Presentations and Publications
Stanier, C., Khlystov, A., Chan, W.R., Mandiro, M., and Pandis, S.N., “A Method for the In-situ Measurement of Fine Aerosol Water Content of Ambient Aerosol: the Dry-Ambient Aerosol Size Spectrometer (DAASS)”, Aerosol Science and Technology, Vol 28(S1), 2004, pp. 215-228.
Hygroscopic growth of atmospheric particles affects a number
of environmentally important aerosol properties. Due to the hysteresis
exhibited by the aerosol hygroscopic growth, the physical
state of particles and the amount of aerosol water are uncertain
within a wide range of relative humidities (RHs) found in the troposphere,
leading to uncertainties in optical and chemical properties
of the aerosol. Here we report the design and tests of an automated
system that was built to assess the amount of aerosol water
at atmospheric conditions. The system consists of two scanning
mobility particle sizers (SMPS) and an aerodynamic particle sizer
(APS) that measure the aerosol size distribution between 3 nm and
10 μm in diameter. The inlets of the instruments and their sheath
air lines are equipped with computer-controlled valves that direct
air through Nafion dryers or bypass them. The Nafion dryers dehydrate
the air streams to below 30% RH at which point ambient
particles are expected to lose most or all water. The switch between
the dried and the ambient conditions occurs every 7 min and is
synchronized with the scan times of the aerosol spectrometers. In
this way the system measures alternatively dried (below 30% RH)
and ambient aerosol size distributions. A comparison of the ambient
RH and the dried RH size distributions and the corresponding
integrated volume concentrations provides a measure of the physical
state of particles and the amount of aerosol water. The aerosol
water content can be treated as a growth factor or as an absolute
quantity and can be calculated as a time series or as a function of
RH (humidigram). When combined with aerosol composition measurements,
the DAASS can be used to compare hygroscopic growth
models and measurements.