Use of two different acidic aerosol samplers to measure acidic aerosols inHsinchu, Taiwan

Acidic aerosol concentrations measured by an annular denuder system (ADS) a nd a honeycomb denuder system (HDS) in Hsinchu, Taiwan, were compared. Aero sols were also sampled by a MOUDI (micro-orifice uniform deposit impactor) and analyzed by an ion chromatograph to determine the size distributions of different species. Using the measured aerosol size distribution, theoretic al analysis showed that positive HNO3 artifact due to volatilization of NH4 NO3 is generally negligible for both samplers. Comparing two different denu der samplers, the average concentration of HNO3 measured by the ADS was fou nd to be lower than that measured by the HDS, while the difference between the two samplers for the average concentration of other species was found t o be within +/-15%. A possible cause of the difference in HNO3 concentratio ns is due to a greater loss of HNO3 in the cyclone used by the ADS than in the impactor used by the HDS. The study also showed incomplete absorption o f the evaporated HCl and HNO3 from the particles on the Teflon filter by th e first nylon filter in the filter pack of the ADS. Collection efficiency a nd capacity of HCl and HNO3 by the nylon filters need further investigation .