Cabin Air Quality in Cars and Vans

Cabin air quality is the measure of the air quality within the vehicle itself. While you sit in traffic and drive through cities in towns, your vehicle should filter out the harmful pollutants to keep you safe.

Why is Cabin Air Quality important?

Cabin air quality is the measure of the quality of the air within a vehicle. Cabin air quality is not just about comfort, but also safety.

High levels of cabin carbon dioxide are associated with stale air but can also have cognitive effects that might lead to increased reaction times and drowsiness. Aerosol particles which enter the vehicle from outside can not only smell bad, but exposure to them is often associated with chronic health effects including heart disease, strokes and cancer.

Particles and carbon dioxide exposure are not regulated inside the vehicle cabin, even though they are at the tailpipe.

As a consequence there is little awareness of how effective the ventilation system of a vehicle is to prevent external pollutants entering the cabin.

Poor cabin air quality means drivers and passengers are being exposed to potentially dangerous levels of pollution.

What affects Cabin Air Quality?

Air coming into the vehicle should be filtered, however, there are currently no regulations for how effective ventilation systems and filters need to be. Tests commissioned by the AIR Alliance reveal some cars will filter just 30% of pollutants from the outside air, while others are able to filter more than 80%.

Cabin air quality can be affected by a range of factors, such as:

  • Quality of the basic air filtration system
  • Presence of more advanced technology such as climate control and active carbon filters
  • How the car is used – traffic and urban driving will increase exposure to higher levels of pollution
  • Maintenance of the filtration system

Cabin Air Quality in Leading Vehicles

As cabin air quality isn’t yet regulated, manufacturers aren’t required to measure their cabin air quality or effectiveness of their air filtration systems.

Safety tests conducted by Emissions Analytics in 2018 first showed a huge level of variation in the ability of some leading models to filter out harmful pollutants. At that time some vehicles had cabin air quality as bad as the polluted air outside, whereas others filtered 90% of the harmful pollutants.

In 2020 the AIR Alliance began the process to collect data and publish easily understood information with the real facts about the protection offered by the ventilation systems and filters in the cars we use and travel in.

The Cabin AIR Index, launched in 2023, provides drivers and passengers, and in particular professional drivers, who are in vehicles for several hours each day, the ability to compare vehicles and the filter systems, enabling choice, for the first time based on scientific data.

How to Improve Cabin Air Quality

Cabin air quality has been a widely neglected measure despite being both an issue of safety and an environmental concern.

In order to deliver significant improvements in cabin air quality, we’ll need to see:

  • The introduction of cabin air quality regulations
  • A simple and easy way to measure and check the cabin air quality of a vehicle
  • Reduction of pollution and harmful emissions on our roads
  • Commitment from car manufacturers to produce and introduce clean air technology

The pathway to delivering international regulation of cabin air quality is through the United Nations Economic Commission for Europe (UNECE), which cascades to national governments. At the 27th meeting of the vehicle interior air quality working group in May 2023 the methodology to collect vehicle data, initiated by  the AIR Alliance, was cited as a building block to cabin air quality regulations.

Whilst supporting the work of the UNECE in developing regulations, the AIR Alliance offers a consumer-led approach, providing independent, easily understood ratings of ventilation and filter systems. The aim is to highlight the practical and low-cost actions that anyone can take in their own vehicle today, to reduce the ingress of outside pollutants.   

Cabin Air Quality Ratings – the Cabin AIR Index

The Cabin AIR Index is one of three AIR Index ratings, published by the AIR Alliance to provide clear and transparent emissions information when choosing and operating a car or van, based on data collected through independent testing during real-world urban driving.   

The Cabin AIR Index is the first rating system to reveal accurately how much pollution enters a vehicle compared to the outside air. We have developed it to inform and empower drivers, passengers, fleet owners and policy makers with the facts about the protection offered by ventilation systems and filters in the cars they travel in.

As with the AIR Index ratings for NOx and CO2, the Cabin AIR Quality is a simple A-E colour-coded rating, comparing the effectiveness of the ventilation system to filter outside pollutants entering the system in urban driving.

The Cabin AIR Index allows comparison with other vehicles, and other filters installed in the same vehicle, based on scientifically robust, repeatable, on-road vehicle testing according to the new CWA 17934 methodology.

The AIR alliance has now commissioned a programme of vehicle and filter testing and results will be published periodically.

What is the new vehicle interior air quality testing method, CWA 17934 all about?

