Despite hostile weather, odd-even cut pollution: CSE

New Delhi: The Delhi government's odd-even scheme has been given a thumbs up by Centre for Science and Environment, a green think tank, which said it helped bring down air pollution levels in the city and reduce traffic congestion.

In its note submitted to the Supreme Court, Environment Pollution (Prevention and Control) Authority has also said the odd-even scheme brought about a clear reduction in pollution levels, a gain which has been lost within a week of the experiment ending.

Anumita Roychowdhury, executive director at CSE, said the agency had analysed air quality data from real-time monitoring of Delhi Pollution Control Board for the period from November 2015 to January 2016 to assess the benefits of the odd-even scheme. The pollution this winter had been found to be higher than that of the previous season.

"The odd-even scheme, although limited in scope and ambit, managed to slow down the peaking of pollution even when weather was hostile-no winds and lower temperatures. Even this benefit was lost immediately after the scheme came to an end as is evident from the air quality trends during the first three working days since the scheme ended," said Roy Chowdhury.

CSE's analysis shows that on January 18, the first Monday after the odd-even scheme ended, PM 2.5 levels shot up by 57% during the day and was in the "severe" category with an average city-wide concentration of 277 microgram per cubic metre (mg/cum).

On Tuesday, the levels rose further to touch 281 mg/cum. On Wednesday, the levels fell slightly to 266 mg/cum, but this was attributed by CSE to improved wind conditions.

"Without wind, the build-up would have been much higher. On Monday, pollution build-up within the day was massive, by 101 mg/cum. This was greater than the highest build-up observed during odd-even days, which was a jump of 75 mg/cum on January 11 and despite the fact that Monday was much windier," said Roychowdhury.

CSE says that during the odd-even fortnight, there was a clear pollution curve, which has flattened out in the post-scheme days, indicating pollution build-up throughout the day.

According to DPCC data, January 15 and 16, the last day of the odd-even scheme and a day later, were the cleanest days of this winter. On January 15, PM 2.5 levels dropped to 155 mg/cum followed by 130 mg/cum on the next day. The cleanest day before this was November 5, 2015 but it had rained in the city that day, bringing down pollution levels.

"There was no rain during the odd-even fortnight but the weekend after it ended was also the windiest of the season. The wind started to slow down on Sunday but due to relatively low traffic, PM 2.5 levels rose only marginally to 176 mg/cum," said Roychowdhury.

To demonstrate the fall in pollution levels during the first fortnight of January, CSE has used data on wind speed to show how despite a calm environment, pollution levels fell faster during the odd-even experiment. "During days before the odd-even scheme began, pollution levels increased when wind speed was low. However, even when there was no wind to blow the pollution away, the odd-even scheme succeeded in arresting an upward trend of pollution. Of the severe smog episodes this winter, peak pollution during odd-even programme has been the lowest despite hostile weather conditions," said Roychowdhury.

The organisation compared live traffic updates from Google for January 15 and for January 19 which showed that congestion has gone up on most Delhi roads after scheme ended, the average journey speed touching 50 kmph during the odd-even period against 20-25 kmph on regular days.

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