Monitoring of road-traffic emissions with a mobile photoacoustic system.

Ammonia and ethene are pollutants which are arousing concern as regards their environmental impact, e.g. as greenhouse gases. Road traffic is an increasingly important emission source for these gases. As part of an atmospheric pollution measurement campaign, we performed in situ measurements of NH3, C2H4 and CO2 concentrations at the mouth of a freeway tunnel with a time resolution of 1 min using a mobile laser-based photoacoustic system. Measurements were performed over a period of 5 weeks. In good temporal correlation with traffic counts, we observed peak concentrations of >600 ppb (>1200 ppb for Friday afternoon peaks) for NH3, of up to 400 ppb for C2H4 and >2000 ppm for CO2. Preliminary comparisons with previous measurements at the same location indicate a considerable increase in ammonia and CO2 peak concentrations (greater than the increase in traffic over the same period) and a less pronounced increase in C2H4 concentrations.