Particulates

Smoke from more than 100 wildfires burning across Canada has been rolling into North American cities far from the flames. New York City, Denver, Chicago, Minneapolis and Detroit each made the list of the most polluted cities in the world at times in May and June 2023 because of the fires. The smoke has triggered air quality alerts in several states. We asked Chris Migliaccio, a toxicologist at the University of Montana who studies the impact of wildfire smoke on human health, about the health risks people can face when smoke blows in from distant wildfires. What’s in wildfire smoke that’s a problem? When we talk about air quality, we often talk about PM2.5. That’s particulate matter 2.5 microns or smaller – small enough that it can travel deep into the lungs. Exposure to PM2.5 from smoke or other air pollution, such as vehicle emissions, can exacerbate health conditions like asthma and reduce lung function in ways that can worsen existing respiratory pr...

As part of its effort to reduce air pollution and cut greenhouse gas emissions that contribute to climate change, California is pursuing aggressive policies to promote clean trucks. The state already requires that by 2035, all new cars and other light-duty vehicles sold in the state must be zero emission. Its powerful Air Resources Board has adopted rules requiring that most trucks be zero emission by 2035, and is now proposing that all trucks sold by 2040 must be zero emission. The Conversation asked a panel of transportation experts from the University of California, Davis what’s involved in such a rapid transition. 1. Why is California targeting medium- and heavy-duty trucks? Although diesel engines are valuable for moving heavy loads, they also are major polluters. Diesel trucks account for one-fourth of greenhouse gas emissions and about half of conventional air pollution from transportation in U.S. cities. Pollutants in diesel exhaust include nitrogen oxides, fine...

Clouds form when water vapor – an invisible gas in the atmosphere – sticks to tiny floating particles, such as dust, and turns into liquid water droplets or ice crystals. In a newly published study, we show that microplastic particles can have the same effects, producing ice crystals at temperatures 5 to 10 degrees Celsius (9 to 18 degrees Fahrenheit) warmer than droplets without microplastics. This suggests that microplastics in the air may affect weather and climate by producing clouds in conditions where they would not form otherwise. We are atmospheric chemists who study how different types of particles form ice when they come into contact with liquid water. This process, which occurs constantly in the atmosphere, is called nucleation. Clouds in the atmosphere can be made up of liquid water droplets, ice particles or a mixture of the two. In clouds in the mid- to upper atmosphere where temperatures are between 32 and minus 36 F (0 to minus 38 C), ice crystals...