How we measure CO₂ removal

We remove CO₂ from the atmosphere. As of now, we have two carbon removal pathways housed under our two umbrella projects:

1. Darjeeling Revival Project (DRP) — Enhanced Rock Weathering.
2. Bengal Renaissance Project (BRP) — Biochar.

I want to walk you through the science of Enhanced Rock Weathering; what equipment we use to measure weathering rates and determine the CO₂ we remove. This is not an exhaustive list, but a quick reckoner on some of the equipment in our labs. Before we begin, what is Enhanced Rock Weathering? 

We use a novel carbon removal method called Enhanced Rock Weathering (ERW), which involves sourcing a volcanic rock (waste basalt) from mines and spreading it across agricultural fields. This basalt rock not only improves soil health and crop yields but also reacts naturally with rainwater to remove carbon dioxide. When CO₂ in rainwater falls on basalt dust, a chemical reaction converts it into stable bicarbonate ions that are stored in the soil. Over time, these ions travel through river networks to the ocean, where they eventually reside as calcium carbonate (CaCO₃) for over 10,000 years. But measuring carbon removal is the harder part of the process.

What goes into that process?

ICP-OES — Reading colour

Think of a fireworks display. That deep crimson red comes from strontium compounds. The bright green is usually copper. Optical Emission Spectroscopy (OES) works on the same underlying principle, but in a controlled and precise way. When you supply enough energy to an atom, it emits light at specific wavelengths that are unique to that element. By reading that light, you can identify exactly what the material is made of.

We collect 1000s of soil, water and river samples to understand the Co₂ we remove. These samples are first dissolved and sprayed into a blazing-hot ionic soup called plasma; an electrically charged flame hotter than the surface of the Sun (~6000K). In this plasma, atoms lose their calm structure and become excited. Each element then emits light at its own unique color. Think of it as a unique fingerprint. The instrument measures this light and translates it into how much calcium, iron, sodium, or dozens of other elements are present. By measuring these elements, we can gauge how much CO₂ we remove.

Humans have known about splitting lights since the 17th century*. The modern leap came in the 1960s–70s, when scientists learned how to use plasmas, making measurements stable, fast, and accurate.

Another way to understand the ICP-OES; this machine measures the nutritional label of the universe, just like how we check our soda cans. It’s great for seeing the array of chemical entities, like checking if there’s too much calcium in your water. 

Fun fact: If your tap water leaves white deposits on your kettle, ICP-OES can tell you exactly how much calcium is causing it. When cities like Chennai and Bengaluru faced water crises, labs used ICP-OES to check whether tanker water contained excess calcium, iron, or heavy metals.

ICP-MS — Weighing the invisible

ICP-Mass Spectrometry (MS) asks a much sharper question: not just what elements, but how rare, how small. 

Mass spectrometry began in 1897 when J.J. Thomson, experimenting with cathode ray tubes, discovered the electron by bending charged particle beams with magnets. By applying electric and magnetic fields, he showed that these particles could be bent, and that the amount of bending depended on their mass and charge. From this, he discovered the electron and demonstrated a radical idea: charged particles can be separated and measured by how heavy they are. 

During World War II, MS became a necessity. For example, the Manhattan Project needed to separate two nearly identical forms of uranium: uranium-235 and uranium-238. They differ only in mass, but that difference determines whether an atomic bomb works or not. The ICP-MS helps determine this. 

The ICP-MS and ICP-OES have the same plasma principle; strip atoms down to charged particles. But instead of looking at light, ICP-MS sends these ions racing through a vacuum, sorting them by mass. 

Imagine you dissolve a sugar cube in a swimming pool, then you scoop up a cup of water from it to see if there is any signature of the sugar cube in the water. The ICP-MS can detect that with extremely high precision. Its accuracy is critical to measure minute changes*.

IRMS — Tracing a droplet to a cloud

The first two machines told us what elements and how much of it was present, but they did not tell us their story. The Isotope Ratio Mass Spectrometry (IRMS) is where the detective steps in. It’s the storyteller. And my favourite equipment. 

Imagine two passengers, both named Carbon. They look identical and they weigh almost the same, yet they are not truly the same. One passenger is just a little heavier because he grew up in a cornfield: Carbon-13. The other is slightly lighter because he grew up in a paddy field: Carbon-12. To the naked eye they are indistinguishable, but to the IRMS, their past is written into their weight.

