The impact of odd-even on air pollution remained unclear with the Delhi Pollution Control Committee saying farm fires in Punjab and Haryana might have played spoilsport in the second phase of the car rationing scheme.
The report said the air was less polluted a week before the restriction than the weeks during and after the restriction.
The peak pollution levels before the scheme, however, were higher compared to the first week of the restriction.
The second week saw higher peaks and this was because of the farm fires, said the DPCC report.
Pollution peaks are the highest concentration of a pollutant in the air during a set time period.
“During the event period (first week of odd-even II, April 15 to April 21) with normal weather conditions the range of concentration of particulate matter was decreased as compared to previous week, despite having same wind speed as before. However, in the second half of the event (April 22 to 30), the pollution level increased due to dip in the wind speed,” the report says.
A closer analysis of the DPCC report reveals that the average particulate matter was lower before the restriction and almost similar after the restriction was imposed. What changed were external factors such as wind speed and farm fires.
The average PM 2.5 concentration a week before the restriction was 89 micro gram per cubic metre.
This rose to 111 micro gram per cubic metre during the first week of the restriction. In the second week the concentration rose to 154 micro gram per cubic metre. The week after odd-even II ended, the pollution concentration was 114 micro gram per cubic metre.
The pollution levels and the wind speed were similar in the first week of May and April 15 - April 21 (odd-even first week) indicating a close relationship between the two.
The DPCC acknowledges the relationship.
“The analysis of the data generated before, during event and after the event shows that the total period was highly influenced by metrological parameters such as wind speed, wind direction, ambient temperature, etc. It is observed that local and trans-state movement of pollutants also influenced the air quality of Delhi. The probable factors are crop residue burning in Haryana, Punjab, local fires in Delhi including fire in land fill sites and Uttarakhand,” the report said.