Other types of IN can include bacteria, leaf fragments, and even in certain cases soot and pollen. However, the IN activity of these particles can be suppressed or inhibited by coatings of soluble species, such as sulfate coatings on dust or soot. Then, these can actually serve as giant cloud condensation nuclei (CCN). 

CCN on the other hand are smaller, semi- or fully soluble species such as particles from pollution plumes (organic, sulfate, nitrate), fires, and sea salt. Sea salt actually serves as a giant CCN, which can have different climatic effects compared to normally, smaller CCN.

The ice forming nuclei are water insoluble particle (e.g Ag, PbI2, CuS) against to the CN and their structure has hexagonal symmetry similarly to the ice crystals.

I can offer you Prupacher and Klett (2010): Microphysics of cloud and precipitation. Springer, Dortrecht/Heidelberg/London/New York which details the results about concentration, sources and chemical composition of IN.

Sorry to mix I

Yes Ice Nuclei (IN) are the insoluble particles or the insoluble part of atmospheric particles but the mentioned compounds Ag, PbI2 CuS, do not exist at all in the atmosphere. In the atmosphere it are mostly dust particles.

Perhaps you thought of cloud seeding: this is the process of stimulating precipitation. In this case indeed lead iodide is used from aircraft

You might google for dr Roelof Bruintjes who is a world leading expert in cloud seeding

Nir

We know that dr Demott is world expert in ICN, but give us the citation and also: which fraction is active: the insoluble particles?

Scientific American of June 2014 has an article on seeding

pg 56-63

The equation is a parameterization to be used in climate models and it is an empirical relation coming from many study flights by the scientists mentioned as authors, not only Demott. In the conclusions it mentions that the eq applies for their data but in other regions this cdan be different depending on composition of the particles

Other types of IN can include bacteria, leaf fragments, and even in certain cases soot and pollen. However, the IN activity of these particles can be suppressed or inhibited by coatings of soluble species, such as sulfate coatings on dust or soot. Then, these can actually serve as giant cloud condensation nuclei (CCN). 

CCN on the other hand are smaller, semi- or fully soluble species such as particles from pollution plumes (organic, sulfate, nitrate), fires, and sea salt. Sea salt actually serves as a giant CCN, which can have different climatic effects compared to normally, smaller CCN.

You can read my recent book "Physics and Dynamics of Clouds and Precipitation" (Pao K.  Wang, 2013, published by Cambridge University Press), Chapter 6 and 7, where different modes of nucleation (condensation nuclei, cloud condensation nuclei, deposition nuclei, immersion freezing nuclei, contact nuclei, etc.) and the physic of nucleation are explained.