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Ozone concentration in Maharashtra cities spikes during lockdown

The Mumbai Metropolitan Region (MMR) comprising - Mumbai, Thane, Navi Mumbai and Kalyan - witnessed a spike in urban ozone during the first three phases of the lockdown over two months.

Updated: May 27, 2020 19:55 IST

By Badri Chatterjee, Hindustan Times Mumbai

There has been an increase in urban ground-level ozone, a harmful pollutant, across 10 Maharashtra cities during the lockdown. (HT PHOTO)

Despite a decline in vehicular pollution during the lockdown due to the Covid-19 pandemic, there has been an increase in urban ground-level ozone, a harmful pollutant, across 10 Maharashtra cities, according to an analysis of the National Clean Air Program (NCAP).

The Mumbai Metropolitan Region (MMR) comprising - Mumbai, Thane, Navi Mumbai and Kalyan - witnessed a spike in urban ozone during the first three phases of the lockdown over two months (March 24 to May 24), according to an analysis released as part of the NCAP tracker on Tuesday by Mumbai-based air quality research group Respirer Living Sciences (RLS) and Delhi-based communications initiative, Climate Trends.

The Maharashtra Pollution Control Board (MPCB) confirmed the findings were accurate.

Surface ozone (O3) is a photochemical oxidant, which is formed when 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 aggravate asthma, cardiovascular diseases and other ailments.

The latest study found a 10.3% rise in ozone across 10 Indian cities during the two month lockdown period. Among monitoring locations across Maharashtra, Khadakpada in Kalyan has shown the highest average ozone levels at 70 micrograms per cubic metre (μg/m³) against the safe limit of 80 μg/m³ (for 24 hours), followed by the Maharashtra Industrial Development Corporation Khutala station in Chandrapur at 64 μg/m³. While the concentration ranged between 23-37 μg/m³ for MMR, a 50% increase in average O3 levels was witnessed when compared to 2019. Comparatively, a 50% reduction for Mumbai and 58% for Thane was witnessed for nitrogen dioxide (NO2) levels that comes mostly from burning of coal and vehicular exhaust.

“The analysis indicates that when NO2 levels remain low, surface ozone is higher as photochemical production can become more efficient during summer months,” said Ronak Sutaria, founder and director, RLS. “Breathing air with high ozone poses a risk for people with asthma and other lung ailments especially for children, older adults, and those active outdoors such as daily wage workers.”

MPCB said they were investigating the spike in the pollutant by comparing different station readings.

“Based on our preliminary data collection, ozone is going up across Maharashtra cities,” said SC Kollur, chief scientist, MPCB. “It may be a secondary pollutant arising from the reduction of other major pollutants. Industrial areas do witness such spikes but the increase for major cities comes as a surprise. We have to analyse the source.”

For Mumbai, MPCB plans to study background data from the Borivli station (near the national park) to check reasons for an increase in ozone. “The station data is down due to a broken cable for a week. The data is crucial as it gives background data and human induced emissions are not present,” said Kollur.

All 10 Maharashtra cities are part of the NCAP where the Centre seeks to reduce pollutant concentrations by 20-30% by 2024 with the target pollutant as particulate matter (PM2.5 and PM10). Data was compiled from state pollution control board monitoring stations over two months. The tracker is a web portal that monitors the achievement of state specific air quality targets for 122 Indian cities, and whether funds released for each city are being appropriately utilised.

“Assessing how pollutants behaved during the lockdown the rise in ozone is an alert at a time when cities are already facing a health crisis. The findings should equip policy making and callsfor more studies to identify the impact of other pollutants apart from PM,” said Aarti Khosla, director, Climate Trends.

A recent study by the Indian Institute of Technology, Delhi and two Chinese universities also showed a 20% rise in ozone for western parts of India. The study suggested that secondary pollutants such as ozone need to be considered by NCAP. “China witnessed a similar rising trend for ozone and adopted measures to reduce the pollutant. India is already showing the indication of higher O3 when other pollutants reduce.

During summer months, the Centre should consider precursors to ozone for non-attainment cities and in addition to PM, O3 has to be kept in mind while preparing action plans,” said Harsha Kota, professor, IIT-Delhi.

NCAP apex committee and professor, Indian Institute of Technology-Kanpur, SN Tripathi said, “Ozone has not been a problem in India over the years barring occasional spikes, which is regularly observed abroad across cities. An increase has been observed during lockdown due to its function as a precursor to declining NOx concentration but remained below safe limits. Ozone should be considered by NCAP as a secondary pollutant. Studies show PM followed by ozone contributes to 85-90% human related adverse health impacts. The current data is giving us the opportunity to understand O3 mitigation strategy.”


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