has taken several steps to reduce vehicular emissions. In 2015, the Supreme Court imposed an environmental compensation charge (ECC) on all commercial vehicles entering Delhi, in addition to the regular toll. The government also shifted public transport and autos to CNG, considered cleaner than petrol and diesel. Diesel cars older than 10 years and petrol cars older than 15 years are banned from operating on Delhi-NCR roads. Another well-known measure is the odd-even scheme, introduced during periods of high AQI. Vehicles with odd number plates run on odd dates and those with even plates on even dates. Reports noted a 24% reduction in private cars, 22% in autos, and a 14% increase in buses. Traffic volume fell by 15-20%, and travel time was reduced by 30-50%. However, AQI improvements were only marginal. The government has also pushed cleaner fuels under Bharat Stage VI norms, offered EV incentives to residents, and the Delhi Transport Corporation (DTC) has launched a fleet of electric buses. Going forward, improving bus frequency and network connectivity will be crucial to shift more commuters from private vehicles to public transport.