Urban Ammonia Source Characterization Using Infrared Quantum Cascade Laser Spectroscopy

Ammonia in cities can be an important source of particulates due to elevated levels of nitrogen oxides in urban areas. Instrumentation using quantum cascade (QC) infrared laser absorption has been developed to characterize sources of ammonia. QC lasers operate without cryogenic cooling which makes them much more robust and convenient for field measurements than conventional lead-salt tunable diode lasers. An extractive sampling version of the instrument has been mounted in a mobile van for fast response (sub-second), high precision (0.5 ppb) mapping of emission sources. The van is also equipped with an aerosol mass spectrometer for measurements of ammonium in particles. Simultaneous measurements of CO2 are used to distinguish combustion sources of ammonia associated with automobile traffic from other sources. An open-path, retro-reflector version of the instrument has been developed to measure ammonia emissions in automobile exhaust as individual vehicles pass through the laser beam. Data from recent studies in Mexico City and in Boston will be presented and compared with other measurement techniques including long path FTIR spectroscopy.

⁽¹⁾ E-mail: mz@aerodyne.com