Fog is a “suspension of very small, usually microscopic water droplets” that “reduce horizontal visibility at the Earth’s surface to less than 1 km” (WMO, 2017). Fog may also be considered as a cloud in contact with the Earth’s surface. Dew is a “deposit of water drops on objects, produced by the direct condensation of water vapour from the surrounding air” (WMO, 2017). Both fog and dew formation are driven by the condensation of water vapor to liquid water in the very lowest part of the atmospheric boundary layer, i.e., in association with air masses with terrestrial or marine surface contact. Fog as a phenomenon is the object of various science and engineering fields such as meteorology, transportation safety, hydrology, and biology. Fog can scavenge airborne pollutants in urban and industrial areas, creating a health hazard, but can also deliver nutrients to natural environments. As part of the ecohydrology of natural systems around the world, fog creates unique endemic species distributions. Through its unique impact on humans’ perception of the environment, fog has also found its way into literature and the art of painting. In some areas of the world, fog is even utilized as a valuable source for freshwater production. To lesser degree, this is also true for dew, which may be collected with the aim to generate potable water.
The triannual International Conference of Fog, Fog Collection and Dew started some 20 years ago in Vancouver (Canada, 1998), went on through St. John's (Canada, 2001), Cape Town (South Africa, 2004), La Serena (Chile, 2007), Münster Germany, 2010), Yokohama (Japan, 2013), Wrocław (Poland, 2016), and will be continued in Taipei (Taiwan) in 2019. This special issue of “Aerosol and Air Quality Research” (AAQR) is a selection of contributions as presented at the most recent 7th International Conference of Fog, Fog Collection and Dew at the University of Wrocław from 24 through 29 July, 2016. Of the 162 contributions to the conference, 33 were submitted to AAQR as manuscripts to be included in this special issue. Twenty one were accepted after a peer-review process and guest editors’ decisions.