Improvement of the New NO Detection Method Using Laser-Induced Two-Photon Ionization with a TOF Mass Spectrometer
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- 作者：Shan-Hu Lee ; Yoshizumi Kajii ; and Hajime Akimoto
- 刊名：Environmental Science & Technology
- 出版年：2000
- 出版时间：October 15, 2000
- 年：2000
- 卷：34
- 期：20
- 页码：4434 - 4438
- 全文大小：87K
- 年卷期：v.34,no.20(October 15, 2000)
- ISSN：1520-5851
文摘
We have developed a new method to detect lowconcentrations of tropospheric NO, using laser induced two-photon ionization (Lee, S.-H.; Hirokawa, J.; Yoshizumi, Y.;Akimoto, H. Rev. Sci. Instrum. 1997, 68, 2891). This methoduses a frequency-doubled pulsed-dye laser operatingnear 226 nm to photoionize NO by resonance enhanced two-photon ionization via its A2X2 (0,0) band. This workreports our recent results regarding the improvement ofthe overall instrumental performance obtained by applyinga time-of-flight (TOF) mass spectrometer and furtherdiscusses the water vapor influence in this method. NOion signals were discriminated efficiently from the other ionsgenerated by impurities in the ionization cell by using aTOF mass spectrometer. The obtained sensitivity of thismethod was 10 pptv (S/N = 2), at a laser power of 44 
J andan integration time of 1 min. Also, the background signalwas decreased from 5 to 0.25 Hz as compared to the previousstudy, indicating that a nearly signal-limited conditionwas obtained, which enables NO detection free frombackground noise. In our laser ionization instrument, theuncertainty in NO ion intensity caused by the fluctuation oflaser power was deviated less than 3% from a long-termaverage. Moreover, by comparison with the ozone-chemiluminescence method, water vapor influence hasbeen investigated by introducing humid sampling gases intothe molecular beam. As the relative humidity in thesampling gases varied from 0 to 85% at room temperature,no significant change in the NO detection efficiency wasobserved. This demonstrates an important advantage overthe ozone-chemiluminescence method, although furtherfield intercomparisons are required to certify the applicabilityof this new NO ionization method into the atmosphericstudy.
J andan integration time of 1 min. Also, the background signalwas decreased from 5 to 0.25 Hz as compared to the previousstudy, indicating that a nearly signal-limited conditionwas obtained, which enables NO detection free frombackground noise. In our laser ionization instrument, theuncertainty in NO ion intensity caused by the fluctuation oflaser power was deviated less than 3% from a long-termaverage. Moreover, by comparison with the ozone-chemiluminescence method, water vapor influence hasbeen investigated by introducing humid sampling gases intothe molecular beam. As the relative humidity in thesampling gases varied from 0 to 85% at room temperature,no significant change in the NO detection efficiency wasobserved. This demonstrates an important advantage overthe ozone-chemiluminescence method, although furtherfield intercomparisons are required to certify the applicabilityof this new NO ionization method into the atmosphericstudy.