Hot, sunny weather increases the amount of air pollution released from asphalt roads by up to 300 per cent, study shows
- A US report reveals pollutants in the air are produced by asphalt on the streets
- The black, sticky, grainy substance is used to layer roads, pavements and roofs
- But its effects are hardly ever considered in urban air quality management plans
- The substance emits high levels of aerosol under sunlight and high temperatures
Asphalt is a big source of air pollutants in urban areas, especially on hot and sunny days, a new study claims.
The sticky, black substance, often seen being pressed down by road rollers at building sites, is found on roads, roofs, pavements and driveways.
But scientists believe its chemical emissions have been unaccounted for in urban air quality management plans.
Yale researchers found chemical emissions from asphalt produce greater quantities of secondary organic aerosol – small particles with public health effects – under summertime conditions.
Emissions from road asphalt rose with just 'moderate' exposure to solar radiation by a massive 300 per cent, they found.
Asphalt is a near-ubiquitous substance found in roads, on roofs and in driveways, but its chemical emissions are rarely considered in urban air quality management plans
Emissions from fuel-burning motor vehicles are likely to decrease in the years ahead, as they're gradually replaced by electric cars.
However, asphalt emissions will continue to have an impact on air pollution and public health, especially under high light and heat conditions.
Finding ways to make roads more environmentally friendly is therefore as important as doing the same for cars and trucks, the experts claim.
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'A main finding is that asphalt-related products emit substantial and diverse mixtures of organic compounds into the air, with a strong dependence on temperature and other environmental conditions,' said study author Peeyush Khare at Yale University.
'That's important from the perspective of air quality, especially in hot, sunny summertime conditions.'
It's well known that emissions from motor vehicles degrade urban air quality, such as nitrogen dioxide, from burning diesel in car engines, and particulate matter – microscopic solids and liquids from exhausts, car tyres and other sources.
But some sources that don't even undergo a form of combustion, like vehicle exhausts, have also become contributors of organic compounds in the air.
They emit secondary organic aerosol (SOA), a major component of overall PM2.5 – particulate matter under 2.5 micrometers in diameter.
Asphalt being laid onto a road. Under different conditions simulating different life cycle stages (storage, paving and use by vehicles), common road and roofing asphalts produced complex mixtures of organic compounds, including hazardous pollutants
PM2.5 pollution has already been shown to be associated with increases in mortality from diseases such as heart disease and stroke in later life.
The researchers collected fresh asphalt and heated it to different temperatures to simulate different seasonal weather conditions.
This ranged from 104°F (40°C) to 392°F (200°C) in a temperature-controlled tube furnace.
Overall, at typical temperature and solar conditions simulating different life cycle stages (storage, paving and use by vehicles), common road and roofing asphalts produced complex mixtures of organic compounds, including hazardous pollutants.
These include polycyclic aromatic hydrocarbons, which are also produced by tobacco smoke.
Asphalt emissions doubled when the temperature increased from 104°F to 140°F – temperatures the material typically reaches in the summertime.
They then climbed by an average of 70 per cent per 68°F increase.
Although asphalt emissions slowed over the course of one week, they persisted at the summer temperatures, especially when the material was exposed to sunlight.
This suggests there are long-term, continued emissions from asphalt in real-world conditions.
The team also examined what happens when asphalt is exposed to moderate solar radiation or sunlight.
They saw up to a 300 per cent jump in emissions for road asphalt compared to conditions without sunlight, showing that both heat and light is part of the issue.
The different stages of asphalt production and its use, all of which give off emissions in the form of SOA
Sulphur-containing compounds showed the greatest increase (700 per cent) followed by oxygen-containing compounds (400 per cent) and hydrocarbons (300 per cent).
'That's important from the perspective of air quality, especially in hot, sunny summertime conditions,' Khare said.
Paved surfaces and roofs make up approximately 45 per cent and 20 per cent of surfaces in US cities, respectively.
Because of the types of compounds asphalt emits, its potential SOA formation is comparable to motor vehicle emissions in Los Angeles, a key city for urban air quality case studies.
The effect of asphalt emissions on the formation of ozone (O3) – which causes a smoggy haze that can damage the lungs – was, however, minimal compared to motor vehicles and volatile chemicals in personal care and cleaning products.
Cleaning products are another key emerging source of reactive organic emissions that produces large quantities of SOA in urban areas.
'It's another important non-combustion source of emissions that contributes to SOA production, among a class of sources that scientists in the field are actively working to constrain better,' said Drew Gentner, associate professor of chemical & environmental engineering at Yale.
Future studies may use different methods to capture the extent of the emissions released both during and after asphalt application.
The study has been published in the journal Science Advances.
Revealed: MailOnline dissects the impact greenhouse gases have on the planet - and what is being done to stop air pollution
Emissions
Carbon dioxide
Carbon dioxide (CO2) is one of the biggest contributors to global warming. After the gas is released into the atmosphere it stays there, making it difficult for heat to escape - and warming up the planet in the process.
It is primarily released from burning fossil fuels such as coal, oil and gas, as well as cement production.
The average monthly concentration of CO2 in the Earth's atmosphere, as of April 2019, is 413 parts per million (ppm). Before the Industrial Revolution, the concentration was just 280 ppm.
CO2 concentration has fluctuated over the last 800,000 years between 180 to 280ppm, but has been vastly accelerated by pollution caused by humans.
