Understanding Traffic & Air Quality: How Does Urban Mobility Affect Air Pollution?

Understanding Traffic & Air Quality: How Does Urban Mobility Affect Air Pollution?

Air pollution is widely considered to be the world’s leading environmental health threat, accounting for over 7 million deaths on an annual, global scale. Among those, 4.2 million are a direct result of ambient air pollution with traffic and mobility being the largest contributing factors for those fatalities.  

Global transport carbon dioxide (CO2) emissions in 2018 amounted to 8 billion tonnes, 74% of which were due to road vehicles. Since over half of the world’s population live in urban areas where a larger density of traffic tends to present, it is estimated that residents of cities are among those at a higher risk of health-related problems due to air pollution in addition to the subsequent effects on the environment and local economy.

Let’s examine the relationship between traffic and air quality as well as the many complexities and developments that have evolved throughout the years.

How does traffic contribute to air pollution in urban areas?

In many urban areas, traffic remains one of the main sources of air pollution. The transportation sector is considered to be the largest contributor to CO2 emissions in the U.S., surpassing the electric power sector for the total emissions used. Transportation currently accounts for more than 30 percent of total U.S. CO2 emissions resulting from energy consumption per year.

Pollutants being emitted from petrol and diesel engines of cars consist of carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), volatile organic compounds (VOCs), and particulate matter (PM).  

This complex and variable mixture of secondary pollutants formed in the atmosphere exhausts from vehicles along with evaporative emissions, and non-combustion emissions (e.g., road dust, and tire wear) are typically referred to as traffic-related air pollution (TRAP). They are thought to be the leading cause of poor air quality in cities and urban areas, negatively affecting large portions of the world’s population, causing further harm to the environment, and contributing further to climate change.  

Electric vehicles have also been shown to contribute to air pollution depending on whether the energy they use is generated by conventional means, such as coal power plants. Additionally, primary PM emissions are also created through friction from tires and brake wear. Nitrogen dioxide (NO2) and VOCs which are released by vehicles on roads create something otherwise known as photochemical smog in cities by forming photochemical reactions that result in ground-level ozone (O3). 

On a more global scale, the transportation sector is yet again named as a major polluter since it was recorded that in 2021 alone, it produced more than seven billion metric tons of carbon dioxide (GtCO2). It was reported that passenger cars were the largest source of emissions that year, accounting for approximately 39 percent of global transportation emissions.

What is the health impact of air pollution from traffic?

A World Bank report estimated that the cost of health damage from air pollution amounted to about $8.1 trillion a year, equivalent to 6.1% of the global GDP. 

It is additionally reported that more than 95 percent of those fatalities have occurred in countries where people of low- and middle-income households are regularly exposed to both indoor and outdoor concentrations of pollution particles (within a 300-500 meter distance of area with heavy traffic) which ranges significantly higher in percentage than guidelines established by the World Health Organization.

Aerosols also referred to as fine particulate matter or PM2.5 are the primary cause of pollution-related deaths each year, typically resulting in health conditions such as stroke, heart disease, lung cancer, chronic obstructive pulmonary disease, pneumonia, neonatal disorders, and type 2 diabetes.  

Both long-term and short-term exposure to air pollutants has been shown to cause various health issues. Groups of society that are thought to be most at risk include infants and young children, the elderly, and those who live near busy motorways or work with dangerous chemicals. People with pre-existing health conditions such as asthma, bronchitis, chronic inflammatory lung disease, and emphysema are also at risk of experiencing adverse health effects from traffic-related air pollution since it can make their condition worse, and trigger asthma attacks, infections, and various complications.

The development of transport-related air pollution over time

The link between air pollution and cars was initially established in the early 1950s by a California researcher who was able to determine that it was pollutants from traffic that were to blame for smoggy skies across cities in the U.S. At this time, conventional cars were found to emit about 13 grams of hydrocarbons (HC) per mile, 3.6 grams of nitrogen oxides (NOx), and 87 grams of carbon monoxide (CO).

The 1970s Clean Air Act

As a result, stricter policies were put in place to bring down levels of such pollutants, setting a new standard for the auto industry which prompted a variety of developments in new emission control technologies. Over time, Congress authorized the U.S. Environmental Protection Agency (EPA) to take control of regulating emissions from other sources of transport such as heavy-duty trucks, locomotives, various marine engines, and even construction and domestic equipment. This set the way for a series of milestones in transportation with the help of technological advances in engine design which in turn led to the creation of higher-quality fuels.

