The World’s Largest Air Filter
The Badalona NOxOFF Project
Transforming urban infrastructure into active air pollution reduction using photocatalysis.
35% documented NOx reduction.
Equivalent to removing 2,200 cars.
Measured in on-site. Documented by research. Designed to last.
The Project at a Glance
A New Standard for Air Quality
Every day, thousands of people in their vehicles move along the C-31 highway in Badalona, Spain — a vital artery connecting the city to Barcelona.
Like many urban roads, it carries traffic, movement, and the invisible burden of air pollution.
But in Badalona, something changed.
Instead of being only a source of nitrogen oxides (NOx), the highway became part of the solution.
Using NOxOFF photocatalysis technology, Photocat transformed the asphalt surface into the world’s largest artificial air filter.
Through advanced photocatalysis, the road now actively reduces NOx emissions directly from the surrounding air when exposed to sunlight.
This is measurable, documented NOx reduction under real urban conditions.
It is evidence that cleaner air is achievable — at scale.
Treated Surface
- 100,000 m² asphalt + 10,000 m² concrete
- applied in two night operations without traffic disruption
Monitoring
- Indipendent
- Measured by CARTIF Research Center using calibrated air quality stations
NOx Reduction
- Documented decrease in nitric oxide (NO) concentrations under live traffic conditions
- 50–80% NO₂ Reduction
Health Savings
- The projected public health cost reduction per year
- Equivalent to removing 2,200 cars from circulation
Project Scope: C-31 Badalona Installation
In August 2023, the C-31 highway in Badalona became the site of one of the largest real-world applications of photocatalytic technology in Europe.
Over the course of two carefully coordinated night operations, 110,000 m² of active road surface were treated with NOxOFF technology. The intervention covered:
- 100,000 m² of asphalt roadway
- 10,000 m² of concrete elements along the corridor
The installation was executed lane by lane during low-traffic hours to ensure operational continuity. At no point was the corridor fully closed, and traffic flow was maintained throughout the process.
The application was completed efficiently and without technical challenges. No disruption to mobility, no interference with infrastructure integrity, and no impact on surrounding communities.
This was not a laboratory test or a pilot patch.
It was a full-scale urban intervention on a high-density traffic corridor running through a residential environment. – Michael Humle, Photocat A/S , CEO.
The objective was clear:
- Reduce NOx concentrations in a heavily trafficked urban artery
- Improve ambient air quality in surrounding neighborhoods
- Demonstrate that photocatalysis can operate effectively under real traffic conditions
The C-31 project marks a transition from experimental surface treatment to city-scale air pollution reduction infrastructure
Roads as Active Air Pollution Reduction Systems
At the core of the Badalona project is photocatalysis — a light-activated chemical reaction that neutralizes nitrogen oxides (NOx) directly from ambient air.
Photocat’s proprietary NOxOFF technology contains engineered Titanium Dioxide (TiO₂). When exposed to natural sunlight, particularly UV radiation, the surface activates and initiates a catalytic process that:
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Oxidizes nitrogen monoxide (NO) and nitrogen dioxide (NO₂)
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Converts harmful NOx gases into stable nitrates
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Allows residues to be washed away naturally by rain
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Operates continuously without electricity
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Requires no filters, no mechanical systems, and no moving parts
The road itself becomes a passive and continuous NOx reduction system.
Unlike conventional air filtration infrastructure, NOxOFF does not require energy input or ongoing operational intervention. Once applied, the surface remains active for the lifetime of the treated structure.
This makes photocatalysis particularly suited for:
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High-traffic urban corridors
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Ring roads and access routes
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Airports and logistics hubs
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Dense residential areas exposed to vehicle emissions
The C-31 installation demonstrates that outdoor air pollution can be addressed directly at infrastructure level.
18 Months of Independent Monitoring
To ensure scientific transparency, the Badalona C-31 project was monitored by the independent CARTIF Research Center over an 18-month period.
Three air quality stations were installed:
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Two at NOxOFF-treated sections
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One at a comparable untreated reference section 700 meters away
This setup allowed direct comparison under identical traffic conditions.
Measured NO Reduction
Data shows a 15–35% reduction in nitric oxide (NO) concentrations compared to the untreated reference road.
The reduction becomes particularly visible during daylight hours, when sunlight activates the photocatalytic surface.
Measured NO₂ Reduction
Even more significant reductions were recorded for nitrogen dioxide (NO₂):
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50–80% reduction in NO₂ concentration
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Treated section recorded levels below WHO guideline thresholds
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Reference section showed concentrations up to 2.5 times higher than WHO recommendations
This is critical, as NO₂ is one of the most harmful components of traffic-related air pollution.
Controlled Traffic Conditions
Particulate matter (PM2.5 and PM10) levels remained comparable between treated and reference sections.
This confirms that:
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Traffic intensity was similar
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Emission sources were consistent
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The reduction in NOx is directly attributable to NOxOFF photocatalysis
The findings validate that this is measurable air pollution reduction, not statistical variation.
Environmental, Health and Economic Value
The Badalona C-31 project translates measured NOx reduction into tangible environmental and societal benefits.
Based on monitored performance:
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2,200 kg of NOx removed per year
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Equivalent to removing 2,200 cars from circulation annually
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Comparable to planting 11,000 mature trees
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Estimated €176,000 in annual health cost savings
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10-year projected value creation: €1.76 million
Documented efficacy model:
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50 m² treated surface = 1 kg NOx reduced per year
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50,000 m² application = 1,000 kg NOx reduced annually
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Payback period estimated at 1–3 years
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Photocatalytic effect lasts for the lifetime of the treated surface
Beyond numbers, the impact extends to surrounding residential areas, schools, and public spaces located along the C-31 corridor.
The project demonstrates that urban air quality improvement can be embedded into existing infrastructure, without restricting mobility or altering traffic flow. This positions NOxOFF technology as a scalable urban air pollution reduction solution.
FAQ
Can outdoor air pollution really be reduced through infrastructure?
Yes. As the Badalona project demonstrates that photocatalytic surface treatment can measurably reduce NO and NO₂ concentrations in real-world traffic conditions.
What pollutants does NOxOFF reduce?
Primarily, NOxOFF targets nitrogen oxides (NO and NO₂), key contributors to urban air pollution and secondary particulate formation. It can also help degrade certain sulfur oxides (SOx) and volatile organic compounds (VOCs) present in ambient air.
Does NOxOFF require electricity or maintenance?
No. The photocatalytic reaction is activated by sunlight. The system operates passively without energy input or mechanical components
How long does the photocatalytic effect last?
The anti-NOx effect lasts for the lifetime of the treated surface structure under normal conditions.
Can NOxOFF be applied in other cities?
Yes. The technology is scalable and suitable for:
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Highways and urban corridors
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Airports and airside pavements
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Ring roads and tunnels
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Logistics hubs and industrial areas
Is this the largest artificial air filter in the world?
The Badalona C-31 installation is widely recognized as one of the largest documented photocatalytic air pollution reduction projects globally.