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Isotopomeric characterization of N 2 O produced, consumed, and emitted by automobiles
Author(s) -
Toyoda Sakae,
Yamamoto Seiichiro,
Arai Shinji,
Nara Hideki,
Yoshida Naohiro,
Kashiwakura Kiriko,
Akiyama Kenichi
Publication year - 2008
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.3400
Subject(s) - isotopomers , chemistry , combustion , catalytic converter , catalysis , nitrous oxide , analytical chemistry (journal) , flux (metallurgy) , nitrogen oxide , nitrogen , environmental chemistry , nox , organic chemistry , molecule
Fossil fuel combustion is the second largest anthropogenic source of nitrous oxide (N 2 O) after agriculture. The estimated global N 2 O flux from combustion sources, as well as from other sources, still has a large uncertainty. Herein, we characterize automobile sources using N 2 O isotopomer ratios (nitrogen and oxygen isotope ratios and intramolecular site preference of 15 N, SP) to assess their contributions to total global sources and to deconvolute complex production/consumption processes during combustion and subsequent catalytic treatments of exhaust. Car exhaust gases were sampled under running and idling state, and N 2 O isotopomer ratios were measured by mass spectrometry. The N 2 O directly emitted from an engine of a vehicle running at constant velocity had almost constant isotopomer ratios ( δ 15 N bulk = −28.7 ± 1.2‰, δ 18 O = 28.6 ± 3.3‰, and SP = 4.2 ± 0.8‰) irrespective of the velocity. After passing through catalytic converters, the isotopomer ratios showed an increase which varied with the temperature and the aging of the catalysts. The increase suggests that both production and consumption of N 2 O occur on the catalyst and that their rates can be comparable. It was noticed that in the idling state, the N 2 O emitted from a brand new car has higher isotopomer ratios than that from used cars, which indicate that technical improvements in catalytic converters can reduce the N 2 O from mobile combustion sources. On average, the isotopomeric signatures of N 2 O finally emitted from automobiles are not sensitive to running/idling states or to aging of the catalysts. Characteristic average isotopomer ratios of N 2 O from automobile sources are estimated at −4.9 ± 8.2‰, 43.5 ± 13.9‰, and 12.2 ± 9.1‰ for δ 15 N bulk , δ 18 O, and SP, respectively. Copyright © 2008 John Wiley & Sons, Ltd.