Simultaneous Measurement of Nitric Oxide (NO) and Nitrogen Dioxide (NO₂) in Simulated Automobile Exhaust Using Medium Pressure Ionization—Mass Spectrometry

Abstract

In previous papers we have demonstrated two different, two-color resonance-enhanced multiphoton ionization (REMPI) schemes for the simultaneous measurement of trace amounts (ppbV to pptV) of nitrogen monoxide (NO) and nitrogen dioxide (NO(2)). The goal of this study is to provide a laser ionization-mass spectrometric scheme capable of measuring ppmV to ppthV concentrations of NO and NO(2) within vehicle exhaust containing up to ppthV of aromatic hydrocarbons and a time frame of seconds. Two ionization schemes are used here to measure NO and NO(2) in simulated automobile exhaust with three different sources. REMPI Scheme 1 uses broad-bandwidth light and an effusive source to measure NO (limit of detection (LOD) 300 ppmV), NO(2) (LOD 100 ppmV), and aromatic hydrocarbons (via photoionization) along with fragments (via electron impact). REMPI Scheme 2 uses narrow-bandwidth light and a medium pressure laser ionization (MPLI) source to measure NO (LOD 60 ppmV), NO(2) (LOD 3 ppmV), and fragments (via electron impact). The LOD is determined using 10-second sampling times. A newly developed delayed-ion extraction technique for MPLI is then applied to REMPI Scheme 2, dramatically reducing the electron impact signal, so that only NO and NO(2) are observed. We conclude that Scheme 2 with delayed-electron extraction is best suited for measuring in situ NO and NO(2) within engine exhaust.

Electrospray ionization/atmospheric pressure photoionization multimode source for low‐flow liquid chromatography/mass spectrometric analysis

“…Use of a repeller electrode has been previously demonstrated to enhance ion collection at reduced pressures with the photoionization technique of medium pressure laser ionization, either increasing ion intensity26 or ion selectivity;27 however, at atmospheric pressure, the resulting effects are influenced by solvent or solvent‐cluster interactions. As seen in Fig.…”

Passive monitoring of nitrogen dioxide in urban air: A case study of Durban metropolis, South Africa

“…All the oxides of nitrogen are collectively referred to as NOx. Some NO is oxidised to NO 2 before reaching the tailpipe of the exhaust and small volumes of NO (Short et al, 2006) are also released with exhaust gas and oxidised later (Lindqvist et al, 1982) to NO 2 . NOx, generally, and nitrogen dioxide in particular, are considered to be dangerous to materials, animals and humans.…”

Proof of concept for an optogalvanic gas sensor for NO based on Rydberg excitations

“…As a result no further means to distinguish between e.g. NO and NO 2 have to be taken [26,27]. We shine the lasers in a co-propagating manner into the cell through a transparent glass frame made from quartz glass in order to allow transmission of the ω 1 laser light at 225 nm.…”