After the capital city opted for a test run of the odd-even scheme, pollution levels on New Year day showed a "marked" decrease compared to the previous year, the Delhi government said on Saturday.
The ambient air data collected by mobile dust samplers on January 1 showed that the PM 2.5 (particulate matter suspended in air with diameter less than 2.5 microns) levels ranged between 121-226 at all 24 locations, a government statement said.
The mobile units of the Delhi Pollution Control Committee (DPCC) collected this data, after monitoring each of the 24 locations for 20 minutes each.
The PM 2.5 levels at the corresponding time on January 1, 2015, hovered around 250 across the national capital, the government said, adding "air pollution levels within Delhi are showing a decreasing trend".
PM 2.5 are the particulate matter capable of causing harm to human respiration, if present above permissible levels. The DPCC prescribes 60 units of PM 2.5 levels as the standard level.
Areas like Rohtas Nagar, Patparganj and Kondli bordering Uttar Pradesh showed higher air pollution levels compared to areas towards central Delhi, the government said.
"It shows that the National Capital Region (NCR) towns need to take effective steps to curb air pollution," it said.
An analysis of the DPCC data over the past 24 hours however revealed that pollution on New Year day dropped as the day proceeded, but rose steeply from the evening onwards.
The PM 2.5 levels at the DPCC's Anand Vihar monitoring station recorded a staggering 480 at 7 p.m. on January 1, as against 238 units at 11.30 a.m.
Environmental experts said pollution levels remained high due to high concentration of pollutants close to ground level in winter season, despite enforcement of an odd-even scheme.
"Pollutants in the air stay close to the ground in winters. This could be one of the reasons for high pollution. Also, fireworks on New Year and high vehicular movement in the early hours of New Year impacted pollution levels," said Vikrant Tongad, an environmentalist working with Social Action for Forest and Environment.
The Air Quality Index (AQI) of the national capital, as measured by the Central Pollution Control Board (CPCB), stood at a "very poor" level of 384.
At this level, respiratory illness due to prolonged exposure is possible, the CPCB said.