**Preface**

Air pollution poses a significant risk to human health. Emissions from industrial activities, energy production, transport, waste management activities, and natural sources contribute to the many air pollution-induced problems, such as reduced visibility, adverse health effects, and global climate change. Air pollution is not a local concern. The residence time of pollutants in the atmosphere can extend from several days to months, and the corresponding spatial transportation scales are proportionally large, ranging from local to continental. Even though there is no region not affected by air pollution at some level, the situation is significantly worse in urban areas.

The aim of this Special Issue was to gather up-to-date research knowledge aiming at assessing air pollution at the urban and regional level, including both experimental and monitoring studies and mathematical/numerical modeling studies. The publications of the issue covered the subjects of air pollution with particulates and gaseous pollutants, Particulate Matter (PM) sources and source apportionment, Carbonaceous species (Organic and Elemental or Black Carbon) in the atmosphere, and Ozon-related pollution.

> **Elena Hristova, Manousos Ioannis Manousakas, Anik ´o Angyal, and Maria Gini** *Editors*
