As per the Delhi Pollution Control Committee's (DPCC) hourly data, the most polluted spot of Delhi, AnandVihar, read 923 ìg/m3 PM 10 level at 7:30 pm. This is nine times the normal level of 100 ìg/m3. PM 2.5 read at 480 ìg/m3 which is eight times the normal level of 60 ìg/m3. And these readings were taken near the closing time of the oddeven car rationing scheme - 8 pm.

This was, in fact, one of the most polluted days in the city after November 11, Diwali, when pollution levels hit an alarming high. On Diwali, AnandVihar had clocked a PM 10 level of 2,308 ìg/m3 around 11 pm and PM2.5 level of 619 ìg/m3 at midnight.

Even on a regular weekday, the subcity bordering UP's Ghaziabad and Sahibabad has a PM 10 reading of 500-600 ìg/m3. For instance, on 1 November, 2015, AnandVihar's PM 10 reading from 8-9 pm was 676 ìg/m3. On 9 October, 2015, it was 553 ìg/m3.

Vehicle emission are a key source of carcinogenic PM as per a recent report brought out by IIT (Kanpur) on Delhi's air pollution. While there were very few motorists on roads as majority of private offices remained closed on the first day of the year, the air quality was far from normal. Environmentalists attributed the high pollution levels to a number of exemptions given by the Delhi government particularly to the two-wheelers that pollute more than cars.

Anumita Roy Chowdhry, Executive Director at Centre for Science and Environment (CSE), which is spearheading Delhi's anti-pollution campaign, said: "Estimates show that two-wheelers because of their staggering numbers (55 lakh bikes in the city) contribute as much as 31 per cent of the total particulate load from vehicles. If this segment is left out and with a sizeable number of cars also being driven by women, who have been exempted, the overall effectiveness of the programme is compromised."

"The government cannot rely on the odd-even plan forever. It will have to strategise further, bring in newer ideas like hiking parking charges, improving public transportation etc to reduce air pollution," she added. Even the AAP government, which hailed the odd-even debut day as grand success, acknowledged that the city air wasn't safe still. Health Minister Satyendra Jain, who briefed reporters outside the Delhi Secretariat on Friday, said, "The levels are still up three to four times." He was pointing at the digital display screen flashing real-time air quality data installed outside the secretariat. "Imagine if you are five feet tall. You are standing in water that is 15 feet in height, which means that it still three times above your tolerable level," the minister explained.

Dr GufranBeig, Senior Scientist and Project Director, SAFAR, IITM (Pune), said, "On Friday in Delhi, PM 2.5 levels started to reduce sharply in the morning hours, from 8 am onwards, and later slowly until 2 pm, roughly a 10 per cent fall. This was probably a sign of reduced vehicular emissions from the odd-even plan."

After 2 pm there was an increase in PM 2.5 as compared to data from previous days. "Why this happened needs to be examined scientifically. Probably, maximum temperature levels played a role," said Beig adding it is still premature to conclude anything with just 10 hours of data available for comparison.

Live meters to record pollution were installed at six locations in Delhi for monitoring real-time air quality. A portable air monitoring station was also deployed in the city for air quality assessment.