| Abstract: | A continuous flow streamwise thermal gradient cloud condensation nuclei (CCN) counter with an aerosol focusing and a laser-charge-coupled
device (CCD) camera detector system was developed here. The counting performance of the laser-CCD camera detector system was
evaluated by comparing its measured number concentrations with those measured with a condensation particle counter (CPC) using
polystyrene latex (PSL) and NaCl particles of varying sizes. The CCD camera parameters (e.g. brightness, gain, gamma, and
exposure time) were optimized to detect moving particles in the sensing volume and to provide the best image to count them.
The CCN counter worked well in the particle number concentration range of 0.6–8000 #·cm−3 and the minimum detectable size was found to be 0.5 μm. The supersaturation in the CCN counter with varying temperature difference
was determined by using size-selected sodium chloride particles based on K?hler equation. The developed CCN counter was applied
to investigate CCN activity of atmospheric ultrafine particles at 0.5% supersaturation. Data showed that CCN activity increased
with increasing particle size and that the higher CCN activation for ultrafine particles occurred in the afternoon, suggesting
the significant existence of hygroscopic or soluble species in photochemically-produced ultrafine particles. |
