For years it was ignored. Now scientists say this gas may be the major contributor to air pollution

Urban air pollution has long been viewed through the lens of familiar enemies: vehicle smoke, industrial emissions, and visible pollution particles hanging over crowded cities. However, new scientific research suggests that a hidden chemical process may be changing how experts understand polluted air. Researchers from Tampere University and the University of Helsinki have discovered that nitric oxide (NO), a gas traditionally believed to reduce aerosol formation, can actually help create pollution particles under certain urban conditions.

The discovery challenges decades of atmospheric science assumptions. Nitric oxide is widely known as a harmful air pollutant released by cars, power plants, and combustion activities. Yet the new findings show that this same gas may contribute to the creation of tiny airborne particles that affect human health, climate systems, and visibility.

The study, published in Nature Communications, reveals that nitric oxide can accelerate the transformation of aromatic carbonyl compounds into low-volatility substances that become aerosol particles. These particles are among the most concerning elements of urban air pollution because they can enter deep into the lungs and influence long-term health.


For years, scientists believed nitric oxide acted mainly as a chemical barrier against aerosol formation. But the new research presents a more complicated reality. Urban air chemistry is not controlled by isolated pollutants. Instead, different compounds interact through complex reactions that can create unexpected outcomes.

How nitric oxide changes the science behind urban air pollution

Nitric oxide has traditionally been considered a pollutant that limits the formation of certain atmospheric aerosol precursors. Many atmospheric models treated the gas as a chemical compound that reduced the production of highly oxygenated molecules needed for particle growth.

The new study shows that this understanding may be incomplete. Researchers examined aromatic carbonyl compounds, which are released from vehicle emissions, industrial activities, and everyday consumer products. When these compounds interact with atmospheric oxidants, they can transform into substances that contribute to aerosol formation.

This changes the way scientists look at urban air pollution. The atmosphere is not a simple mixture where each pollutant acts independently. Instead, gases can combine, react, and create entirely new compounds with different environmental effects.

The discovery is especially important for cities where nitrogen oxide emissions and aromatic pollutants exist together. In busy urban environments, traffic emissions provide both the nitric oxide and organic compounds needed for these reactions.

Why aerosol particle formation remains a major air pollution mystery

Aerosol particle formation is one of the most complicated challenges in atmospheric science. These tiny particles can influence climate, reduce visibility, and create serious health risks. Yet scientists still do not fully understand every pathway that produces them.

The newly identified nitric oxide pathway adds another missing piece to this puzzle. Researchers believe that existing atmospheric models may have overlooked important chemical reactions occurring in real urban environments.

Particulate matter pollution is especially dangerous because smaller particles can travel deep into the respiratory system. Long-term exposure has been linked with increased risks to human health, making accurate pollution forecasting a global priority.

The findings from Tampere University and the University of Helsinki suggest that future air quality models need to include these overlooked reactions. Without them, predictions may underestimate the true level of urban aerosol pollution.

New research reveals a hidden future for cleaner urban air

The discovery of nitric oxide’s unexpected role marks a major shift in the understanding of urban air pollution. A gas once viewed mainly as a suppressor of particle formation may actually contribute to pollution under specific conditions.

This does not mean nitric oxide alone creates harmful air. Instead, it shows how interconnected atmospheric chemistry really is. Pollutants can interact in surprising ways, creating new challenges for researchers and policymakers.

Scientists believe these findings can improve atmospheric models used around the world. More accurate predictions could support better pollution warnings, smarter urban planning, and more effective strategies to protect public health.

FAQs:

Why are tiny airborne particles considered a major environmental concern?
Small pollution particles can remain suspended in the air for long periods and travel across regions. Their size allows them to enter deeper into the human respiratory system, while also affecting visibility, weather patterns, and climate processes.

Can reducing vehicle emissions completely solve city air pollution problems?
Lowering vehicle emissions can significantly improve air quality, but it is only one part of the solution. Pollution can continue changing after release because atmospheric reactions create new compounds that may contribute to particle pollution.

How do everyday products contribute to atmospheric pollution?
Many household and consumer products release volatile organic compounds. These chemicals can react with other substances in the atmosphere and may contribute to the formation of secondary pollutants beyond the original emissions.