Hygroscopic growth

GA Ferron, G Oberdorster, R Henneberg. Estimation of the deposition of aerosolized drugs in the human respiratory tract due to hygroscopic growth. J Aerosol Med 2 271-283, 1989. 

The effect of water on aerosol light scattering is sometimes expressed as the hygroscopic growth factor,... 

United States that had been impacted by anthropogenic emissions had a hygroscopic growth factor of 1.7 0.1, compared to 2.7 0.4 for particles in marine... 

Mclnnes, L., M. Bergin, J. Ogren, and S. Schwartz, Apportionment of Light Scattering and Hygroscopic Growth to Aerosol Composition, Geophys. Res. Lett., 25, 513-516 (1998). 

Wet deposition processes depend mostly on microphysical properties of the aerosol, cloud formation, conversion of cloud droplets into rain drops, sedimentation, and evaporation of rain (Kanakidou et al., 2005). Recently, Gysel et al. (2004) discussed the deliquescence properties of water-soluble organic matter and how they affect the hygroscopic growth of atmospheric OAs. Depending on the chemical... 

The interaction between molecules in the gas phase and the surface of particles and droplets in the atmosphere is central to important phenomena such as ozone depletion in polar areas, hygroscopic growth of particles, aging, acid rain, particle growth and cloud droplet formation. 

Ming Y. and Russell L. M. (2001) Predicted hygroscopic growth of sea salt aerosol. J. Geophys. Res. 106,... 

Hygroscopic growth factor Increase of any aerosol property or phase change with increasing RH Light scattering, mobility diameter, etc. -h... 

Berg OH, Swietlicki E, Krejci R (1998) Hygroscopic growth of aerosol particles in the marine boundary layer over the Pacific and Southern Oceans during the First Aerosol Characterization Experiment (ACE 1). J Geophys Res 103 16535-16545... 

Crowley TJ (2000) Causes of climate change over the past 1000 years. Science 289 270-277 Cruz CN, Pandis SN (2000) Dehquescence and hygroscopic growth of mixed inorganic-organic atmospheric aerosol. Environ Sci Technol 34 4313-4319... 

The second reason for the difference between the deposition of stable aerosols and many therapeutic aerosols is hygroscopic growth and evaporation. For drugs to be effective, they must show an appreciable aqueous solubility. Solid drug particles may pick up water vapor and dissolve, and droplets of drug solutions can exchange water with the environment to equalize vapor pressure. The relative humidity profile in the respiratory tract depends on the ambient conditions and the breathing pattern [67]. 

Ferron GA, Kreyling WG, Haider B. Inhalation of salt aerosol particles—II. Growth and deposition due to hygroscopic growth. J Aerosol Sci 1988 19 611-631. 

Chan HK, Eberl S, Daviskas E, Constable C, Young I. Changes in lung deposition of aerosols due to hygroscopic growth a fast SPECT study. J Aerosol Med 2002 15(3) 307—311. 

Chemical Properties of Aerosols. Surface chemical properties of aerosol particles can also be tailored to improve deaggregation [273]. Hygroscopic particles absorb water when inhaled into the humid airways [282-284], increasing particle size and density in the process, as well as creating the potential for capillary bridge formation between particles. Hygroscopic growth can be reduced by the use of hydrophobic additives [285] or compounds with low aqueous solubility [286,287]. 

Figure 1. Predicted hygroscopic growth factor of NaCl / (NH4)2S04 aerosol at 75% RH as a function of particle size in metres.

If, on the other hand, a droplet of a watery solution which exerts a SVP less than that of pure water is exposed to air saturated with water vapour, it will grow in size. Such growth is described as hygroscopic growth . Hygroscopic growth is a complex topic but may be usefully approached in a series of stages. 

Evaporation is accompanied by local cooling and condensation by local warming. The addition of mas s to droplets and the conduction of latent heat away from the surface of the droplet or particle are, as has been pointed out by Pritchard (1987), the determining processes of particle growth. Under conditions of turbulent airflow, conduction of heat away from the surface of droplets or particles is enhanced and hygroscopic growth rates exceed those found under still conditions or under conditions of laminar airflow. The implications of this will be considered later. 

The effect of hygroscopic growth of particles was considered by the Task Force and is considered in detail below. 

HYGROSCOPIC GROWTH OF AND NEUTRALIZATION OF ACIDIC DROPLETS IN THE AIRWAYS... 

This figure shows the mass deposition fraction plotted against the initial geometric particle size. Martonen et al (1985) argued that a critical particle size could be defined Dc. For hygroscopic particles initially smaller than this size, hygroscopic growth would be expected to reduce... 

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