The first instrument, the TROPOspheric Monitoring Instrument known as TROPOMI, flies aboard the European Space Agency’s Sentinel-5 Precursor satellite and measures the dry-air column-volume mixing ratio of methane, abbreviated XCH4, across swaths of the planet every day. Because TROPOMI observes the entire atmospheric column between the ground and the satellite, it excels at revealing broad regional patterns: which provinces accumulate the most methane, how those concentrations shift with the seasons, and whether the overall burden is rising or falling over time. What it cannot do, given pixels that span several kilometers, is pinpoint a single leaking pipeline valve or a specific corner of a landfill.

That is where the second instrument comes in. EMIT, the Earth Surface Mineral Dust Source Investigation, was installed on the International Space Station originally to map the minerals in desert dust, but its imaging spectrometer turned out to be remarkably good at something else entirely: detecting the narrow absorption fingerprints that methane plumes leave in reflected sunlight. With spatial resolution fine enough to distinguish individual facilities, EMIT can spot a plume drifting downwind of a gas processing plant or a waste dump and, by modeling how much gas must be present to produce the observed spectral signal, estimate the emission rate in tonnes per hour. The Pakistani team leveraged both instruments in tandem, using TROPOMI to establish the big picture and EMIT to zoom in on the culprits.

The regional picture that emerges from the TROPOMI record is sobering. Between 2019 and 2024, the average atmospheric methane concentration over Pakistan climbed from 1878 ± 13 parts per billion to 1933 ± 14 parts per billion, an increase of roughly 55 parts per billion in just six years. That trajectory mirrors the global rise in methane, which has been accelerating since 2007, but it underscores that a country with rapidly growing energy demand, expanding cities, and a large agricultural sector is tracking at the high end of concern. Methane is more than eighty times more effective than carbon dioxide at trapping heat over a twenty-year horizon, so changes of this magnitude translate into meaningful warming pressure in the near term.

Geographically, the highest methane columns appeared repeatedly over the eastern parts of the country. The Rann of Kutch, the Larkana district, and major urban and industrial centers including Islamabad, Karachi, Lahore, Hyderabad, Multan, Faisalabad, and Gujranwala all registered elevated values. The researchers attribute these hotspots to a combination of natural and anthropogenic activity: dense populations, heavy traffic, industry, agriculture, and in the case of the Rann of Kutch, wetland and seasonal flooding dynamics that foster microbial methane production. The clustering of hotspots over Punjab’s cities and Sindh’s industrial corridor aligns with earlier studies of Pakistan’s air quality, which have ranked several of these cities among the most polluted in the world for particulate matter as well.

Seasonality added another layer to the analysis. Methane concentrations peaked in autumn at 1937 ± 17 parts per billion, followed by summer and then winter. This seasonal rhythm likely reflects a mix of factors, including the timing of rice cultivation and crop residue burning, temperature-driven microbial activity in wetlands and landfills, and atmospheric circulation patterns that either ventilate or trap emissions over the region. The Asian monsoon in particular is known to lift pollution from South Asia into the upper atmosphere, and seasonal wind reversals can redistribute methane across national borders, complicating any attempt to attribute concentrations to sources within a single country.

The most consequential findings, however, came from the EMIT observations, which allowed the team to move from regional averages to named facilities. Between January 2023 and December 2024, the researchers identified and quantified methane plumes originating from three sectors: oil and gas infrastructure, landfills, and electricity generation. The oil and gas sector dominated the tally. The study documented 26 plumes with emission rates exceeding 0.5 tonnes of methane per hour from oil and gas sites, together releasing approximately 78.3 ± 14.7 tonnes of methane every hour. Sustained over a year, emissions of that scale represent millions of tonnes of carbon dioxide-equivalent warming potential, all from a set of facilities that could, in principle, be repaired.

One location stood out above all the rest. Daharki, a town in Sindh province at the heart of Pakistan’s gas-producing region, accounted for the largest number of plumes, with 12 separate detections and total emissions approaching 53.2 ± 9.2 tonnes of methane per hour. In other words, a single cluster of facilities near Daharki was responsible for roughly two-thirds of the oil and gas emissions quantified in the entire study. This pattern echoes what researchers have found in other major producing basins around the world, from the Permian Basin in Texas to offshore platforms in the Gulf of Mexico: a small number of so-called super-emitters, often operating under abnormal process conditions such as equipment malfunctions or venting events, contribute a disproportionate share of total emissions. The implication is that targeted leak detection and repair at a handful of sites can deliver outsized climate benefits.

Landfills emerged as the second major source category, and the detections were unambiguous. The team identified strongly emitting landfill sites releasing between 1 and 5.3 tonnes of methane per hour at Jam Chakro in Karachi, Losar in Rawalpindi, and Lakhodair in Lahore. These are the principal waste disposal sites serving three of Pakistan’s largest cities, and their methane output is the natural consequence of organic waste decomposing anaerobically in massive open dumps. The finding carries a double significance. First, it confirms that unmanaged waste in rapidly urbanizing South Asian cities is a methane source of global relevance, consistent with satellite surveys that have uncovered large landfill emissions worldwide. Second, it points to an opportunity: capturing landfill gas for energy generation, a strategy long discussed in Pakistan, would simultaneously reduce emissions, improve local air quality, and produce usable fuel.

