• SULFATE AEROSOL GENERATION
  • in the MARINE ATMOSPHERE

  • Roger J. CHENG
  • Atmospheric Sciences Research Center
  • State University of New York at Albany

The generation of maritime cloud condensation nuclei (CCN) through the ejection of jet and film droplets from bursting whitecap-produced bubbles on the ocean surface has been well documented. The processes involved in the transformation (evaporation and crystallization) of these liquid droplets into their solid form under varying conditions, however, has not previously attracted much attention from atmospheric researchers.

A set of laboratory investigations and field observations of the characteristics, both physical and chemical, of seawater droplets during phase change in a controlled environment have revealed the following startling and very significant phenomena:

(1) The ejection of sulfate aerosols (CaSO4,MgSO4) with size range of 0.1mm to 10 mm. The concentration and chemical composition of the ejected aerosols, identified by the techniques of scanning electron microscopy and energy dispersive x-ray spectroscopy, were dependent on the rate of droplet evaporation. Sea-salt aerosols could be classified into three categories: (A) NaCI crystals, (B) Crystals of sulfates (CaSO4,MgSO4) and (C) Chloride droplets (MgCI2, KCI).

(2) The formation of hollow spherical sea-salt particles (>5 mm). A secondary ejection of aerosols was detected during melting by the busting of air bubbles, which were formed when the hollow particle was moved into a high-moisture environment or dissolved into a water droplet.

(3) A thin film of chlorides (MgCl2, KCI) observed on the surface of sea salt particles present a highly hygroscopic surface to initiate the condensation of water vapor in an environment with RH As low as 40%. Sodium Chloride (NaCI-75%RH) plays only a minor role for the formation of cloud droplets in the marine atmosphere.

Characterization of the ejected sulfate aerosols in comparison with field observation, chemical processes inside the evaporating seawater droplets and the mechanisms for the generation of secondary aerosols in the marine atmosphere are presented with illustrations.

 

 
 
           

 

AIR BUBBLES FORMATION:
DURING MELTING of A HOLLOW SEA SALT PARTICLE.
  • ROGER J CHENG-ASRC-SUNYA
  • MICRO-SIZE of MARINE AEROSOL ( CCN with SULFATE )
  • WILL BE GERERATED by BUSTING of AIR BUBBLES.
  • This ACTION INDICATED
    The TRANSFORMATION of SULFATE from OCEAN to the ATMOSPHERE.
    ****************************************************************************************************************************************************
  • 1. "The Formation of Hollow Sea-Salt Particles from the Evaporation of Drops of Seawater"
  • ATMOSPHERIC RESEARCH, Vol. 22, No. 1. June 1988 (Cheng, Blanchard & Cipriano)
  • .
  • 2. "The Generation of Secondary Marine Aerosols: The Crystallization of Seawater Droplets"
  • A. LECTURE NOTES IN PHYSICS, 309, Atmospheric Aerosols and Nucleation, Ed: P.E Wagner and G. Vail, Springer-Verlag. 1988.
  • B. International Conference on Atmospheric Aerosols and Nucleation, Vienna, Austria. August 22-27, 1988
  • 3. "Sulfate Aerosols Generation in the Marine Atmosphere: The Evaporation of SeawaterDroplets"
  • International Conference on Global and Regional Environmental Atmospheric Chemistry, Beijing, China. May 1989.
PRESENTED by : ROGER J. CHENG, ASRC-UALBANY

 

 

  • On the Phenomenon of Nuclei Enhancement
  • during the Evaporative Stage of a Cloud
Atmospheric Research
Volumes 47-48, June 1998, Pages 15-40

T. P. DeFelice(a) and R. J. Cheng(b)

  • a.-- Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA
  • b.-- Atmospheric Sciences Research Center, State University of New York, Albany, NY 12205, USA

Abstract

The number of nuclei observed just after a cloud evaporates is classically equal to the sum of the number of interstitial nuclei plus the droplet number density. There are occasional reports of more nuclei produced in the vicinity of evaporating cloud droplets than the classical amount. The purpose of our paper is to provide an overview of the phenomenon of nonclassical nuclei production, with the ultimate purpose of laying the foundation for future efforts designed to formalize the mechanism that explains this phenomenon. The available literature is discussed in conjunction with field and laboratory measurements and suggests that a nonclassical generation of particles depends on the (i) relative humidity of the air surrounding the droplets, RH, and (ii) the physical and chemical characteristics of the evaporating clouds. Implicit within the available literature is the importance of the temporal and spatial resolution of sampling during the final stage of a cloud cycle and shortly thereafter. A possible explanatory mechanism is presented and is naturally preliminary.

Author Keywords: Nuclei enhancement; Cloud; Relative humidity

Article Outline

1. Introduction
2. Results and discussion
2.1. The dependence of the nonclassical generation of nuclei on the RH of the air surrounding the evaporating droplets
2.2. Dependence of nonclassical generation of nuclei on the chemical characteristics of the evaporating droplets
2.2.1. Laboratory 2.2.2. Field
2.3. Nonclassical generation of particles from the fragmentation of the emergent nuclei during a phase transition
2.4. Our explanation of what occurs during cloud droplet phase changes
 
 
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