| Περίληψη: | The hygroscopic behavior of atmospheric aerosols influences their size, composition,
lifetime, chemical reactivity, and light scattering. Hygroscopic growth plays an
important role in a number of air pollution problems including visibility impairment,
climate change, acid deposition, longrange transport and the ability of particles to
penetrate the human respiratory system. The absorption of water by aerosol particles
often exhibits a hysteresis. Thus, the physical state (liquid or solid) of particles and the
amount of aerosol water at a specific relative humidity (RH) are uncertain, as they
depend on the history of these particles.
In this work, the reduced version of the Dry Ambient Aerosol Size Spectrometer
(DAASS) that measures the water content of atmospheric aerosols has been
redesigned and optimized. The DAASS measures the number distribution of the
aerosols at ambient conditions and at low RH thus drying the particles. A comparison
of these distributions allows the determination of the physical state of the particles and
their water content.
The new version of the DAASS is capable of operating at higher RH values than its
predecessor. The instrument has been characterized regarding particle wall losses, in a
set of smog chamber experiments using (NH4)2SO4 particles. An algorithm checking
the consistency of the measurements and the applicability of the assumptions used in
the data analysis was developed. The water concentrations observations were
compared to the predictions of the aerosol thermodynamics model EAIM.
Ambient measurements, using the original and the improved version of DAASS, were
conducted during two different time periods in a suburban area in Patras. These tests
allowed the testing and assessment of the operation of the DAASS and also the
examination of the hygroscopic behavior of particulate matter. The original version
was used during a moderate RH period, in which the water content of the aerosol
represented 0-50% of the fine aerosol mass. The improved DAASS operated during
high RH conditions. The particles retained water throughout the duration of the
measurements. The measured volume growth factors were quite higher than the
measured ones during the moderate RH period. The water concentrations observations
were compared to the predictions of the aerosol thermodynamics model EAIM.
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