New neutral molecular cluster formation observed in real time under atmospheric conditions

    It has been known for several years that sulfuric acid (SA) contributes to the formation of tiny aerosol particles, which play an important role in the formation of clouds. And a new study recently published stated that dimethylamine (DMA) can enhance new particle formation. The formation of neutral (i.e. uncharged) nucleating clusters of sulfuric acid and dimethylamine was observed for the first time.

    Scientists reported on experiments form the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions.

the CLOUD experiment in October, 2013.

Credit: Maximilien Brice/Copyright: CERN

    The capability of sulfuric acid molecules together with water and ammonia to form clusters and particles has been recognized for several years. However, clusters that form in this manner can vaporize under the conditions that exist in the atmosphere and an evaporation rate for particles can be concluded. For this experiment scientists stated that new particle formation in SA-DMA system has evaporation rates that are effectively zero. Therefore, the system of sulfuric acid and dimethylamine forms particles much more efficiently because even the smallest clusters are essentially stable against evaporation. The science daily referred the DMA as 'superglue' for clusters to against evaporation.

Molecular weight and composition of neutral clusters during a new

particle formation event with SA and DMA. (A) Mass defect plot measured

with the CI-APi-TOF mass spectrometer for an experiment with 10 pptv DMA

and 3 x10e7 cm−3 SA. The mass defect is the difference between the exact

mass and the nominal (integer) mass of the cluster. The symbol size is proportional

to the logarithm of the signal intensity (count rate). Background

ions and clusters (not containing SA or DMA) are indicated by gray symbols.

(B) The same data with the signals grouped to show the number of SA and

DMA molecules in the cluster.

Kürten et al. 2014

    The PNAS publication concludes that their new observation demonstrate that a cluster containing as few as two sulfuric acid and one or two dimethylamine

molecules is already stable against evaporation. Moreover, their result bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth.

As for the science daily article, I think it did a fairly good job in describing the new observation and explaining it to readers. The writer also added some basic knowledge of particle formation and how particle formation can impact climate. So this article is relatively plain for readers without relative backgrounds. However, I think this article leaves out many details from original paper and slightly overstated the role DMA plays in nucleation by using terms such like 'superglue',and 'tremendously'. Personally, I'll rate this article 6/10 because it do attracted reader’s attention and figured a new breakthrough in atmospheric chemistry, but explained it in an exaggerating and vague way.

Reference:

ScienceDaily:http://www.sciencedaily.com/releases/2014/10/141008083636.htm

PNAS:http://www.pnas.org/content/early/2014/10/02/1404853111

Supporting Information:http://www.pnas.org/content/suppl/2014/10/02/1404853111.DCSupplemental/pnas.201404853SI.pdf#nameddest=SF3