Ad description

A radio ad for the expansion of the Ultra Low Emission Zone (ULEZ) in London, heard between February and March 2023, started with the sound of traffic from an open car door and then featured a voiceover that stated, “You do up your seat belt and check your rear-view mirror. You’ve got air bags and anti-lock brakes. Everything in your car is designed to protect you, but none of that will protect you from this … the air you’re breathing. According to research, one of the most polluted places in London is inside your car. That’s why the ULEZ is expanding across all London boroughs. Search ULEZ 2023 to find out about the support available. Let’s clear the air.”


The complainants challenged whether the claim “According to research, one of the most polluted places in London is inside your car” was misleading and could be substantiated.


The Greater London Authority (GLA) said multiple research studies had shown that the inside of a car was one of the spaces most exposed to air pollution. They provided ten reports – a pilot study, four reviews of studies in this area, four studies on the level of air pollution to which drivers were exposed and a study that examined levels of pollution to which children were exposed when travelling to school. They also provided a video produced by The Guardian newspaper and King’s College London, a 2017 newspaper article, and referred to the Chief Medical Officer’s annual report 2022.

The GLA said they regularly reported on air pollution by using the city’s air quality monitoring network to analyse the long-term trends in the level of pollution in the air. The most recent model they had produced was the London Atmospheric Emissions Inventory (LAEI) 2019. The LAEI modelled ground level concentrations of pollutants such as nitrogen dioxide (NO2) and particulate matter (PM10 and PM2.5) in µg/m3 at 20m grid resolution. They said that the dataset from 2019 demonstrated that the limits for NO2 and PM2.5, as established by the World Health Organisation (WHO) in 2021, were not achieved anywhere in London. They referred to three points within the 2019 LAEI. Firstly, that all areas of London exceeded safe limits of air pollution as defined by the WHO. Secondly, that road transport was the single largest source of both nitrogen oxides (NOx – the collective term for nitrous oxide and nitrogen dioxide) and PM2.5 emissions in London. Thirdly, concentrations of NO2 were higher alongside roads in comparison to surrounding areas.

They said that their evidence showed that exposure to air pollution was highest when people were closer to the source of emissions. It also demonstrated that road transport was the single largest source of NOx and PM2.5 emissions, which were two of the main air pollutants in London, and that levels of NO2 concentrations and exposure were highest alongside roads. And finally, that travelling within a car or van could expose a person to more air pollution than any other form of road transport.

Radiocentre said they agreed with the GLA’s response.



The ASA considered listeners would understand the claim “According to research, one of the most polluted places in London is inside your car”, in the context of an ad about the expansion of the ULEZ, to mean the level of air pollution in a car in London ranked among the places with the highest levels of air pollution in the city. We therefore expected to see evidence that compared the level of air pollution in cars in London to the level of air pollution in a variety of other contexts in which a person in London might find themselves.

We assessed the evidence provided by the GLA. The pilot study focused on the levels of air pollution, specifically PM2.5 and PM10, NO2, and carbon dioxide (CO2), to which professional drivers of taxis, waste removal trucks, hospital shuttlebuses and ambulances were exposed when working in London. The level of air pollution inside the cabin of their vehicles was compared with the level of air pollution at two roadside monitoring stations at Marylebone Street and Honor Oak Park. The study found that occupational drivers faced levels of PM and NO2 concentration similar to those found at the Marylebone Road site, and at a higher NO2-to-PM ratio than at the site in Honor Oak Park. While the study did suggest that those car users were exposed to air pollution it did not comment on why these monitoring sites had been chosen and whether the level of pollution at them was representative of levels across London, or whether the average non-professional driver would spend similar average amounts of time in traffic to those who participated in the study. We considered the experience of the drivers in the study was likely to be different to that of the average non-professional driver – for example, the amount of time spent in heavy traffic, and how often their car doors were opened. While the study did offer a comparison between car users and two locations in London, we did not consider that the extent of this comparison aligned with how the claim in the ad would be interpreted.

