It is a well-known fact that NO2 has far more harmful effects as compared to NO. NO2 creates ozone, which causes eye irritation and exacerbates respiratory conditions. This leads to an increased emergency departments’ visits and hospital admissions for respiratory issues, especially asthma. Under current situation, majority of regulations deal with total NOx emissions, without looking at the break-up of NO2 and NO. However, there is a feeling in emissions regulation community to implement regulations on NO2 emissions. There are standards to measure total NOx emissions. However, these standards are not equipped enough to measure NO2 emissions accurately. The effect of sample line length on NO2 emissions is not fully understood to date. Also, the standards only suggests maximum of 10 seconds residence time regardless of what the line length is. In this study, a systematic experimental test campaign has been conducted to understand the effect of sample line length on NO2, NO distribution. The residence time was maintained below 10 seconds in accordance with the SAE ARP1256D standards. A Rolls-Royce gas turbine combustor and different calibration cylinders have been used to study the effect of sample line length. A numerical study has also been done to predict the conversion of NO2 to NO. It has been found that with increasing sample line length, more NO2 gets converted to NO and overall NO2 emissions show a reduction, whereas this would not be the case at engine exhaust. This effect of sample line length can be used as a loophole in giving lower NO2 emissions readings.

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