The objective of this study was to measure ammonia (NH{sub}3) emissions from modern technology vehicles since information is scarce about this important source of particulate matter (PM) precursors. Test variables included the emission level to which the vehicle was certified, the vehicle operating conditions, and catalyst age. Eight vehicles with low-emission vehicle (LEV) to super-ultralowemission vehicle (SULEV) certification levels were tested over the Federal Test Procedure (FTP75), a US06 cycle, a hot running 505, a New York City Cycle (NYCC), and a specially designed Modal Emissions Cycle (MEC01v7) using both as-received and bench-aged catalysts. NH{sub}3 emissions in the raw exhaust were measured by tunable diode laser (TDL) absorption spectroscopy. The results show that NH{sub}3 emissions depend on driving mode and are primarily generated during acceleration events. More specifically, high NH{sub}3 emissions were found for high vehicle specific power (VSP) events and rich operating conditions. For some vehicles, NH{sub}3 emissions formed immediately after catalyst light-off during a cold start.
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