Roger J. CHENG ASRC UALBANY SUNY

大气中的微观世界系列

纽约州立大学，大气科学研究中心郑均华研究员主持的科研项目

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

海洋中的微观世界---'The MICRO-WORLD in the MARINE ATMOSPHERE"

由纽约州立大学奥尔巴尼分校大气科学研究中心的大气学者郑均华先生开展的显微镜测量:

	海上的云凝结核（CCN）通过飞沫喷射和爆破对海洋表面whitecap产生的气泡喷射一代已经有据可查。在不同条件下將其固体这些液滴转化（蒸发和结晶）所涉及的过程，但是，以前沒有引起研究者的关注。一个调查和实验室的特点，物理和化学过程在受控环境中相变海水飞沫，实地观察设置，道出了以下惊人的和非常显著的现象：
	• 1，弹射从结晶微液滴大小气溶胶。 • 2，形成的海盐颗粒空心球体。 • 3，外壳结构的氯化物（MgCl/2和KCl）在表面喷出的气溶胶和海盐粒子。

The FORMATION of HOLLOW SEA-SALT PARTICLES

from the EVAPORATION of DROPS of SEAWATER

Roger J. Cheng, Duncan C. Blanchard and Ramon J. Ciprianoa

Atmospheric Sciences Research Center
State University of New York at Albany
Received 12 December 1986; accepted 31 July 1987.

Abstract

Some non-volatile materials dissolved in water drops will, upon evaporation of the water, produce a hollow shell of the material. Though known for years in the chemical engineering literature, this fact was not appreciated by those working with the marine sea-salt aerosol. Our laboratory experiments show that a majority of seawater drops in free fall in air with a relative humidity less than about 60% evaporate, become salt-saturated, and change phase to produce hollow sea-salt particles. Some hollow salt particles have been found in marine air, though further investigation is required to show the extent of this phenomenon. Expressions have been derived from which both the size of the original drop of seawater and its salt supersaturation at the time of phase change can be calculated from the inner and outer radii of the salt shell. If hollow particles are common in the marine aerosol, then instruments that measure particle size cannot be used to obtain particle mass.

Résumé

Certaines substances non volatiles dissoutes dans les gouttes d'eau produisent, à l'évaporation de l'eau, des coquilles creuses. Ce processus est bien connu en génie chimique, et pourtant il n'en est pas tenu compte dans les travaux sur les aérosols salins océaniques. Nos expériences de laboratoire montrent que lorsque des gouttes du de mer tombent en chute libre dans de l'air à moins de 60% d'humidité relative, la plupart d'entre elles arrivent à saturation et changent de phase pour produire des particules salines creuses. On a d'ailleurs trouvé des particules creuses de sel dans de l'air marin, mais d'autres recherches sont nécessaires pour connaître l'étendue du phénomène. On présente des relations qui donnent la dimension de la goutte originale d'eau de mer, ainsi que la sursaturation au changement de phase, à partir des rayons intérieurs et extérieurs de la coquille de sel. S'il est prouvé que les particules creuses sont courantes dans l'aérosol marin, on ne pourra pas utiliser les appareils qui mesurent les dimensions des particules pour évaluer la masse de l'aérosol.

Atmospheric Research

Volume 22, Issue 1, Pages 15-25
June 1988,

SHELL STRUCTURED MARINE AEROSOL:
- A LABORATORY OBSERVATION

Roger J. CHENG ASRC UALBANY SUNY
Atmospheric Sciences Research Center
State University of New York

Laboratory investigation revealed that a shell structure of chlorides (MgCl/2 and KCl) is always present on the surface of marine aerosol. Close examination by a polarizing microscope of an individual seawater droplet has resulted in the following observations: Evaporation of water increased the salt concentration. At first, a thin layer of brine formed at the surface of the evaporating droplet; this was followed by clearly sequential precipitations of numerous microcystals of sulfates (CaSO/4, MgSO/4), and by a crust of many relatively larger cubic NaCI crystals correspondent with their individual solubility and concentrations.

During this process solution of chlorides (MgCl/2, KCl) mixed with microcrystals of sulfates or NaCl were situated beneath the surface of the droplet. Finally, a seasalt particle with chloride film on the surface was formed. The shell structure of chlorides film present on the surface of the marine aerosol confirmed via optical and scanning electron microscopy is of extreme importance to understanding the fundamental nucleation processes in the atmosphere.

A chloride film presents a highly hygroscopic surface and was found to initiate the condensation of water in an environment with RH as low as 40%. Sodium chloride (NaCI) crystals, on the other hand play only a minor role in initiating condensation (RH 75%) for cloud droplets formation in the atmosphere.

To be presented at the Annual Meeting of the American Association
for Aerosol Research (AAAR),
Oak Brook, ILL. October 11-15, 1993

A NEW MECHANISM for the GENERATION of

HIGH SULFATE ENRICHED AEROSOLS in the MARINE ATMOSPHERE

(CaSO/4, MgSO/4---NOT DMS)

Roger J. CHENG: ASRC SUNY UALBANY

****大气中的微观世界系列****

纽约州立大学，大气科学研究中心郑均华研究员主持的科研项目

Presented at: 9th WORLD CLEAN AIR CONGRESS

AUGUST 30- SEPTEMBER 4, 1992

MONTREAL, QUEBEC, CANADA

The MICRO-WORLD in the ATMOSPHERE

MARINE AEROSOL PROJECT:

REFERENCES

Roger J. CHENG -ASRC UALBANY

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.
4. "A New Mechanism for the Generation of High Sulfate Enriched Aerosols
in the Marine Atmosphere"
9th World Clean Air Congress, Montreal, Quebec, Canada. 1992.
5. "Shell Structured Marine Aerosol: A Laboratory Observation"
Annual Meeting of American Association for Aerosol Research,
Oak Brook, Illinois. October 11-15, 1993.
6. "On the Phenomenon of Nuclei Enhancement During the Evaporative Stage of a Cloud"
ATMOSPHERIC RESEARCH, Vol. 47, No. 48, 1998. ( DeFelice and Cheng )
CITATIONS:
A. AN INTRODUCTION TO METEOROLOGICAL INSTRUMENTATION
AND MEASUREMENT
By Dr.Thomas P. DeFelice, Prentice Hall, 1998.
B. "A Wind Tunnel Study on the Drop-to-Particle Conversion"
JOURNAL of AEROSOL SCIENCES, Vol.23, No.3, 1992.
(Confirmation by Dr. Pruppacher's term at Institute of Atmospheric Physics, Germany)
C. MICROPHYSICS OF CLOUDS AND PRECIPITATION ;
By Dr. Pruppacher and Dr. Klett, Second Revised and Enlarged Edition.
Kluwer Academic Publishers, 1997
.
D. " Microscopic Investigation of Marine Aerosol "
ALBANY-Fall 1996-University at Albany Magazine.


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