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.