Abstract
Hydrogen is a ubiquitous but often neglected gas. In analytical measurements hydrogen—as a harmless gas—often is not considered so no studies on hydrogen in indoor air can be found. For metal oxide semiconductor (MOS) gas sensors that are increasingly pushed into the application as TVOC (total volatile organic compounds) sensors, hydrogen is a severe disturbance. On the other hand, hydrogen can be an intentional choice as indicator for human presence similar to carbon dioxide. We present a field-study on hydrogen in indoor air using selective MOS sensors accompanied by an analytical reference device for hydrogen with an accuracy of 10 ppb. Selectivity is achieved by siloxane treatment combined with temperature cycled operation and training with a complex lab calibration using randomized gas mixtures, yielding an uncertainty of 40–60 ppb. The feasibility is demonstrated by release tests with several gases inside a room and by comparison to the reference device. The results show that selective MOS sensors can function as cheap and available hydrogen detectors. Fluctuations in hydrogen concentration without human presence are measured over several days to gain insight in this highly relevant parameter for indoor air quality. The results indicate that the topic needs further attention and that the usage of hydrogen as indicator for human presence might be precluded by other sources and fluctuations.
Highlights
Indoor air quality (IAQ) is a general term comprising a multitude of parameters like temperature, humidity, air flow or the concentration of many trace gases [1]
The term is known since 1970 and of increasing interest during the last decades [2]. Among these trace gases are specific harmful pollutants like nitrogen dioxide (NO2 ); formaldehyde or benzene [3,4]; carbon dioxide (CO2 ), which is often used as indicator for human presence [5,6]; many organic compounds, often referred to as VOCs [7]; and others
All events labelled below the traces of the Partial least least squares squares regression (PLSR) model predictions indicate ventilation events, i.e., the window and/or door of the room were opened, and the room thoroughly ventilated to achieve a clean baseline before and after the conducted release tests
Summary
The term is known since 1970 and of increasing interest during the last decades [2] Among these trace gases are specific harmful pollutants like nitrogen dioxide (NO2 ); formaldehyde or benzene [3,4]; carbon dioxide (CO2 ), which is often used as indicator for human presence [5,6]; many organic compounds, often referred to as VOCs (volatile organic compounds) [7]; and others. Despite this high complexity inexpensive sensors are wanted for the purpose of IAQ monitoring. Nondispersive infrared sensors (NDIR) for CO2 monitoring are state of the art for demand-controlled ventilation if concentrations are above
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