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The thermal degradation of asphalt pavement on hot days releases invisible pollutants that directly affect the quality of life in urban centers.
The widespread use of asphalt paving in urban centers is under new scientific scrutiny following the discovery that the material releases dangerous pollutants under specific conditions.
A recent study revealed that asphalt is a significant source of ultrafine particles and toxic organic compounds, whose emission is intensified by solar radiation and rising temperatures. The research raises an alert about public health risks, especially in cities suffering from the urban heat island effect, where dark surfaces absorb and re-radiate thermal energy.
The relationship between heat and asphalt emissions
Researchers observed that when exposed to high temperatures, asphalt undergoes a chemical degradation process that results in the release of secondary organic aerosols. These compounds, known as ultrafine particles, are small enough to penetrate deeply into the human respiratory system and reach the bloodstream.
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The study demonstrated that the amount of pollutants emitted doubles when the surface temperature rises from 40°C to 60°C, a common level during intense summers. Even without tire friction or mechanical wear, simple solar heating is enough to turn the pavement into a polluting source.
Laboratory analysis indicated that fresh asphalt releases a varied range of hydrocarbons that contribute to smog formation in large metropolises. However, the most concerning data is that old asphalt, even after years of exposure, continues to emit these ultrafine particles persistently. Ultraviolet radiation acts as a catalyst, accelerating chemical reactions in the material’s surface layer and releasing volatile substances throughout the day.
This discovery suggests that the environmental impact of paved roads and streets may have been underestimated in traditional air quality metrics.
Impacts on public health and air quality
Constant inhalation of asphalt-derived compounds is directly associated with an increase in cardiovascular diseases and chronic respiratory problems in urban populations.
The ultrafine particles emitted by hot asphalt are particularly dangerous due to their ability to transport toxins to vital organs. In addition to direct damage, these pollutants react with other gases in the atmosphere to form ground-level ozone, a severe lung irritant. Children and the elderly are identified as the most vulnerable groups to this invisible pollution emanating directly from the city ground.
The concentration of these pollutants tends to be higher in areas with low air circulation and high paving density, such as urban canyons surrounded by tall buildings. The study reinforces the need to re-evaluate urban planning, as the presence of ultrafine particles can negate some of the benefits obtained from the transition to electric vehicles.
If asphalt continues to emit toxic gases regardless of the type of engine circulating over it, the solution for clean air requires structural changes in the choice of civil construction materials.
Alternatives and mitigation for urban centers
Given the evidence regarding the release of ultrafine particles, scientists and urban planners are beginning to explore alternative paving materials that have a smaller chemical footprint. Solutions such as permeable pavements, light-colored concretes, and the use of vegetative covers are pointed out as effective ways to reduce surface temperature and, consequently, emissions. Reducing direct solar exposure on streets through tree planting has also proven to be a viable strategy to curb the release of toxic compounds.
The development of asphalt sealants that block the volatilization of hydrocarbons is another research front mentioned as a possible short-term mitigation.
However, the absolute priority lies in the awareness that asphalt is an active component in urban atmospheric chemistry, and not just an inert surface. Continuous monitoring of ultrafine particles from pavement will be essential to create more effective health policies and cities more resilient to heat.
The transition to cooler infrastructures thus emerges as an urgent necessity to protect citizens’ breathing in the future.
Click here to access the study.
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