The study arrives at a politically charged moment. Under the Global Methane Pledge, more than 150 countries have committed to cutting global methane emissions by at least 30 percent from 2020 levels by 2030, and Pakistan’s biennial transparency reporting obligations under the UN climate convention require it to account for its emissions with increasing rigor. Until now, the country’s methane inventories have relied heavily on bottom-up estimates and global models that may poorly represent local conditions. By demonstrating that freely available satellite data can both track national trends and expose specific leaking facilities, the researchers have effectively handed Pakistani regulators, and the international community, a verification toolkit. The technical approach, pairing a wide-swath column instrument with a point-source imaging spectrometer, is the same two-tier strategy now being applied in China, India, and the United States, and the Pakistani analysis shows it works even in data-scarce environments. Whether the plumes over Daharki, Jam Chakro, and Lakhodair translate into repairs and policy action remains to be seen, but the era of invisible methane over South Asia is clearly coming to an end.

Subject of Research: Satellite detection and quantification of methane hotspots and emission sources over Pakistan using TROPOMI and EMIT observations

Article Title: Detecting methane hotspots and anomalies from space over Pakistan: analysis using sentinel-5P TROPOMI and EMIT observations

Article References: Mariam, A., Haq, Z. U., & Batool, S. A. (2026). Detecting methane hotspots and anomalies from space over Pakistan: analysis using sentinel-5P TROPOMI and EMIT observations. Air Quality, Atmosphere & Health, 19(10), Article 230. https://doi.org/10.1007/s11869-026-02108-z

Image Credits: AI Generated

DOI: 10.1007/s11869-026-02108-z

Keywords: methane, TROPOMI, EMIT, Pakistan, satellite remote sensing, greenhouse gases, oil and gas emissions, landfills, super-emitters, air quality, climate change, Sentinel-5P

The scale of the underlying waste problem in Uganda provides essential context for the results. The country’s eleven major cities are home to roughly 5.5 million residents and visitors, about 12.1 percent of the national population, and this urban concentration has driven a sharp rise in solid waste generation. Kampala Capital City alone produces approximately 28,000 tons of municipal solid waste every month, a figure that has more than doubled over the past two decades. Globally, the World Bank projects that waste generation could reach 27 billion metric tons per year by 2050, and developing countries with limited collection infrastructure and low recycling rates face the steepest challenges. In Uganda, the waste stream is dominated by food scraps, paper, cloth, plastic bags and bottles, glass, medical waste, and metals, with plastics accumulating across all landfills in forms that include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polycarbonate, polyurethane, and polyvinyl chloride.

Composting has been embraced as a practical response to this mounting waste burden. By converting biodegradable material into nutrient-rich manure, composting reduces waste volume, recycles organic matter back into farmland, lessens dependence on commercial fertilizers, and improves soil quality. The technology adopted at Ugandan landfill sites is conventional and simple, consisting mainly of open windrows in which mixed waste is left to decompose. The trouble is that very little of the incoming waste is segregated. Only three of the eleven sites studied, Mukono, Lira, and Fort Portal, perform any manual pre-treatment to remove non-compostable materials before composting begins, and even that removal is incomplete. When plastic-laden mixed waste enters the windrows, mechanical weathering, oxidation, and photocatalytic breakdown progressively fragment the larger plastic items into microplastics, defined as synthetic polymer particles smaller than 5,000 micrometers.

To quantify this contamination, the research team designed a sampling campaign that controlled for both spatial and temporal variability. All samples were collected during a single two-week window in the dry season of June 2025. At each site, three mature compost piles were independently sampled, with each pile divided into top, middle, and bottom sections sampled at a depth of 5 to 15 centimeters using a stainless-steel shovel. The sections were homogenized, and material from the three piles was combined into a single composite sample of 300 grams per site, which was then sieved through a 5-millimeter stainless-steel mesh, sealed in airtight paper bags, and transported in a cool box to the laboratory. Compost maturity was verified before analysis: every sample exceeded a germination index of 70, showed a carbon-to-nitrogen ratio below 20, total nitrogen below 3.0 percent dry weight, and a pH between 7 and 9, confirming that the material analyzed was genuinely finished compost rather than raw waste.

The laboratory extraction followed an adapted wet peroxide oxidation protocol. Twenty grams of sieved, oven-dried compost were digested with Fenton reagent, a mixture of 20 milliliters of 30 percent hydrogen peroxide and 20 milliliters of 0.05 molar acidified ferrous sulphate, heated to approximately 75 degrees Celsius in a laminar flow fume hood until the organic matter disappeared. Density separation followed, using a saturated zinc chloride solution at 700 grams per liter with a density of 1.7 grams per cubic centimeter. After an hour of settling, the supernatant was filtered through a glass microfiber filter with an 11-micrometer pore size, and the captured particles were air-dried for three to four days before examination under a ZEISS Stemi 508 stereomicroscope fitted with an Axiocam 208 color camera. The researchers distinguished genuine plastic from natural particles using the hot needle and break tests, and rigorous quality controls, including blank tests with distilled water, non-plastic sampling equipment, cotton lab clothing, and glassware cleaned three times with distilled water, confirmed that no contamination was introduced during handling. Statistical comparisons across sites used a one-way ANOVA followed by Tukey’s HSD test at a significance threshold of 0.05.

