Simulation of Multicomponent New Particle Formation in a Heavily Polluted Urban Atmosphere by Experiments in the CLOUD Chamber

New particle formation (NPF) is a significant source of atmospheric aerosols and of cloud condensation nuclei, affecting climate and air quality. A wide variety of species are known to participate in NPF, including sulfuric acid, ammonia, amines, and organics. NPF has also been observed in heavily polluted urban environments, however, the underlying processes are far from being quantitatively understood. Specifically, NPF is also observed when the high condensation sink of the preexisting aerosol is thought to preclude significant new particle formation. Here we report on measurements of NPF in mixtures of a number of precursors representing polluted boundary layer conditions in the CLOUD chamber at CERN. The dependence of both formation and growth rates on the concentrations of sulfuric acid, ammonia, amines, oxidation products of aromatic volatile organic compounds such as toluene, trimethylbenzene and naphthalene, NOx, as well as temperature and condensation sink will be presented, and a comparison to ambient measurements will be made. Mass spectrometric data will be used to provide a quantitative understanding of the involved processes.