Nitrogen dioxide
The gas nitrogen dioxide (NO2) comes from burning fossil fuels, car exhaust emissions and the use of nitrogen-based fertilisers used in agriculture.
Although there is far less NO2 in the atmosphere than CO2, it is between 200 and 300 times more effective at trapping heat.
Sulfur dioxide
Sulfur dioxide (SO2) also primarily comes from fossil fuel burning, but can also be released from car exhausts.
SO2 can react with water, oxygen and other chemicals in the atmosphere to cause acid rain.
Carbon monoxide
Carbon monoxide (CO) is an indirect greenhouse gas as it reacts with hydroxyl radicals, removing them. Hydroxyl radicals reduce the lifetime of carbon dioxide and other greenhouse gases.
Particulates
What is particulate matter?
Particulate matter refers to tiny parts of solids or liquid materials in the air.
Some are visible, such as dust, whereas others cannot be seen by the naked eye.
Materials such as metals, microplastics, soil and chemicals can be in particulate matter.
Particulate matter (or PM) is described in micrometres. The two main ones mentioned in reports and studies are PM10 (less than 10 micrometres) and PM2.5 (less than 2.5 micrometres).
Air pollution comes from burning fossil fuels, cars, cement making and agriculture
Scientists measure the rate of particulates in the air by cubic metre.
Particulate matter is sent into the air by a number of processes including burning fossil fuels, driving cars and steel making.
Why are particulates dangerous?
Particulates are dangerous because those less than 10 micrometres in diameter can get deep into your lungs, or even pass into your bloodstream. Particulates are found in higher concentrations in urban areas, particularly along main roads.
Health impact
What sort of health problems can pollution cause?
According to the World Health Organization, a third of deaths from stroke, lung cancer and heart disease can be linked to air pollution.
Some of the effects of air pollution on the body are not understood, but pollution may increase inflammation which narrows the arteries leading to heart attacks or strokes.
As well as this, almost one in 10 lung cancer cases in the UK are caused by air pollution.
Particulates find their way into the lungs and get lodged there, causing inflammation and damage. As well as this, some chemicals in particulates that make their way into the body can cause cancer.
Deaths from pollution
Around seven million people die prematurely because of air pollution every year. Pollution can cause a number of issues including asthma attacks, strokes, various cancers and cardiovascular problems.
Asthma triggers
Air pollution can cause problems for asthma sufferers for a number of reasons. Pollutants in traffic fumes can irritate the airways, and particulates can get into your lungs and throat and make these areas inflamed.
Problems in pregnancy
Women exposed to air pollution before getting pregnant are nearly 20 per cent more likely to have babies with birth defects, research suggested in January 2018.
Living within 3.1 miles (5km) of a highly-polluted area one month before conceiving makes women more likely to give birth to babies with defects such as cleft palates or lips, a study by University of Cincinnati found.
For every 0.01mg/m3 increase in fine air particles, birth defects rise by 19 per cent, the research adds.
Previous research suggests this causes birth defects as a result of women suffering inflammation and 'internal stress'.
What is being done to tackle air pollution?
Paris agreement on climate change
The Paris Agreement, which was first signed in 2015, is an international agreement to control and limit climate change.
It hopes to hold the increase in the global average temperature to below 2°C (3.6ºF) 'and to pursue efforts to limit the temperature increase to 1.5°C (2.7°F)'.
Carbon neutral by 2050
The UK government has announced plans to make the country carbon neutral by 2050.
They plan to do this by planting more trees and by installing 'carbon capture' technology at the source of the pollution.
Some critics are worried that this first option will be used by the government to export its carbon offsetting to other countries.
International carbon credits let nations continue emitting carbon while paying for trees to be planted elsewhere, balancing out their emissions.
No new petrol or diesel vehicles by 2040
In 2017, the UK government announced the sale of new petrol and diesel cars would be banned by 2040.
From around 2020, town halls will be allowed to levy extra charges on diesel drivers using the UK's 81 most polluted routes if air quality fails to improve.
However, MPs on the climate change committee have urged the government to bring the ban forward to 2030, as by then they will have an equivalent range and price.
The Paris Agreement, which was first signed in 2015, is an international agreement to control and limit climate change. Pictured: air pollution over Paris in 2019.
Norway's electric car subsidies
The speedy electrification of Norway's automotive fleet is attributed mainly to generous state subsidies. Electric cars are almost entirely exempt from the heavy taxes imposed on petrol and diesel cars, which makes them competitively priced.
A VW Golf with a standard combustion engine costs nearly 334,000 kroner (34,500 euros, $38,600), while its electric cousin the e-Golf costs 326,000 kroner thanks to a lower tax quotient.
Criticisms of inaction on climate change
The Committee on Climate Change (CCC) has said there is a 'shocking' lack of Government preparation for the risks to the country from climate change.
The committee assessed 33 areas where the risks of climate change had to be addressed – from flood resilience of properties to impacts on farmland and supply chains – and found no real progress in any of them.
The UK is not prepared for 2°C of warming, the level at which countries have pledged to curb temperature rises, let alone a 4°C rise, which is possible if greenhouse gases are not cut globally, the committee said.
It added that cities need more green spaces to stop the urban 'heat island' effect, and to prevent floods by soaking up heavy rainfall.
