The Hindustan Times issued a gloomy forecast in early 2018, leading with a story that deaths linked to air pollution are expected to triple by 2050. And they know what they’re talking about in India. According to the World Health Organization (WHO), the capital city of New Delhi topped the 2015 list of cities with the highest levels of air pollution on earth. All over the world, the situation is particularly critical in megacities such as Mexico City, Cairo, or Seoul. Nitrogen oxides, carbon dioxide, and ozone are all a source of air pollution, but particulate matter (PM) is especially harmful to human health. How dangerous is it really? Where does it come from? And what can we do about particle pollution?

Its sources are as diverse as its size

Particulate matter is a mixture of organic and inorganic
substances. Natural sources such as volcanoes, dust storms, and forest fires produce 90 percent of the particulate matter in the air, with humans responsible for the other ten percent, mostly caused by power plants, industry, and households. On the roads, particulate matter is produced by fuel combustion and brake, tire, and pavement wear. Fine dust particles have a diameter of under ten micro-meters (μm). Can you imagine how small that is? Maybe the size of a grain of sand? Too big, sand has a diameter of around 90 μm. Perhaps the diameter of a human hair? Still too big, that’s around 50 to 70 μm. Fine dust particles cannot be seen by the naked eye, and the dust produced when braking is especially small: more than 90 percent of these particles are no bigger than 0.55 μm.

What’s harmful isn’t the chemical compound – but its size

According to a WHO report, over three million deaths a year are linked to exposure to outdoor air pollution. In the U.S., around 12,000 lives could be saved every year if levels of fine particulate matter nationwide were cut by just one microgram per cubic meter of air (μg/m³). This was the conclusion reached by a study conducted at Harvard University. How does particulate matter harm human health? It’s not its chemical composition but rather the size of the dust: the smaller the particles, the more hazardous they are. Inhalable particles with a size of up to 10 μm (PM10) reach the nose, throat, and the airways. Respirable dust particles of up to 2.5 μm (PM2.5) in size reach the bronchial tubes. Ultrafine particles with a diameter of less than 0.1 µm even manage to reach the alveoli and the circulatory system. In addition, particles smaller than 2.5 µm remain permanently in the body and cannot be broken down and eliminated. Potential consequences include organ damage, strokes, and allergies. Research is also examining the links between particulate matter and both premature birth and dementia.

Megacities most affected

The problem is greatest in cities, where high levels of particle pollution and large numbers of people coexist. In New Delhi, the Indian Medical Association declared a national health emergency last year. According to official figures, concentrations of particulate matter PM10 reached levels of around 1,000 μg/m³ in November 2017. Air pollution meant planes could no longer land, schools were closed, and driving bans were imposed. In Seoul, the capital of South Korea, levels of particulate matter with a size of up to 0.1 μm reached over 50 µg/m³ on two consecutive days last November. Emissions from industrial production and Asian dust from China’s deserts pollute the city’s air. In China itself, the term “airpocalypse” has become popular since the wave of smog that hit Beijing and its 22 million people in 2012. In Germany, too, a synonym for poor air has gained currency – the “Neckartor”: the air monitoring station in Stuttgart regularly records values that exceed legal limits. The city being situated directly in a valley adds to the high levels of fine dust pollution.

Particulate matter enters the lungs through the respiratory tract, and from there into the circulatory system. The body’s circulation tries in vain break down the dust particles, and this causes inflammatory responses. Consequences can include cardiovascular disease, asthma, and lung cancer.

Prof. Hans Schweisfurth, Director of the Institute for Pulmonary Research in Cottbus, specialist in respiratory medicine.


A team of researchers from the Indian Institute of Technology has developed a small filter for the airways that is placed in a person’s nostrils. Fitted with a flexible membrane, it traps dust particles of size PM2.5 without impairing breathing. The authorities are testing the use of water cannons installed on a flatbed truck that can be moved around the city. The water sprayed into the air aims to bring fine dust particles down to the ground.


At times, the situation in South Korea’s capital has been so critical that the city has taken the emergency decision to allow its residents to use public transport free of charge during the rush hours. Authorities also distributed over a million filter masks – primarily to babies, children, pregnant women, and senior citizens.


Rigorous action in Beijing: factories and building sites were shut down for months. That meant compulsory leave for hundreds of thousands of workers. The Chinese government has its sights on coal combustion for electricity generation; no new coal-fired power plants are to be built. Steel production will be reduced by ten percent in the winter months.


The city authorities installed a 100-meter moss-covered wall, which aims to absorb particulate matter from the air, near the Neckartor last year. Prior to this, the city used cleaning machines that spray water from a nozzle and then collect the particular matter bound with the water droplets. During a particulate matter alert, the use of non-essential fireplaces is prohibited and commuters are asked to use public transport instead of their cars.

Filtration helps

The public debate on particulate matter often focuses on exhaust emissions. A vehicle’s particulate emissions, however, also include tire and pavement wear, which sends particles into the air. Even worse, braking in city traffic causes seven to eight times as much dust as exhaust gases in a Euro 6 vehicle. These sources of particulate matter are also found in electric vehicles. It’s therefore important to consider a vehicle’s overall particulate emission footprint. This is where MANN+HUMMEL comes in, with its “fine dust eaters” research project. The filtration specialists have developed four applications to help reduce particle pollution in city environments. A fine dust particle filter that can be installed at various points on a vehicle separates particulate matter from the ambient air. A brake dust particle filter fitted to the brake system is designed to minimize the release of brake dust to the environment. Occupants are protected by an NO2 fine dust combi filter. In addition, stationary particle filters can also help to improve air quality. The “fine dust eaters” will soon be out on the streets of India. As we know, they’re needed much more over there.

MANN+HUMMEL is using the “fine dust eaters” to capture particle emissions wherever they’re actually produced: near the brakes, the tires, and the exhaust of a vehicle. It is also focusing on heavily polluted areas where people are severely affected by poor air: traffic junctions, railway stations, and bus stops.


With the StreetScooter delivery vehicles in its fleet, Deutsche Post DHL Group is cutting down on significant quantities of harmful gases such as carbon dioxide and nitrogen oxide, as well as reducing noise emissions. Thanks to the particulate matter filter from MANN+HUMMEL, they also tackle fine dust emissions – making the StreetScooter the company’s first zero-emission vehicle. In terms of its overall emissions footprint, this means zero carbon dioxide (CO2), zero nitrogen oxide (NO2), zero noise, and zero particulate matter. The filter modules are initially being installed in five StreetScooter test vehicles. Following successful testing, the company will be looking into the standard use of the particulate matter filter.