Most factors behind the haze in Delhi are applicable for Patna too, especially the ultrafine particulate matter, scientifically termed PM10 and PM2.5. The situation aggravates, at least visibly, in the winter season when the pollutants settle down close to earth’s surface, forming a layer of smog in the lower level of atmosphere.

With regard to the haze in the city on Tuesday, weathermen at Patna Meteorological Centre claimed that visibility came down to as low as 800 metres. “The comparatively lower temperature and wind speed in the winter season make the particulate matter heavier. As a result, they do not escape in the upper layer of atmosphere and settle down close to earth surface leading to formation of smog,” said S Sengupta, director at Patna Meteorological Centre, adding that there is no forecast of fog over the next few days.

Air pollution, primarily higher level of respiratory suspended particulate matter (RSPM), has been a cause of concern in Patna even on normal days. The level of particulate matter is normally recorded thrice the normal level of respective standard of 100 micrograms per cubic metre. Even on Tuesday evening, the level of PM2.5 in Patna was measured at 282 micrograms per cubic metre.

Particulate matter apart, Patna’s Air Quality Index (AQI), released by the Central Pollution Control Board (CPCB) on Tuesday, stood at 191, putting it in the “moderate” range. The AQI is an assessment of the air quality taking into account eight pollutants – PM2.5 (particulate matter less than 10 microns), PM10 (particulate matter less than 10 microns), nitrogen oxides, sulphur dioxide, ozone, carbon monoxide, ammonia and lead.

S Chandrashekhar, member-secretary at Bihar State Control Board (BSPCB), said the AQI was hovering in the range of 120-190 on Tuesday. “Though the AQI is being measured at moderate level for the time being, we have kept our fingers crossed as November-December is considered crucial period with regard to particulate matter. The soot-like particles settle down under low temperature conditions, making the air in the lower level of atmosphere more polluted,” Chandrashekhar told TOI.

Incidentally, the pollution control board in its advisory issued on December 14 last year stated that AQI of Patna crossed 400 mark in November-December, breaking all its past records in the state capital.

In fact, suspended particulate matter is the biggest contributor to air pollution in Patna. In a report titled ‘Air quality management in Patna’ published in 2014 by Delhi-based Shakti Sustainable Energy Foundation, dust particles and brick kilns were found to be the highest contributor to particulate matter in Patna followed by vehicular emission in the third place.

Environmental experts said clean roads and eco-friendly construction practices are necessary for bringing down the level of particulate matter. “The situation in Patna is not very different from Delhi. Patna is more prone to higher level of dust particles owing to its proximity to the Ganga. As the Ganga has shifted, it has left the diara land on its bank, which contains new alluvium soil. New alluvium being lighter is lifted easily by air. Besides, hardly any eco- friendly measures like putting cover on construction sites are followed in building construction activities,” said Ashok Ghosh, chairman of state level Expert Appraisal Committee, the technical committee of State Level Environment Impact Assessment Authority (SEIAA).