Miniature parallel-plate denuder for the collection of inorganic trace gases and their removal from aerosol-laden air

A miniature parallel-plate denuder (MPPD), composed of a set of 27 equally spaced microscopy cover slips, was developed for the collection of inorganic trace gases and their removal from aerosol-laden air. The novel denuder features a length of only 8 mm and a rather small outer diameter of 37 mm. The MPPD can be coated, loaded in a filter stack, and be extracted much like a coated filter. At a flow rate of 10 l/min the collection efficiency was essentially 100% for NH3, better than 98% for HCl and HNO3, and 92% for SO2. Loading capacities, specified as the amount of gas collected with an integral efficiency >95%, increased with the amount of coating on the denuder and amounted to as much as 1 mg for HNO3 with a 5% coating solution. Evidence is provided that the absorbed gases permeate deeply into the coating, making use of up to 50% of the mass of the coating. The use of the MPPD in denuder-filter systems was explored with a PM 2.5 inlet. The experiments revealed almost negligible particle losses for accumulation-mode aerosol matter, i.e. the observed losses were at the limit of detectability (2±2% per individual MPPD).