How Organic Acids Form Atmospheric Particles
Understanding how atmospheric aerosol particles form and affect cloud formation could improve climate models.
Organic acids are an important component of atmospheric aerosols and are found in abundance in a variety of urban, rural, and marine environments. A recent study combined experimental and theoretical techniques to shed light on their role in the initial stages of aerosol particle formation.
Newly formed atmospheric aerosol particles can influence the formation and properties of clouds, potentially having a major impact on global climate. New insights into mechanisms controlling this process can be harnessed to develop more accurate climate models.
Organic acids, particularly dicarboxylic acids, play a key role in the formation of atmospheric aerosol particles. These particles, in turn, can promote formation of cloud droplets, thereby having a major impact on climate. However, the precise mechanisms by which organic acids promote aerosol particle formation, especially during early stages, have remained unclear. To address this question, researchers from the Department of Energy’s Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility, and Pacific Northwest National Laboratory studied the properties of dicarboxylic acid homodimer complexes. These complexes are thought to play an important role in atmospheric aerosol particle formation. The researchers integrated experimental photoelectron spectroscopy measurements and high-performance computational capabilities of EMSL’s NWChem computational chemistry code and Cascade high-performance computer, as well as the Computer Network Information Center, Chinese Academy of Sciences. Experimental data showed that the dimer complexes, which are two identical molecules linked together, are extremely stable. Theoretical calculations revealed that strong hydrogen bonds are extremely important in enhancing the stability of these complexes and that thermodynamically, they are likely to form under low evaporation rates. Taken together, the findings suggest that dicarboxylic acid homodimer complexes play an important role in promoting the formation and growth of atmospheric aerosol particles.
This work was supported by the U.S. Department of Energy’s (DOE) Office of Science, Office of Biological and Environmental Research, including support of EMSL, a DOE Office of Science user facility; the EMSL Intramural Aerosol Science Theme Funding; and DOE’s Office of Basic Energy Sciences.
Hou, G.-L., M. Valiev, and X.-B. Wang. 2016. “Deprotonated Dicarboxylic Acid Homodimers: Hydrogen Bonds and Atmospheric Implications,” Journal of Physical Chemistry A 120(15), 2342-49. DOI:10.1021/acs.jpca.6b01166.