From flames to haze, wildfire smoke transforms as it travels

Wildfire smoke travels thousands of miles, changing chemically and physically as it moves. When a wildfire burns, it releases fine particulate matter (PM2.5), nitrogen oxides, and volatile organic compounds (VOCs). These pollutants can harm human health, affecting the lungs, heart, and other organs, and may include carcinogens. The smoke’s behavior depends on the fire’s temperature: hot, intense flames produce nitrogen oxides and reactive carbon compounds, while cooler, smoldering fires release aromatic oxygenates and ammonia. The smoke’s journey is shaped by wind speed, atmospheric temperature, and sunlight. Massive wildfires can lift smoke high into the atmosphere, where high-altitude winds transport it across the continent. This process is studied by atmospheric chemists, such as those at the NOAA Chemical Sciences Laboratory, using research aircraft and controlled fuel burns to track smoke evolution.

As wildfire smoke travels, it undergoes rapid changes due to sunlight and atmospheric chemistry. Within hours of being emitted, the smoke reacts to form ground-level ozone, a component of smog that irritates the lungs. If smoke is lofted high into cold air, chemical aging temporarily stops until the air sinks closer to the surface, where warmer temperatures restart reactions. When smoke passes over a city, it can mix with urban pollution like car exhaust, creating additional ozone. The aging process also alters the smoke’s smell and color. Compounds responsible for the campfire aroma, such as phenolic compounds, are destroyed by sunlight within hours. Dark, light-absorbing particles are chemically bleached, turning the smoke from a dark plume into a milky white haze that scatters blue and green light, creating an all-day sunset effect.

Wildfire smoke poses serious health risks, even when it travels hundreds of miles from its source. The fine particulate matter (PM2.5) and other pollutants in smoke can harm the respiratory system, cardiovascular system, and other organs. Long-term exposure to certain compounds in smoke, such as aromatic hydrocarbons, may increase the risk of cancer. Ground-level ozone, formed as smoke ages, can irritate the lungs and worsen conditions like asthma. The health threat is not limited to areas near wildfires; distant communities can also experience poor air quality due to smoke transported by wind. This issue is a major air quality concern in North America and is expected to worsen in the coming years. Research is ongoing to better understand and predict the impacts of wildfire smoke on human health.

Scientists use advanced tools to study how wildfire smoke moves and changes over time. Organizations like the NOAA Chemical Sciences Laboratory track smoke behavior through controlled fuel burns in labs and by flying research aircraft through smoke plumes. These efforts help predict the smoke’s chemical fate and its impacts on air quality. Wildfire plumes can sometimes generate their own weather, creating pyrocumulonimbus clouds that inject particles into the stratosphere. High-altitude winds then transport the smoke thousands of miles across the continent. Understanding these processes is crucial for managing air quality and protecting public health, especially in regions frequently affected by wildfire smoke.