Bamboo can help Delhi retain its air quality gains due to lockdown

Ecologists say bamboo can be planted along with native broadleaf species and shade-loving shrubs

The air pollution level in Delhi had hit an eight-month high on Thursday but reduced slightly on Friday with favourable wind speed helping in dispersion of pollutants

The nationwide COVID-19 lockdown that was imposed on March 24 and lifted partially on June 1 has significantly improved the quality of air in Indian cities. One can see clear skies. There is no haze. Reports say Himalayan peaks Yamunotri and Gangotri are visible from the usually dusty town of Saharanpur in Uttar Pradesh.

The novel coronavirus that causes COVID-19 has made the air breathable by attacking the cells of the very apparatus through which we breathe. But rather than allowing us to enjoy the outdoors, it has forced us to stay indoors. It is like being in a sea and unable to drink.

The International Energy Agency (IEA) has estimated that global energy-related CO2 emissions were set to fall by 8 per cent this year. It says this is the largest decrease in emissions ever recorded and six times the previous record drop of 400 million tonnes in 2009 after the financial meltdown.

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The environmental website, Carbon Brief, says India’s CO2 emissions fell by 1.4 per cent (30 million tonnes) in the year ending March 31. During the month, it says, CO2 emissions dropped by 15 per cent and likely fell by 30 per cent in April due to the lockdown.

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In April and May, Bengaluru had only green or light green days—the colour codes for the Central Pollution Control Board’s Air Quality Index (AQI) denoting good or fairly good air. During these months last year, 38 of 61 days were colour-coded yellow, denoting moderate air quality in the six-rung AQI, in which ‘severe’ is the worst.   

Chennai too had good (green) or fairly good (light green) days during the lockdown. Last year, 17 of 61 days were moderate in the city.

Hyderabad too had only green or light green days in April and May, except for six days when they were moderate. The yellow range of AQI is from 100 to 200. But in Hyderabad’s case, it was within 110. During these two months last year, 32 of 61 days were moderate.

Mumbai’s air quality was green or light green throughout April and May. It did not change much from the air quality last year, when only two days were moderate. Perhaps, a strong sea breeze and pre-monsoon winds keep the city’s air clean.

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Kolkata had four moderate days out of the total 61 days. The rest were green or light green. There was not much change from last year, when nine days were moderate.

However, the biggest change was witnessed in Delhi, where the air quality had been poor due to construction and roadside dust, high CO2 emissions from a large number of vehicles and dusty conditions in summer that concentrate fine particulate matter.

Last year, 34 of 61 days in April and May were poor or very poor; the air quality count ranged from 200 to 400. Twenty-six days were moderate, or one step above poor. There was just one day when the air quality was fairly good, against 18 days this year. There were just two days when the air quality was poor in 2020. There were no very poor days.

Since Delhi is the odd city out, how could it retain the air quality gains of the lockdown?

N Bharathi, a scientist from Tamil Nadu Agricultural University, recommends plantations of bamboo along the banks of the Yamuna on raised bunds. He has a company in Hosur which specialises in making tissue-cultured clones of a fast-growing and dense variety of bamboo called Bambusa Balcooa, which does not produce seed and, in turn, do not die.

The variety does not have thorns either and so snakes do not brush past them to shed slough. That makes it easier to harvest. The hole in the middle as narrow as a finger. It is input-responsive and grows vigorously up to 55 feet when given nutrients and water.

Bharathi says each bamboo culm or pole absorbs 450 kg of CO2 a year. Indians, on average, emitted 1.7 tonnes of CO2 in 2014, according to the World Bank. It would take four bamboos per person to neutralise India’s annual emissions. Since rural folk pollute less, city dwellers will need to plant more.

Forty tonnes of bamboo harvested from an acre can produce 10,000 litres of ethanol, says Bharathi. The yield is better than that of cane.

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The cane juice when converted entirely into ethanol can yield 2,400 litres per acre, says Bakshi Ram, director of the Sugarcane Breeding Institute in Coimbatore. This is from the blockbuster variety, Co-0238, which he has developed. If the cane juice is used to make sugar, the ethanol yield from the by-product molasses drops to a fifth.

Ethanol is also produced from maize. An acre of maize in the US yields on average of about 1,775 litres of ethanol, according to data posted on the website of the University of Nebraska-Lincoln.  Average US maize yield is much higher than that of India.

Maize and sugar are food products; bamboo has no such claim. But the capital cost of the digesters and fermenting vats in which the pulped fibres are broken down into starch and sugar with enzymes and converted into alcohol is too high to be viable.

But S K Barau, the managing director of Numaligarh Refineries in Assam, says the Finnish technology it has been using makes it viable because of byproducts like furfural and acetic acid. He says the company is not re-thinking the ethanol-from-bamboo project it is setting up with a grant from the Central government, though the prices of crude oil and petroleum products have slumped. The company is producing ethanol to blend it with petrol.

N Harish Kumar of Sri Mahalaxmi Printing and Dyeing Mills, Erode, says he has maintained a bamboo plantation for about 12 years to reduce the total dissolved salts (TDS) from the discharge of a bleaching unit.

The discharge contains TDS of more than 3,000 units but bamboo absorbs the salts and stores it in its culm. Because of the plantation, the water in a nearly well has TDS levels of 1,000-1,200 units, he says—well within the norms. The bamboo leaves that fall on the ground produce humic acid on decomposing and mitigate the alkalinity of soil.

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Bharati says raw sewage that is discharged into the Yamuna could fertilise bamboo plantations. Besides having economic value, they can provide employment too, he says.

But, are bamboo plantations along the Yamuna advisable?

CR Babu, an ecologist and professor emeritus at Delhi University’s Centre for Environmental Management of Degraded Ecosystems (CEMDE), says an eco-system approach is necessary. He does not favour bamboo-only plantations.

They can be planted on the slopes of the bunds and elevated flood plains of the Yamuna, not in ribbons but with native broadleaf species and shade-loving shrubs, says Babu.

He is advising the Delhi Development Authority on bio-diversity parks, and the Delhi government on replacing Vilayati Kikar, an invasive Mexican shrub, with native species on the Ridge. Babu says a three-tier community of mixed species, comprising bamboo and broadleaf trees with shrubs in between can efficiently scrub the columns of air passing through them of CO2 and particulate matter like PM 10 and PM 2.5.

Of course, cities must check the sources of pollution: vehicle exhausts, construction and roadside dust, and in the case of north Indian cities, smoke and soot in winter from burning paddy stubble. Three-tiered urban forests of mixed species are part of that holistic approach.

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