We will address the issue of particulates in the candlelight in the studio with: Prof. Hartmut Herrmann of the Leibniz Institute for Tropospheric Research (IfT)DW-TV: Candles aren’t all that much of a problem worldwide, but wood-burning stoves are. In developing countries people use wood as fuel for heating and cooking. How does wood-burning compare, say, with traffic in terms of pollution? Hartmut Herrmann: In Germany it produces about the same mass a year as the whole of the traffic, which is a lot. Worldwide it constitutes a lot of air pollution - especially in developing countries. There is, for example, the development of more clean-burning stoves to fight this pollution from wood burning in developing countries, so it's a big factor.   Getting back to Europe, the EU has instituted legislation limiting the emissions of different kinds of fine particulates. How fine do they have to be pose a health risk? There's a regulation aimed at particles with a diameter of up to 10 micrometers, but these smaller particles are probably more risky – especially when they are very small and constituted of organic compounds such as we find them in diesel soot. Nowadays, nanoparticles are all the rage in all kinds of applications. Do these really tiny particles pose an even greater danger? Potentially yes, if they can be released into the environment, but the atmosphere produces very small particles by itself. This is an area of intense study. How can we keep these particles out of the air we breath? We need to go to the sources and do some abatement strategies. For example: we equipped some chimneys with filters, and so we have such regulation now in Germany. I think this is a way of doing it – to have some regulation at the sources. How much do particles in the troposphere affect our climate? They do it a lot: either directly by interacting with radiation or indirectly by triggering cloud formation, and the clouds also interact with the...