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The United States Environmental Protection Agency (EPA) has finalized a reporting rule for the Greenhouse Gases (GHGs) emissions including Nitrous Oxide (N₂O) from all sectors of the economy. In addition, EPA and the National Highway Traffic Safety Administration (NHTSA) have been working together on developing a National Program of harmonized regulations to reduce GHGs emissions and improve fuel economy of light-duty vehicles (LDV). As a consequence, the limiting value for N₂O emission from LDV is set to 0.01 g/mile. Considering this regulatory limit of N₂O emission from LDV, if the exhaust gas is diluted and stored in a sample storage bag, the concentration of N₂O becomes very low which requires a highly sensitive analyzer for accurate measurement. In the previous study, an instrument based on Quantum Cascade Mid-IR Laser (QCL-Mid IR) Spectroscopy has been developed for measuring ultra-low level of N₂O in automobile exhaust gas sampled in a sample storage bag.

Nitrous oxide (N₂O) emission reduction has gained large prominence recently due to its contribution to the climate change as a greenhouse gas. The United States Environment Protection Agency (US-EPA) together with the United States Department of Transport (DOT) has already regulated the N₂O emissions from light-duty vehicles (LDV) to 0.010 g/mile. For LDV, N₂O measurement should be done from sample storage bags over the light-duty FTP drive cycles. N₂O emission standard of 0.10 g/bhp-hr for heavy-duty engines (HDE) is also finalized. The final N₂O standard becomes effective in 2014 model year for diesel engines. Usually raw or diluted exhaust is measured for HDE emission testing. Therefore, an analyzer capable of measuring N₂O from bag and from diluted sample continuously is required to support both LDV and HDE regulations.

In the engine and vehicle test procedures described in Parts 1065/1066 of Title 40 of the Code of Federal Regulations (CFR), the United States Environmental Protection Agency (US-EPA) allows for the measurement of N2O emissions from sample storage bags, from a continuous dilute stream or a raw exhaust stream. Typically, batch (Bag) sampling has better accuracy and repeatability, but continuous sampling is more efficient in terms of test cell running time and provides test-mode emissions with good correlation to bag measurements. In this study, correlations between bag sampling and continuous dilute exhaust sampling were investigated using a fleet of vehicles with a wide range of N2O emission levels. Very good correlation between these two sampling methods was observed for the majority of tests conducted. In the best cases, differences in average N2O concentration levels measured by these two methods were less than +/− 1%.