Delhi, the capital city of India has been in the news ever since WHO declared it world’s most polluted city (summer 2014). Both national and international media, science communities, governments, NGOs and the even public is talking about the pollution in Delhi. Securing the top rank in the polluted cities list is definitely helping Delhi to curb/mitigate its pollution. The pollution problem is not new for Delhi (and entire IGP region). Delhi has been very polluted by any standard for more than 2-3 decades. Government tooks steps such as promoting CNG buses, emission certificate for cars with routine renewal, banning of cars older than 15 years and road side waste burning / leaf burning. But, the rising pollution level in the city has never been a top priority for the govt. and public never demanded a solution to the problem. However, with growing population in the capital city, public participation was crucial to the success of any government initiated policies. Finally, Delhi is getting its long due attention and both govt and public are forced to practice mitigation strategies.
During the first half of January this year, Delhi government undertook the odd-even formula for cars as a pilot project. Since the announcement, it has been in the news every single day. There have been several short studies and claims about the impact of the odd-even formula on the level of pollution in Delhi. The claim ranges anywhere from 18% to 60% reduction in PM2.5 level during those 15 days period. These claims and science behind the pollution level evaluation is all over the place, some of them are too vague to even comment on. Personally, I am in favor of such efforts but its operation can be questioned on many grounds. The first thing I would like to make very clear is that by any formula if you take lakhs of cars off the road, then emission has to be reduced – there should not be any doubt or question about this. But, the bigger question is how much? and is it sufficient to curb the pollution level in the city? There are many more questions that need to be answered before any effective mitigation strategy can be planned and implemented.
Potential sources of pollution in Delhi include power plants, vehicles, waste burning, dust from constructions, roadside dust, industries, residential and industrial power generation by diesel operated generators and transport from surrounding regions. This list is not complete and there are many more unknown and small sources. The transport from surrounding regions is one of the components, which has been completely missing from all of the discussion. The transport can contribute significantly and potentially by itself can raise pollution level high enough to cause health concerns. Transport is very seasonal: in winter Delhi gets tons of pollution (mainly smoke leading to haze) from agricultural waste burning (and other forms of open burning) happening in the upwind regions of Punjab and Haryana. On a given day, if the meteorological conditions are favorable, the smoke itself can enhance pollution level in Delhi many folds. Due to this reason, I strongly feel that the timing of odd-even formula pilot run is a very poor choice. Looking at the current satellite images over India, it can be easily seen that most of the region is blanketed by smoke from the burning happening in the northern India. This makes, the situation very difficult and it becomes an extremely complex problem to assess the impact of odd-even formula on the local pollution levels. Separating contribution from the transport and from the measurements taken on the ground is not any easy task. It can be done by the combination of measurements and modeling studies.
Now moving to summer time (pre-monsoon period), due to favorable wind directions, Delhi receives a large amount of dust originating in the Thar desert and Arabian peninsula. Again, similar to smoke in winter, dust blankets Delhi and the region for many days and enhance the air pollution many folds. Therefore, I am also not very positive about the proposed timing (May-June 2016 – as reported in some news) of the second phase for the odd-even formula.
Both smoke and dust contribute significantly to PM2.5 level in Delhi and it has strong seasonal dependency. Usually, dust particles are large in size (>1 micro meter) whereas smoke particles are fine (<1 micro meter), and this can be easily seen in the ground-based AERONET measurement over Delhi.
Figure showing size distribution on December 17, 2009, and Jun 19, 2009, as retrieved by AERONET near Delhi). Measurements clearly show small particles dominating in the winter (mainly transported smoke and local pollution) whereas large particles dominate in the summer (mainly transported dust.
Many source apportionment studies found that vehicles in Delhi should be contributing about 20-30% (upper range) to total PM2.5. Now considering a total contribution, no one can claim that removing a certain number of cars from the road for the short period of time will reduce PM2.5 by 60% -- this is just absurd.
It is very important to make integrated efforts in research, policy making, and enforcement of regulations as well as educating public and spreading awareness. This task is not a short-term project; government needs to think long term and come up with 5-10 year programs. Forming of a group of experts and outlining short term and long term goals and tasks will move things in the forward direction. Everyone should assist in this effort.
In the next post, I will try to illustrate the complex nature of pollution problem using some satellite and surface-based observations.