Optimization and field application of a filter pack system for the simultaneous sampling of atmospheric HN03, NH3 AND SO2

Optimization and field application of a filter pack system for the simultaneous collection of atmospheric gas-phase HN03, NH3 and S02 have been studied. A Teflon prefilter was used to remove particulate matter. Nylon filter, oxalic-acid-treated Whatman 41 filter and sodium-carbonate-treated Whatman 41 filter were used for the collection of HN03, NH3 and S02, respectively. For the collection of gas-phase HN03, nylon filters had better efficiency and capacity as compared to NaCl-impregnated Whatman 41 filters for long sampling periods of more than 30 h. All treated filters and nylon filters worked with the collection efficiencies of greater than 95%. About 2% of the gas-phase ammonia has been retained by the nylon filters during simultaneous collection experiments done in the laboratory but the retained ammonia on the nylon filter sometimes reached to about 25% of the gaseous total ammonia collected on the oxalic-acid-impregnated filter in the field experiments. Other than ammonia no significant retention or volatilization from the filter pack system was observed during the simultaneous experiments carried out in an urban atmosphere.