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 (NH3) and particulate ammonium (NH4+) in ambient air is presented. NH3 is sampled in a cylindrical wet effluent diffusion denuder (CWEDD) and analyzed online by a continuous flow system with a fluorescence detector (FLD), while NH4+ 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 NH3 and NH4+ 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 NH3/NH4+ in ambient air with a time resolution of 1 s. The optimized method was used for the determination of NH3/NH4+ 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.