In-line measurement of exhaust mercury emissions by an instrumented light-duty vehicle using both on-road and test track experiments.

The initial purpose of this study has been to develop an instrumental platform for monitoring mercury (Hg) emissions from vehicle exhausts under actual traffic conditions. The platform was then mounted onto a fully-instrumented passenger car to identify emission proxies and factors governing the emissions of gaseous elemental Hg (GeM) and its complementary fraction (GdPM). Data obtained from the road were complemented by data acquired on a test track at either stabilized speeds or well-characterized speed variations. GeM emissions increased overall with both driving speed and fuel consumption; nonetheless, they were influenced by the sequence of accelerations and duration associated with the preceding idling or low-speed driving situations. GdPM emissions varied considerably over the course of trips or track tests, with medians ranging from 7% to 70% of the total Hg emissions stemming from fuel. Such high percentages could be explained by a series of redox reactions, whose kinetics and yield were influenced as much by exhaust gas temperature as by driving conditions or the exhaust system structural configuration. Lastly, an analysis of the GeM and GdPM signals showed that urban cores constitute emission hotspots during rush hour when handling low-speed driving and stop-and-go traffic.