Instrument development and characterization of atmospheric aerosol physical properties through airborne measurement

To increase the speed of submicron aerosol size distribution measurements, a mixing condensation nucleus counter (MCNC) has been developed. By carefully designing the mixing chamber and condenser, the response time of the MCNC was significantly reduced. Our experiments demonstrate that a differential mobility analyzer (DMA) coupled with the developed MCNC can measure complete aerosol size distributions in as little as 2 seconds.; The effects of bends and elbows on the diffusional losses of particle in nanometer range were studied. The results show that the effect of bends and elbows on particle diffusion loss is significant, and for Reynolds number smaller than 250, the enhancement of diffusion losses due to bends and elbows is sensitive to both the relative orientations of the bends and elbows and the lengths of straight tubing between them. When the Reynolds number exceeds 250, the enhancement is insensitive to the actual flow configurations. Experimental results are presented, which can be used for design of aerosol flow systems at Reynolds number larger than 250.; To minimize the airborne sampling bias, an advanced differential mobility analyzer (DMA) system for measuring submicron aerosol size distribution at ambient relative humidity, with special attention to implementation on aircraft, has been developed. The system includes an active RH controller, a cylindrical differential mobility analyzer (CDMA), and a condensation nucleus counter. A cascade controller maintains the RH inside the CDMA at ambient RH by actively adding or removing water vapor from the air stream. The flows are controlled with feedback PID controllers, which compensate for the variation of pressure as the aircraft changes altitude.; During the ACE-Asia experiment, the above DMA system, together with an aerodynamic particle sizer (APS), was used to characterize aerosol size distributions in East Asia on board of CIRPAS Twin Otter aircraft. Besides providing the aerosol size characteristics, the data were combined with chemical composition measurements to predict the vertical profile of aerosol extinction, which was compared with those derived from simultaneous sunphotometer measurements. Agreement between the predicted and derived aerosol extinction varies for different scenarios, but the discrepancies were generally within the calculated uncertainties.