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After two days of the Odd-Even policy's success, everyone's eyes are on Monday, 4 January. This will be the first-fledged working day of the Arvind Kejriwal government's 15-day experiment to save Delhi from hazardous air pollution.
Will it be a success? The short answer is that it's hard to say. While most car-driving Delhiites seemed to have followed the rule on the first two days, pollution in the city both fell and rose sharply on those days, confusing experts. And the same repeated on Sunday, when the rule wasn't in place.
As per the Odd-Even policy, on 1 January, only cars whose registration numbers ending with an odd number were permitted to ply. This was in effect from 8 am to 8 pm.
What happened? Let us look at data from the RK Puram monitoring station of the Delhi government's Delhi Pollution Control Committee.
Air pollution dipped from the morning to afternoon.
At RK Puram, for example, the level of PM2.5 (Delhi's main pollutant) fell sharply from 691 micrograms per cubic metre at 8:50 am to 142 by 1:50 pm.
But by the evening it climbed to 329. It continued to rise, and by 8 pm it reached 599, and 636 by 11 pm.
And this was on a day when most establishments were shut, including schools. Seeing how pollution rose by 8 pm, it appears that traffic was a cause. But this only means that Monday will be a colossal failure as offices and schools will be reopening after the long weekend and many Delhiites would have returned after their vacations.
2 January also witnessed a similar swing in pollution, although the levels were lesser.
PM2.5 was about 308 at 8:50 am. After rising briefly it steeply fell to 133 by 2:50 pm.
Like on 1 January, it started climbing by about 5:50 pm till it reached 400 by midnight.
By 4 am on 3 January, the pollutant was at 625.
This may start to look like a trend -- pollution falls after about 9-10 am, and picks up around 7 pm. Optimists may attribute this to the Odd-Even policy. But what's baffling is the same trend played out on Sunday, when the rule is not applicable.
Here's what happened on Sunday:
At about 9 am the PM2.5 levels were around 460.
They fell through the day, touching a base on 144 by 5 pm.
They began climbing again. At 7 pm, the pollution was at 230.
These trends were observed at other pollution monitoring stations in Delhi - Mandir Marg, Punjabi Bagh and Anand Vihar.
What explains all this? Only time can tell, say scientists. Weather conditions have not been favourable enough to exactly point out what happened.
Weather is important because PM 2.5 is a particle. It can be blown away by the wind and get trapped near the ground by cool air. So, changes in pollution can be attributed to reasons like less cars on roads only when weather conditions remain the same over a set of days.
When weather conditions fluctuate too much, it becomes hard to separate the different causes based on just a few days' data. That's what seems to have happened, which makes it difficult to find a trend from data of the last two-three days, says Dr Gufran Beig, project director of the System of Air Quality and Weather Forecasting and Research (SAFAR). SAFAR is the central government's specialised air quality monitoring agency based in Pune.
For example, it was warmer on Saturday, which may have reduced pollution in the day. Dr Beig said at least one week's data is required to separate weather conditions from the effect of having lesser cars on roads. For a better trend, data from all 15 days of the policy would need to be studied, he added.
This is understandable -- SAFAR's own data shows that nothing can be said about the Odd-Even formula just yet.
Its air quality measurement for Delhi shows that pollution levels have not improved after 1 January. SAFAR's numbers are a better measure of pollution than DPCC because it gives 24-hour averages, and health standards are based on a full day's exposure.
The good news is that air pollution since Christmas is far lower than it was in the same period last year.
The bad news is that pollution levels haven't improved from 1 January. If anything, air quality has marginally worsened (from 126 on Christmas Day, PM2.5 rose to 211 on 1 January and was 180 on the 2nd).
So nothing can be said yet about the Odd-Even formula. It also means there is no point judging Odd-Even by comparing current pollution with levels of last year, because the overall pollution seems to be lower even without the policy.
For now, SAFAR's forecast for 4 January is not heartening -- it expects PM2.5 to average around 190, still over 3 times the mandated limit of 60. As car owners of Delhi return to work from a long weekend, even returning to the city by car, we can only wait and watch.
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