Also discussed here: Elemental carbon as an indicator for evaluating the impact of traffic measures on air quality and health (8 page pdf, M.P. Keuken. S. Jonkers, P. Zandveld, M. Voogt, S. Elshout van den, Atmospheric Environment, Dec. 2012)

And here:Harmful traffic pollution falls within Munich low emission zone(Science for Environment Policy, May 30, 2013)

Today we review some research aimed at evaluating the impact of the introduction of a Low Emission Zone (LEZ) in Munich, Germany by restricting high emission vehicles from entering the city core. London’s LEZ combined this vehicle restriction with a cordoned congestion charging which together produced the improvements in downtown air quality noted elsewhere. Results indicate a 60% reduction in traffic particulates and elemental carbon in the LEZ suggesting perhaps that the more difficult introduction of congestion charging may not be worth the spending of municipal political capital in countries such as the US and Canada where this idea is unpopular.

Key Quotes:

“Approximately 41,000 vehicles passed through the area [Munich] every day. In 2008, a LEZ was introduced for the area which restricted access of heavy-duty, high-emission vehicles. Only passenger cars and light trucks with Euro 3 and Euro 4 vehicle emission standards are allowed into the area.”

“the LEZ had a strong beneficial effect on traffic-based pollution…Particles from traffic were reduced by 60%, and the ‘elemental carbon’ from traffic exhaust, an important component of aerosol pollution which has been linked to respiratory problems, fell from 1.1 to 0.5 micrograms per m3”.