Gurugram turned up on top of the Central Pollution Control Board's list of the 28 most polluted cities on Wednesday with an air quality index (AQI) of 322. It got worse on Thursday, rising to 347 but was pushed to second by alarmingly high pollution levels recorded in Haldia (392), an industrial city in West Bengal. AQI above 300 is classified as 'very poor' and can be the trigger for respiratory illnesses.

Gurugram's air quality has been consistently very poor through the winter, except a short spell earlier this week when wind brought pollution levels down. The other severely polluted cities were Faridabad, Ahmedabad, Agra and Delhi.

There is, however, a catch. Unlike Delhi, pollution in Gurugram is monitored from just one station, in the old city, and officials have repeatedly pointed to this aspect to underscore that the reading does not accurately reflect the condition of air across the city.

An official of the Haryana State Pollution Control Board (HSPCB) said heavy traffic around the air monitoring machine could be a factor. "Though there can't be a single factor responsible for increase of pollutants in the atmosphere, increased movement of vehicles and traffic congestion around the stationary air quality monitoring machine at VikasSadan in the last few days could be blamed," said the official.

But if huge vehicular volume were to be taken as the benchmark, Gurugram in general has a very high density of cars on its road and is notorious for traffic congestion — all contributing factors to higher levels of pollution.

Digging work on various infrastructure projects, including the underpasses on NH-8, and at construction sites have also increased dust emission, worsening overall air quality. "Since construction of underpasses has started at two points — IffcoChowkand Rajiv Chowk —air pollution has increased in the city. It has also been causing traffic congestion on the highway," said Vivek Kamboj of Haryali, an environmental NGO.

The met department has forecast a comparatively brighter and warmer Friday and Saturday. "We are expecting the minimum and maximum temperatures to remain around 9 and 23 degrees Celsius, respectively. There might be shallow fog in the morning. However, the sky will be clear and days will be brighter," said a Met official. There could be some respite from pollution if wind speed picks up again.