London's Car Pollution Crisis: A Critical Analysis

Transport is the largest emitting sector of greenhouse gas emissions in the UK, and cars are a significant contributor to air pollution in London. In fact, new analysis shows that diesel cars emit three times as much pollution as trucks and lorries combined. With the UK transitioning towards net-zero targets, London has implemented measures to tackle air pollution, such as the Ultra Low Emission Zone (ULEZ), which requires vehicles to meet certain exhaust emission standards or pay a daily charge. Despite improvements in vehicle emissions standards and reductions in some air pollutants since 1990, the impact of car pollution on the health of vulnerable urban populations remains a key concern.

Diesel cars cause three times more pollution than trucks and lorries in London

London's air pollution problem is well-documented, and road transport emissions are a key focus. While diesel vehicles have long been a major contributor to tailpipe emissions, new data reveals that diesel cars emit up to three times as much pollution as trucks and lorries (heavy goods vehicles or HGVs) in London. This is a surprising finding, as one might expect heavier vehicles to produce more pollution. However, the data shows that the share of harmful NOx emissions from diesel and petrol cars has risen in almost every London borough. NOx emissions contribute to the formation of nitrogen dioxide (NO2), a toxic gas that has been linked to adverse health effects, including stunted lung growth in children.

The high level of NO2 emissions from diesel cars is concerning given their impact on human health. Nitrogen dioxide can inflame the airways and, over time, impair lung function. In London, NO2 has been implicated in the deaths of 4,000 people annually and has left children with permanent lung damage. To address this issue, London introduced the world's first 24-hour Ultra Low Emission Zone (ULEZ) in its centre in 2019, later expanded to include inner London. This initiative requires vehicles to meet certain exhaust emission standards or pay a daily charge, incentivising the use of ULEZ-compliant cars that meet emissions standards in both lab and real-world driving conditions.

While European (Euro) standards set limits on vehicle exhaust emissions, the results obtained in labs do not always reflect real-world driving scenarios. This discrepancy has led to stricter EU tests that better simulate city driving conditions, which heavy vehicles have been able to comply with. However, carmakers have been criticised for not implementing effective NOx reduction technology in diesel cars due to convenience and cost. The Clean Cities Campaign has urged local councillors and London 2022 candidates to prioritise clean air policies, including phasing out polluting diesel cars, reallocating space for active transport, and giving priority to buses.

To summarise, diesel cars in London emit significantly more pollution than expected relative to trucks and lorries. This has led to a renewed focus on reducing vehicle emissions and improving air quality, with campaigns advocating for a shift towards cleaner modes of transportation. While steps like the ULEZ are a step in the right direction, more needs to be done to address the issue of diesel car pollution and its impact on the health of London's residents.

London's Ultra Low Emission Zone (ULEZ) helps reduce toxic air

London's Ultra Low Emission Zone (ULEZ) is the world's largest clean air zone, covering every borough of London and benefiting the capital's nine million residents. It was introduced in April 2019 to improve air quality in central London by reducing the number of older, more polluting cars in the city. The ULEZ was later expanded in October 2021 to include the inner London area bounded by the North and South Circular Roads. In August 2023, the ULEZ was expanded again to cover all London boroughs.

The ULEZ scheme aims to limit the types of vehicles that emit high levels of nitrogen oxides, carbon dioxide, and harmful particulate matter. These gases and particles comprise what is referred to as traffic-related air pollution, or TRAP. Scientific consensus indicates that exposure to air pollution, even at levels commonly experienced throughout London, poses significant health risks. For example, high levels of nitrogen dioxide, which is primarily formed by emissions from diesel and petrol cars, can inflame the airways and affect lung function over time.

By encouraging the use of ULEZ-compliant vehicles that meet the latest emissions standards, London's ULEZ is helping to reduce toxic air and improve public health. Evidence shows that the ULEZ is already having a positive impact. In the first year of operation, roadside nitrogen dioxide concentrations in London were up to 4.8% lower than expected without the ULEZ expansion. Particulate matter (PM2.5) exhaust emissions from cars and vans in outer London are also estimated to be 31% lower due to the ULEZ, resulting in a PM2.5 exhaust emission saving of 9.1 tonnes in 2024.

Furthermore, any net revenue raised through the ULEZ is reinvested into improving London's public transport network, promoting a shift away from private car usage. This two-pronged approach of reducing vehicle emissions and improving public transport is expected to further enhance the air quality and health benefits for London's residents and road users.

