Central Pollution Control Board(CPCB) has put the AQI in Patna in the 'severe' category, which means breathing such air affects healthy people and seriously impacts those with existing diseases.

Incidentally, the Bihar State Pollution Control Board (BSPCB) had issued an advisory to the state government last year after the AQI of Patna crossed 400 mark in November-December, breaking all its past records in the state capital.

The AQI is an assessment of the air quality taking into account eight pollutants: PM2.5 (particulate matter less than 10 micron), PM10 (particulate matter less than 10 micron), nitrogen oxides, sulphur dioxide, ozone, carbon monoxide, ammonia and lead.

Air pollution, primarily higher level of respirable suspended particulate matter (RSPM), has been a cause a 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 443.99 micrograms per cubic metre. Suspended particulate matter is the biggest contributor to air pollution in the state capital.

BSPCB chairman and forest department principal secretary Vivek Kumar Singh admitted the higher level of air pollution in the city and claimed that compressed natural gas (CNG) would be introduced by the end of 2017 to bring down the pollutants level.

"Though we have been able to introduce clean brick manufacturing technology, high level of vehicular density in the city still remains a cause of concern. We need to hit the root cause of pollution; hence, we are soon going to introduce CNG for vehicles," Singh told TOI.

"We are already in talks with GAIL as they are presently developing a CNG pipeline network passing through Bihar. They have assured us to provide the pipeline connectivity to Patna by 2017-end," Singh said.

BSPCB member-secretary S Chandrashekhar attributed the surge in AQI to the onset of winter conditions and dust on roads. "The level of particulate matter or dust particles in the air in Patna is recorded quite higher than the respective permissible level. Moreover, November-December is considered a crucial period with regard to the particulate matter. The soot-like particles settle down in low temperature conditions, making the air in the lower level of atmosphere more polluted," Chandrashekhar told TOI on Tuesday.

He said the BSPCB would issue an advisory to the state government to take necessary action to bring down the 'alarming' level of AQI in the state capital. Incidentally, several recommendations made by the BSPCB in its last year's advisory to curb air pollution are already gathering dust. (See Chart)

Though the advisory sought the removal of all over 15 years old diesel-operated vehicles and a decision in this regard had already been taken in October, 2013, but the transport department officials are still clueless about its implementation.