Comparison of BTX Measurements Using a Differential Optical Absorption Spectroscopy and an On-Line Gas Chromatography System

Abstract

The suitability of the DOAS system for the analysis of aromatic VOCs including benzene, toluene, and xylenes in air were tested against an on-line GC measurement technique. Results of our study indicate that the compatibility between two different methodologies, when checked in terms of various standards, is highly variable depending on species. If the differences in measured values between the two are calculated in terms of percent differences, the level of agreement is found to decrease on the order of toluene (-3.4%), xylenes (-45.5%), and benzene (-83.0%). The results of linear regression analysis indicate that the correspondence between the two methods can be expressed as follows: Benzene (DOAS) = 0.240 Benzene (GC) + 0.514 (r = 0.128) Toluene (DOAS) = 0.857 Toluene (GC) + 0.692 (r = 0.711) Xylenes (DOAS) = 0.771 Xylenes (GC) + 0.269 (r = 0.647) A comparison of the data sets obtained by the two distinctive systems reveals that toluene maintains the strongest compatibility between the two systems, while benzene tends to record the least agreement. Although the system-to-system bias is different among different chemical species, the overall results of our study suggest that the use of the commercial DOAS system can provide reliable information of temporal and spatial distribution patterns of major aromatic VOCs, depending on their concentration levels in ambient air (e.g., well above their detection limits).