**Preface to "Atmospheric Heavy Metal and Nitrogen Deposition Using Mosses as Biomonitors"**

Air pollution has a negative impact on various compartments of ecosystems, posing a threat to the natural environment and human health, and also causing significant economic damage.

Due to their specific features, mosses are recognized as one of the main bioindicators and biomonitors of air contamination, with toxic elements including those originating from anthropogenic and natural sources. The determination of elemental concentrations in mosses is easier and cheaper than conventional precipitation analysis, and a much higher sampling density can be achieved by employing moss biomonitoring.

In recent decades, naturally growing mosses have been used successfully in biomonitoring campaigns for checking the atmospheric fallout of heavy metals and nitrogen (N) across Europe, and the approach has been extended in many regions of the world for characterizing multi-elemental deposition sources.

Quantification of heavy metals and N in selected moss species provides a time-integrated measure of the spatial patterns and temporal trends of heavy metal deposition from the atmosphere to terrestrial ecosystems, and a good indication of ecosystems at risk from high N deposition.

The Special Issue "*Atmospheric Heavy Metal and Nitrogen Deposition Using Mosses as Biomonitors*" belongs to the section *Air Quality and Human Health* of the journal "*Atmosphere*" and includes a collection of papers related to aspects of passive moss biomonitoring of air quality in various regions of the world regarding the pollution sources of potentially toxic elements, heavy metal air pollution in the lockdown period due to the COVID-19 pandemic, trends in element atmospheric deposition and relevance for ecological integrity and human health. Most of the studies were carried out in the framework of the *International Cooperative Program on Effects of Air Pollution on Natural Vegetation and Crops* (ICP Vegetation) of the *United Nations Economic Commission for Europe* (UNECE).

> **Antoaneta Ene** *Editor*

*Article*
