New Delhi: The odd-even road rationing scheme, which was implemented for the second time in Delhi in the second half of April, saw pollution levels declining initially, but rising from 23 April onwards.

In an analysis, the Centre for Science and Environment (CSE) said that farm and forest fires may be to blame.

The second phase of the odd-even scheme was implemented by the Delhi government from 15 to 30 April.

According to CSE, the average particulate matter or PM 2.5 level during the first nine days of the scheme was 24% lower than the average of the previous fortnight. But after 23 April, the PM 2.5 level increased by 92% and the nitrogen dioxide level increased by 47%.

Between 23 and 30 April, data from the earth sciences ministry’s System of Air Quality and Weather Forecasting and Research (SAFAR) showed that PM 2.5 rose from 77 µgm-3 to 190 µgm-3.

Referring to satellite images from the National Aeronautical and Space Administration (Nasa), CSE observed that before the odd-and-even scheme and during the first few days, there was virtually no crop fire in Punjab and Haryana. But 21 April onwards, there was a sudden rise in crop fires that became widespread and intense from 23 April.

The Delhi transport minister had said last week that an increase in the number of fire incidents during the second phase of the odd-even scheme had caused significant damage to the capital’s air quality.

“There has been no tradition of landfill fires. The data of fires in comparison to last year shows a three-fold increase from last year," transport minister Gopal Rai said while addressing a press conference on the issue.

The Delhi Pollution Control Committee will submit its report on the second phase of the odd-even scheme to the Delhi government on 9 May.

Experts say that meteorological factors could have played an important role in Delhi’s air pollution. “While the burning of agricultural residue in Punjab and Haryana could definitely be a reason for the sudden spike in pollution levels, meteorological factors such as a dry summer can also lead to more dust as drier soil leads to more soil becoming airborne," said B. Sengupta, former member secretary, Central Pollution Control Board.

CSE concluded its analysis by saying that the odd-even scheme is a temporary measure to help control worsening pollution, and will have to be accompanied with longer-term solutions for lasting air quality gains.

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