Below-cloud ammonia scavenging in convective thunderstorms at a coastal research site in Tampa, FL, USA

Sequential sampling of ammonium in wet deposition was conducted at a coastal research site in Tampa, Florida to determine and model the intra-storm variability of ammonium deposition to the Tampa Bay Estuary. Ammonium concentrations decreased with increasing precipitation depth according to an inverse power-law relationship of the form, CNH4=aD-b, where D is the cumulative rainfall and a and b are fitted parameters. These results show that during a precipitation event, the majority of ammonium is delivered to Tampa Bay during the initial stages of the storm. An aqueous-phase accumulation model was used to predict sequential ammonium concentrations at the Gandy Bridge site with reasonable agreement. A relationship between precipitation intensity and scavenging coefficient will facilitate the calculation of dry and wet deposition of ammonia to the Tampa Bay Estuary. The scavenging coefficients calculated with the Tampa Bay model compared well with those predicted with the Asman model.