The simple answer to this question is: Yes, pollution in the nation’s capital will drop as there will be less cars on the road.
On the morning of 28th December, there was a PM2.5 (the most harmful type of particle to human health) concentration of 266.1 µg/m³. The EU safety guidelines states that exposure to more than 25 µg/m³ of PM2.5 over a prolonged period of time. The concentration in Delhi rarely dips below 200 µg/m³ during the winter.
A big contributor to this pollution are diesel engines. On 22nd August, Delhi implemented a ‘car ban’ between a Red Fort and India Gate. Although it was widely derided as the ban was held on a holiday when there would have been less cars anyway, according to official measurements, the CSE found that particulate matter reduced by upto 60% of the average rates.
There are nearly 85 lakh (8.5M) private vehicles on the road in New Delhi as at 31st March. Of these, 26.5 lakh (2.65M) are cars and the rest is nearly all bikes and scooters.
In addition to the private vehicles there are 3.65 Lakh (365K) commercial vehicles on the road. Commercial vehicles primarily use diesel engines because they are cheaper and better suited at moving heavy loads.
It would be incorrect to assume that there are always 26.5 lakh cars on the road every single day. However, even a conservative estimate would say that there will be between 6 to 10 lakh less vehicles in the capital each day.
That said, alternating number plates to reduce the air pollution levels is always going to be a temporary solution. New Delhi sees around 2 lakh cars being registered every single year. It will only take three or four years for there to be as many cars on the road as there are now even with the alternating number plate scheme.
Additionally, as this is India and the population always finds creative work arounds to Government imposed problems. It probably won’t be long until there is a thriving black market of temporary number plates where you can switch over in the morning to meet the rules. Failing that, the wealthier people will simply buy a new car.
Alternating number plates is a good temporary step to try and bring down Delhi’s poisonous air. However, more long term solutions are needed, some of which are outside Delhi’s control such as the burning of the paddy fields in Haryana.