- Methane-monitoring satellites and isotopic studies reveal landfills that could be potentially targetted for methane mitigation in India.
- Using satellite-based observations, a group of scientists zoomed in on methane emissions hotspots in Buenos Aires, Delhi, Lahore, and Mumbai landfills. Through isotopic studies, another group of scientists found that natural gas and waste sectors were the major sources of methane in Pune.
- Large Indian landfills are in the news often due to fires. There are technical challenges to collection and recovery of landfill gas (methane capture) in large landfills because they are not operated scientifically.
Methane-monitoring satellites that zoom in on sources of the climate-warming gas show that landfills contributed to more than 25% of methane emissions in Mumbai and 6% in Delhi. In Pune, isotopic studies, which rely on methane’s atomic makeup, point to significant landfill emissions of methane and a potential natural gas leak.
“A tiered observation system, where all of these things work together to get a full picture of what’s going on, can help identify candidates for methane emissions mitigation,” says J.D. Maasakkers, an expert on atmospheric chemistry and emissions at SRON (Netherlands Institute for Space Research) in the Netherlands.
The Global Methane Assessment 2021 states that the atmospheric concentration of methane has more than doubled since pre-industrial times. Methane is second only to carbon dioxide (CO2) in driving climate change. Limiting warming to 1.5 degrees Celsius or likely two degrees Celsius requires deep, rapid, sustained reductions of other greenhouse gases, such as methane, alongside rapid reductions of carbon dioxide emissions to net zero, states the Intergovernmental Panel on Climate Change’s (IPCC) latest dispatch on climate change mitigation.
More than half of global methane emissions stem from human activities in three sectors: fossil fuels (35% of human-caused emissions), waste (20%) and agriculture (40%). Methane is a short-lived climate forcer (SLCF), a compound that warms or cools the Earth’s climate over shorter time scales – from days to years – than greenhouse gases like carbon dioxide, whose climatic effect lasts for decades, centuries or more. Reducing SLCF emissions is critical to meeting long-term climate goals and might help to reduce the rate of climate change in the short term.
“Methane has a lifetime in the atmosphere of about ten years. But per molecule, it’s a much stronger greenhouse gas over that period. So that means it’s responsible for a large part of the warming that we’re experiencing today. It also means that if we reduce methane emissions now, we’ll see some impact on a decadal timescale. That doesn’t take away the need to reduce carbon dioxide emissions as well because as long as we keep adding carbon dioxide, it keeps accumulating in the atmosphere,” explained Maasakkers..
“But it (mitigating methane emissions) is something we really need to do in addition to reducing carbon dioxide emissions to slow down climate change. And to know how to reduce emissions, we need to know where they are,” he added.
Maasakkers and team used data from the TROPOMI instrument on board the European Space Agency’s Copernicus Sentinel-5 Precursor satellite and GHGSat’s space-based emissions monitoring systems to detect, locate, and quantify emissions from strong methane point sources around the world. Using this approach, they spotlighted methane emissions hotspots in Buenos Aires, Delhi, Lahore, and Mumbai.
“Our urban estimates are based on 2020 TROPOMI data (the guidance of GHGSat is based on earlier TROPOMI data). The landfill estimates are based on 2020-2021 GHGSat data.What we see as a hotspot is an area where there are large methane emissions that we can spot from space. These urban areas have a lot of methane emissions. And partly that’s because of the landfills in those urban areas, that we were able to look at, with GHGSat,” added Maasakkers.
Landfills that have the largest methane emissions would then be sensible targets for emission mitigation. A clutch of satellites with more precision is set to be launched in 2023, including the Environmental Defense Fund’s MethaneSAT, which aims to track not only the rate of methane emissions and location but also how those emissions are changing. Such observations will be useful to initiatives such as the International Methane Emissions Observatory (IMEO) launched at the G20 Summit, a data-driven, action-focused initiative by the UN Environment Programme with support from the European Commission. “The idea is that they will gather all the observations and then form the bridge to the people responsible for the emissions,” added Maasakkers.
Maasakkers also says the synergy between ground-based measurements and satellite-based analysis is crucial. “We cannot look at isotopes from space, but you can do that on the ground. And if you think about seeing emissions from specific facilities, we’re always only going to be seeing large emissions from space. When we look at aggregate emissions over areas, we look at the total but to pinpoint that to specific facilities, you can see much more if you’re on the ground, just because you’re closer. So, there’s absolutely a lot of value in these local observations on the ground,” Maasakkers said.
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Urban landfills generate emissions
In a closer look, scientists at IITM, Pune, monitored methane concentrations and their carbon isotopic ratio between March 2018 and December 2020. They found that microbial and fossil fuel emissions are two major methane sources in Pune. Natural gas was the dominant sector in the fossil fuel sector, while the waste sector was the major segment in microbial emissions. The measurements also coincided with the COVID-19 lockdown, they said in a recent paper.
“In Pune, landfill emissions are very high with respect to other sources. There is a chance that Pune has methane emissions from natural gas (pipeline leaks). It could be methane in CNG stations, CNG pipeline, and CNG gas networks, and it needs to be investigated,” said Abirlal Metye, a study co-author. While the dominant signal of methane emissions was from the waste sector during the COVID-19 lockdown, both natural gas and waste contributed to the emissions before the lockdown in 2018 and 2019.
Scientifically any landfill which is more than six metres deep has the potential to generate methane, adds Suneel Pandey, Director, Environment & Waste Management Division, TERI.
Landfills in Kolkata (Dhapa), Mumbai (Deonar) and Delhi (Bhalswa and Ghazipur) are often been in the news for landfill fires. “It’s a challenge, and it not only causes greenhouse gas emissions but whenever landfills are on fire, they also lead to local pollution in the area. And the situation worsens if it happens in the winter because, in wintertime, the air rises up slowly because of low temperatures. So any smoke or any pollution coming out can persist in the lower layers for longer periods,” Pandey told Mongabay-India.
Because the landfills in India are not scientifically engineered during inception (they don’t have bottom liners and gas harvesting systems during the development of the landfill), collection and recovery of landfill gas (methane emissions) is a technical challenge. “Also, generally, we don’t maintain the history of waste disposal in the landfills. So, sometimes it’s very difficult to determine where more organic waste is disposed of in the landfill, leading to overestimating landfill gas.
As an example, Pandey explains that the overestimation of landfill gas concentration led to claiming of more carbon credits in Mumbai’s Gorai landfill closure and gas capture project, which was implemented in the Clean Development Mechanism framework, the world’s largest carbon offset programme, established under the Kyoto Protocol. The project was shaped by the thrust on mitigating methane emissions (monitoring and capturing methane for clean energy) post the study done by the United States’ Environmental Protection Agency-supported Global Methane Initiative for the ten large waste disposal sites in the country for exploring the possibility of harvesting landfill gas.
“The key question we get after detecting the landfill gas emissions is what is to be done. Most of the large landfills in India are in the process of remediation implemented in the second phase of the Swachh Bharat Mission (Clean India Mission). But for, the current remediation practices are not looking at landfill gas much. For smaller landfills, it’s not much of a problem because there is not much methane there. For larger landfills, once you start opening the landfills, many times the gas escapes and catches fire,” said Pandey, adding that one possible solution to manage landfill emissions is to look at the United States EPA’s Superfund site model for improperly managed contaminated sites such as manufacturing facilities, processing plants, landfills and mining sites.
Banner image: A landfill in Mumbai. According to methane monitoring satellites, landfills contributed to more than 25% of methane emissions in Mumbai and 6% in Delhi. Photo by India Water Portal/Flickr.