We use isotopes of oxygen (¹⁸O, ¹⁷O, ¹⁶O) and hydrogen (¹H and ²H) to understand the story of a single drop of water; from the moment it evaporated, to the clouds it traveled through, to the rain falling outside your window. The IRMS is something of a piece of wonder, because of how it can model a story with a simple 1ml of water. 

Every drop of rain water has a memory. Let’s trace this story from the ocean. Sunlight lifts the lighter water molecules first, leaving heavier ones behind. As vapor cools into clouds and storms take shape, that quiet sorting continues. Temperature and distance shifts the balance of this water. By the time this evaporated drop of water falls to earth, its isotopic makeup has been altered at different stages. What looks like simple rain water is a record of the journey it takes from an ocean, through the skies and falls to us as rain in the land.

With every cloud, every storm, and every shift in temperature, a single water droplet’s isotopic makeup has changed. By the time it reached the ground, its isotopic framework has altered. The IRMS can decode this journey. 

Carbon exchanged by plants carries a different isotopic signature than carbon released from rocks or fossil fuels. By reading these subtle differences, we can distinguish biological carbon from geological carbon. This tells us about how much CO₂ we have removed, and from where. 

Unlike plasma-based instruments, IRMS does not use extreme heat. Instead, the sample is gently converted to gas, and ionized using electron impact, where a beam of electrons knocks electrons off the molecules, allowing their masses to be compared with extraordinary precision.

Fun fact: The IRMS machine has a lot of practical real-world applications. It can be used to detect sugar adulteration in honey, fake basmati rice, adulterated fruit juices, whether ghee is truly cow-derived or mixed*.

IC — Reading Water’s identity

We use Ion chromatography (IC) to read water samples. We analyse different kinds of water samples. Groundwater, seawater, riverwater, porewater, and rainwater. They may all look the same, but carry different chemical histories. 

Water contains charged chemical species: chloride, nitrate, sulphate, fluoride and phosphate. Our water samples are pushed through a narrow column packed with charged sites. Each ion interacts with the column differently. Some stick longer, some move faster. As a result, they separate in time. One exits first, then the next, then the next. Time becomes the identity.

After separation, the instrument does something clever and almost invisible: it suppresses the background chemistry of the water itself. What remains is measured by ‘electrical conductivity’, which simply means how easily electricity flows through water because of the dissolved ions. Pure water conducts almost nothing; the more ions present, the stronger the signal. A conductivity detector then measures each ion as a clean, sharp peak.

This is why ion chromatography dominates water analysis. It directly measures what matters for potability, pollution, corrosion, and nutrient loading, without destroying the sample or guessing from proxies. In simple terms, IC asks what the water has been carrying.

Fun fact: During Delhi’s winter smog season, scientists analyze particulate matter (PM2.5) collected from the air. It can also track arsenic contamination in groundwater — something that has killed thousands in the past.

CHNS Analyzer — The fundamentals of soil

We all know soil is the giver of all life. We have written many odes to the story of our soils. We think of soil as a compressed archive of biological and environmental history. Inside that grain are traces of plants that grew, microbes that lived and died, fires that burned, and years that quietly passed. The question to ask: what is this soil made of at its most basic level?

This is where a CHNS analyzer steps in. 

Our samples are placed into the instrument and exposed to intense heat (~1100°C) in a stream of oxygen. The material breaks down completely, returning to its elemental building blocks:

• Carbon becomes carbon dioxide 
• Hydrogen becomes water 
• Nitrogen becomes nitrogen gas, and 
• Sulfur becomes sulfur dioxide. 

These gases are then carried forward and measured using ‘thermal conductivity’. Thermal conductivity describes how efficiently a substance carries heat. Different gases carry heat differently, just as different metals feel warmer or cooler to the touch. As each gas passes the detector, it slightly changes how heat flows, and that change is measured.

This is fundamentally different from electrical conductivity (like in Ion Chromatography), which measures how easily electricity flows through a material due to charged particles. Electrical conductivity depends on ions or electrons. Thermal conductivity depends on molecular motion and heat transfer, not charge. In a CHNS analyzer, the gases are neutral, so heat becomes the fundamental property to distinguish these elements.

From these heat changes, the instrument determines how much carbon, hydrogen, nitrogen, and sulfur were present in the original sample. These four elements may sound ordinary, but together they define life, soil fertility and decay. A soil rich in carbon hints at long-term stability. Nitrogen speaks of productivity. Sulfur can point to pollution or geology. In biochar, they hint at permanence. In sediments, they whisper about past environments.

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