Bases produce cloud droplets at concentrations of one part per trillion

Sulphuric acid and dimethylamine work together efficiently in atmospheric conditions to form particles. The results of CERN’s CLOUD Project indicate that both natural amine emissions, as well as those caused by man have an impact on particle formation and, in this way, perhaps influence the formation of cloud droplets and impact the climate. Finnish researchers have had a significant role in this research both in carrying out tests and formulating theory. The Finnish group is headed by Academy Professor Markku Kulmala. The study’s newest results were published in Nature.

Measurements of unprecedented precision, regarding the compounds related to formation of particles in the lower atmosphere, were carried out as part of the CLOUD (Cosmics Leaving OUtdoors Droplets) Project at CERN, the European Organization for Nuclear Research. The study found that dimethylamine significantly promoted the formation of sulphuric acid particles, when its concentration was just one part per trillion (PPT).

The study also found that the impact of cosmic rays on formation of sulphuric acid‑dimethylamine particles was nearly non-existent. For this reason, changes in solar activity do not have a significant effect on the number of cloud droplets formed in this way.

Amines are base compounds closely related to ammonia. They are either released into the atmosphere as a result of human activities (e.g. cattle farming and burning biomass) or occur naturally (oceans and soil). Amine emissions may increase in the future, as amines will likely be used for capturing carbon dioxide emissions from fossil-fuelled power plants.

The results of Cern’s CLOUD Project indicate that both natural and man-made amine emissions have an impact on the formation of particles and, in this way, perhaps influence the formation of cloud droplets and impact the climate. The project’s objective is to find answers to today’s burning questions in atmospheric sciences: how are new particulates formed in the atmosphere and how do these aerosol particles impact the climate?

CLOUD is the first project in which physicists from CERN and atmosphere researchers have worked together. A total of 17 institutes from nine countries are participating. Finnish participants include the University of Helsinki, the University of Eastern Finland and the Finnish Meteorological Institute.

Finnish researchers carry out both practical testing and theoretic study

Researchers from the University of Helsinki are responsible for the CLOUD Project’s instruments that measure the smallest, never-before-detected, particulates. A computing model has also been developed at the University of Helsinki that depicts particle formation of sulphuric acid and bases on the molecular level.

The CLOUD Project is the first study that has successfully been able to both measure and reliably model the particle formation process starting from the molecular level. The results show that models based on quantum mechanics can be effectively support trial measurements for particle formation. Models can, for example, provide information on the molecular structure of the smallest particulates, and they can be used to estimate the impact of changes in conditions (e.g. temperature) on the speed of particle formation when no measurements are available.

Long-term observations on the formation of particles in the atmosphere have been collected by the University of Helsinki at its field station in Hyytiälä in forest conditions, as well as by the Finnish Meteorological Institute at a very clean area at Pallas. The series of observations are important when striving to understand how current formation of particles differs from corresponding past (preindustrial) formation and the impact man-made atmospheric impurities have had.

Source: Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere, Advance Online Publication (AOP), Nature 6.10.2013,, doi 10.1038/nature12663,

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