# Mdpj _sciences_
## 5 Pollutant Reduction Results
### Particulate Matter (PM) Reduction  
Several studies have quantitatively evaluated the performance of green walls in reducing particulate matter (PM). [PERSON] et al. [46] studied a vegetative environmental buffer surrounding an animal feeding operation and found substantial differences in PM absorption between day and night, considering the kinetic energy associated with turbulence to which the systems were exposed. The VEB was less efficient during the day but mitigated PM presence more effectively at night. Overall, the capture efficiency ranged from 21% to 74%, depending on atmospheric conditions. [PERSON] et al. [36], in comparing active and passive green walls, found that, without mechanical ventilation, PM concentrations inside a room were 101.18 \(\pm\) 0.29 \(\mu\)g m\({}^{-3}\). The active botanical filter reduced PM by 42.6%. [PERSON] et al. [27] experimented with a new component called evaporative media (EM), which enhanced the active green wall's ability to reduce particulates, achieving a removal efficiency of 54.5 \(\pm\) 6.04% for PM2.5 and 65.42 \(\pm\) 9.27% for PM10.  
Laboratory tests conducted by [PERSON] et al. [54] showed that the species _P. nigra_ was the best at capturing PM, with the highest amount of accumulated PM found on its leaf surfaces (PM10: 114.6 \(\mu\)g cm\({}^{-2}\); PM2.5: 8.99 \(\mu\)g cm\({}^{-2}\); PM0.2: 4.13 \(\mu\)g cm\({}^{-2}\)). [PERSON] et al. [47] identified Padus Virginiana \"Red Select Shrub\" as the most effective species for capturing particles of various sizes in a vegetative environmental buffer, accumulating the most PM on its leaves with 18 \(\mu\)g/m\({}^{3}\) of PM2.5 and 64 \(\mu\)g/m\({}^{3}\) of PM10. [PERSON] et al. [29] found that the species _S. trifuscita_ applied to an active green wall module could decrease PM2.5 from 41.67 \(\mu\)g m\({}^{-3}\) to 13.20 \(\mu\)g m\({}^{-3}\).  
Considerations on the effective range of biofilters were made by [PERSON] et al. [41], who found differences in PM capture at various distances from the urban greenery system. For example, considering a normal concentration of \(<\)50 mg/m\({}^{3}\), the PM10 concentration was 21.32 \(\mu\)g m\({}^{-3}\) far from the biofilter, whereas it was 13.86 \(\mu\)g m\({}^{-3}\) near the biofilter. [PERSON] et al. [42] noted that the height-to-width ratio significantly impacts vegetation efficiency and particulate concentration. An increase in the H/W ratio led to higher PM2.5 concentrations, with the system achieving a reduction of up to 24.41%. [PERSON] et al. [22] verified the effective reduction of PM due to the presence of a living wall in an indoor environment, measuring reductions of PM0.3-1 by 1.9-9.4 \(\mu\)g m\({}^{-3}\) (about 2.4-14.3% compared to the environment without a living wall); 5.1-13.3 \(\mu\)g m\({}^{-3}\) for PM1-2.5 (about 10.3-11.3% compared to the environment without a living wall); and 5.9-6.2 \(\mu\)g m\({}^{-3}\) for PM2.5-10 (about 4.7-10.3% compared to the environment without a living wall).  
Analyses by [PERSON] et al. [38; 39] on windbreak wall-vegetative strip systems installed near livestock buildings found a range of TSP reduction from 36% to 58%. Field analyses by [PERSON] et al. [45] and [PERSON] et al. [32] on urban greenery systems and active green walls examined both PM reduction and harmful gases like O\({}_{3}\) and NO\({}_{2}\). [PERSON] et al. [45] found a removal rate of 0.00-0.28 g m\({}^{-2}\) per ppb for PM10 and 0.00-0.16 g m\({}^{-2}\) per ppb for O\({}_{3}\). [PERSON] et al. [32] found O\({}_{3}\) concentrations of 15.02 \(\pm\) 0.24 ppb, NO\({}_{2}\) concentrations of 5.16 \(\pm\) 0.19 ppb, and PM2.5 concentrations of 4.08 \(\pm\) 0.31 \(\mu\)g/m\({}^{3}\) in an office with an active green wall. These values were compared to 19.50 \(\pm\) 0.27 ppb, 6.75 \(\pm\) 1.33 ppb, and 7.16 \(\pm\) 3.20 \(\mu\)g/m\({}^{3}\), respectively, in a reference office without an AGW (Figure 11).