Delhi Government's recent mandate to ban refuelling for end-of-life vehicles has brought one big question back into focus: why are old vehicles considered such a massive threat to air quality? For years, experts have said that older cars, bikes, and commercial vehicles are among the biggest contributors to the toxic air we breathe in India's cities, but what exactly makes them so polluting? Let's break it down in simple terms. Wear And Tear Makes Engines Emit More PollutionThe single biggest reason old vehicles pollute more is simple: engines, exhaust systems and other mechanical parts naturally wear out with age. Over time, piston rings, valves and seals inside the engine become less efficient, causing incomplete combustion of fuel. When fuel doesn't burn fully, it releases more harmful gases like carbon monoxide (CO) and unburned hydrocarbons. These pollutants not only damage the environment but can also directly affect human health by triggering respiratory diseases. Old Vehicles Run On Outdated Emission TechnologyModern vehicles are built to stricter emission norms than older ones. For instance, cars made after 2020 in India must comply with Bharat Stage VI (BS6) standards, which are much cleaner than the older BS II, III, or IV norms. These newer vehicles have advanced catalytic converters, fuel injection systems, and onboard sensors that limit harmful emissions like nitrogen oxides and particulate matter (PM). Older vehicles, on the other hand, were designed under looser standards and lack the advanced filters and sensors that trap or reduce pollutants. Also Read: What To Do With Your End-of-Life Vehicle After Delhi's Fuel Ban Bad Maintenance Makes An Engine Produce More PollutionThe pollution problem with old vehicles gets even worse when maintenance is ignored. Many older cars or two-wheelers skip regular servicing, oil changes, or filter replacements, partly because owners don't want to spend much on a vehicle that's already at the end of its life. A clogged air filter, worn spark plug or dirty fuel injector can make an old engine burn even dirtier. Leaking fuel lines and oil seals can also cause old engines to drip fluids onto roads, contributing to both air and soil pollution. In winter, when air quality is already at its worst, the thick smoke from poorly maintained old diesel engines makes smog conditions in cities like Delhi even more severe. Are Old Diesel Cars Worse Than Petrol Ones?Diesel vehicles, especially older ones, are major culprits. Older diesel engines were built for durability, not clean emissions. They emit large amounts of tiny particulate matter, microscopic soot particles that hang in the air and can go deep into people's lungs. Modern diesel engines do have diesel particulate filters (DPFs) that trap soot, but older ones don't. That's why Delhi specifically bans diesel vehicles older than 10 years, while petrol vehicles get a 15-year life.