How black carbon emissions are affecting rainfall in the North East

What tastes better – his mother’s recipe for a chicken gravy dish cooked on a liquid petroleum gas cylinder or on an open wood fire? “Of course, the slow-cooked chicken on an open wood fire,” Shahjahan is quick to put any doubts to rest.

Shahjahan, a farmer who doubles up as a computer technician in Tezpur on the banks of the Brahmaputra river in Assam, a river basin state, observes that most households in his village have a gas cylinder but burning wood (biomass) is the preferred cooking method.

Shahjahan and his neighbours’ experiences with the clean fuel transition – stacking up cooking gas against biomass (khori) use – are also reflected in the fifth National Family Health Survey data that shows that despite having cooking gas connections, many do not use it for cooking. “The cooking gas is used when we need to quickly serve tea, heat water for bath or warm milk,” noted Shahjahan. “It takes more time to start the biomass fire, but the food is tastier.”

The hike in cooking gas costs is another deterrent. “Three to four years ago we bought the gas cylinder at Rs 550, now the cost is around Rs 1,000,” the 25-year-old added, pointing to the shed to stockpile khori abutting fields of gourd and paddy. “In contrast, the khori [discarded bamboo poles used to support crop growth] we use is easily available on our farms.”

He said they have started cooking outdoors in recent years to eliminate the fumes that choke up their indoor environment and harm health.

Biomass burning also spews tiny particles called black carbon. Black carbon aerosol is formed by the incomplete burning of fossil fuels, biofuels, biomass (caused by human actions) and by natural sources such as wildfires. The air pollutant is the dominant form of light-absorbing particulate matter in the atmosphere.

It warms the atmosphere because it absorbs light (solar energy). Although it remains in the atmosphere for just a few days or weeks, compared to a century or more for carbon dioxide, it is a major short-term contributor to global warming. The warming effects of black carbon aerosols are second only to carbon dioxide – it has a heat-trapping power a million times more than carbon dioxide and can travel long distances on air currents.

Shahjahan’s family’s kitchen is one of the survey spots for budding scientists at Tezpur University’s Department of Environmental Science who regularly troop in with an aethalometer – an instrument to collect and analyse black carbon, commonly known as soot. They are trying to unpack more information about black carbon and aerosol sources. Shahjahan’s home is one of the several households the team surveyed for their aerosol research as the family transitioned from biomass to padding up their cooking fuel use with cooking gas.

“Before we started using LPG three years ago, we installed a biogas cookstove, but there were challenges to address the waste disposal – we volunteered to move onto cooking gas when we saw others in the neighbourhood also using it,” Shahjahan said, referring to the transition from biogas to liquid petroleum gas.

Black carbon influences

Understanding the ground realities in the energy transition is key to teasing apart the role of aerosols (mainly black carbon) in tinkering with atmospheric processes including those that drive rain in northeast India, where extreme rainfall and floods in this year’s pre-monsoon months have upended life and livelihoods.

Apart from stringent implementation of clean cooking schemes and transport policies in northeast India, reducing emissions in the Indo-Gangetic Plains is an equally important link in the chain to integrate climate action with pollution control in the Brahmaputra river basin region.

Tezpur University’s Raza Rafiqul Hoque and his team find that black carbon loading around Tezpur in the Brahmaputra river basin is “almost at par” with the levels in the rural Indo Gangetic Plains.

“In the Brahmaputra river basin region, we see black carbon signatures from fossil fuel burning (coal, petrol) in transport, brick kilns, tea gardens and agricultural and household biomass burning,” Hoque said. “We also receive a substantial amount of black carbon via air mass transport from Indo-Gangetic Plains (mainly in the pre-monsoon) and peninsular India and neighbouring Bangladesh (in the monsoon season), which has a heavy concentration of brick kilns.”

“When we were doing the measurements, we were puzzled to see a lot of coal signatures coming in the monsoon months because the brick kilns stop operating in these months,” he said. “But it is the peak season for tea industries in northeast India and they rely on coal-burning for their energy needs.”

Sharad Gokhale at Indian Institutes of Technology-Guwahati’s Air and Noise Pollution Laboratory said that aerosols, including black carbon, most influence the western part of northeast India closest to Indo Gangetic Plains.

Gokhale’s lab’s recent modeling study showed that rising black carbon emissions lead to a decrease in low-intensity rainfall while pushing up severe rain in the pre-monsoon season in northeast India. Co-author and research scholar Neeldip Barman explains that the presence of higher aerosol amounts suppresses rain formation, which in turn subdues lower-intensity rainfall.

“But an increase in black carbon concentration pushed up the moisture levels,” Barman said. “Increased black carbon also helps transfer more moisture to the upper atmosphere.”

“It moves the cloud water to the upper atmosphere, where it converts to ice/hail,” Barman said. “Melting of ice/hail produces severe rainfall. An increase in cloud cover at a height of 10 km [above ground level] contributed by ice is a possible cause and validation of this mechanism.”

Black carbon sources

The pre-monsoon rains have a special place in northeast India’s rainfall distribution spectrum.

