Quantification of Ammonium in Aerosols by Near-Infrared Photothermal Spectroscopy

Abstract

The potential of near-infrared photothermal spectroscopy for the analysis of aerosols collected on filter membranes is demonstrated. Laboratory-generated aerosols consisting of ammonium sulfate and soot are collected on Teflon® filters by the use of a dichotomous sampler. The N-H overtone/combination band at 2110 nm is used to determine ammonium in these mixtures. The presence of soot is shown to have a deleterious effect on the detectability of ammonium. The extent of this limitation is examined with the employment of well-characterized samples. An empirical expression, based on Beer's law, is developed which relates the photothermal signal to the relative soot and ammonium sulfate loadings.