how air purifiers work in cars?

This article discusses how air purifiers work in a car. Furthermore, we discuss why it is essential to have an air purifier installed in the car, and what could be its potential side effects.

Do cars require an air purifier?

Yes, cars require an air purifier system.Over the past years, the ambient air quality has declined steadily. This effect is more pronounced in urban areas, due to the numerous human activities which contribute to it.

Not only does this have negative implications to climate change in the long run, they can also adversely affect human health when subjected to short term as well as long term exposures.

This steady degradation of air quality is predominantly due to anthropogenic (i.e., human based) activities. Out of these, traffic has been one of the biggest contributors to pollution.

In a study conducted in 2017 on the formation of the winter smog in Delhi, it was found that traffic related air pollution (TRAP) was the biggest contributor to the exacerbation of the air quality.

It is clear that the occupants within the car are most susceptible to the effects of TRAP. Hence, it is essential to have an air purifier installed within a car.

Different types of air purifiers and how they work

There are mainly three different types of air purifiers that are used in cars. These are:

  • Air ionisers
  • Air purifiers with HEPA filters
  • Activated carbon filters

We shall discuss in brief about each one’s mechanism.

Air ionisers

Air ionisers are air purifiers that use charged ions for cleaning the air. They release ions generated by a process called corona charging in the vicinity of the device. 

These ions attract pollutants present in the ambient air which have the opposite charge, and repel particles with a negative charge, and in this manner, they keep the air clean around the individual.

These ions are good against fine PM and ultrafine PM (i.e., particles equal to or less than 1 micrometer in aerodynamic diameter).

However, studies show that their typical efficacy is less in comparison to other types of air purifiers available. Another major drawback observed in these filters is that they generate ozone in their operation, which acts as an irritant.

Air purifiers with HEPA filters

HEPA stands for High Efficiency Particulate Air  filters. These filters are made out of  borosilicate glass fibers or plastic fibers (e.g., polypropylene) bound together with up to 5% acrylic binder, which is the same compound that binds latex paint to a house.

These filters are very effective against PM pollution, as their typical efficiency is more than 99% for particles equal to or more than 0.3 micrometers.

HEPA filters, however, fail against gaseous air pollutants, which can cause odors or even act as irritants to the respiratory system.

Activated carbon filter

Activated carbon filters are composed of charcoal particles. These are very efficient against gaseous air pollutants that are typically released from vehicular exhausts.

The activated carbon filter actively absorbs the gaseous air pollutants within, due to which they get eliminated from the car’s air.

These filters are usually paired with HEPA filters, or with the car’s internal HVAC system. The latter helps to keep the air clean with each successive circulation.

What are the various forms of pollutants present in TRAP

TRAP contains many forms of pollutants, which can be harmful to health if one is subjected to short term as well as long term exposures. The various pollutants include:

  • Particulate matter (PM)
  • Nitrous oxides (NOx)
  • Sulphur dioxide (SO2)
  • Carbon monoxide (CO)
  • Ozone (O3)

More about each species is discussed in detail.

Particulate matter (PM)

There are several different species of pollutants present within TRAP, but amongst these, the worst one is particulate matter, or simply PM, which refers to particles in the sub-micron range that are suspended in the air. 

There are two forms of particulate matter: coarse particulate matter (PM10) and tiny particulate matter (PM2.5). PM2.5 is a prevalent problem among them.

There are many sources of PM in the ambient air. Some of the main sources include factories, power plants, refuse incinerators, fumes from automobiles, construction activities, fires and natural windblown dust.

Numerous studies have shown that exposure to polluted air containing particulate matter have been shown to cause various issues, such as:

  • premature death in people with heart or lung disease
  • nonfatal heart attacks
  • irregular heartbeat
  • aggravated asthma
  • decreased lung function
  • increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing.

Given the variety of PM present, they have various sources. These particles can originate from a variety of sources, which can be indoors, or outdoor pollution that enters through doors, windows, seeps, cracks, and so on.

This is where air purifiers come in the picture. Air purifiers mainly work on particulate matter, and rid the indoor ambient air of the PM pollution in the room, thereby cleaning the indoor air.

Nitrous oxides (NOx)

NOx species refers to various compounds that contain nitrogen and oxygen atoms in varying numbers.

These are a pollutant of concern, as they increase the risk of respiratory infection. NOx are primarily traffic-related pollutants, since they are emitted from vehicular exhausts.

Various studies have shown that NOx species, particularly NO2, are responsible for the onset of asthma in children and young adults.

