A Delhi-Mumbai story: Which city's air quality is worse?

Air Pollution

India's financial capital Mumbai and national capital Delhi are yet again competing for the top spot, but this time a dubious one, in the air pollution category.

According to data from the Central Pollution Control Board, as of 4 pm on October 19, Mumbai had an average AQI (air quality index) score of 156 while New Delhi was at 121.

However, air quality in Delhi on October 20, 21, and 22 surged past the 160 levels seen in Mumbai during the corresponding period and skyrocketed to 250 plus levels, reaching a peak of 340 on the night of October 21.

While the financial capital has been waking to a thick blanket of smog owing to a rapid increase in construction activity, the national capital has been falling asleep to a ghastly layer of clag that has engulfed the city for the past three days.

According to experts, the situations in both cities could worsen, setting the stage for a dangerous winter.

Hawa mein kuch kaala hai

Delhi

According to data from the Central Pollution Control Board (CPCB), Delhi is witnessing its most polluted October since 2020, and expectations are that things are likely to get worse in the coming days.

Data from the Ministry of Earth Sciences accessed by Moneycontrol showed that on October 21, the contribution of stubble burning in the AQI was 21.5 percent and on October 22, it was 16.38 percent.

However, as per the dynamic forecast monitoring system of the ministry, the contribution of stubble burning is likely to go up to 30.5 percent on October 23, and 32.7 percent on October 24.

As per the last bulletin issued (at 4 pm) by the CPCB on October 22, Delhi's air quality index hit the "very poor" category at 313.

Graded Response Action Plan (GRAP) categorises actions into four stages: Stage I – 'Poor' (AQI 201-300); Stage II – 'Very Poor' (AQI 301-400); Stage III – 'Severe' (AQI 401-450); and Stage IV – 'Severe Plus' (AQI >450).

The reason for the worsening air quality, according to scientists in the Central and Delhi governments, is a combination of factors ranging from low wind, low temperature, stubble (biomass) burning and local factors such as road transport, dust and so on.

"Wind speeds in Delhi have been on the lower end of when compared to the city's average in the last few years, owing to the lower influence of western disturbances, which has resulted in lower dispersion of particulate matter in the city," a senior scientist from the India Meteorological Department (IMD) told Moneycontrol.

He added that due to the lower influence of western disturbances, Delhi has also experienced fewer rainy days this October. Rain was a big reason for the city's lower AQI in the past three years.

"Rains help settle down particulate matter in the air, which improves air quality," the scientist said.

Similarly, another scientist from the CPCB told Moneycontrol that a combination of the ongoing cricket World Cup and the illegal use of fireworks, more cars on Delhi's roads, and grander festivities in October this year around Navratri and Durga Puja are also contributing to the city's bad air quality.

Mumbai

Mumbai, a coastal city, has long benefited from the natural sea breeze to help keep pollution levels in check. However, environmental experts now believe that this is no longer enough, as global warming is changing wind and weather patterns.

One of the key factors contributing to Mumbai's worsening air quality is the slowdown of surface winds. Normally, a coastal city such as Mumbai would experience a wind reversal every three to four days, with wind speeds reaching up to 12-13 kmph.

This helps to disperse air pollutants and particulate matter. However, in recent years, wind speeds have dropped to just below 4-5 kmph, resulting in pollutants getting trapped in the air.

The ongoing infrastructure projects as well as large-scale building construction and demolition works have raised dust particles into the air, impacting the health of people. “A combination of high moisture and dust is caused due to the multiple redevelopment and construction projects that are operational across the city,” India Meteorological Department (IMD) scientist Sushma Nair told Moneycontrol.

“There is moisture, and anti-cyclonic wind circulation, which does not allow the wind to ascend. The anti-cyclone is right over Mumbai,” she added.

“Every year after the withdrawal of the southwest monsoon, PM2.5/PM10 increases due to low night temperature under clear sky conditions as well as due to soil becoming dry in the absence of rains. Vehicular movement raises ground dust and increases PM10,” said Dr BS Murthy, a scientist at the Indian Institute of Tropical Meteorology.

Another major contributor to Mumbai's air pollution, according to the Mumbai Climate Action Plan 2022, is vehicular emissions, which account for 20 percent of the total emissions in the city. Solid waste also plays a role, accounting for 8 percent of total emissions.

