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Atmospheric modelers and development engineers need accurate measures of NO2 emissions from motor vehicles. Due to the oxidative reaction of oxygen with NO, these measurements (typically taken from a bag sample) can be inaccurate if care is not taken to minimize the sample residence time in the bags. This reaction occurs slowly at low NO concentrations, however, at higher NO concentrations the reaction can rapidly speed up (for example, 50 ppm NO will experience a 10% concentration reduction in 6.5 minutes). This report explores the factors contributing to this artifact for emissions test cells. Estimates of the error in NO2 emission rate measurements for several scenarios are presented. Additionally, kinetic expressions of the reaction rate are shown to be fairly accurate for our test conditions, but should not be used in general without verification of the non-existence of competing, hindering or accelerating species within the sample bag.

The use of Selective Catalytic Reduction (SCR) for NOx emissions control has resulted in a new challenge for the emissions measurement community. Most SCR systems require injection of urea or ammonia into the exhaust stream. Residual ammonia present in vehicle exhaust can have deleterious effects on NOx analyzers using chemiluminescent detectors (CLD). Ammonia can poison converter catalysts in CLD NOx analyzers and may react with NO2 across the converter. Both of these issues lead to erroneous NOx measurements, as well as increased maintenance costs and downtime. This paper will describe the development and use of a low-cost, simple ammonia scrubber that can easily be integrated into sampling systems and requires little change in test cell maintenance procedures. Validation results show the scrubber to have capacity sufficient to last for a full day of testing of typical vehicles.

Previous research into Particulate Matter (PM) emissions from a spark-ignition engine has shown that the main factor determining the how PM emissions respond to transient engine operating conditions is the effect of those conditions on intake port processes such as fuel evaporation. The current research extends the PM emissions data base by examining the effect of transient load and speed operating conditions, as well as engine start-up and shut-down. In addition, PM emissions are examined during “real-world” driving conditions - specifically, the Federal Test Procedure. Unlike the previous work, which was performed on an engine test stand with no exhaust gas recirculation and with a non-production engine controller, the current tests are performed on a fully-functional, production vehicle operated on a chassis dynamometer to better examine real world emissions.