TRACE-P P-3b Instrumentation used by Clarke group, University of Hawaii

1) A size-resolved thermo-optic aerosol discriminator (1min avg.):

In order to characterize the aerosol size distribution from 0.12 up to 7.0 mm, often where most aerosol mass, surface area and optical effects are dominant, we have a modified commercial Laser Optical Particle Counter (OPC) system to provide 256 size channels of data.  A computer controlled thermal conditioning system is used upstream of the OPC (airstream dilution dried) which results in a system that operates as a Thermo‑Optic Aerosol Discriminator (TOAD).  The TOAD is used to characterize aerosol components volatile at temperatures associated with sulfuric acid (150C), ammonium sulfate/bisulfate (300C) and refractory aerosol at 300C (sea salt, dust and soot/flyash).  In polluted regions (INDOEX in Indian Ocean) we have operated at 380C in order to remove most organic species soot (T. Novakov-based upon INDOEX data-personal correspondence) but leave refractory (see examples below). Volatility observations can be combined with bulk aerosol chemistry to generate size-resolved information of the composition, state of mixing and refractive indices. A paper describing this system, its calibration and results of comparisons has been published (Clarke, 1991) and further description of the system will not be repeated here.

2) Condensation Nuclei - heated and unheated (available at 1Hz)

     Two butanol based condensation nuclei (CN) counter (TSI 3010) have been modified for aircraft use and count all particles between 0.01‑3.0 um.  In this fashion we obtain total CN, refractory CN (those remaining at 300C after sulfate is removed) and volatile CN (by difference) as a continuous readout.  The ratio of refractory to total CN can be used as a fundamental indicator for air mass variability since it is not directly dependent on aerosol concentration (Clarke, 1993).  We have observed that polluted and continental aerosol often have ratios near about 0.8 whereas more pristine regions tend to be far more volatile with low ratios often approaching zero (Clarke et al., 1996).  Variability in the refractory component also appears to reflect sources of continental combustion (soot) or dust aerosol whereas in "clean" marine regions this fraction is generally lower (Clarke et al., 1996).

3)  Aerodynamic Particle Sizer – (APS-TSI3320) – (<5min/scan)

To further characterize larger “dry” particles, including dust, we will operate an APS which classifies particles from 0.8 to 20 mm into 50 channels.  In addition to detecting particles larger than the OPC and with improved coarse particle counting statistics (due to a higher sample flow rate and detection scheme), it sizes particles aerodynamically, thus avoiding the calibration uncertainties associated with Mie scattering. 

4) Differential Mobility Analyzer (DMA) with thermal conditioning – (<5min/scan)

We have successfully flown a modified differential mobility analyzer (DMA) with thermal analysis (see discussion for OPC above) that provide size information (mass, surface area, number distributions) over the 0.01 to 0.3mm size range (Clarke et al., 1998) for sampling times of about 1-3 minutes.  This size range reveals much of the dynamic evolution of the aerosol in response to coagulation, growth and cloud processing.  In clean regions aloft this size range can also account for significant aerosol surface area. Analysis of DMA data can also be used to assess those aerosol most likely to be activated as cloud condensation nuclei.

5)  Nephelometer  (10^-7 m^-1 detection,  continuous and averaged over 10sec. interval)

We plan to use a 3 wavelength nephelometer (TSI  3560) with a 1mm impactor in the inlet stream switched to provide both total and submicrometer scattering values (and thereby coarse dust scattering by difference).  These separate measurements of total and submicrometer scattering are critical for assessments of variable aerosol plume structures and during descent profiles (see examples below).  This is particularly important for characterizing the mixed fine and coarse Asian aerosol types (pollution and dust) we have encountered over the North Pacific and expect to be common during TRACE-P.

6)  Absorption Photometer (PSAP-Radiance Research; detection <0.1mg m^-3 for 5 min. avg ) – A continuous light absorption photometer will be used to quantify the light absorption coefficient of the aerosol related generally to fine particle pollution soot concentrations but also associated with coarse particle dust.  The PSAP will also be switched using the same impactor as the Nephelometer so that the absorption in fine (pollution) and coarse (dust) size classes are determined and linked to corresponding scattering properties. 

7)  Forward Scattering Spectrometer Probe – [FSSP; continuous]   This wing mounted instrument provides information on aerosol sizes from about 0.5 to 40um under ambient conditions.  This provides surface areas under ambient conditions for larger sizes that are less readily sampled through aircraft inlets.  It also sizes cloud droplets and will provide a mesurement of cloud liquid water and surface areas of significance to heterogeneous and aqueous phase reactions in clouds.  Combined with our other aerosol measurements, the FSSP can help establish relationships between cloud droplet number and the aerosol upon which they form, of significance to the aerosol indirect-effect and precipitation assessments etc.

Clarke, A. D.  "A Thermo-optic technique for in-situ analysis of size-resolved aerosol physicochemistry",  Atmos. Env., 25A, 3/4, 635-644, 1991

Clarke, A. D.,  "A Global Survey of Atmospheric Nuclei in the remote Mid-Troposphere: Their Nature, Concentration and Evolution, Jour. Geophys. Res. Atmospheres, 98, D11, 20,633-20,647, 1993a.

Clarke, A.D., T. Uehara and J.N. Porter, Lagrangian evolution of an Aerosol Column during ASTEX, Jour. Geophys. Res., 101, p4351-4362, 1996

Clarke, A.D.,  J. L. Varner, F. Eisele, R. Tanner, L. Mauldin and M. Litchy, Particle production in the remote marine atmsophere: Cloud outflow and subsidence during ACE-1, Jour. Geophys, Res., 103, 16,397-16,409, 1998.