Atmospheric nanoparticles formed from heterogeneous reactions of organics

Atmospheric aerosols directly and indirectly affect the radiative balance of the Earths atmosphere. Nanoparticles are a key component of atmospheric aerosols, growing rapidly under ambient conditions. Organic species are thought to lead to the growth of nanoparticles smaller than 20 nm (refs5, 6), but the identity of these species and the underlying chemical mechanisms remain elusive. Here we exposed nanoparticles to a range of organic vapours2,4-hexadienal, glyoxal and trimethylamineand monitored particle size to determine the contribution of organic vapours to nanoparticle growth. We show that organic species enhance the growth of nanoparticles, producing non-volatile oligomers, polymers and alkylaminium sulphates in the particle phase. Nanoparticle growth increased with relative humidity in the presence of glyoxal and trimethylamine, but decreased at higher relative humidities in the presence of -2,4-hexadienal, dependent on the reaction mechanism of the organic species involved. Oligomerization and polymerization were largely suppressed in particles smaller than 4 nm and nanoparticle growth increased with particle size. Our findings help to explain the presence of previously measured, but unidentified non-volatile compounds in atmospheric nanoparticles and to improve model simulations of new particle formation.