Cabin fever

Why vehicle interior air quality is worse than in your garage

In our last newsletter we looked at the unethical challenge set by a high profile academic to see whether you would die if locked inside your garage with an internal combustion engine (ICE) vehicle running. Answer: no if you choose a current model, but probably yes if you choose something else and run it in a single garage.  Don’t take the risk.  But what happens if we invert the question?  How safe is it to be inside the same car driven in the open air?  That may sound like a stupid question, as most of us put ourselves in that position regularly, but how much do we really know about the quality of air inside a vehicle?  Is it very different from standing in a garage with an idling engine?

The challenge of the garage test is that tailpipe emissions are being emitted into a confined space with limited air to dilute it.  The question of air quality inside the vehicle cabin is actually the same: pollution from the ambient air is sucked into the sealed, confined space of the vehicle cabin.  In fact, the interior air volume of the car is substantially less than the volume of the garage.  This problem of pollution build-up, and the potential effect on driver health, has become more marked as the construction quality of vehicles has improved such that there is little air exchange except through the ventilation system.

To evaluate this, Emissions Analytics performed tests for vehicle interior air quality across over one hundred vehicles in Los Angeles in the US, Oxford in the UK, and Stuttgart in Germany.  For each test, the interior air quality was measured in real-time for particle number (PN) and carbon dioxide (CO2) concentrations, simultaneously with testing for the same pollutants immediately outside the vehicle from a second, matched, analyser.  Particle number was chosen as probably the single biggest health threat, and CO2 build-up is a driver safety issue representing the stuffiness of the interior air.

The test protocol was modelled on a new standardised methodology from CEN (Comité Européen de Normalisation or European Committee for Standardisation), published in September 2022.  The CEN Workshop Agreement (CWA) 17934 was the product of Workshop 103, which was initiated and chaired by the AIR Alliance and attracted around 40 industry experts in its development and validation.  

The US results, which were performed on a repeated thirty-minute route around Los Angeles International Airport, saw average external PN concentrations of 22,901 particles per cm3.  For comparison, fresh country air is typically around 2,600 particles per cm3, and the concentration out of a post-2018 diesel exhaust averages just 10,000 per cm3.  Across 97 recent model year light-duty vehicles tested on this route, the average interior PN concentration was 21,419 particles per cm3, so only 6.5% below the ambient. As an average this might suggest that filtration via the vehicle ventilation system is largely ineffective, but this is not true.  The range of results was between 9,388 and 47,977 particles per cm3.  On the Cabin Air Quality Index (CAQI) defined under CWA17934, the values were between 0.31 at the best-performing end, and 2.10 at the worst end.  In other words, the vehicle with the best ventilation system protected its occupants by reducing PN pollution by 69% compared to outside, but the worst vehicle saw double the outside concentrations.  This can be the case due to the accumulation of particles in a well-sealed cabin, and where the interior air is not properly refiltered.  A similar pattern was seen on the European tests in terms of the relative concentrations between the inside and outside, but the outside concentrations in absolute terms were, about double – for example, around Oxford the average concentration was 43,312 particles per cm3.  This may come as a surprise, but might be explained by the higher proportion of diesel vehicles with no or compromised particulate filters in Europe.

Thinking back to the garage thought experiment, over one hour with the idling gasoline vehicle in a single garage, the PN concentration rose from the 2,600 background to just 3,529 particles per cm3.  Therefore, concentration rose by about a third, but remained 84% below the average exposure suffered by the occupant of the vehicle testing on the roads of Los Angeles.  The chart below shows the instantaneous and cumulative concentrations from the road test on a Ford Explorer with average performance, compared to the modelled garage PN build-up.  So, by a large margin, you are exposed to fewer particles in the sealed garage than driving in normal on-road conditions, and this is true due to two main factors.  First, the exhaust filtration on new cars has an efficiency of over 99.9%, so these vehicles are emitting a very small net number of particles, even when the ambient air is relatively clean.  Second, the ambient air for the road test has PN concentrations well above background, which must in turn come from sources other than modern vehicles with exhaust filters – most likely from older vehicles, non-exhaust emissions, industrial sources, farming and home heating.  In other words, these modern vehicles with filtered exhausts are not a significant source of PN pollution, yet the occupants may still suffer the pollution from other proximal sources.