GLA referred to a study by the Institution of Occupational Health and Safety, which examined the level of exposure to diesel pollution that professional drivers based in London faced. The study monitored the levels of exposure to black carbon that 141 professional drivers of buses, vans (electric and diesel), ambulances, fire engines, lorries, taxis and waste trucks faced while at work and in their daily life over a four-day period via an air quality monitoring device with GPS capacity. The study placed the locations the drivers were monitored at into four categories: ‘At work driving’ (during work hours and moving); ‘At work not driving’ (during work hours and stopped); ‘Commuting’ (outside of work hours and moving); and ‘At home’ (outside of work hours and stopped).

The study showed that the more time participants faced driving at work in comparison to ‘At work not driving’, ‘Commuting’ and ‘At home’, the greater the level of their exposure to pollution. It found that ‘At work driving’ exposure was 3.8 times higher than ‘at home’ exposure. Additionally, it outlined that when a participant was in their vehicle, they were more likely to be more exposed to pollution than when they were not. For example, when 18.6% of their time was spent ‘At work driving’, this resulted in 36.1% of total pollution exposure, and when 54.4% of time was spent ‘At home’ this only contributed 31.8% of total exposure. Additionally, the study noted that average ‘Commuting’ exposures were relatively high, but with only 4% of time spent in this activity, it only contributed 7.9% to the total exposure. We acknowledged that the report highlighted that a notable amount of the British population was employed in jobs involving driving and recommended that to limit pollution exposure people should avoid congested areas, including central London. However, we did not consider that the experience of professional drivers when in their vehicle, due to factors such as the length of time, the locations visited, the frequency of stopping and starting, or the type of vehicle used, were necessarily representative of the experiences, and therefore exposure to pollution while in a car, that the average listener would have. While the experience of the drivers in the study, who were based in London, when not at work, was relevant, the study did not detail what ‘commuting’ constituted beyond that it referred to exposure that occurred outside of work hours while the participant was moving. It did not necessarily exclusively refer to exposure that had occurred in a car being used in a similar capacity to an average driver. The study did demonstrate that most of the pollution that professional drivers in London were exposed to occurred when they were driving. It had not, however, demonstrated that this aligned with how non-professional drivers used a car or whether the exposure during a participant’s non-work hours arose from being in a car.

GLA provided four reviews of studies in this area. Two reviews examined the level of air pollution commuters were exposed to when using different modes of transport in various European cities, including London. The London-focused studies were conducted between 1998 and 2008. Some preceded the implementation of the congestion charge in 2003, and all preceded the implementation of the original ULEZ in 2019. We considered that these policies could have changed London’s air quality, and any comparison to substantiate the ad’s claim would therefore need to take into account London’s ambient air quality in 2023. Furthermore, we acknowledged that the reports had made a comparison between pollution exposure when in a car and other forms of travel, such as walking or cycling. However, we considered the ad suggested that the inside of a car was one of the most polluted places in London, and that the evidence would need to demonstrate this, including in relation to other forms of travel and a variety of other locations across London. The third review article pertained to air pollution in Germany and the different ways in which people were exposed to pollutants when in a car. We therefore considered it was not relevant substantiation for the claim, which was specific to London and where a ULEZ zone had already been implemented.

The fourth review was produced by the Environmental Research Group. It was funded by the GLA, but its analysis was independently prepared. It observed that a study had found that commuting accounted for 6% of a person’s time, but was responsible for approximately 30% of a person’s exposure to air pollution. The review itself focused on Traffic Related Air Pollution (TRAP), a combination of particulate and gaseous pollutants from vehicle exhausts as well as particles produced from the wear of road surfaces, tyres and brakes. It outlined that levels of TRAP were highly localised to the roadside and that they fell rapidly as the distance from the roadside was increased. It then reasoned that road users themselves occupy the highest pollutant microenvironment and were therefore disproportionately exposed to TRAP. We acknowledged the review had established that being in a car led to a high level of pollution exposure, that cars were amongst the modes of transport that led to the most pollution exposure, and that some of the studies included within the review had focused on London. We acknowledged a study within the review had shown that commuting led to a disproportionately high level of pollution exposure in comparison to the proportion of time spent doing it. However, the review’s comparison had only focused on pollution exposure when using different modes of transport. It had not commented on pollution exposure in other parts of daily life, and we did not consider that it had necessarily outlined that the inside of a car was one of the most polluted places in London.

