[[[THIS IS A REPETITION OF EMAIL FROM MARCIA BAKER ORIGINALLY POSTED ON SEPTEMBER 30, 1998. THE MIME FORMAT PORTION OF THE ORIGINAL MESSAGE HAS BEEN DECODED HERE. ]]] From: Marcia Baker Date: Wed, 30 Sep 1998 14:29:29 -0700 (PDT) Subject: homework for ice initiative Dear Gabor Andy Heymsfield and I don't always find it easy to find each other, so I am sending you my wish list of parameters to measure in both the external environment and the cloud before I have Andy's feedback. This list was compiled by discussions with Dr. Steve Wood (a new postdoc working with me who comes from a PhD dissertation on ice nucleation on Mars!) and Dr. Dave Covert (an aerosol expert) here. Both would like to have their names added to our mailing list; they are quite knowledgeable and would add alot. Their e-mail addresses are below. In addition, the two graduate students you met are also quite interested in this subject and would like to have their names added. I hope this is OK; I would very much like to have them along if it is. e-mails: Neil Bacon neilb@geophys.washington.edu Lane Seeley lseeley@u.washington.edu Dave Covert dcovert@u.washington.edu Steve Wood sewood@atmos.washington.edu You will see that the list we put together is long. It was our unanimous conclusion that unless we try to generalize our characterization of the system we will be in danger of missing something very important. Since all these parameters are now being measured in flight by various groups, nothing is in principle impossible and everything here can be supported by a literature reference. If I hear from Andy and we can combine our efforts more than has been possible so far, we will certainly do so. I didn't want to hand in my first homework late. Marcia ____________________________________________ Dear Andy Here is my tentative list of the environmental and cloud parameters that should be measured if we want to learn what are the major ice nucleation pathways. I envision three sets of measurements: I. Measurements of environmental parameters II. Measurements made on those particles that are found within ice in clouds and which form ice in a diffusion chamber outside of cloud III. Measurements of cloud parameters I. Characterization of the out of cloud environment 1. Molecular composition of (a) gas phase Since the gas phase plays important roles in determining the chemical composition and surface properties of the particles, we should know its composition. We would focus on gases likely to condense at ice cloud temperatures. (b) particulates (sorted by size) Single particle chemical composition can be measured down to 0.2 microns or so by mass spectrometry. Electron microscopy can give elemental composition down to about 50 nm. We of course want to establish the compositions of smaller particles and this instrumentation is not yet available. However, what is available is much more detailed and accurate than the old volatility measurements, from which composition was only inferred. We need both organic and inorganic components. 2. Size distributions of the particles, down to large ions and 3. Phase (liquid or solid) of particles. There are several options, in principle, that could be developed here. 4. Electric charge on particles. Total charge is easy to measure: surface charge is not. The net charge distribution can be measured concurrently with the number-size distribution to give charge as a function of size. 5. Surface morphology/crystallinity. Electron microscopy is useful here again down to about 50 nm. 6. Thermodynamic and dynamic parameters, of course---T, p, RH, w. II. Measurements made on particles on which ice forms (which may or may not be nuclei) and those on which it does not. This set of measurements assumes the relevant agents are aerosol particles/small solution droplets. The two classes of particles can be separated either by sending them through a diffusion chamber (which introduces its own problems) or a Counterflow Virtual Impactor, if in cloud. On these we would like to measure and compare 1. Molecular chemical composition 2. Size 3. Charge 4. Surface morphology/crystallinity III. In-cloud parameters 1. Droplet size spectra 2. Humidity, temperature, pressure, updraft velocity 3. Charges on droplets as function of size. Data for water droplets in clouds have already been collected by a number of groups.