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These substances can generate air pollution particles.
As traffic slows down, research is gathering momentum.
A study finds that higher ozone levels correlate with slower performance times for college endurance athletes.
US ozone pollution has fallen in recent decades, but exposure to low levels of ozone still has serious effects on human health and well-being.
The US government is set to make it easier for oil and gas firms to leak methane into the atmosphere.
Can Walmart go green while maintaining its commitment to low prices?
AP Photo/Tom Uhlman
Two business professors spent five years studying Walmart's ambition project to bring sustainability to its millions of budget-conscious customers – a plan that began with the birth of a granddaughter.
Taj Mahal is one of the most beautiful buildings in the world, but over the last four centuries it has aged and darkened from pollution.
Rob from Harwick, Stockton-on-Tees, where life expectancy is low, spoke to BBC Panorama about health inequalities.
In a developed country like the UK, why can life expectancy within just a few miles differ by as much as 18 years?
A clear day at Acadia National Park in Maine.
US national parks protect some of America's most spectacular outdoor settings. But new research shows that ozone pollution levels in the parks are roughly as bad as in major cities.
Fire burns the hillsides along Highway 129 near Lake Berryessa in Yolo County, California, on July 3, 2018.
(Randall Benton/The Sacramento Bee via AP)
And wildfires rage along the West Coast of North America, parents should know the impact on their children's health, and how to protect them.
Afternoon traffic into Nairobi’s CBD.
Research shows that cities benefit from car-free days in many ways.
Daily routine affects how much polluted air we breathe.
A large dust storm, or haboob, sweeps across downtown Phoenix on July 21, 2012.
AP Photo/Ross D. Franklin, File
New research projects that climate change could greatly increase airborne dust levels in the southwestern US, causing higher hospital admissions and premature deaths from heart and lung ailments.
Two air pollution experts analyse the government's plan.
Smog alert in Cleveland, Ohio, July 20, 1973.
EPA Administrator Scott Pruitt wants to change the grounds for setting US air pollution targets. An environmental lawyer explains why Pruitt's approach misreads the law and could roll back decades of gains.
The landmark Harvard Six Cities study found a strong link between air pollution and health risks.
The EPA intends to limit what scientific studies can inform policy – a change long sought by industry. A long-time public health researcher explains the single study at the root of the controversy.
High intensity logging burns and the resulting smoke plume near Mount Baw Baw, April 2018
Photo Chris Taylor.
Every autumn Victoria copes with smoke haze from planned burns that reduce bushfire risk, but a large part of that pollution actually comes from industrial logging activity.
Good for you, bad for the air?
New research is spotlighting personal care products, such as shampoos and skin lotions, as a significant source of chemicals that contribute to urban air pollution.
Lava flow moves in the Leilani Estates subdivision near Pahoa on the island of Hawaii, May 6, 2018.
USGS via AP
Fountains of lava from Hawaii's Kilauea volcano are dramatic, but the most deadly impacts of volcanic eruptions are toxic gases and ash and mud flows.
Morning smog in New Delhi, India.
AP Photo/Manish Swarup
According to one study, more than 8 million people per year die early from air pollution exposure.
Pollutants can increase stress levels, which in turn affects judgment and makes some people more likely to commit crime.