One of the other more likely health risks in the garage experiment was from asphyxiation due to high CO2 levels, arising from the engine combustion. The parallel in the vehicle cabin is elevated CO2 due to respiration of the occupants. Human harm tends to occur when concentrations exceed 15,000 ppm, although cognitive impairment can occur well below that, which might lead to reduced reaction times and increased accident risk. While the garage concentration reached 8,509 ppm after half an hour, concentrations inside the vehicle when tested on the road reached just 1,564 ppm after the same time, even with the ventilation system on the ‘recirculation’ mode. On fresh air mode, concentrations rose by an average of just 13% above the 417 ppm background. As with PN concentrations, there were big variations between vehicle models as to how fresh the air was kept on recirculation: CO2 increased by 103% in the best case and 275% in the worst.

Overall, therefore, the particle exposure inside the cabin is a bigger risk than when locked in a garage with an idling ICE vehicle of the current generation. While CO2 concentrations in the garage were higher than in the cabin, driving a vehicle is operating a complex, mobile machine and, therefore, even a modestly elevated level of CO2 could compromise safety. It should be noted that some relevant pollutants have not been studied here. Particle mass was not chosen due to the relatively low levels being emitted from modern tailpipes and entering the cabin even with low-quality filters and ventilation systems. Nitrogen dioxide (NO2) emissions are extremely low from gasoline vehicles – the dominant powertrain now – and concentrations in the cabin are also very low. A major area of focus in our future work is the role of volatile organic compounds (VOCs). These tend to be low from tailpipes, although some species can be highly toxic even in low concentrations. Inside the cabin, these VOCs arise mainly from interior materials, especially in hot conditions. Some mix of compounds, of varying potential toxicity, evaporate from seats, carpets, dashboards and other plastics. In short, the greatest risks in the cabin are PN, CO2 and VOCs, while in the garage it is PN, CO2 plus carbon monoxide (CO) for gasoline vehicles and NO2 for diesels.

Taking this complex area and turning into something that vehicle owners and buyers can use practically, the AIR Alliance this month is launching its Cabin AIR Index, based on CWA17934. The most immediate action that can be taken, rather than changing the vehicle itself, is to swap the filter in the ventilation system. Changing the filter regularly is important to avoid degradation, and then the choice of filter brand is important. The initial test results – comparing six different filters on the same vehicle – show that the best filter reduced the interior pollution almost three times more than the worst filter. Therefore, this simple component of typically around $40 in value, can make a significant difference in chronic pollution exposure in the cabin.

Of all the vehicles Emissions Analytics has ever tested, the Tesla Model X achieved the best cabin air quality rating, achieving PN concentrations more than 92% below outside levels. Both its bioweapon defence mode and its normal modes achieved excellent protection, thanks to a combination of HEPA (High Efficiency Particulate Air) filters. The downside of this approach is a large physical size (about 1.2 metres wide) and the relatively high replacement cost. The upgrade is around $500 currently. While originally only available on the Models S and X, since late 2021 it was also standard on the Model Y.

In summary, we have shown in previous newsletters that we are thinking about vehicle pollution in the wrong way now. New ICE vehicles emit almost no pollutants from the tailpipe, except CO2. To solve this decarbonisation challenge, we are moving to heavier electric vehicles, and in doing so are creating a tyre emissions problem that dominates anything from the tailpipe, as shown in a previous newsletter. In this newsletter, we have shown that being inside a vehicle can be more hazardous than being outside. In short, apart from replacing older vehicles as soon as possible, we should be concerned with non-exhaust and non-vehicular emissions rather than the tailpipe, focusing particularly on fine particles and VOCs from plastics and tyres. We have a good instinctive grasp of exterior air quality problems, but need to improve our understanding of interior pollution. Tesla is stealing a lead on the competition by acknowledging the issue of cabin air quality, and offering a practical solution today. Let us hope that other manufacturers follow, and the new CWA17934 standard can be used to prove their effectiveness.

