Science 4 min read

The Unexpected Side Effects of Cleaning Urban Air Pollution

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Scientists have discovered that cleaning up air pollutants from urban areas could lead to an increase in organic hydroperoxides, noxious chemical compounds, through atmospheric autoxidation.

Urban pollution is the result of mostly human-made emissions from various sources, such as industrial and household activities along with car traffic (exhaust fumes), which is responsible for a quarter of airborne pollutants in the form of particulate matter (aerosols).

While actions taken to purify the air we breathe reduces the effects of airborne pollutants on health and the environment, a new study claims they could also give rise to another class of harmful compounds.

In short, cleaning up urban air could lead to an increase in other harmful chemical compounds.

Air Pollutants Undermine Public Health and Welfare

The primary pollutants found in the urban atmosphere are nitrogen oxides (NO and NO2), carbon monoxide (CO) and a number of other volatile organic compounds. Concentrations of these pollutants in the urban atmosphere vary according to seasons, meteorological conditions, and human activity.

Air pollution can trigger the development of respiratory diseases (chronic obstructive pulmonary disease), cardiovascular diseases, strokes, and lung cancer. Scientists have also found a link between air pollution and adolescent delinquency and lower IQ.

Annually, air pollution causes the premature death of 7 million people in the world, or,  according to the World Health Organization, one in eight of total deaths. The organization subsequently declared air pollution as the world’s largest single environmental health risk.

“Cleaning up the air we breathe prevents noncommunicable diseases as well as reduces disease risks among women and vulnerable groups, including children and the elderly,” claim WHO experts.

Measures against atmospheric pollutants (such as reducing car use, limiting urban access to vehicles, and better urban development) have allowed a significant improvement in air quality in many large cities in the U.S such Los Angeles, New York, and Chicago.

The EPA, or the Environmental Protection Agency, says that the Clean Air Act (passed in 1970, and amended twice, in 1977 and 1990) allowed Americans to breathe less polluted air, and helped to cut the toll of pollution on the economy and environment.

The Flip Side of Fighting Air Pollution

The increase in air quality standards instigated by the Clean Air Act has helped to cut the emissions of (six main) pollutants (like nitric oxide and hydrocarbons) in the U.S by 70% since 1970. However, in doing so, they may have also triggered an increase in organic hydroperoxides not usually found in the air.

This serious and unexpected downside to cleaning up the air has been revealed by scientists at California Institute of Technology, Caltech, and the University of Copenhagen, UCPH, in Denmark.

Researchers noted that, compared to the dramatic drop in nitric oxide, the decline of hydrocarbons has been significantly slower. Their research found that this disparity could possibly trigger the production of organic hydroperoxides.

Not common over cities, organic hydroperoxides are usually found in rural areas and regions where not much tailpipe exhaust and other sources of nitric oxides are produced.

Besides the natural process which involves light interaction, researchers found another chemical process that can trigger the production of organic hydroperoxides molecules. This process, known as gas-phase autoxidation, occurs when hydrocarbon molecules can’t find enough nitric oxide to react with.

“As these nitric oxide concentrations go down by another factor of two over the next five to seven years, we’re going to start making more and more organic hydroperoxides in urban areas,” says Caltech’s Paul Wennberg, lead author of the study. “… we haven’t seen large concentrations of hydroperoxides in heavily populated areas, so we don’t know how the formation of gas and aerosol hydroperoxides will impact public health. But we do know that breathing in particles tends to be bad for you.”

Will the fossil fuel industry use these new findings against the Clean Air Act, which is already under attack? Or do you see this as a temporary side-effect to creating a cleaner environment within our urban areas? Let us know your thoughts in the comments section below.  

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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