New Delhi, Nov 15 (PTI) Pollution levels were higher in Delhi this Diwali as compared to last year and it could be attributed to bursting of firecrackers, higher share of stubble burning and unfavourable meteorology during the festival season, according to the Central Pollution Control Board.
In a special report, the apex pollution watchdog said almost all pollutants reported higher values on Diwali this year as compared to 2019.
'Pitampura recorded an increase in PM and SO2 indicating impact of firecracker bursting on Diwali day,' it said.
As observed from real-time monitoring network, the hourly average concentration of PM2.5 started increasing from 11 pm on Sunday.
'At most of the stations, it reached the peak at around 1 am and continued at higher levels till 5 am,' the CPCB report said.
Average PM10 and PM2.5 concentrations on Diwali day were 645 µg/m3 and 483 µg/m3 respectively.
PM2.5 is fine particulate matter which is about three per cent the diameter of a human hair and can lead to premature deaths from heart and lung diseases.
The CPCB said Diwali was in mid-November this year which has unfavourable meteorological conditions for dispersal of pollutants as compared to 2019 when it was in the last week of October.
The contribution of stubble burning in Delhi's PM2.5 concentration was 32 per cent on Diwali day this year as compared to 19 per cent last year.
'Therefore, it may be inferred that elevated PM2.5 concentrations in 2020 in comparison to previous year had enhanced contribution of stubble burning and the same is also reflected in elevated levels of CO and NO2,' it said.
On Diwali day, the mixing height was 300 metres. It dropped to 60 metres during night hours. The average wind speed at Parivesh Bhawan was 3.4 kmph on Diwali day, the lowest in the last five years, and it created unfavorable dispersion conditions.
'As such, the impact of meteorology on air pollution levels during the festival season is evident,' it said.
Mixing height is the vertical height in which pollutants are suspended in the air. It reduces on cold days with calm wind speed.
The CPCB said that 7 out of 10 locations observed, noise levels increased on Diwali night this year compared to 2019.
Only three stations (ITO, Anand Vihar and Dilshad Garden) recorded a slight decline in night time noise on Diwali this year compared to last year. Day time noise reflected a similar trend, it said.
Delhi recorded an overall AQI of 414 on Diwali day this year.
It had recorded a 24-hour average AQI of 337 on Diwali last year (October 27), and 368 and 400 on the next two days. Thereafter, pollution levels remained in the 'severe' category for three days on the trot.
In 2018, the 24-hour average AQI (281) on Diwali was recorded in the 'poor' category. It deteriorated to 390 the next day and remained in the 'severe' category on three consecutive days thereafter.
In 2017, Delhi's 24-hour average AQI on Diwali (October 19) stood at 319. It, however, slipped into the 'severe' zone the next day and stood at 403.
The CPCB carried out ambient air quality and noise level monitoring on selected pre-Diwali day and Diwali day in Delhi like previous years.
Ambient air quality was monitored at 40 locations (3 manual stations and 37 real-time stations), while ambient noise level was monitored at 16 locations (6 manual and 10 real-time stations). PTI GVS AAR