PM2.5

When wildfire smoke is in the air, doctors urge people to stay indoors to avoid breathing in harmful particles and gases. But what happens to trees and other plants that can’t escape from the smoke? They respond a bit like us, it turns out: Some trees essentially shut their windows and doors and hold their breath. As atmospheric and chemical scientists, we study the air quality and ecological effects of wildfire smoke and other pollutants. In a study that started quite by accident when smoke overwhelmed our research site in Colorado, we were able to watch in real time how the leaves of living pine trees responded. How plants breathe Plants have pores on the surface of their leaves called stomata. These pores are much like our mouths, except that while we inhale oxygen and exhale carbon dioxide, plants inhale carbon dioxide and exhale oxygen. A highly magnified view of stomata in a maize leaf. Umberto Salvagnin/Fli...

When wildfires rage, the immediate threat is obvious – but smoke from the fires actually kills far more people than the flames. As fires become more frequent, that smoke is leading to a public health crisis. In a new study published in the journal Science Advances, we found that wildfire smoke likely contributed to more than 52,000 premature deaths across California alone from 2008 to 2018, with an economic impact from the deaths of more than US$430 billion. Previous studies have examined the short-term health risks from wildfire smoke, but few have assessed how exposure to wildfire smoke over years adds up to shorten human lives. Smoke from far-off wildfires turns the skies orange over San Francisco in 2020. Running in wildfire smoke carries harmful particles deep into a person’s lungs. AP Photo/Tony Avelar Wildfire risk and severity have grown as the climate has changed and as more...

Dozens of wildfires are burning across Canada in May 2024 and sending unhealthy smoke blowing into the northern U.S. again. At the same time, the southeastern U.S. is getting smoke from Mexico, where drought conditions have been fueling fires. Last year, Canada’s record 2023 wildfire season introduced millions of Americans across the Midwest and northeastern states to the health hazards of wildfire smoke, with air quality alerts that reached levels never seen there before. Professional baseball games were postponed and the skies in New York City turned orange with haze, at times exposing millions of people to the worst air quality in the world. In some regions, the smoke hung on for days. The pressing question on many people’s minds: “Is this the new normal?” From our perspective as air quality scientists, we think the answer is likely “yes.” Global warming means more fires Hotter, drier conditions, coupled with dry grasses and underbrush...

Did you receive a mail-order package this week? Carriers in the U.S. shipped 64 packages for every American in 2022, so it’s quite possible. That commerce reflects the expansion of large-scale retail in recent decades, especially big-box chains like Walmart, Target, Best Buy and Home Depot that sell goods both in stores and online. This has led to the growth of distribution centers that fulfill these orders. While mail-order commerce is convenient, these centers also have harmful impacts, including traffic congestion and air and water pollution. I study environmental history, and I am part of a group of scholars examining the environmental impacts of big-box stores like Walmart, Target, REI and Bass Pro Shops. Sustainability is a hot topic in the retail sector, but my research on the history of Target – the sixth-largest retailer in the U.S. – shows how retail companies have largely escaped the kinds of environmental regulations that affect other sectors such...

The U.S. Environmental Protection Agency has announced a new standard for protecting the public from fine particulate air pollution, known as PM2.5 because the particles are smaller than 2.5 millionths of a meter. These minute particles can penetrate deeply into the body and have been linked to many serious illnesses. The new rule sets an annual limit of 9 micrograms per cubic meter of air, down from the previous level of 12 micrograms. States will be required to meet this standard and to take it into consideration when they evaluate applications for permits for new stationary air pollution sources, such as electric power plants, factories and oil refineries. Under the Clean Air Act, the EPA is required to set air pollution standards at levels that protect public health. In the four articles that follow, scholars wrote about the many ways in which exposure to PM2.5 contributes to cardiovascular disease, lung cancer, other illnesses such as dementia, and premature deaths. 1. An...