Design and performance of an automatic regenerating adsorption aerosol dryer for continuous operation at monitoring sites

摘要

Sizes of aerosol particles depend on the relative humidity of their carriergas. Most monitoring networks require therefore that the aerosol is dried toa relative humidity below 50% r.H. to ensure comparability ofmeasurements at different sites. Commercially available aerosol dryers areoften not suitable for this purpose at remote monitoring sites. Adsorptiondryers need to be regenerated frequently and maintenance-free single columnNafion dryers are not designed for high aerosol flow rates. We thereforedeveloped an automatic regenerating adsorption aerosol dryer with a designflow rate of 1 m3/h. Particle transmission efficiency of this dryer hasbeen determined during a 3 week experiment. The lower 50% cut-off wasfound to be smaller than 3 nm at the design flow rate of the instrument.Measured transmission efficiencies are in good agreement with theoreticalcalculations. One dryer has been successfully deployed in the Amazon riverbasin. We present data from this monitoring site for the first 6 months ofmeasurements (February 2008–August 2008). Apart from one unscheduledservice, this dryer did not require any maintenance during this time period.The average relative humidity of the dried aerosol was 27.1+/−7.5% r.H. compared to an average ambient relative humidity of nearly 80% andtemperatures around 30°C. This initial deployment demonstrated thatthese dryers are well suitable for continuous operation at remote monitoringsites under adverse ambient conditions.