Benzene levels in Mumbai saw spike during Covid-19 lockdown even as other pollutants dipped: CPCB report
Contrary to most air quality reports during the Covid-19-associated lockdown, a study showed that benzene concentration in Mumbai was higher during all phases of the lockdown as compared to levels in 2019.
Contrary to most air quality reports during the Covid-19-associated lockdown, a study showed that benzene concentration in Mumbai was higher during all phases of the lockdown as compared to levels in 2019. The findings were released by the Central Pollution Control Board (CPCB) in its report titled “Impact of Lockdown on Ambient Air Quality” released on Wednesday. Benzene is a volatile organic compound (VOC) released in the air from anthropogenic sources such as emissions from crude oil, gasoline and industrial processes. In urban areas, the presence of benzene is most detected (through scent) at petrol pumps. Long-term exposure to benzene can cause serious health effects, said doctors.
The CPCB report showed 30-35% average rise in benzene levels during lockdown. “Benzene increased in all phases of lockdown, compared to the levels during the same period in 2019. It is possible that certain industries, especially those consuming or releasing benzene, might have started operating, resulting in the increase. Local influence of emissions on monitoring stations is also a possibility,” the report said.
VK Shukla, principal investigator of CPCB’s report, said, “We must realise that Mumbai experiences very different meteorological variations as compared to other urban cities. The higher benzene emission could be a localised issue near our monitoring stations. We are not sure of the exact source, but based on Mumbai’s source apportionment, there are 39 types of industries (excluding power plants), and benzene rise could be due to some functional industries during lockdown. The report is based on data collated by various stations, but exact reasons for this rise still needs to be investigated.”
A similar analysis by Mumbai-based air quality research group UrbanSciences using CPCB data showed similar results. “Areas such as Worli consistently reported unsafe benzene levels with 24-hour averages over 15 micrograms per cubic metre (µg/m3). The two month benzene average (two lockdown phases) at Worli was 13.1 µg/m3. Sion reported the next highest daily averages with most days above safe limits. Kurla reported an abnormal spike of up to 58 µg/m3 between April 24 and 30,” said Ronak Sutaria, founder and chief executive officer, UrbanSciences. The annual safe limit for benzene in India is 5 µg/m3 but countries like Israel have more stringent norms (3.9 µg/m3 for 24 hours). “Elevated benzene levels in few areas of Mumbai are a cause for concern and need immediate investigation, especially in locations where the 24-hour averages are above the safe limits,” added Sutaria.
Doctors said benzene was a proven carcinogen with severe health effects from long-term exposure. “The pollutant affects the urinary system, mainly the kidneys. It has been shown to cause bladder cancers. Levels are very high at petrol stations where VOCs are emitted. It is surprising that levels would be higher during lockdown when such activities were on hold,” said Dr Sundeep Salvi, director, Chest Research Foundation, Pune.
Experts, however, said the benzene data may not be reliable. “The spike is highly unusual and data has been collated from very few stations. Also, long-term data has not been maintained for this pollutant in Mumbai,” said Professor SN Tripathi, head of civil engineering, Indian Institute of Technology-Kanpur and apex committee member of National Clean Air Programme (NCAP).
Meanwhile, the reduction in industrial and vehicular activity during lockdown was divided into two phases (March 25 to April 19 and April 20 to May 3) showing a decline in major pollutant concentration such as particulate matter (PM10, PM2.5), sulphur dioxide (SO2), and nitrogen dioxide (NO2) as compared to levels during pre-lockdown (March 1 to 21) and the same period in 2019.
PM10 fell by 40% as compared to 2019 levels and 20% than pre-lockdown levels, NO2 fell 56% and 69% compared to the phases, while SO2 fell 56% and 48%. “PM2.5 levels increased during the first lockdown phase by 5% but decreased by 9% in the second phase, as compared to levels during 2019,” the CPCB report said, explaining that from April 22 onwards the Maharashtra government revoked permissions for activities (e-commerce companies, electrical supplies, sweet shops, confectionaries, courier services, activity related to agriculture products, restaurants). “The larger reduction in the second phase of lockdown may be due to this fact,” said Shukla adding, “Overall, like other cities Mumbai witnessed a transitional change in air pollution levels during lockdown, bringing down air pollution and achieving background air quality.”
30% RISE IN OZONE LEVELS IN MUMBAI DURING LOCKDOWN: NCAP EXPERT MEMBER
NCAP member professor Tripathi said Mumbai was among major urban cities in India that witnessed a 30% rise in ozone (O3). He explained that O3 rise was a complex phenomenon associated with a decline in NO2 and other pollutants, as well as meteorological factors among other reasons.
Surface ozone (O3) is a photochemical oxidant, which is formed when pollutants like volatile organic compounds and oxides of nitrogen (NOx) chemically react in the presence of heat and sunlight. Ground-level ozone is harmful for humans as it can lead to asthma, cardiovascular diseases and other health ailments.
“There is an immediate need for a massive urban zone like Mumbai to commence real-time source apportionment (RTSA) monitoring for pollutants like PM2.5 rather than depending on older information for pollution sources. This needs to be done on priority,” said Tripathi. IIT-Kanpur’s RTSA study for Delhi was included in CPCB’s report which highlighted source-specific decline in pollution levels during lockdown.