Concentration of PM2.5 saw a fall of about 33% on Sunday, compared to Friday. The highest PM2.5 level recorded on Sunday was 188.54 micrograms per cubic metre (g/m3) at 5am, compared to Friday's peak of 280.45g/m3, and Saturday's peak of 200.62g/m3 (6% dip), all figures recorded at 5am. However, it was still three times the prescribed value of 60g/m3.

The level of carbon monoxide, though, still remained 4-5 times higher on Sunday, compared to its prescribed value. Air Quality Index (AQI) was also above 200, which is considered 'Very Unhealthy'.

The Haryana State Urban Development Authority (HSPCB) said light showers helped in dispersing particulate matter. "Even light showers help disperse suspended particulate matter in the lower atmosphere. That's why a significant difference was noticed in pollution level. Also, wind speed increased slightly. Air quality in Gurgaon has always been better than Delhi, as there arefewer polluting industries, though diesel autos are a major cause of air pollution here," said a HSPCB official.

Vertical wind speed, which also helps in dispersal of pollutants in the lower atmosphere, rose from 0.01m/sec on Friday, through 0.02m/sec on Saturday, to 0.06m/sec on Sunday.

With the Met department forecasting foggy days to return by end of next week, experts called for immediate measures to be taken, as this should also push up pollution levels. "Even though weather is expected to be clearer and sunny over the next 4-5 days, foggy days are expected by the end of next week. Visibility is also expected to reduce but conditions might not be as severe as it were last week," said a Met official.

Niranjan Raje,ex-member of Environment Pollution (Prevention and Control) Authority, said, "The dip in pollution level was witnessed due to natural factors. However, wind speed is still low, so even one foggy day will again lead to rise in concentration of particulate matter in the atmosphere. There is definitely an urgent need to take anti-pollution measures as per weather forecast."

"Even though PM2.5 level has fallen from last week's highs, it is still three times over the prescribed limit. We've been raising the issue of taking measures such as closing down highly polluting industries and restricting entry of diesel vehicles in the city as soon as pollution increases. However, there has been no response from the authorities. It seems measures will be taken only after the situation gets worse," said Jai Bhagwan, a retired professor of environmental sciences.