How can citizens breathe again?

Delhi

As Delhi's air quality plummeted to the season's worst on October 23, the national capital's environment minister called for an inter-departmental meeting to review the situation and discuss the implementation of Stage-II of the graded response action plan (GRAP) which was invoked by the Commission for Air Quality Management (CAQM) on October 21.

The meeting will be held on October 23 and senior officials said a fresh set of measures are likely to be announced.

According to senior officials from the CAQM, measures such as reducing the operating timing of trucks and other commercial vehicles in the city and implementing of odd-even schemes will be discussed as part of the meeting.

When asked whether the government is considering implementing strict measures mandated under Stage-IV of GRAP, which includes imposing the odd-even car rationing rule, closure of schools and promoting work from home for offices, a senior official in the Delhi's government's environment department said it would be "premature" to announce any such measures as they are to be implemented if the air quality index (AQI) is expected to cross 450.

Measures under Stage-I include a ban on the use of coal and firewood in tandoors at hotels, restaurants, and other eateries; acting against polluting industrial units; Shutting thermal power plants within 300 kilometres of Delhi. These have already been implemented.

However, despite the CAQM invoking Stage II of GRAP, measures such as increasing parking fees to discourage the use of private vehicles and adding an additional metro fleet to increase the frequency of the service have not yet been implemented.

It also directs the governments in Delhi-NCR to augment CNG and electric buses, which is pending more with the administrations of Uttar Pradesh and Haryana, a senior Delhi government official said, requesting anonymity.

All public buses in Delhi were already CNG-based and now the national capital has the highest fleet of electric buses for public transportation compared to any other state or union territory. Delhi currently has an operational fleet of 7,135 public buses, of which 6,335 are CNG buses and 800 are pure electric buses — the most in any city in India.

However, although transitioning from old polluting diesel vehicles, Haryana and Uttar Pradesh, which have NCR cities such as Faridabad, Gurugram, Ghaziabad and Noida, have been sluggish in inducting even CNG buses, let alone electric buses.

Mumbai

Civic officials of the Brihanmumbai Municipal Corporation (BMC) held a joint review meeting on October 20 to tame the rising pollution in the city.

The civic body has set out new guidelines for dust and pollution control that are to be followed by all the entities and systems, according to a press statement.

The BMC has laid out certain measures to bring the pollution levels under control. They include installing sprinklers at construction sites within 15 days and a smog gun system within a month. The measures come as the city grapples with a spurt in the number of dust particles in the air owing to ongoing construction.

The BMC has directed that buildings under construction that are about 35 feet. high be covered with iron sheets or a cloth to prevent the spread of dust. Instructions were also given to monitor the air quality in the vicinity of refineries.

Two days after issuing new air-quality guidelines to check rising pollution in the city, the BMC on Sunday deployed vehicle-mounted mist spraying machines, aka anti-smog guns, at eight locations to control dust.

The anti-smog guns were used at Worli Sea Face, Haji Ali, Pedder Road, Girgaum Chowpatty, Nariman Point, Fashion Street, Badhwar Park and World Trade Center.

The BMC has also floated tenders to procure 30 anti-smog machines, which it hopes to increase to 60 soon. Of these 60 units, 30 will have a misting range of about 50 metres and the remaining will have a 30 metre range

Earlier this year, policy influencing think tank Mumbai First suggested a slew of measures that the authorities can undertake to address the situation.

Among the key solutions provided by the think tank were stopping open refuse burning and landfill site burning, tackling road dust from paved and unpaved roads, controlling emissions from bakeries and crematoria, etc.

“The only way to reduce air pollution and increase air quality in urban areas is to reduce emissions at the source, adopting eco-friendly technologies, using renewable energy, etc,” Murthy said.

In February, the Brihanmumbai Municipal Corporation (BMC) adopted an action plan to impose stringent measures to control air pollution in the city. The civic body had outlined guidelines that include installing air purifiers in the most crowded areas of the city.

“Mumbai needs to implement dust management, as there is a lot of construction being undertaken in the city at the moment and that is contributing significantly towards air pollution in the city,” said Rishi Aggarwal, founder, Mumbai Sustainability Centre.