1. What is CWA 17934?

CWA 17934 provides a test methodology for collecting comparable interior air quality test data for different light duty vehicle makes and models. The methodology sets out how to conduct tests and report results, including equipment, calibration, test boundaries and outputs.  By standardising data collection, vehicles and their ventilation systems can be compared in a transparent, consistent and concise manner, and allow the aggregate of data from multiple sources.

The AIR Alliance initiated a CEN Workshop, bringing together more than 40 stakeholders across Europe, to develop the CWA 17934 methodology. This enables repeatable and comparable tests to reveal the actual levels of particulate matter, both number and mass, which enters the vehicle.

2. What is the scope of the methodology?

The scope has been defined to achieve two priorities. First, the data shall be most relevant to the increasingly understood problem of the health effects of poor air quality inside light-duty vehicles, in particular from particle ingress from outside.  Second, the methodology has been created to measure a characteristic value of pollution ingress that is independent of how the vehicle is driven and the absolute exterior pollution concentrations.  In other words, the degree of ingress for a given vehicle is constant if the boundaries of the test method are met.  This constant value can then be compared between vehicles.

3. What ventilation settings are used?

The default setting should have the heating and ventilation system in automatic mode, set to 19°C and air conditioning switched off.  The ventilation flaps should be open, and the fan speed set to 50%/medium if controllable.  These settings have been chosen to balance best real consumer experience and repeatability of the measurements.  If the vehicle does not have automatic mode, 50%/medium temperature should be used, in fresh air mode. 

4. How can you characterise the vehicle interior air quality in such simple terms?

The insight behind this methodology is that the ratio of interior to exterior pollution converges, over the period of the test, to a stable value characteristic of that vehicle.  This value does not depend on the absolute exterior pollution or the test route, within certain wide boundaries.  This is called the ‘Cabin Air Quality Index’ or ’CAQI.’  This approach collapses the number of variables in assessing the otherwise highly complex system of vehicle interior ventilation.

5. What are the test boundaries?

To achieve convergence of the stable CAQI value, the test must be at least 30 minutes long.  Average speeds must be between 30 and 50 km/h to reflect urban driving – the type of driving where the risk of particle ingress is at its greatest, due to traffic flow and congestion.  Ambient temperature must be between 5 and 25°C, with bounds also on humidity and pressure.

6. The Cabin AIR Index rates the number of particles filtered, but why can’t the mass of the particles be relied upon?

Particle mass measurement is specified in the methodology for reporting, but cannot be relied upon for calculating a CAQI yet.  During validation of the CWA 17934 methodology, the repeatability was not sufficiently good.  By reporting results using this protocol, more data will be gathered to reassess the repeatability, with a view to upgrading the status of these measurement.  In contrast, the repeatability of particle number measurements was robust. 

7. Why is the test route so broadly defined – does this lead to a lack of reproducibility?

The definition of the test route is left broad, as it has been shown that the ratio of interior and exterior pollution converges to the same characteristic value in a wide range of driving conditions.  During the validation of the method, the same value was reproduced in multiple different locations across Europe, by different testers, who were each allowed to define their routes.  There are, nevertheless, certain boundaries that define primarily urban driving and an average speed reflective of this.

8. What will the Cabin AIR Index allow to happen?

The aim of all AIR Index ratings is to provide clear and transparent emissions information that enables practical action to be take. Our research shows that the same vehicle, fitted with different filters and tested to the CWA 17934 methodology shows a wide variation in the ability of the ventilation system to reduce outside pollutants entering the vehicle.

This information enables drivers and fleet owners to make informed choices about the filter they fit to the vehicle and reducing the health impact from outside pollutants. The difference in particle reduction offered by filters costing between €10 and €26 is remarkable, and the effectiveness is not related to the price. In the same car, with the same ventilation system, one filter will reduce 30% of the particles from outside, whilst another will reduce 82%. By way of reference the cheapest and most expensive filters BOTH achieved the same level of reduction (48%).

9. Why can’t these objectives be fulfilled by other official methods?

Today there are no regulations addressing the exposure to harmful pollutants inside the vehicle. Until now, there has not been an agreed method to collect the data. Developing regulations and standards takes years, but the health impacts on people inside vehicles cannot wait.

The Cabin AIR Index is a game-changer in shedding light on an issue which affects everyone who uses a car or van, but most particularly professional drivers exposed to pollutants throughout their daily lives. We will publish our results in the AIR Index so consumers, policy makers and fleet owners can make informed decisions based on the ability of vehicles to protect drivers and passengers from harmful pollution levels.