Cooking up a supercool atmosphere

With the barbecue season in full swing, chemists in the US are cooling things down with a claim that grilled meat might give off supercooled droplets, speeding up reactions with atmospheric ozone. 

Geoffrey Smith and John Hearn at the University of Georgia, took mixtures of the main organic acids given off from cooking meat, and investigated their reaction with atmospheric gases. They discovered supercooled droplets of organic acid mixtures, and changes in reaction rates compared with non-supercooled mixtures of the same composition. 'The reactivity of ozone with oleic acid was drastically faster than in the liquid-solid mixtures,' said Smith. 


Organic particles from cooking meat could affect atmospheric processes

© iStockphotos

Supercooled droplets are liquid below their freezing point. Supercooled mixtures haven't been included in atmospheric chemistry predictions before, and these lab results highlight new possibilities.  

'Because particles generated from grilling meat are created at elevated temperatures, it is possible that they exist in the atmosphere as supercooled droplets,' said Smith. 'The faster reactivity of the supercooled particles could have a big impact on the overall reactivity of organic particles in the atmosphere,' he added. 

Organic particles can initiate cloud-condensation and reflect sunlight, as well as reacting with atmospheric gases. Tom Baer, from the University of North Carolina at Chapel Hill, US, said Smith and Hearn's work is significant because 'it points out that we must consider the possibility of supercooling of substances in the atmosphere'.  

Before sending warnings likely to ruin environmentally conscious meat-lovers' appetites, Smith remains cautious about the reality of supercooled meat vapours. Baer agrees: 'Supercooling is usually associated with pure substances in the absence of nuclei that can cause condensation. Because aerosol particles in the atmosphere are probably quite "dirty", they may not be disposed to supercool as do laboratory made particles.' 

Katharine Sanderson 


J D Hearn and G D Smith, Phys. Chem. Chem. Phys., 2005, 7, 2549 (DOI: 10.1039/b506424d)