From mcmurry@me.umn.edu Mon Jul 1 10:25:48 1996
Date: Mon, 01 Jul 1996 08:14:41 -0500
From: Peter McMurry
Reply to: Peter McMurry
To: ace1@pmel.noaa.gov
Subject: Nucleation & Growth W.G.
Summary of Working Group on Nucleation and Growth (Peter McMurry, July 1 1996)
We separated our discussions into the subtopics of "growth" and "nucleation."
In the context of our discussions "growth" designates the addition of
nonvolatile or semivolatile species to aerosols, not water uptake. Processes
that are known to contribute to such growth include condensation of low vapor
pressure species that are produced by gas phase reactions, and the addition of
nonvolatile particulate species by liquid phase reactions, such as occurs in
cloud droplets.
1. Growth
a. Ultrafine particle growth rates: Growth rates of ultrafine particles
determine the rate at which freshly nucleated particles grow into the Aitken
mode. Accurate calculations of these growth rates in atmospheric aerosol models
is essential; we will attempt to use ACE-1 data to evaluate model predictions
for growth rates. If we are successful at measuring growth rates we will
attempt to reconcile the measured values with calculated values for condensation
of measured gas phase precursors (H2SO4, DMSO2, NH3, etc.). A variety of
methods will be used to estimate ultrafine particle growth rates, including:
i. evolution of size distributions during Lagrangians (Russell).
ii. evolution of 3-10 nm size distributions in nucleating regions such as cloud
outlfows (Weber, McMurry, Russell).
iii. time for particles to grow past 3 nm and past 10 nm in cloud outflow
regions (CNC data only) (Clarke).
iv. time for particles to grow downwind of Macquarie (Weber, McMurry, Russell,
Kreidenweis).
v. search SEMS and CNC data for evidence of growth at surface sites: diurnal
trends in the ultrafine regime; time for appearance of ultrafine particles after
a perturbation such as rainfall or front, etc. (Kreidenweis, Wiedensohler).
b. Growth due to cloud processing: The effectiveness of cloud processing at
growing particles into the optical subrange has been well document for both
marine and nonmarine aerosols. We will examine ACE-1 data for evidence of this
effect. Clarke has seen evidence for such processing in his SEMS data, and
Kreidenweis and Quinn have seen evidence for several different characteristic
size distributions. The following analyses will be conducted:
i. C-130 Data: will be examined for characteristic size distributions and for
transformations from one distribution type into another (Clarke).
ii. Cape Grim data: will be examined for types of characteristic size
distributions. Also the single particle data will be analyzed to investigate
possible impact of cloud processing on individual particle compositions
(Wiedensohler, Anderson, Jefferson).
iii. Discoverer data: will be examined for types of characteristic size
distributions (Quinn).
2. Nucleation. We saw evidence of nucleation in several circumstances during
ACE-1. We will analyze the data to determine conditions that lead to
nucleation. We will also examine the data for quantitative insights into the
relationship between particle production rates and concentrations of likely
precursor gases.
a. phenomenological descriptions:
i. C-130 data: will be examined in an effort to determine conditions that lead
to nucleation (Clarke); also, the UMN PHA data will be examined for widespread
regions of very low ultrafine particle counts in an effort to determine if
particles might be formed at a steady but very low rate (Weber).
ii. Surface platform data (Discoverer, Cape Grim, Macquarie): will be examined
to study the relationship between ultrafine particle "events" and post frontal
pressure bumps (Kapustin, Kreidenweis, Wiedensohler).
iii. C130/Discoverer data: will be examined to understand the origin of
ultrafine particles observed on the Discoverer (Kapustin, Clarke).
b. relationship to gas phase species: C130 data will be examined to determine
the relationship between the production of new particles and the concentrations
of possible nucleating species (H2SO4, HN3, H20, DMSO2, ??), aerosol surface
area, meteorological variables, etc. (Weber, McMurry).
Peter McMurry
130 Mechanical Engineering, U of M
Voice: (612) 625-3345
FAX: (612) 625-6069