1 research outputs found
Application of Time-of-Flight Aerosol Mass Spectrometry for the Online Measurement of Gaseous Molecular Iodine
Here we present a new application of a time-of-flight
aerosol mass
spectrometer (TOF-AMS) for the measurement of atmospheric trace gases
in real-time. Usually, TOF-AMS instruments are not sensitive to gas-phase
species due to the aerodynamic particle focusing inlet system which
reduces the gas phase species by a factor of about 10<sup>7</sup> relative
to the particle phase. This efficient removal of the gas phase and
the resulting high relative enrichment of particles is one reason
for the very high sensitivity of TOF-AMS instruments for particle
phase compounds (detection limits in the sub-μg/m<sup>3</sup>-range for online measurements with 1 min integration time), which
allows application of the instruments even under clean atmospheric
conditions. Here we use artificially generated particles as sampling
probes to transfer selected atmospheric trace gases into the particle
phase before entering the AMS (gaseous compound trapping in artificially
generated particles-AMS, GTRAP-AMS). The sampling probe particles
are mixed with the gaseous analytes upstream of the TOF-AMS in a 0.5
L flow tube. As an exemplary application of the method, the measurement
of trace levels of gaseous molecular iodine is demonstrated. α-Cyclodextrin
(α-CD/NH<sub>4</sub>Br) particles are used as selective sampling
probes to transfer molecular iodine into the AMS. A detection limit
in the subparts-per-billion (sub-ppb) range was achieved. The method
was compared to a recently developed off-line method that combines
denuder sampling of gaseous I<sub>2</sub> and gas chromatography/mass
spectrometry (GC/MS) analysis. To demonstrate the usability of the
method, temporally resolved I<sub>2</sub> emission profiles from a
brown algae species (<i>Laminaria saccharina</i>) under
exposure of ambient ozone levels were investigated. Total I<sub>2</sub> release rates of 36.5 pmol min<sup>–1</sup> grams fresh weight
(gFW)<sup>−1</sup> at 100 pbb O<sub>3</sub> and 33.4 pmol min<sup>–1</sup> gFW<sup>–1</sup> at 50 ppb O<sub>3</sub> were
obtained within the first hour of ozone exposure