Tiny but Mighty: The Science Behind Moss and Air Purification

Moss is a non-vascular plant that thrives in moist environments such as rocks, walls, and soil. Unlike woody plants, mosses do not have true roots; instead, they use rhizoids — simple structures that help anchor them and absorb water. Photosynthesis in moss operates on the same basic principle as other green plants: converting water (H₂O) and carbon dioxide (CO₂) into glucose and oxygen (O₂) using light energy, with chlorophyll pigments acting as the main catalysts. Though simple, this chemical process results in carbon bonds in the form of organic compounds, effectively helping reduce atmospheric CO₂ levels.

Air Pollution and Environmental Chemistry: A Simple Explanation

In environmental chemistry, air pollution isn’t just the visible smog or dirty dust that cloaks cities. Behind the scenes, invisible chemical compounds play a major role. One of the most well-known is carbon dioxide (CO₂), a major greenhouse gas accelerating global warming [1]. There are also nitrogen oxides (NOx) and fine particulate matter (PM), which are commonly released by vehicle exhausts, industrial chimneys, and the burning of fossil fuels.

CO₂ isn’t directly toxic to humans, but its rising levels contribute significantly to global temperature increases. NOx and PM, on the other hand, are hazardous to human health — ranging from mild respiratory irritation to chronic lung diseases [2]. Chemically, these gases can react with water and oxygen in the air. For example, NOx can transform into nitric acid (HNO₃), a corrosive substance that damages buildings, soil, and vegetation [3]. Such reactions disturb the natural chemical balance of the atmosphere and alter the composition of the air we breathe every day.

Why Moss Matters in Cities

Moss is often seen as a nuisance in the built environment. Growing on rooftops or concrete walls, it traps moisture through its rhizoids, accelerates weathering, and can lead to mold growth or structural cracks. For property managers, moss is a warning sign that a surface is too damp. But this criticism only tells half the story. In the context of urban environments plagued by pollution, moss holds extraordinary potential as a natural absorber of pollutants and CO₂.

Studies have shown that moss is highly effective at absorbing CO₂ and various pollutants — sometimes outperforming larger plants, especially in confined urban spaces. A study from the University of Michigan reported that mosses are capable of storing up to 6.4 billion tons of carbon — surpassing reserves in regions without such vegetation [4][5]. On green roofs in Korea and Greece, moss was found to absorb between 1.24–2.66 kg of CO₂ per square meter annually, while also reducing building energy consumption by approximately 23–28 kg CO₂/m2 per year [6][7].

How Moss Absorbs CO₂ and Other Pollutants

During photosynthesis, moss absorbs CO2 from the air and, with water and sunlight, converts it into glucose and oxygen. This process occurs within the cells containing chlorophyll pigments. The chemical reaction is simple: six molecules of CO₂ and six of H2O are transformed into one molecule of glucose and six molecules of O₂. The glucose is stored for energy, while the oxygen is released back into the atmosphere. While the reaction may appear small, its collective impact is significant — it helps reduce CO₂ levels and slows global warming. Recent experiments even showed that synthetic moss Racomitrium japonicum captured CO₂ most effectively at 25 °C under high light conditions [8].

Beyond CO₂, moss possesses remarkable abilities to absorb heavy metals and other pollutants. Despite their simplicity, moss cell walls are rich in chemical groups like carboxyl and hydroxyl, which are highly reactive. These groups function like “molecular hooks” that attract and bind to metal ions such as lead, cadmium, or copper in the air. This process is known as biosorption — the passive absorption of pollutants without requiring metabolic energy. In essence, moss acts like a natural chemical sponge, trapping harmful substances from the environment.

In fact, moss is a proven natural biosorbent for heavy metals like lead (Pb2+), cadmium (Cd2+), copper (Cu2+), and chromium (Cr3+). For instance, Pb2+ ions can bind to –COOH groups on moss cell walls, forming stable complexes that neutralize the metal’s toxicity. This biosorption mechanism has shown impressive results: moss can retain up to 87% of cadmium and 93% of lead under optimal conditions, as modeled by Langmuir and pseudo‐second‐order kinetics [9].

What makes moss even more effective is its lack of a waxy cuticle, unlike typical leafy plants. This makes its surface more open and moist, enabling it to capture airborne particles like PM2.5 and PM10, as well as toxic gases like NO₂ and SO₂. When these gases contact the water layer on the moss surface, they dissolve and form acidic compounds like nitric and sulfurous acid. These compounds are then absorbed or neutralized by the moss. Despite its tiny size, moss’s ability to filter polluted air is truly exceptional.

Global Inspiration: CityTree and Moss Walls

Urban innovations using moss as air filters have been gaining traction. In several European cities — such as Berlin, London, Oslo, and Amsterdam — structures called CityTrees have been installed: vertical moss panels equipped with sensors, irrigation systems, and air circulation units. These installations are said to absorb fine particles and NO₂ equivalent to the air-cleaning capacity of 275 regular trees [10][11][12].

Picture: Getty Images

Similar projects are underway in Kazakhstan, where moss filters are used to reduce airborne heavy metals, though they remain in pilot stages [13][14]. A study in the International Journal of Plant Biology (2025) also supports the effectiveness of moss walls for air quality monitoring [15].

With all these capabilities, moss is clearly more than just an eyesore on old walls or rooftops. Rather than treating it as a problem, it’s time we start viewing moss as an ally in environmental protection. Amidst escalating climate and air pollution crises, moss offers a natural, energy-efficient, and effective solution for improving air quality around us. If urban planners, architects, and communities begin to recognize its potential, we can create urban spaces that are not only aesthetically pleasing but also healthier and more eco-friendly.

So the next time you spot moss growing in a corner of a wall or sidewalk, perhaps it’s worth pausing for a moment to ask: Could it be quietly helping us breathe better?