NO₂ measurement artifacts in the presence of soot

Nitrogen dioxide is a regulated pollutant, which is measured routinely. Since it can be formed during combustion processes, it is often measured in the presence of soot. This study investigates the possible artifact formation due to the interaction of soot and NO₂ in the sampling lines and instrument prefilters. The transfer of varying NO₂ concentrations through filters and tubes coated with different kinds of soot was investigated by using a dedicated photoacoustic soot and NO₂ analyzer (TwinPAS ). The effects of flow rate, temperature, relative humidity, tubing respectively filter material, soot reactivity, and passivation on the NO₂ measurement artifacts have been investigated. We found significant lags (up to 2 min) of the NO₂ transfer as well as total NO₂ losses of up 10 %.