Rapid Measurements Of Aerosol
Ionic Composition And 3-10 nm Particle Size Distributions On
The NASA P3 To Better Quantify Processes Affecting Aerosols Advected
From East Asia
Rodney
Weber
Georgia Institute of Technology
Yin-Nan Lee
Brookhaven National Lab
This work involves measurements in support of the TRACE-P
objectives of characterizing the aerosol physical and chemical
properties of Asian plumes. The
original proposal was divided into two sub-proposals, parts A
and B.
Part A deals with rapid measurements of aerosol bulk ionic
composition. In
this work, we will deploy an automated instrument that continually
collects particles into a liquid and quantitatively measures,
in real time, the soluble ionic mass concentration via a dual
channel ion chromatograph. The
instrument is capable of measuring the anions; chloride, nitrate,
methanesulfonate (MS), and sulfate, and cations, sodium, ammonium,
potassium, magnesium, and calcium with a sensitivity of ~30 ng m^‑3
(~5 pptv) over a sample integration interval and duty cycle
of roughly 4 minutes. (Methanesulfonate
may require longer anion sampling times (~8 minutes) due to its
low concentrations in remote marine regions). Faster
sampling rates can be achieved (~3 minutes) in polluted regions
where ambient concentrations are higher. The
measurement strategy can be tailored to the scientific objectives
of a specific flight. For
example, more ions measured at a slower rate or fewer ions measured
at a fast rate (possibly down to 3 minutes). In
addition, a pre-impactor can be switched on or off-line for analysis
of coarse (by difference) or fine aerosol composition, or to
duplicate measurement strategies of other aerosol properties
(i.e., scattering coefficients for coarse and fine particles). Moreover,
the analysis is done in real time making data available in-flight. The
quantitative accuracy of the instrument has been verified by
extensive intercomparisons with traditional filter sampling techniques. An
aircraft version is being flight-tested the summer of 2000 to
optimize it for airborne measurements. The
experimental objective of this proposal is to provide aerosol
chemical data on time scales approaching measurements of meteorological
and aerosol physical properties.
Part B involves measurements of 3-10 nm particle spectra
and total ultrafine particle concentrations for studies of new
particle formation and growth. Our
objective here is to identify the locations under which nucleation
occurs and to determine the growth rates of the newly formed
particles. The focus will be to use these and other measurements of gas
phase precursor species to study the microphysical mechanisms
controlling these processes. Measurements
of 3-10 nm spectra will be used to identify regions of freshly
formed particles and estimate particle growth rates. Combined
with measurements of expected gas precursor species, like sulfuric
acid (proposed by F. Eisele et al.), these observations can be
compared to predictions of physicochemical mechanisms of new
particle formation and growth to provide insights into these
processes.
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