UPTAKE OF AMMONIA BY NYLON FILTERS IN FILTER PACK SYSTEMS

Retention of ammonia on nylon filters as a function of the loading wit h gaseous HNO3/HCl mixtures is shown. A strong correlation has been ob served in field measurements by annular denuder-filter pack technique; 0.5-2 mumol of NH4+ have been found in nylon filter extracts in the p resence of 2-4 mumol of total nitrate and chloride. This fact indicate s that ambient levels of NH3 may be underestimated in filter packs if the acid-absorbing nylon filter (which precedes the acid-impregnated f ilter for NH3 collection) is not also analysed for ammonium ion.