The effect of dioctyl phthalate films on the ammonium nitrate aerosol evaporation rate

Abstract

The evaporation of submicrometer ammonium nitrate (NH 4NO 3) aerosol coated with an organic film was measured in order to determine the effect of the film on mass transfer rate and equilibration time of the semi-volatile inorganic. Ammonium nitrate (NH 4NO 3) particles 100–200 nm in diameter were coated with dioctyl phthalate (DOP) and allowed to evaporate in a constant temperature laminar flow reactor. Evaporation rates for the organic-coated particles were compared to pure ammonium nitrate evaporation at 22 and 27°C. A decrease, up to 50%, in NH 4NO 3 evaporation rate due to the presence of the DOP film was observed. The decrease in evaporation due to the DOP can be described mathematically at 22°C by a decrease in the accommodation coefficient for NH 4NO 3, α NH 4NO 3 , from 0.4 (the pure NH 4NO 3 value) to 0.25 for the DOP-coated NH 4NO 3. Similarly, at 27°C, a decrease in α NH 4NO 3 from 0.3 for the pure NH 4NO 3 to 0.25 for the DOP-coated particles was estimated. The decrease in evaporation rates can also be explained by a decrease in NH 4NO 3 effective diffusivity. The implications to NH 4NO 3 formation and evaporation in the atmosphere are discussed.