“If you look at the seasonal distribution of rainfall in the northeast, the amount of rainfall received in pre-monsoon is second to the monsoon rainfall,” said climate scientist Jayanarayanan Kuttippurath at IIT-Kharagpur’s Centre for Oceans, Rivers, Atmosphere and Land Sciences. “If you look at statistical trends, the rainfall in the pre-monsoon months is roughly equal to the average annual rainfall across northeast states.”

These months also happen to be the season when aerosol loading is highest in the North East.

There are regional and seasonal differences in aerosol loading and in northeast India, the aerosol loading is relatively highest in the pre-monsoon season. Long-term trends show that while pre-monsoon rainfall is declining, aerosol in this region is increasing. “So this part of India presents a fascinating case study to understand the rainfall-aerosol interactions,” added Kuttippurath.

Kuttippurath said agricultural biomass burning, especially in shifting cultivation practices in hilly regions in northeast India in the pre-monsoon months of February, March and April, also accounts for high black carbon levels.

The biomass burning in pre-monsoon months in northeast India represents one of the two major peaks in fire count in India – the other prominent count coming in from the Indo Gangetic Plains. The Indo Gangetic Plains fire counts coincide with the region’s two harvesting seasons (April-June and October-November) and associated winter stubble burning.

Neeldip Barman said that their research shows the overall proportion of black carbon dumped onto the Brahmaputra basin/northeast India from Indo Gangetic Plains is higher than that generated in the basin itself. Zooming in on Assam, Rajarshi Sharma at the lab in Indian Institutes of Technology-Guwahati is parsing through sectors that spout black carbon to create a black carbon emissions inventory for the state during 2018-2019, to get a clearer picture.

The key sectors are transport, industry, residential fuel (including biomass and kerosene), open burning and diesel consumption in the non-transport sectors.

“When divided into fossil fuel and biomass sources, we saw that fossil fuel contributed to approximately 60% of total emission, while biomass burning contributed 40%,” he added. “Firewood burning and kerosene lamps for lighting, both of which comes under the residential fuel sector, when considered individually, account for higher black carbon levels than the transport sector emission from the entire state [3.44 gigagram].”

Key pollutants

As expected, vehicles are the primary sources of black carbon in urban areas (such as Kamrup Metropolitan district). But residential fuel consumption (in the form of biomass burning and kerosene lamps for lighting) turned out to be the primary source of black carbon in suburban and rural areas, reflecting the rural population’s energy needs and diverse ecology.

“Policies to electrify transportation in urban areas, replace coal with renewables, upgrade vehicles to the latest auto emission norms [Bharat Stage VI] and switch to clean cooking fuels are already in place; we need to execute them stringently and also curb fossil fuel use,” said Gokhale.

Pallav Purohit who works on energy policy and pollution management research at International Institute for Applied Systems Analysis, Austria, said enacting new policies later on and incorporating them through regional cooperation among states and neighbouring countries (such as Nepal, Bhutan, Bangladesh and Pakistan) can achieve enhanced benefits.

The pollutants contributing the most to both local and transboundary air pollution problems are sulfur dioxide, nitrous oxides, ammonia, volatile organic compounds and fine particulate matter. They mostly originate from the same sources as greenhouse gases.

“There are strong interactions between strategies designed to improve air quality and those addressing climate change,” added Purohit. “Many sources of carbon dioxide also produce health-harming air pollutants (such as coal use in thermal power plants). This means that climate action to limit emissions from these sources also reduces air pollution and its health and economic impacts, even though carbon dioxide itself is not harmful to human health (except at very high concentrations).”

Despite the obvious overlaps in climate mitigation and air quality improvement efforts, Gufran Beigh, founding project director of India’s System of Air Quality and Weather Forecasting And Research, said that there is a dearth of synergy between climate scientists and air quality research community in the country. “Addressing black carbon issues presents us with a unique opportunity to kill two birds with one stone,” Beigh told Mongabay-India.

Climate change mitigation

Meanwhile, the Assam Climate Change Management Society, the government body coordinating the implementation of the Assam State Action Plan on Climate Change and other climate change-related activities, has drafted the revised State Action Plans on Climate Change (2021-2030) with a focus on adaptation and climate change mitigation.

“To curb harmful emissions, on the anvil are the introduction of electric vehicles in urban transport and cleaner brick production technologies,” the Assam Climate Change Management Society told Mongabay-India.

Tezpur University’s Hoque maintains that policies that target climate mitigation and cleaner air must factor in local realities, practices and the gender dimension.

“Because biomass burning has a substantial impact on the regional air quality and rainfall characteristics in northeast India, it makes sense to first supply cooking gas to households that do not have landholdings because, in the absence of landholdings, they cannot produce biomass and can rely on clean fuels [LPG] instead,” added Hoque in the context of Tezpur.

“For households with landholdings, one way is to provide clean cookstoves that burn biomass more efficiently and cleanly than existing stoves,” Hoque said. “The important thing is to improve the burning conditions.”

Shahjahan said, “In recent years, the younger generation of women in our household, with more education and awareness of health implications of indoor biomass burning, have taken to newer applications, so they prefer LPG over wood-burning stoves.”

“They also are not keen to do the labour to collect biomass for firing up the cookstove – using LPG saves them time to take up other pursuits,” explained Shahjahan.

This article first appeared on Mongabay.