NEW international Cabin AIR Index launched

Fleet owners, policy makers and drivers now have access to independent, standardised vehicle ventilation ratings 

• Easy to understand and comparable ratings provide clarity for drivers and car buyers.

• The first independent data set enabling policy makers to protect vehicle occupants.

• The independent Cabin AIR Index rates the ability of each filter and ventilation system to protect vehicle occupants from exterior pollution.

• The A-E colour-coded rating is endorsed by global air quality and vehicle emissions experts.

• Moe information available at www.airindex.com/emissions-ratings/cabin-air-quality-in-cars/   

25 July 2023: Today’s launch of the Cabin AIR Index reveals, for the first time using scientific data, the effectiveness of vehicle ventilation systems and the choice of filters in reducing the exposure of vehicle occupants to harmful pollutants.

Developed from more than five years of independent, international research the new Cabin AIR Index ratings reveal accurately how much pollution enters a vehicle compared to the outside air, when it is used in towns and cities.

Exposure to high levels of pollutants in the air can cause a range of serious health issues including respiratory problems, heart disease, strokes and lung cancer¹.

The air quality inside cars and vans (M1 and N1 categories²) is unregulated, leaving drivers and passengers unaware of the levels of exposure to damaging pollutants. In Europe alone, air pollution is estimated to cause more than 300,000 premature deaths each year³. 

The Cabin AIR Index has been created to inform and empower drivers, passengers, fleet owners and policy makers with the real facts about the protection offered by the ventilation systems and filters in the cars they use and travel in. A simple A-E colour-coded rating, based on a new real-world standard, shows the difference in effectiveness in filtering harmful pollutants.

In 2021 more than 97% of the urban population was exposed to concentrations of fine particulate matter above the health-based guideline level set by the World Health Organization⁴. Drivers and passengers, and in particular professional drivers who are in vehicles for several hours each day are now able to compare vehicles and the filter systems, enabling choice, for the first time based on scientific data.

Today’s launch of the Cabin AIR Index also reveals the significant variation in protection offered by the same vehicle, depending on the type of interior air filter used. When tested on the same car, the combination of ventilation system and one filter was only able to reduce the level of exposure to outside particles for drivers and passengers by 30% during the course of the test, whilst the best performing combination of system and filter achieved 82%.

The Cabin AIR Index ratings show ‘at a glance’ how effective the vehicle ventilation system is, allowing comparison with other vehicles, and other filters installed based on scientifically robust, repeatable, on-road vehicle testing according to the new CWA 17934 methodology.

Massimo Fedeli, Co-founder and Operations Director of the AIR Alliance said: “The health effects of breathing fine particulate matter in urban air are now, sadly, well established and estimated to cause more than 300,000 premature deaths in Europe each year. Drivers and passengers in urban areas may assume that closing windows and using the ventilation system prevents exposure to particulate matter, but that is not necessarily the case.

“Following five years of research, today the AIR Alliance is launching the Cabin AIR Index which rates the ability of the ventilation system to filter the number of particles from outside the vehicle and presents the results in a simple A-E colour coded scale.

“The Cabin AIR Index is the first opportunity for drivers and passengers to see the protection offered by vehicle ventilation systems, and also reveals the difference in performance between different filters fitted to the same vehicle, enabling drivers to make a choice when selecting the filter for their car or van.”

Nick Molden, Co-founder of the AIR Alliance said: “The Cabin AIR Index is based on data collected according to the CWA 17934 methodology, the independent, scientifically robust methodology to collect real drive vehicle interior air quality data. In the absence of any regulations for air quality inside cars and vans, drivers and passengers are unaware of the levels of pollution, and in particular the number of particles which enter the cabin.

