Assessment of Low Levels of Particulate Matter Exhaust Emissions Using Low-Cost Ionization-Type Smoke Detectors

Traditional smoke opacity measurement, performed on diesel engines during regular emissions inspections, sensitive primarily to larger particles of elemental carbon, is very little sensitive to nanoparticles and to semi-volatile “organic carbon” particles. For this reason, it no longer suffices as a high emitter detection tool for modern vehicles with a particle filter or for advanced low-emissions technology where semi-volatile organic particles are the dominant fraction of particulate matter. This paper investigates the potential of common low-cost ionization type smoke detectors, produced in mass quantities for fire detection in buildings, as a tool to measure particle emissions in vehicular exhaust. Two ionization chambers were used to measure both raw and diluted exhaust of various engines powered by diesel fuel and biofuels under laboratory conditions as well as on the road. Laboratory results suggest that the ionization chamber signal correlates best to total particle length, with correlation to number and mass dependent on particle size distribution. Particle filter regeneration events were clearly discerned from the ionization chamber readings. With detection limits on the order of 0.1 mg/m³ and 10⁶ particles/cm³ in raw exhaust, the method appears to be sufficiently sensitive for inspection of vehicles equipped with particle filters and for preliminary measurements of particle emissions from modern engines.