Odours in Asphalt: Analysis of the Release of H2S from Bitumen by a Mass Spectrometric Residual Gas Analyser

During the production and laying phases of hot-mixing asphalt (HMA), various volatile organic compounds (VOCs) and noxious gases such as H2S are released into the atmosphere. These emissions are a serious environmental problem, a risk to human health, and expose workers and residents to unfriendly odours. The aim of this study was the development of a fast and sensitive analytical method to detect the H2S emitted from hot bituminous binder that is generally used in the various stages of asphalt production, processing, handling and during road construction. The method consisted in the analysis of evolved H2S from a flask with molten bitumen, using nitrogen as a carrier gas to lead the volatile compounds into a residual gas analyser equipped with a quadrupole mass spectrometer. The analysis was performed following the H2S-specific signals at m/z 33 (HS+) and at m/z 34 (H2S+) in real time, directly on the sample without laborious and expensive pre-treatments and with short response times (<6 s). Calibration with a standard mixture of 1000 ppm of H2S in nitrogen allows semi-quantitative H2S detection. The sensitivity and rapidity of the method were evaluated by quenching the release of sulphur compounds with commercial odour-suppressing agents. Upon addition of 0.1% of additive in two minutes, the H2S signal drops about 80% in two minutes, confirming the good response of the method, even with a very complex matrix.