Abstract
Abstract. In this study, we report on the development of a lamp-based vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in our laboratory; it is composed of a radio-frequency-powered VUV lamp, a VUV photoionizer, an ion-migration lens assembly, and a reflection time-of-flight mass spectrometer. By utilizing the novel photoionizer consisting of a photoionization cavity and a VUV light baffle, the baselines of the mass spectra decreased from 263.6 ± 15.7 counts to 4.1 ± 1.8 counts. A detection limit (2σ) of 3 pptv was achieved for benzene after an acquisition time of 10 s. To examine its potential for real-time monitoring applications of samples, the developed VUV-PIMS was employed for the continuous measurement of urban air for 6 days in Beijing, China. Strong signals of trace-level volatile organic compounds, such as benzene and its alkylated derivatives, were observed in the mass spectra. These initial experimental results reveal that the instrument can be used for the online monitoring of trace-level species in the atmosphere.
Highlights
Volatile organic compounds (VOCs) are an important group of air pollutants: they are active in the formation of photochemical smog and ground-level ozone production; several VOCs present in urban air, such as benzene and its alkylated derivatives, are considered carcinogenic (Gee and Sollars, 1998; Lee et al, 2005)
We report the design of a sensitive VUVPIMS, which was employed to measure trace-level VOCs such as benzene
A lamp-based VUV-PIMS was developed in our laboratory
Summary
Volatile organic compounds (VOCs) are an important group of air pollutants: they are active in the formation of photochemical smog and ground-level ozone production; several VOCs present in urban air, such as benzene and its alkylated derivatives, are considered carcinogenic (Gee and Sollars, 1998; Lee et al, 2005). Conventional detection approaches such as gas chromatography–mass spectrometry and high-performance liquid chromatography– mass spectrometry involve a time-consuming chromatographic separation step (Muhlberger et al, 2002) For these reasons, it is imperative to develop real-time online monitoring instruments with high sensitivity for the detection of VOCs. The use of the highly sensitive proton-transfer-reaction mass spectrometer (PTR-MS) has been demonstrated for the real-time measurement of trace gases in the atmosphere with limits of detection (LODs) at the pptv level (de Gouw and Warneke, 2007). The instrument design, calibration results, and urban air measurements will be discussed
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