Simultaneous Determination of Gaseous Ammonia and Particulate Ammonium in Ambient Air Using a Cylindrical Wet Effluent Diffusion Denuder and a Continuous Aerosol Sampler

A sensitive and fast method for simultaneous determination of gaseous ammonia (NH 3 ) and particulate ammonium (NH 4 + ) in ambient air is presented. NH 3 is sampled in a cylindrical wet effluent diffusion denuder (CWEDD) and analyzed online by a continuous flow system with a fluorescence detector (FLD), while NH 4 + bound to aerosol particles is sampled in parallel by a condensation growth unit—the aerosol counterflow two-jet unit (CGU-ACTJU) sampler—and analyzed online with another FLD. The sensitive fluorescence detection of ammonium in concentrates of the CWEDD and the ACTJU is based on its reaction with ortho -phthaldialdehyde and sulfite to form isoindol-1-sulfonate. The calibration curve of ammonium is linear in the concentration range of 5 × 10 –9 to 2 × 10 –6 M. The limit of detection (LOD = 3 s/n) values of NH 3 and NH 4 + are 3.52 ng m –3 (5.05 ppt) and 1.04 ng m –3, respectively. The developed method enables online measuring of distribution of NH 3 /NH 4 + in ambient air with a time resolution of 1 s. The optimized method was used for the determination of NH 3 /NH 4 + in urban air in Brno in two campaigns during the winter and summer of 2018. The results obtained by the developed method were compared with a reference method based on the sampling on filters and “dry” diffusion denuders coated by phosphoric acid.