SHIPBORNE AEROSOL AND CHEMISTRY INSTRUMENTS
a. University of Maryland (R. Dickerson)
Size-segregated aerosol impactors: UMD and NOAA/AOML will jointly measure size-
segregated aerosol composition with six-stage cascade impactors (Sierra Series 230).
These measurements are essential to Objectives 1 and 2, and useful to Objective 3.
Calibration: Known sources of errors include mass flow, collection efficiency, and ionic
concentration. The discussion by the University of Miami group describes uncertainties,
calibration, and procedures for flow, atomic absorption spectroscopy and ion
chromatography. The source of uncertainty most difficult to quantify is sampling and
collection efficiency (Winkler, 1974; Lawson, 1980; Wang and John, 1987; Savoir, 1984).
To address this problem we will compare total aerosol mass with results from bulk
samplers of known high collection efficiency (Savoie and Prospero, 1977). Further we
will run parallel samples with a Multiple Orifice Uniform Deposit Impactor (MOUDI)
instrument and test the response of impactors to known size-number distributions of
aerosol particles generated in our laboratory.
Performance: These instruments have been well characterized and used extensively on both
islands and ships (Knuth, 1984; Pszenny, 1992; Carsey et al., 1996).
Ozone and Water Vapor Sondes: UMD will facilitate acquisition and will launch
ozone/frostpoint hygrometer sondes. The cryogenic dewpointers yield highly sensitive
measurements of upper tropospheric water vapor and will provide comparison for specially
calibrated commercial (Viasala) sondes. They are classified as category 2 "hard to do
without" for Objective 1, and 2, and essential for Objective 3.
Calibration: The sondes will be in the laboratory in a specially temperature and pressure
controlled chamber calibrated prior to launch (Kley et al., 1996; Oltmans et al., 1996).
Performance: These sondes have proved highly successful on ships (Kley et al., 1996;
Oltmans et al., 1996).
NO, NO2 , NOy: NO will be measured with O3 chemiluminescence using a specially-
NO detector that employs photon counting, a superior PMT, and the reaction chamber
design of Ridley and Grahek (1990) that provides a detection limit of approximately 2 ppt
for hourly data. NO2 will be measured by photolytic conversion using an instrument based
on the design of Kley and McFarland (1980) as refined by Ridley et al. (1988). Our
system, uses a 300 W Xe lamp and a 40 x 300 mm Pyrex photolysis cell. The residence
time, about 5 s, was selected to balance conversion efficiency and losses of NO to reaction
with ambient O3. The instrument is air-cooled, and will be operated in the air conditioned
lab on the ship thus interference from PAN or HO2NO2 is not expected. The system
automatically cycles through background, NO, NOx every few minutes; calibration gas and
zero air are introduced every 8 hr. NOy will be measured with the converter described
Calibration: NO and NOy will be calibrated as described above. NO2 will be calibrated
with permeation tubes and gas phase titration. We check for artifact formation with high-
quality zero air and charcoal traps.
Performance: This NO detector and NO2 / NOy converters performed successfully in
Bermuda and on the R/V Malcolm Baldrige (Carsey, et al., 1997; Dickerson et al., 1995;
Rhoads et al., 1997).
Surface CO: Carbon monoxide is a conserved tracer on time scales of sulfate production
and loss from the atmosphere, and as such is essential for identifying the origin of air
masses. Allen et al. (1996) demonstrated the usefulness of CO measurements in evaluating
the dynamics of CTM's. As a tracer, CO plays a strong supporting role in Objectives 1 and
2, and as a sink for OH, CO is central to Objective 3. We will employ modified
commercial NDIR/GFC instruments, that have been thoroughly tested under field
conditions, and have proved to provide highly accurate and reliable data (Dickerson and
Delany, 1988; Doddridge et al., 1993; Dickerson et al., 1995). The technique compared
very favorably to grab sample GC analysis and to tunable diode laser spectroscopy,
(Poulida et al., 1991; Doddridge et al., 1994; Novelli et al., 1997).
Calibration: We will employ transfer standards of CO in compressed air for field
calibration, and compare these to NIST standards before and after the field experiment.
Instruments will be calibrated every two weeks.
Performance: The instruments have been used for up to five years on remote island sites
and have proved highly reliable (e.g. Doddridge et al., 1994; Dickerson et al., 1995).
Rhoads et al. (1997) showed that they are also well suited to ship use.
Surface O3: Ozone is central to understanding radiative effects of the gaseous
atmosphere, and plays a central role in the photochemistry of the troposphere and
stratosphere. It therefore is of primary importance to Objectives 2 and 3, and a strong
supporting role in Objective 1. We will employ UV absorption to detect ozone on the ship
and island site of Male.
Calibration: The instruments will be compared to the NIST standard instrument before and
after INDOEX, and tested for zero drift and line losses during the experiment.
Performance: The ozone technique has been used on island sites for up to 20 years without
significant problems (Oltmans and Levy, 1994; Dickerson et al., 1995) and on ships with
equal success (Carsey et al., 1997; Rhoads et al., 1997).
UV Radiation: Ultraviolet radiation drives photochemical reactions that form and destroy
ozone and transform sulfur precursors into sulfate. Modeling the processes of Objectives 1,
2, and 3 need such information. We will use radiometers (Meteorologie Consult GMBH)
or actinometers to determine the radiative flux and photolysis rate coefficients.
Calibration: Chemical actinometry for NO2 photolysis rate coefficient measurement
depends primarily on the NO2 conversion efficiency and volume flow. We will calibrate
conversion efficiency with the same techniques as for direct measurements of NOy. The
flow will be measured with mass flow controllers calibrated with bubble flow meters.
Radiometers will be calibrated against direct measurements and at the factory before and
after the field experiment.
Performance: Actinometers have proved highly reliable for field, ship, and aircraft use
(Kelley et al., 1995; Rhoads et al., 1997); the radiometers are new.
b. NCAR Mobil CLASS Sounding System: The CLASS sondes will be needed to
estimate the height of the MBL as a function of distance from the ITCZ and the coast line,
and to obtain the vertical variation of temperature and humidity. Better thermodynamic
measurements from the sondes in conjunction with the cloud condensation nuclei
measurements are crucially important for conducting cloud numberical modeling studies.