A hydrocarbon detector for the remote sensing of vehicle exhaust emissions

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Abstract
A new remote sensor for measuring on‐road carbon monoxide, carbon dioxide, and hydrocarbon exhaust emissions in under 1 s from vehicles passing the sensor is described. The new design adds the capability for measuring exhaust hydrocarbons and eliminates the need for liquid–nitrogen‐cooled detectors while improving upon the overall signal to noise. Under typical field operating conditions, sensitivity to 0.05% propane with a precision of 0.014% propane is observed. Two types of water interferences important to the measurement of exhaust hydrocarbons are reported. The water vapor present in all auto exhaust causes a small positive bias dependent on the analytical wavelength chosen. A much larger interference is caused by liquid water (often called ‘‘steam’’) plumes seen behind cold vehicles at low temperatures.