Excimer laser fragmentation-fluorescence spectroscopy as a method for monitoring ammonium nitrate and ammonium sulfate particles

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is shown to b e an effective detection strategy for ammonium nitrate and ammonium sulfate particles at atmospheric pressure and room temperature. Following photofra gmentation of the ammonium salt particle, fluorescence of the NH fragment i s observed at 336 nm. The fluorescence signal is shown to depend linearly o n particle surface area for laser intensities varying from 1.2 x 10(8) to 6 x 10(8) W/cm(2). The 100 shot (1 s) detection limits for ammonium nitrate range from 20 ppb for 0.2 mum particles to 125 ppb for 0.8 pm particles, wh ere these concentrations are expressed as moles of ammonium ion per mole of air. For ammonium sulfate, the 100 shot (1 s) detection limits vary from 6 0 ppb for 0.2 mum particles to 500 ppb for 1 mum particles. These detection limits are low enough to measure ammonium salt particles that form in the exhaust of combustion processes utilizing ammonia injection as a nitric oxi de control strategy. (C) 2001 Elsevier Science Ltd. All rights reserved.