An integrated approach to emission control also highlighted a very important underlying factor which was the need for extensive and continuous collaboration between EPA and vehicle, engine, and fuel manufacturers, followed closely by the involvement of state and local governments, urban planners, and transport providers. As a result of the 1970s Clean Air Act, it’s been reported that air pollution has dropped by about 62%. By eliminating lead from fuels, sulfur levels are 90% lower now than before the regulation was put in place. New vehicles are also 98-99% cleaner for most major pollutants compared to cars from the 1960s, for example.

Further developments

It has been estimated that for every $1 USD spent on reducing emissions from mobile sources, $9 USD goes towards initiatives that benefit public health, productivity, and the environment, as well as cutting costs. According to the EPA, it is expected that by 2030, air quality emissions will have in place the vehicle standards needed to achieve significant results in the prevention of over 40,000 premature deaths annually, including 34,000 avoided visits to the hospital as well as compensating for 4.8 million lost work days. But even with all of these accomplishments, the transportation sector is still considered to be the primary source responsible for over 55% of the total NOx emissions in the country.

In the European Union, it has been reported that since the 1990s, sulfur oxides (SOx) emissions from road transport have dropped by 99%, non-methane volatile organic compounds (NMVOCs) by 89%, carbon monoxide (CO) emissions by 88%, and nitrogen oxides (NOx) by 60%. This still leaves primary PM2.5 emissions from braking, tire wear, and road abrasions which have gradually increased by 22% since the 2000s. In 2017, to be specific, non-exhaust PM2.5 was proven to have accounted for nearly 46% of the total emissions from the road transport sector.

What does the future of sustainable mobility look like?

There is a growing consensus between governments, city planners, and transport providers when it comes to the need for more sustainable patterns of transport activities. Many experts have looked at the concept of ‘’smart’’ or ‘’green cities’’ as the binding link needed to make a lasting change happen when it comes to reducing urban air pollution and greenhouse gas emissions.

The Evolution of Smart Cities

Such cities hold tremendous potential when it comes to solving a variety of urban issues that have put a great strain on municipalities. They are thought to be able to help with effectively regulating traffic (reducing congestion), promote more environmentally-friendly modes of transport, particularly in the public transport sector, upgrade existing city infrastructure, implement newer, smarter technologies, and replace old and outdated systems, as well as invest in better quality fuels. Greener and more efficient modes of transport are the future of sustainable mobility, through integrated land use along with smart transport planning.  

An overall examination of transport-related air pollution shows an improvement in the sector as the numbers have gradually decreased across many nations, due to the number of environmental legislation and developments in vehicle technology. Some examples include innovations such as diesel particulate filters which have been shown to reduce tailpipe emissions by capturing soot, although they are still partially contributing to some forms of air pollution.  

With that said, there is still a lot of room for development when it comes to improving the mobility sector and building a stable future for cities that aim to be sustainable, caring for the environment and the quality of life of its citizens. Some research shows that building additional vehicle infrastructure further stimulates people to use cars more, which unfortunately only makes the issue of traffic and congestion worse.

Future Strategies

Some strategies for development in the sector that show promising results include the establishment of tax schemes and congestion charges that are predicted to discourage the use of diesel vehicles and driving in cities, in general. Alternatively, it is expected that investing in vehicle and fuel technologies will create a positive impact, along with further initiatives regarding the optimization of urban spaces to reduce vehicle travel demands. Improving areas of public transportation such as reliability, affordability, and accessibility is said to also bring public interest back, further stimulating citizens to choose more sustainable modes of transport. Additionally, encouraging people to use other means of moving around such as walking or cycling is also an option through improved infrastructure and further public initiatives.

With the world’s population steadily increasing and the effects of urbanization and climate change as evident as ever, it’s highly unlikely that there will be a single way of solving the issue of traffic and pollution. The best plan of action is perhaps a combination of carefully planned investments in smart technology, legislation, and infrastructure that promotes wellness and quality of life, with the environment in mind. We’ve already seen a lot of progress when it comes to such examples and we’re excited to see what the future will bring through combined effort and collaboration on a global scale.