A recent study led by Drs. Julia and Alexander Laskin from the Pacific Northwest National Laboratory and Prof. Sergey Nizkorodov from the University of California, Irvine revealed atmospheric chemistry processes that turn white organic aerosol into brown carbon particles. Processes that change the color of organic aerosols are significant because they can convert light-scattering, climate-cooling aerosols into light-absorbing, climate-warming aerosols. The browning is attributed to reactions between various carbonyl species in organic aerosols and ammonia, a common atmospheric pollutant. To characterize the reaction products, the scientists applied DESI-MS analysis to fresh and aged samples of smog-generated aerosols. Detailed analysis of the resulting high resolution mass spectra allowed the team to identify key browning reactions. The study appeared in Analytical Chemistry in February 2010.