On Bhai Dooj (Saturday) nitrogen oxide (Nox) levels rose to 136 micrograms/cubic metre (ug/m3) from 74ug/m3 on Friday. It was at 156ug/m3 on Sunday. The respiratory suspended particulate matter (RSPM) or PM10 (particulate matter with a diameter of 10 micrometers or less) rose to 171ug/m3 on Saturday compared to 162ug/m3 on Friday.

The PM 2.5 levels (particulate matter with a diameter of 2.5 or less) rose to 90ug/m3 on Friday. While it was at 88ug/m3 on Saturday, it dropped to 62ug/m3 on Sunday. PM10 and PM 2.5 are harmful for those who suffer from upper respiratory tract disorders and a heavy concentration of these can cause discomfort to those suffering from bronchitis and asthma.

MPCB officials said the reasons for the spike in the Nox levels needs to be studied and the body did not have any field data. “The rise is unusual as the Nox levels have doubled, with the rise being seen at the very end of the festival. Also, the weather in the city being windy since Friday, chances of high concentration of pollutants were slim,” said SC Kollur, scientific officer, MPCB.

Meanwhile, the noise levels, which were high in 37 of 45 locations in the city on Laxmi Puja, dropped on Saturday. Last year, only nine of the 45 locations had recorded a rise in noise levels.

The maximum noise level on Saturday – 83.9 decibel (dB) – was recorded at Dharavi after 10pm. At most locations the noise levels ranged between 60dB to 75dB. Saturday’s data shows that, this Diwali, Prabhadevi was the noisiest place in the city, with 97.6dB recorded on Friday.

PM10 (particulate matter with a diameter of 10 micrometers or less)

PM 2.5 (particulate matter with a diameter of 2.5 or less)

Nox – Nitrogen Oxide

Permissible limits for air quality

PM 10 - 100ug/m3

PM 2.5 - 60 ug/m3

NOx - 80 ug/m3