## 2 Experiments
### Sampling  
The design of a sampling network and sampling and sample treatment were completed according to the European standard EN 16,414 [41] and respecting the Moss Sampling Manual of the International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops (ICP Vegetation) [30].  
For assessment of a local pollution source, the norm suggests locating sampling points around a source in respect to the direction of the prevailing wind while at least three points should be located on a straight line from a source in the direction of the prevailing wind; two other points in the opposite direction and two leeward, in a greater distance, with a minimal effect from a source. The sampling network was designed respecting these guidelines and based on prevailing wind direction, topography and altitude in the area. The network resulted in 14 sampling sites, as can be seen in Figure 4. The points were located around the primary source of pollution, both in the direction (southeast direction) and in the opposite direction (northwest) of the prevailing wind, but also at a higher altitude (south-south-west--on the hillside of the Javorovy hill (748 m above sea level) and in the opposing direction (leeward) on the Osuvka hill (400 m above sea level). Moss samples were collected in the created network with respect to the presence of the moss; the actual locations of sampling points were recorded using GPS.  
The sampling took place in two seasons in order to investigate the influence of the heating season on the concentrations of analysed elements. The samples supposedly under the influence of sources connected to the heating season were collected in June (hereinafter referred to as a summer sampling); the sampling of samples supposedly out of the influence of the heating season was performed in October (referred to as an autumn sampling) [54]. Both samplings were performed within 1 day, namely, on 27 June 2017 and 26 October 2017. If possible, moss was collected from tree stumps or dead wood to avoid contamination by soil particles and out of a tree canopy [55, 56, 57, 58]. Based on field investigation and species occurrence, _Brachythecium rutabulum_ (Hedw.) was chosen for the study.  
Figure 3: PM\({}_{10}\) pollution rose (**a**); PM\({}_{2.5}\) pollution rose (**b**) at AQM Trinec-Kanada in 2017 (data CHMI [52, 53]).  
_Braclythecium rutabulum_ is a large pleurocarpous moss growing in lax, glossy, bright green or yellowish-green tufts or patches. It is common in Europe and occurs in many habitats, such as soil (both in woodland and non-forest vegetation), tree trunks, logs, stones and rock walls [59]. This species has been previously successfully used in large scale biomonitoring surveys, mainly in Poland and Southern Europe [36; 60; 61; 62].  
One of the basic preconditions for the selection of species for biomonitoring is their absorption capacity. The water absorption ratio in bryophytes depends mainly on the spatial structure of their cushions, which is considerably dense in _Braclythecium rutabulum_. Thanks to this feature, it suits the performed research well. The absorption capacity of dry _B. rutabulum_ is 16.1:1, meaning that the dried plants can absorb an average of 20 g of water with dissolved substances per 1 g of herb [63]. For comparison, this amount is about 75% of the value the cushions of the genus _Splugnum_ (who are record holders in this respect) can absorbed.  
As _Braclythecium rutabulum_ was not present on all sampling sites, one sample in each season is covered by _Hyrum cupressforme_. Detailed information on samples can be found in Supplementary Materials Table S1.