The results painted a picture of pervasive but uneven contamination. Hoima’s compost site exhibited the highest microplastic abundance, more than double the eleven-site average, and was identified as a statistical outlier, significantly exceeding Jinja (p = 0.030), Mbale (p = 0.013), Soroti (p = 0.012), Kabale (p = 0.010), and Fort Portal (p = 0.0027). Jinja, which deploys an advanced Komptech Cribus 3800 mobile screening machine for post-composting processing, recorded a high abundance of 3,050 ± 304.63 particles per kilogram with relatively low variation, suggesting that mechanical screening without upstream segregation may actually break plastics down further and distribute them through the compost. At the low end, Mukono (1,250 ± 312.77 particles/kg) and Kasese (1,300 ± 316.58 particles/kg) showed statistically indistinguishable levels (p = 0.86), while Gulu and Hoima displayed the greatest variability, pointing to intermittent plastic inputs. The Ugandan average sits close to figures reported elsewhere: 2,400 ± 358 particles per kilogram in rural domestic waste compost in Zhejiang Province, China, and 2,800 ± 616 particles per kilogram in municipal organic waste compost in the Netherlands.

Perhaps the most telling result concerned particle shape. Fibres dominated at every site, accounting for 54.98 percent of all identified microplastics, followed by pellets at 15.37 percent, fragments at 15.15 percent, films at 6.06 percent, filaments at 5.41 percent, and foams at just 3.03 percent. Fibrous particles are strongly associated with synthetic textiles, ropes, and sacks, and Soroti’s profile was almost entirely fibrous, suggesting a single dominant source such as woven packaging material. Pellets, which are industrially manufactured primary microplastics often used in personal care products, featured prominently in Jinja, Fort Portal, Gulu, and Mbale. Fragments arise from the degradation of hard plastics such as high-density polyethylene, while films trace back to plastic bags and food packaging. The overwhelming presence of secondary microplastics, particles formed by the breakdown of larger plastic items, led the authors to conclude that poor waste management and inadequate segregation practices are the root cause of the contamination, rather than any single industrial source.

The environmental implications extend well beyond the compost pile itself. Previous research has shown that microplastics alter soil physical properties, including porosity, water-holding capacity, structure, and bulk density, and that polypropylene additions to loess soils can raise concentrations of nitrogen, phosphorus, and dissolved organic matter. Microplastic surfaces also adsorb hydrophobic organic compounds and heavy metals, acting as vectors that transport toxic chemicals through soil, and they can host distinct microbial communities that facilitate the spread of pathogens. Because compost is applied directly to farmland, the particles it carries enter the soil-plant system, where they may influence crop growth rates and nutrient uptake. Studies in both China and Europe have further demonstrated that the composting process itself can increase microplastic abundance by fragmenting larger plastics, with one study recording a rise from 5,133 particles per kilogram in raw material to as much as 11,200 particles per kilogram in finished compost, which helps explain why even screened compost retains substantial plastic loads.

The human health dimension adds urgency to the findings. Microplastics in compost can enter the food chain, and growing research interest now focuses on how these particles are absorbed, distributed, metabolized, and excreted in the human body. Continuous exposure has been linked to inflammation, and microplastics are suspected of interfering with metabolic processes. The authors of the Ugandan study acknowledge important limitations, including the compositing of three piles into a single site-level sample, which prevented assessment of within-site variability, the reliance on stereomicroscopy and the heated needle test rather than advanced techniques such as micro-Raman spectroscopy, FTIR, or pyrolysis-GC/MS for polymer verification, and the absence of recovery-efficiency testing. They also note the lack of standardized protocols for microplastic sampling and extraction. Even so, the central message is unambiguous: compost from municipal solid waste sites across Uganda is considerably contaminated with microplastics, and the most effective remedy lies upstream. Enhancing source segregation at the household and municipal levels, the researchers argue, would reduce the plastic entering composting facilities in the first place and lower microplastic concentrations in the final product applied to the nation’s farmland.

Subject of Research: Microplastic contamination of compost produced from municipal landfill waste in Uganda

Article Title: Identification and quantification of microplastics in compost from municipal landfills in Uganda

Article References: Tumwebaze, A., Twinomujuni, D., Baluku, E., Ogwal, F. S., Akankwasah, B., & Komakech, R. (2026). Identification and quantification of microplastics in compost from municipal landfills in Uganda. BMC Environmental Science, 3(1), Article 22. https://doi.org/10.1186/s44329-026-00064-8

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00064-8

Keywords: microplastics, compost, Uganda, municipal solid waste, landfills, waste management, soil contamination, food chain, plastic pollution, composting, environmental science, zinc chloride density separation