Black carbon – a short-lived climate pollutant emitted into the air by incomplete combustion of fuels – is a both major contributor to climate change and a concern for public health in cities. At the global scale, black carbon has been identified as the second most important human emission contributing to climate change. At the local level, studies have shown that there is a link between exposure to black carbon and a range of illnesses that include asthma, respiratory infections, and birth defects. According to the World Health Organization (WHO), 3.7 million premature deaths resulted from outdoor air pollution in 2012, 88% of which occurred in low- and middle-income countries.

Sustainable transport systems and clean technologies can play an important role in reducing black carbon emissions, as over 90% of air pollution in major cities is attributed to vehicle emissions. Many cities in developed countries have already made substantial progress in reducing black carbon emissions within the transport sector. These actions to reduce black carbon in cities worldwide will improve public health and combat global climate change.

Black carbon is a global and local problem

Though black carbon only exists in the atmosphere for about a week, it can have a very strong impact on climate. Black carbon increases global and regional temperatures and reduces the cooling effect of large reflective surfaces such as glaciers. This short-lived climate pollutant has the potential to trap 900 times more heat than carbon dioxide in the atmosphere over a 100-year period and 3,200 times more heat over 20 years.

Many developing cities experience harmful levels of black carbon. The increase in black carbon emissions is a public health concern because black carbon is a key component in PM2.5, fine particles that can penetrate and lodge deep inside the lung and give rise to premature mortality and a range of cardiovascular and respiratory diseases. In China, for example, the number of deaths due to outdoor air pollution rose by 5% between 2005 and 2010.

Developing cities working to reduce black carbon emissions in transport

As much as 92% of the concentration of black carbon in urban areas is due to local emissions. Diesel vehicles are significant emitters of local black carbon in cities and the overall levels of black carbon are expected to increase as vehicle use rises. Options to reduce emissions from diesel transport include emission control technologies, new vehicle and fuel standards, fiscal incentives to encourage higher quality fuel supply, and reducing the number of diesel producing vehicles on the road by prioritizing sustainable transport.

A number of cities in developing countries, particularly those that are expected to grow rapidly, are taking significant actions to regulate black carbon. For example:

• Cebu, the second largest city in the Philippines, is aiming to reduce black carbon and improve sustainable transport by upgrading its bus rapid transit (BRT) vehicles;
• Istanbul has experimented with diesel particulate filter retrofitting pilot projects;
• Jakarta is investigating refinery upgrades and vehicle emissions standards; and
• Mexico City has made multiple interventions to improve air quality, including reducing private vehicle use by expanding sustainable transport options such as bus rapid transit (BRT) and public bike-share, and has prioritized pedestrians and cyclists in its new mobility law. The city also launched a real-time monitoring program to track black carbon concentrations in ambient air in five selected sites across the city.

Realizing the benefits of reducing black carbon in cities

Since the 1980s, the state of California has enforced regulations on black carbon because smog was turning the air in Los Angeles and other cities brown. Regulations on diesel engines have led to a 90% reduction in black carbon levels over the past 45 years, the equivalent of removing more than four million cars off the roads every year. These reductions in black carbon emissions stem mainly from the introduction of low-sulfur fuel, cleaner burning engines, tighter emissions standards, and other technology improvements required by regulation. California’s success regulating diesel engines and fuels provides important lessons for developing countries that face rapidly expanding vehicle fleets.

If the benefits from places like California can be achieved in major cities, the potential to curb climate change and save lives would be significant. As part of a broad shift towards sustainable, cleaner forms of urban transport, regulations on black carbon emissions should be a priority for cities worldwide.