“Drivers, and especially professional drivers who are in the vehicle for several hours each day, should be aware that the choice of interior air filter can make a significant difference to the quality of air that they breathe. Our tests show that the same ventilation system fitted with different, but compatible filters, reduced the level of exposure to outside particles for drivers and passengers between 30% and 82%.

“We have worked hard over the last three years with our independent, expert academic and industry group to define standardisation of data collection through the CEN Workshop Agreement 17934. We rate data collected by this method on the Cabin AIR Index providing comparative information between vehicles using fair testing criteria, all conducted on-road in real driving conditions. The same standardised test is applied to each different car type.

“For the first time policy makers and fleet owners have the ability to protect vehicle occupants, using the Cabin AIR Index to define the minimum standards expected to protect occupants.”

The results of the seven filters tested for the AIR Alliance on a 2018 Nissan Qashqai and rated in the Cabin AIR Index are:

*Cabin Air Quality Index (CAQI) as defined in the CWA Workshop Agreement 17934
**the age, make and part number of the interior filter which was pre-installed in the test vehicle was unknown.   

The AIR Alliance has now commissioned a programme of vehicle and filter testing and more results will be added to the Cabin AIR Index periodically.

About the Cabin AIR Index 

Vehicle ventilation systems for cars and vans (M1 and N1 categories2) rated for the Cabin AIR Index are tested according to the CWA 17934 standardised methodology which ensures that the results are independent, repeatable and comparable.

The testing is carried out on a vehicle, sourced independently from vehicle manufacturers, with Pollution In-cabin Emissions Measurement Systems (PIMS) equipment recording the air quality inside and outside the vehicle during on-road driving in towns and cities.

For a result to be considered acceptable for rating in the Cabin AIR Index at least three sperate tests must be conducted on each model, within specific boundary conditions⁵ at an average speed between 30 km/h and 50 km/h, with each test lasting at least 30 minutes.  

Testing is conducted with the ventilation system in ‘fresh air’ mode, the air conditioning turned off, and temperature set to 19°C in either automatic mode, or 50% fan speed if manual, and the vents facing forward and level.

The results of the tests provide the basis to rate the vehicle ventilation systems according to the A-E, colour-coded scale.

Cabin AIR Index ratings

The AIR Index website reports the first tests conducted on a single vehicle with different filters showing Cabin AIR Index ratings A-E. Car buyers and fleet operators should consider carefully the implication for the health of vehicle occupants when selecting the vehicle and choice of filter to minimise the ingress of harmful particles.

Background to the Cabin AIR Index testing process

Emissions Analytics, founded by Nick Molden (Co-founder of the AIR Alliance), was a pioneer in methodologies to test on-road tailpipe emissions using Portable Emissions Measurement Systems (PEMS) equipment. Since 2018 Emissions Analytics has also independently tested the air quality inside vehicles using Pollution In-cabin Emissions Measurement Systems (PIMS) equipment, and the insight gained from more than 100 tests conducted by Emissions Analytics informed the development of the CEN Workshop agreement which led to the CWA 17934 methodology from which the Cabin AIR Index has been created.

For more information see https://www.emissionsanalytics.com/vehicle-interior-air-quality.

¹ World Health Organization https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health

² Vehicle Approval categories https://www.gov.uk/vehicle-approval/individual-vehicle-approval-manuals

³ Air quality impacts in Europe European Environment Agency https://www.eea.europa.eu/publications/air-quality-in-europe-2021

⁴ Europe’s air quality status 2023 https://www.eea.europa.eu/publications/europes-air-quality-status-2023

⁵ More details about CWA 17934 and the boundary conditions are available at the CEN website https://standards.cencenelec.eu/dyn/www/f?p=CEN:110:0::::FSP_PROJECT,FSP_ORG_ID:76650,2654151&cs=1A37B6A2248CB063033111B9F708BAB58

AIR welcomes the publication of a standardised method to collect vehicle interior air quality data

Emissions Analytics was pleased to support the AIR Alliance with testing to validate this new standardised method for measuring vehicle interior air quality, so it can help reduce the exposures to pollution for drivers and passengers.