Fog chemical composition and its feedback to fog water fluxes, water vapor fluxes, and microphysical evolution of two events near ParisAtmospheric Research


D.T. Degefie, T.-S. El-Madany, M. Held, J. Hejkal, E. Hammer, J.-C. Dupont, M. Haeffelin, E. Fleischer, O. Klemm
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Laboratoire de M?t?orologie Dynamique, Institut Pierre-Sim c Laboratory of Atmospheric Chemistry, Paul Scherrer Institu a r t i c l e i n f o

Article history:

Received 22 December 2014

Received in revised form 30 March 2015

Accepted 1 May 2015

Available online 7 May 2015


Radiation fog

Stratus lowering fog certain sizes fog droplets such that it affected the chemical composition of the fog water. For instance, both the the chemical composit are hardly studied as apor on atmospheric

Atmospheric Research 164?165 (2015) 328?338

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Atmospheric j ourna l homepage: www.e lparticles. The size and chemical characteristics of atmospheric aerosol particles determines their hygroscopicity and thus their efficiency to act as condensation nuclei (Pruppacher and Klett, 1978). The growth ? Corresponding author at: University of Munster, 48149 M?nster, Germany. Tel.: +49 251 83 31969; fax: +49 251 83 38338.

E-mail addresses: (D.T. Degefie),Fog is an atmospheric phenomenon that involves various physical and chemical processes. Although the general understanding of fog interactions betweenmicrophysical process and tion of condensation nuclei and the gas phase tha of yet.

Fog forms through condensation of water vNO3? concentration and load decreased fast as compared to NH4+ and SO42? during the deposition period. This suggested that the chemical composition was dependent on fog droplets size. ? 2015 Elsevier B.V. All rights reserved. 1. Introduction formation, and dissipation seems well developed, there are (T.-S. El-Madany), m.he (J. Hejkal), ehammer@hotm (J.-C. Dupont), (M. Haeffelin), elis (E. Fleischer), (O. Klemm). 1 Now at: Grolimund + Partner ? environmental engin 0169-8095/? 2015 Elsevier B.V. All rights reserved.Increases of ion loads and ion concentrations occurred in response to slight downward water vapor flux.

This study also indicates that the turbulent transport of fog droplets contributed to the preferential deposition ofTurbulent fluxes

Chemical compositionon Laplace, Palaiseau, France te, 5232 Villigen PSI, Switzerland a b s t r a c t

The chemical composition of collected fog water and its temporal evolution was studied during the PARISFOG campaign in winter 2012/2013 at the SIRTA (Site Instrumental de Recherche par T?l?d?tection Atmosph?ric) atmospheric observatory outside Paris, France. A further development of the caltech active fog collector was applied, in which the collected fog water gets into contact with Teflon and polyether ether ketone (PEEK) material exclusively. The collector was operational whenever the visibility was below 1000 m. In addition, the turbulent and gravitational fluxes of fog water andwater vapor flux were used to examine in detail the temporal evolution the chemical composition of two fogs. The techniquewas applied to two fog events, one representing a radiation fog and the other one representing a stratus lowering fog.

The result revealed that the dominant inorganic species in the fog water were NH4+, NO3?, Ca2+ and SO42?, which accounted for more than 85% of the ion balance. The pH ranged from 3.7 to 6.2.

In the evolution the two fog events, the interaction among the turbulent fog water flux, gravitational fog water flux and water vapor flux controlled the major ion loads (amount of ions, dissolved in fog droplets per volume of air) and ion concentrations (amount dissolved per volume of liquid water) of the fog water. In the radiation fog event, an increase of ion loads and ion concentrations occurred when the direction of water vapor flux towards to the place where the condensation process occurred. A decrease of ion loads and ion concentrations mainly happened by gravitational fog water flux with a minor contribution from turbulent fog water flux.

However, when the turbulent water vapor flux was oriented downward, it turned the turbulent fog water flux upward and offset the removal of ions in the fog. In the stratus lowering fog event, the turbulent fog water flux and the gravitational water flux together mainly contributed to the fog water deposition and removal of ions.a Climatology Working Group, Institute of Landscape Ecology, bUniversity of M?nster, GermanyE. Fleischer a, O. Klemm aFog chemical composition and its feedback vapor fluxes, and microphysical evolution

D.T. Degefie a,?, T.-S. El-Madany a, M. Held a, J. Hejkal a, (M. Held), (E. Hammer), eering, Bern, Switzerland.o fog water fluxes, water two events near Paris

Hammer c,1, J.-C. Dupont b, M. Haeffelin b,

Research sev ie r .com/ locate /atmosof nuclei by condensation starts at relativities below 100%. For a fast growth of droplets up to sizes of a few ?m and more, they need to be activated. The relative humidity needs to exceed 100% by a few tenths of percent, and the K?hler theory describes the activation process of nuclei and the resulting growth of droplets to eventually form fog. 329D.T. Degefie et al. / Atmospheric Research 164?165 (2015) 328?338When droplets grow in size various aqueous phase reactions as well as gas-phase?aqueous-phase interactions takes place that further affect the chemical composition of fog water. Scavenging of gases and impaction of not-activated aerosol particles during the fog event are more processes that have an influence on the chemistry of fog water. Turbulent process within the foggy air mass control the transport of energy and water vapor to the droplets and thus the size of the droplets and the concentrations of pollutants dissolved in the fog water. The deposition of fog droplets to the surface plays a role as well. When fog droplets evaporate completely, the remaining population of aerosol particles is very different from the aerosol population on which the fog formation took place.