How electrifying the air in parking garages could clean our cities

Technology that removes fine dust from the air in enclosed garages even cleans the air outside

Particulate-matter-technology.jpg
The unit set up in a parking garage (left) collects billions of particles from the air as a tar-like substance (right). (Source: ENS Technology)

Correction: The cost of using this technology would add 10 to 20 cents to the cost of a parking ticket, not 1 to 2 cents. We apologize for the error.


At the start of 2017, parts of China were under red alert for smog. CNN's Chief National Security Correspondent Jim Sciutto tweeted a photo taken from the sky showing the tops of Beijing’s tallest buildings piercing the billowing smog – a stark reminder of how serious the air pollution there has become.

This may be an extreme case, but air pollution is a problem in most cities around the world. According to the World Health Organization, air pollution caused 3 million premature deaths in 2012; reducing air pollution could help countries reduce the incidence of heart disease, lung cancer, stroke and asthma. Some studies have also linked the inhalation of fine dust in the air to Alzheimer’s and Parkinson’s disease. The Organization for Economic Cooperation and Development (OECD) warns that without action, air pollution will be the biggest environmental cause of premature death by 2050.

There may be an answer in the form of technology. In fact, the basis of this technology has been available for decades but has only recently been implemented in a system with high enough efficiency to make it practically feasible.

New research in the Journal of Wind Engineering and Industrial Aerodynamics led by Dr. Bert Blocken, a professor in the Department of the Built Environment at Eindhoven University of Technology (TU/e) in the Netherlands and the Department of Civil Engineering at KU Leuven University in Belgium, reveals that electrically charging the particles that are concentrated in a particular space, such as in an underground carpark, can make the air outside significantly cleaner – and therefore healthier.

Hotspots of air pollution

Particulate matter (microgram per m³) in a city area without (left) and with (right) removal units installed in parking garages. This figure first appeared in Blocken et al, <em>Journal of Wind Engineering and Industrial Aerodynamics</em> (December 2016).

Particulates are ubiquitous in city air. Lots of city activity produces the particles so small that they are invisible individually but possible to inhale, from burning fossil fuels for heating homes and office buildings to braking in the rush hour traffic. Cars are a major source of air pollution: the particles originate not only from exhaust but also from wear and tear on the tires and brakes, which can be equally or even more important.

Prof. Bert Blocken, PhDIt is the traffic-related particulates Dr. Blocken wants to address. He explained:

People often think it’s only the burning of fuel in cars that pollutes the air – it stands to reason, as we can smell and even see what comes out of car exhausts. But it’s also very much the brakes and wearing of tires that generate the particles. If we all went electric, the problem wouldn’t be completely solved as we would still get particles from the metal and polymers from tires. In urban traffic, they can cover more than 50 percent of the total particulate matter pollution.

What makes these particles so dangerous? Our bodies have evolved to filter out large particles from the air, so natural pollutants like sand and dust are caught in the nose and throat. But smaller particles, like the particulate matter (PM) from car exhausts, can reach the lungs and settle in the tiny air pockets there. Particles that are smaller than 100 nanometers can even pass from the lungs into the blood and to other organs, including the brain.

Even at very low concentrations, PM in the air is linked to higher rates of disease and birth defects. The EU has set a limit of 50 micrograms per cubic meter, but concentrations in big cities like Beijing and London far exceed these limits. Location is also important: there are hotspots of pollution that contribute to the PM in the air outside. As well as being the source of the problem, these hotspots might also be part of the solution.

Electrifying particles

Indoor or underground parking garages have concentrations reaching up to 300 micrograms per cubic meter of air – six times the acceptable limit – and beyond. A lot of braking and accelerating happens in these spaces, generating a significant amount of pollution, which escapes to the air outside, contributing to the city’s overall pollution levels.

Taking the particles out of the air in these hotspots could be a way to dramatically reduce their concentration, Dr. Blocken explained:

Hotspots like parking garages are good places to start with purifying the air. Instead of flushing it out in the open and polluting the rest of the city, you can neutralize a lot of it at the source.

Working with the company ENS Technology: Environmental Nano Solutions, Dr. Blocken and his team modeled the effect their technology would have on the air in Eindhoven city center in different enclosed spaces and outside. For the first time, they showed that cleaning the air inside these pollution hotspots can significantly reduce pollution outside.

The technology is a box with a fan that flows air through the box, charging the particles positively. There is a plate on the side of the box that has a negative charge, attracting the particles so they stick like tiny magnets. Over time, billions of particles accumulate and coagulate into a sticky, tar-like substance that can be disposed of.

It’s fascinating to see and measure the effect, especially how fast you see the system collect billions of these particles. Pollution sticks in the city, like a cloud – you would otherwise be inhaling these particles walking through the garage or the city.

The effectiveness of the technology inside has been shown before and, anecdotally, people living near parking garages reported cleaning their windows less often when the technology was used. Dr. Blocken and his team showed how this happens. In a typical situation, with a little outside wind, the particle concentrations in the air in surrounding streets outside were reduced by up to 50 percent.

The technology is available and relatively cheap, so why aren’t cities installing them in every pollution hotspot? Dr. Blocken thinks it has a lot to do with awareness.

What surprised me most is why this technology is not yet applied more intensively. Modules aren’t that expensive; according to ENS Technology, if every person using the garage paid 10 to 20 cents more per ticket – on average much less than 2 percent of the cost of a ticket – that would cover it. But people do not want to pay more for parking, and the health impact of these particles apparently isn’t immediate enough to make people notice. Diseases only come much later.

Dr. Blocken is now setting out further research to increase the efficiency of the technology to make it more appealing to car park owners. He is also running more cases with his model, with different pollution scenarios. His hope is that a city will commit to applying the technology at scale, at which point he will be able to do a similar study for the whole city, along with an intensive measurement campaign to show the real impact on air pollution.

Read the study

Elsevier has published this article open access:


The lead author

Dr. Bert Blocken is Full Professor in the Department of the Built Environment at Eindhoven University of Technology (TU/e) in the Netherlands and part-time Full Professor in the Department of Civil Engineering at KU Leuven University in Belgium. His main areas of expertise are urban physics, wind engineering and sports aerodynamics. He has published 128 papers in international peer-reviewed journals. He developed TU/e’s first Massive Open Online Course, Sports & Building Aerodynamics. He received the 2013 Junior Award from the International Association of Wind Engineering, six best paper awards from the Elsevier journal Building & Environment (2009, 2011, 2012) and at international conferences and a top-cited author award from the Elsevier journal Atmospheric Environment (2010). According to the 2016 Academic Ranking of World Universities (Shanghai Ranking & Elsevier), he is among the 150 most cited researchers worldwide in the fields of Civil Engineering and Energy Science & Engineering.


The journal

The official journal of the International Association for Wind Engineering (IAWE), the Journal of Wind Engineering & Industrial Aerodynamics provides a means for the publication and interchange of information, on an international basis, on all those aspects of wind engineering that are included in the activities of the IAWE: social and economic impact of wind effects, wind characteristics and structure, local wind environments, wind loads and structural response, diffusion, pollutant dispersion and matter transport, wind effects on building heat loss and ventilation, wind effects on transport systems, wind power generation, and codification of wind effects. This journal is published by Elsevier.

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