Nitrogen oxides (NOx) are the most concerning pollutants for health

Nitrogen oxides (NOx) are a combination of nitric oxide (NO) and nitrogen dioxide (NO2). NOx is formed when nitrogen and oxygen, present in the air, combine during the combustion of fuel in gasoline and diesel engines. While NO is harmless, NO2 is a major concern due to its impact on human health. NO2 is a part of car exhaust emissions, and short-term exposure to high concentrations of it can cause inflammation of the airways, increasing susceptibility to respiratory infections and allergens. It can also exacerbate symptoms for those with pre-existing lung or heart conditions.

NOx also affects human health indirectly through the production of surface ozone (O3) and secondary inorganic aerosol. It impacts the environment through eutrophication and acidification of sensitive ecosystems. NOx emissions from vehicles are particularly high in dense urban environments such as London, where the levels were recorded to be more than twice the EU limit of 40 micrograms per cubic metre of air.

The UK emits about 2.2 million tonnes of NO2 annually, with half of these emissions coming from motor vehicles. The switch from petrol to diesel vehicles has worsened the situation as burning diesel produces more NOx overall, with a higher proportion of NO2.

To address this issue, the UK government has proposed a plan to tackle NOx pollution, especially in cities. The introduction of catalytic converters and stricter emissions regulations has helped reduce NOx emissions since 1990, with a 79% decrease recorded between 1990 and 2023. The first Euro standard for vehicle emissions was introduced in 1992, and since then, EU-wide standards have placed tighter limits on exhaust emissions. The current standard, Euro 6, is being upgraded to Euro 6d.

To improve air quality, London implemented a 24-hour Ultra Low Emission Zone (ULEZ) in its centre, later expanded to include the inner London area. Most vehicles now need to meet certain exhaust emission standards or pay a daily charge to travel within the zone.

Air pollution from transport has decreased since 1990

The transport sector is a significant contributor to air pollution, with road transport being the most common concern. Air pollution from transport has several adverse health effects, including respiratory and cardiovascular diseases, cancer, and adverse birth outcomes. In London, diesel vehicles and combustion engines have been identified as major sources of air pollution.

Since 1990, however, air pollution from transport has decreased. This is largely due to the introduction of targeted policies and measures, such as European (Euro) standards, which set limits on acceptable levels of exhaust emissions from vehicles sold in the EU. The Euro standards have become increasingly stringent over time, with the current standard, Euro 6, being fully in place since 2021. These regulations have contributed to a significant reduction in pollutant emissions from road transport.

In London, the implementation of the Ultra Low Emission Zone (ULEZ) in 2019 has also played a role in reducing air pollution from transport. The ULEZ requires vehicles to meet certain exhaust emission standards or pay a daily charge to travel within the zone. This has incentivized the use of cleaner, more ULEZ-compliant vehicles, improving air quality in the city.

While the COVID-19 pandemic caused a temporary reduction in transport volumes and a corresponding decrease in emissions, the overall downward trend in transport-related air pollution since 1990 is significant. This trend is attributed to the combined efforts of policymakers, environmental agencies, and technological advancements in vehicle emissions control.

Despite the progress made, it is important to note that the situation is complex, with some pollutant levels rebounding and certain sectors, such as aviation and international navigation, showing increases in emissions. Nonetheless, the focus on reducing emissions from transport has led to healthier air and significant public health benefits.

Electric cars emit less pollution than petrol or diesel cars

In London, there is a widespread consensus that exposure to air pollution, even at levels commonly experienced in the city, poses significant health risks to the population. One of the key areas of concern is emissions from road transport, particularly tailpipe emissions from diesel vehicles.

To address this issue, London introduced the world's first 24-hour Ultra Low Emission Zone (ULEZ) in its centre in 2019, which was later expanded to include the inner London area. This initiative aims to reduce toxic air pollution by ensuring that vehicles meet certain exhaust emission standards or pay a daily charge to enter the zone.

The transition to electric vehicles (EVs) is a crucial step towards reducing air pollution and improving public health. While the production of EVs may emit more carbon pollution than their petrol or diesel counterparts due to the energy-intensive battery manufacturing process, EVs emit less pollution over their lifetime. This is because EVs produce zero tailpipe emissions, which are a significant source of harmful pollutants in petrol and diesel cars.

Studies have shown that, on average, gasoline cars emit more than 350 grams of CO2 per mile driven over their lifetimes, while fully electric vehicles emit around 200 grams. This means that an average driver in the US could reduce emissions by half by switching to an EV. Additionally, as the world moves towards a lower-carbon electricity mix, the emissions associated with EV charging will also decrease over time.

Furthermore, the benefits of EVs extend beyond just tailpipe emissions. Combustion engines in petrol and diesel cars produce particulate matter and nitrogen oxides (NOx), which have detrimental effects on both human health and the environment. NOx contributes to the formation of smog and acid rain, while particulate matter can cause a range of adverse health impacts. By contrast, EVs do not produce these harmful pollutants, making them a much cleaner option overall.

Frequently asked questions