Optical detection of ammonia inside a stack: Comparison of different techniques

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The quantitative detection of pollutants in industrial emissions, in particular the emissions of biomass burners, requires different types of analyzers. Optical devices are usually sensitive to the transparency and dirtiness of the exhaust gases, so optical measurements are normally carried out by extracting the samples from the stacks. This paper has a twofold aim. First, we will prove that the molecular composition of the exhaust mixture (in particular the concentration of water and carbon dioxide) can deeply affect the outcome of optical analyzers, depending on the adopted detection technique. This is a critical issue, in particular with a view to the necessity of providing suitable reference methods for monitoring biomass burners emissions. Second, we will show how it is possible to measure inside an artificial stack by using an optical multipass cell located across the gas flow, even at 140 °C, or in presence of soot.