Chasing new particle formation: from the CLOUD project to the Everest base camp.
Globally, a significant source of cloud condensation nuclei for cloud formation is thought to originate from new particle formation (aerosol nucleation). Despite extensive research, many questions remain about the dominant nucleation mechanisms. Specifically, a quantitative understanding of the dependence of the nucleation rate on the concentration of the nucleating substances such as gaseous sulfuric acid, ammonia, water vapor and others has not been reached. This is of relevance for climate as the atmospheric concentrations of sulfuric acid, ammonia and other nucleating agents are strongly influenced by anthropogenic emissions.
By providing extremely well controlled and essentially contaminant free conditions in the CLOUD chamber, we were able to show that indeed sulfuric acid is an important component for such new particle formation, however, for the typical temperatures encountered in the planetary boundary layer the concentrations of sulfuric acid are not high enough to explain the atmospheric observations . Moreover, the effect of ammonia , amines  and oxidized organic molecules  on the nucleation rate of sulfuric acid has been investigated in CLOUD so far. Recent developments in instrument technology such as the Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometer have allowed us to investigate the chemical composition of charged  as well as neutral  clusters during such nucleation experiments. We directly compared the relevance of these results with dedicated field campaign at high altitude, first at the Jungfraujoch station (5280 m a.s.l. – Switzerland) and than at the Nepal Climate Observatory at the Pyramid (NCOP) station, which is located close to the Everest base camp at 5079 m a.s.l.. These field campaigns underline the good agreement between the CLOUD experiment and the nucleation observe in the real atmosphere.
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The CLOUD (Cosmics Leaving OUtdoor Droplets) collaboration consists of 20 institutions from Europe and the United States and is funded by national funding institutions as well as the EU training network CLOUD-TRAIN (http://www.cloud-train.eu/).