<human>:  Does Düsseldorf have only a small number of smoggy days each year?
<bot>: Yes, Düsseldorf has only a small number of smoggy days each year. Mercer's 2012 Quality of Living survey ranked Düsseldorf the sixth most livable city in the world. Clean air is an important attribute for a livable city. Smog is a term for air pollution. So, Düsseldorf has only a small number of smoggy days each year.