Reactive Uptake of Trimethylamine into Ammonium Nitrate Particles

Abstract

The reaction of trimethylamine (TMA) vapor with a polydisperse distribution of ammonium nitrate particles (20−500 nm dia.) was studied in a flow tube reactor with particle analysis by laser desorption (1064 nm) 70 eV electron ionization (EI) in an ion trap time-of-flight (IT-TOF) aerosol mass spectrometer. When the TMA vapor concentration was very high, essentially complete exchange of TMA for ammonia in the particles was achieved. When the TMA vapor concentration was lower (∼500 ppb for a reaction time of 23 s), partial exchange was observed, and the initial reactive uptake coefficient was estimated to be on the order of 2 × 10⁻³ at 20% RH. This value suggests that measurable exchange is possible in the atmosphere when particles are exposed to an amine concentration on the order of 1 ppb for a few hours. The effects of particle size, water content, and amine molecular structure on uptake remain to be elucidated.