Brown Smoke over North America: Satellites Documented a Week of Poor Air

For several days in July 2026 dense smoke layers from forest and grassland fires settled over parts of the United States and Canada. Spaceborne observations, supplemented by atmospheric model analyses, tracked the plume’s long-range transport and revealed a pronounced fraction of brown carbon.

What is brown carbon? Brown carbon differs from classical soot (black carbon) in optical properties and composition. It is produced mainly by incomplete combustion of organic material. Whereas black carbon absorbs broadly across the visible spectrum, brown carbon absorbs especially strongly in the blue and ultraviolet bands. That gives haze a brownish tint, alters the radiation balance and thus affects visibility and climate.

Spread and visibility

Satellite data showed extensive smoke layers covering hundreds of thousands of square kilometres. Driven by upper-level winds, the smoke extended from near-surface levels up to several kilometres altitude. At ground level the smoke reduced visibility and raised fine particulate (PM2.5) concentrations; aloft, particle transport and residence time determined further spread. In affected areas visibility declined and sunrises and sunsets appeared intensely red to orange — an effect of stronger absorption of shorter wavelengths by brown carbon.

Health impacts

Fine particles from smoke can penetrate deep into the airways. Children, older people and those with pre-existing heart or lung conditions are particularly vulnerable. Reported complaints ranged from eye and respiratory irritation to reduced lung function and acute cardiovascular problems. Authorities responded with air-quality alerts and behavioural guidance; some facilities temporarily closed in places.

Protective advice

In the short term, avoiding heavy outdoor exposure, wearing suitable filtration masks (FFP2/N95) and using indoor air purifiers help reduce exposure. People with chronic conditions should follow medical advice and keep medications on hand.

Climate and environmental effects

Aerosols from biomass burning affect weather and climate in complex ways. They reflect some incoming solar radiation and can cool near-surface air layers, while absorbing particles such as brown and black carbon take up energy in the atmosphere and warm it there. These opposing effects influence atmospheric stability and cloud formation. When soot particles deposit on snow and ice, they can accelerate melting. Despite progress, interactions among aerosols, clouds and radiation remain uncertain.

Why such smoke events are increasing

Hotter, drier summers, longer growing seasons and changing precipitation patterns increase landscapes’ vulnerability to fire. More lightning without accompanying rain favours new ignitions, and accumulated deadwood can intensify fires. As a result, large-scale smoke events are becoming more frequent and severe in many regions.

Policy and practice

In the short term, protecting health and maintaining critical infrastructure are priorities: clean-air plans, warning systems, temporary closures and support for the most affected groups. Long term, adaptation and prevention gain importance — including adjusted forest and greenspace management, fuel management, early suppression and land-use planning that increases fire resilience. Globally effective emissions reductions remain central to limiting climate-driven risk factors for more frequent and intense fires.

Role of satellite observation

Spaceborne instruments provide wide spatial coverage and continuous time series. Combined with spectral measurements and models, they allow rapid detection of smoke events, estimates of plume height and spread, and delivery of information to authorities and the public. The July 2026 episode highlights how fires, air quality and climate are tightly linked — felt locally while embedded in broader regional processes.