N.: A method for the in situ measurement of fine aerosol water content of ambient aerosols: The dry-ambient aerosol size spectrometer (DAASS), Aerosol Sci

Hygroscopic growth of atmospheric particles affects a number of environmentally important aerosol properties. Due to the hys-teresis exhibited by the aerosol hygroscopic growth, the physical state of particles and the amount of aerosol water are uncertain within awide range of relative humidities (RHs) found in the tropo-sphere, leading to uncertainties in optical and chemical properties of the aerosol. Here we report the design and tests of an auto-mated 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 de-hydrate the air streams to below 30 % RH at which point ambien