A study showed that an increase in 20.4 parts per billion (ppb) was associated with a 67% increase in the risk of asthma-related school absence.

NOx species are deep lung irritants, and if exposed to higher concentrations, they can cause pulmonary edema.

Sulphur dioxide (SO2)

Sulphur dioxide is a major air pollutant. It is released from natural sources such as volcanic activities, and from human activities such as combustion of fossil fuels, particularly from diesel engine vehicles.

Various studies have shown that children, old people, and people with preexisting respiratory illnesses are more prone to skin and lung diseases. 

Sulphur dioxide if present in excess can combine with precipitation to form ‘acid rain’, a phenomenon which severely affects humans and plants if exposed to it. 

SO2 acts as a sensory irritant, and can cause asthma or asthma-like symptoms such as elevated mucus secretion and bronchitis. It can also aggravate pre-existing cardiovascular diseases.

Carbon monoxide (CO)

CO is a gaseous compound formed due to incomplete combustion of fuel and firewood. CO is actively absorbed by activated carbon filters.

CO is a serious pollutant, as  it forms a stable bond with haemoglobin (Hb), a compound present in our red blood cells (RBCs) which is responsible for transporting oxygen from the lungs to various tissues in our body. 

At lower concentrations, CO causes headaches, nausea, fatigue, dizziness, and loss of consciousness. However, at higher concentrations, it can cause issues such as hypoxia, ischemia, and can even cause death.

Ozone (O3)

Ozone is a gaseous molecule which is naturally present in the higher layers of the atmosphere, where it absorbs the harmful UV rays of the sun.

However, when present in the lower atmosphere layers, it acts as a pollutant, and can cause various pulmonary diseases.

Ozone formation in the lower atmosphere is due to interaction of sunlight with fumes emitted from vehicles, which contain hydrocarbons and nitrogen oxides (NOx). 

It is a major component of “Los Angeles Smog”, or summertime smog, which occurs during summer in metropolitan cities, and mainly caused due to TRAP.

Ozone has been shown to cause oxidative stress, inflammatory responses and immunologic disease in laboratory animals.

Ozone has a characteristic pungent odor, which can irritate the inner linings of the airways, as well as the lungs. It can hamper one’s ability to breathe deeply, and reduce lung function.

Ozone has also been shown to cause adverse effects that include functional,morphologic, immunologic, and biochemical alterations. 

Other FAQs about Air Purifiers and Filters that you may be interested in.

The dangers of Negative ion air purifiers

Can air purifiers remove dust?

How air purifiers can be harmful


Air purifiers are an essential component in a car, since not only do they protect the internal components of a car from the harmful effects of certain pollutants, they also help to ensure that the passengers get clean air to breathe.

There are various types of air purifiers for cars, which is because of the multitude of the pollutants emanating from vehicular exhaust.

Amongst these, the most abundant pollutant is particulate matter (PM), sulphur dioxide (SO2), nitrous oxides (NOx), carbon monoxide (CO), and ozone (O3).


Do car air fresheners help against pollution inside the car?

No, car air fresheners do not help against pollution inside the car. Air fresheners are aromatic compounds that simply mask the presence of any unpleasant odor within an enclosure (in this case, a car).

However, these compounds have no significant effect on the pollutants inside the car, since they are only used for the aesthetic appeal their fragrance brings to the vehicles.

Where should I place my air purifier inside a car?

Car air purifiers are small in size and basically, they should be placed somewhere on the front panel on the dashboard. This is because most of the time the passengers will be sitting in the front. 

Furthermore, for most cars, the main inlet and outlet for the air conditioning system is towards the front of the car. By placing the air purifier in such a spot, the efficiency of pollutants being picked up by the air purifier will further increase.

Do all cars need an air purifier?

No, not all cars need an air purifier to be separately installed. The air conditioning system of the car contains air filters which, when the car is running and the air conditioning being used, will filter out the particulate matter efficiently.

However, not all cars have an efficient air filter in their air conditioning system. In such a case, it would be ideal to buy an air purifier separately.

Furthermore, not all cars face the same load. For example, a car stuck in a traffic congestion in a major polluted city like Beijing or Delhi is more susceptible to degradation of air quality due to the infiltration of outdoor pollutants.

In such a case, the regular air filter of the car will not be able to remove all pollutants in an efficient manner. Hence, it would be ideal to have an air purifier installed in the car separately, preferably one with a HEPA filter as well as an activated carbon filter.


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