We assessed the Chief Medical Officer’s annual report 2022. We acknowledged that it established that proximity to the source of emission, such as living near major roads and in higher-density urban settings, was a controlling factor in exposure to short-lived pollutants such as NO2. However, while it did demonstrate that pollution exposure was impacted by proximity, we considered that this did not necessarily equate to demonstrating that the pollution levels inside a car were amongst the highest places of pollution exposure in London. Additionally, we reviewed the study that examined the levels of pollution that children were exposed to when travelling to school. It was funded by the GLA. The levels of pollution that 258 children across five different primary schools in London faced when travelling to and from school were examined. The study found that children who travelled, by a variety of different methods, via busier main roads were exposed to more pollution than those who travelled on quieter side roads. The majority of students did not use a car or bus when travelling to their school. The study noted that it was unable to draw any robust conclusions between these modes of travel and more active modes like walking, cycling or riding a scooter, but that its findings did suggest that children who walked along roads that had heavy traffic could potentially be exposed to higher levels of pollution than children who were driven or took the bus to school. Resultingly, while the report did suggest that proximity to the source of pollution influenced the level of exposure, it had not demonstrated that the inside of a car was one of the most polluted places in London.

We reviewed the LAEI. We understood that it had been produced by the GLA and Transport for London (TfL), and they had received input from Imperial College London, two environment focused consultancy firms, Heathrow airport and the Port of London Authority. It was a dataset focused on London that modelled and made estimates over a range of areas, including but not limited to, emission trends, maps that outlined the concentration of NO2 and PM2.5, and PM10 in 2019 and in the future, and population exposure data for NO2 and PM2.5. It detailed that in 2019 air pollution in London exceeded the WHO’s recommended limits, that road transport was the single largest source of NOx and PM2.5, and that NO2 concentrations were high alongside major roads. We acknowledged that these findings outlined that London’s air was polluted, including alongside major roads, and that road vehicles were a significant contributor to that. However, the LAEI did not indicate the level of pollution found inside a car, or directly compare the level of pollution a person inside a car faced against the level of pollution exposure in other contexts in London.

We assessed the three reports of experiments on the levels of air pollution that car users faced. None of the studies were based in London. The first was based in Leicester, the second was based in Asan and Chunan, South Korea, and the third was based in Los Angeles. We acknowledged that cars within London would not be substantively different to those in Leicester, South Korea and Los Angeles, but we had not seen evidence that clarified the ambient air quality in these cities was the same as London’s and that inside of a car would be one of the most polluted places in London. The Guardian video and newspaper article referred to high levels of pollution exposure when in a car. We acknowledged the experiment conducted in the video demonstrated that car usage led to a higher level of pollution exposure than when using other forms of transport. However, as the video’s experiment, the reports and the newspaper article only compared the level of pollution commuters faced when using different modes of transport or did not focus on London, we did not consider them adequate substantiation for the claim.

The evidence provided had established that proximity to the source of pollution increased exposure, car users were exposed to air pollution when inside their vehicle and that it could be higher than when using other forms of transport, and that London’s air was polluted. However, a direct comparison between the level of air pollution within a car in London to a variety of other locations and contexts around London had not been made. For those reasons we concluded that the claim “According to research, one of the most polluted places in London is inside your car” had not been adequately substantiated and was likely to materially mislead.

The ad breached BCAP Code rules 3.1 (Misleading advertising), 3.9 (Substantiation), and 9.4 (Environmental claims).


We told the Greater London Authority to ensure that relevant evidence was held in support of all objective marketing claims.


3.1     3.9     9.4    

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