Development of a portable CEAS sensor for fast, inexpensive measurements of nitrogen dioxide in urban environments

Nitrogen dioxide (NO₂) is a major air pollutant and strongly associated with vehicle emissions.  At present, there are no fast and low-cost instruments suited to mobile measurements or measurements at roadside sites. In this work, we describe a low-cost Cavity-Enhanced Absorption Spectrometer (CEAS) system for portable, in-situ measurements of NO₂ in urban environments. A blue LED centred at 440 nm was used as a light source with a 12 cm optical cavity, and transmitted light was detected with a silicon photomultiplier.  Sensitivity to NO₂ at low ppb levels (3 ppb) was achieved at the instrument time resolution of 5 s. We discuss the application of the instrument to both stationary and mobile monitoring applications and present early work towards developing a backpack-mounted instrument.