Scientists have uncovered why a particularly dangerous chemical released in wildfire smoke can persist in the atmosphere for far longer than expected.
The study, led by researchers at the University of Bristol in collaboration with the Central Laser Facility at the Science and Technology Facilities Council (STFC), focused on 2,4-Dinitrophenol (DNP) – a toxic compound produced during the burning of organic material.
DNP is part of ‘brown carbon’ – the brownish smoke created by wildfires. Brown carbon absorbs sunlight and traps heat in the atmosphere, while also carrying a cocktail of pollutants harmful to human health.
The Bristol team point out that, as an estimated 1.5 million people die each year due to exposure to wildfire smoke, understanding why toxic compounds like DNP remain active in the atmosphere is key to protecting both people and the climate.
Normally, pollutants in the atmosphere are gradually broken down by sunlight or by reaction with natural oxidants but the researchers found that when DNP dissolves in airborne water droplets, such as those found in mist and clouds, it becomes unusually stable.
This is because the compound has chemical ‘relaxation mechanisms’ that allow it to return to its stable state before sunlight can destroy it. In practice, this means DNP resists photodegradation – surviving longer in the air than many other pollutants.
Dr Igor Sazanovich, Senior Scientist at the STFC Central Laser Facility, said: ‘Our advanced laser techniques allowed us to observe exactly how DNP behaves at the molecular level when it encounters atmospheric water droplets.
‘What we discovered was surprising, the droplets actually shield these toxic compounds from breaking down. This finding could change how we model the persistence of wildfire pollutants in our climate systems.’
DNP is toxic to plants, animals and humans, and its persistence adds to concerns about the long-term effects of brown carbon pollution. Beyond health risks, its ability to absorb sunlight and release heat into the lower atmosphere means it directly contributes to global warming.
And the problem extends beyond wildfires, given that DNP is also produced by: vehicle emissions from fossil fuels, residential heating and controlled agricultural burning.
The research comes at a time when wildfires are increasing in frequency and intensity worldwide. Four of the five worst years on record for wildfires have occurred since 2020, including in regions previously unaccustomed to such events, like the UK and Sweden.
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