# Mdpj _sciences_
## 1 Introduction  
Air pollution is a critical issue impacting human health, environmental quality, and overall quality of life in urban areas worldwide [1; 2]. According to the World Health Organization, air pollution is responsible for approximately 7 million premature deaths annually [3]. Rapid urbanization and industrial activities have significantly increased the concentration of pollutants such as particulate matter (PM), volatile organic compounds (VOCs), carbon dioxide (CO\({}_{2}\)), nitrogen oxides (NO\({}_{\lambda}\)), sulfur dioxide (SO\({}_{2}\)), and ozone (O\({}_{3}\)) in the atmosphere [4; 5]. These pollutants are linked to severe health problems, including respiratory and cardiovascular diseases, and contribute to climate change and environmental degradation [6]. Consequently, there is an urgent need for effective air pollution mitigation strategies in urban environments.  
Green systems, including green walls, active green walls, and urban greenery systems, have emerged as promising solutions to mitigate air pollution [7; 8]. These systems utilize plants' natural ability to absorb, filter, and sequester pollutants, providing an eco-friendlyand sustainable approach to improving air quality. Green walls, for example, can be installed on building facades, acting as living filters that trap particulates and absorb gases [9]. Active green walls enhance this effect with integrated ventilation systems that increase airflow through the vegetation, boosting the pollutant capture rate [10]. Urban greenery systems, which include trees, shrubs, and hedges, serve as barriers and sponges for airborne pollutants, improving air quality at the city scale [11].  
Over the past decade, five significant reviews have addressed the topic of environmental pollution reduction through green systems [12; 13; 14; 15; 16]. The primary differences among these reviews lie in their objectives, the pollutants they address, the types of green systems employed, and the environments in which they are applied. Specifically, [PERSON] and [PERSON] [12] discuss the benefits of living walls on thermal comfort and CO\({}_{2}\) sequestration from the environment. [PERSON] et al. [13] and [PERSON] et al. [14] focus on the purification of indoor environments, emphasizing potted plants and the potential of active green walls. [PERSON] et al. [15] and [PERSON] and [PERSON] [16] address pollutant mitigation in urban settings.  
Despite these contributions, there remains a need for a comprehensive review that not only updates the knowledge provided in earlier studies but also expands the scope to cover various technologies and plant species used in green systems. This proposed review does not examine the reduction of energy consumption, thermal properties, or green roof systems. Instead, it analyzes the performance of various technologies, including green walls, active green walls, and urban greenery systems, with specific insights into the plant species used. It evaluates multiple application environments and considers a wide range of pollutants.  
The objective of this study, in addition to updating the knowledge provided in earlier reviews, is to serve as a reference for future experiments investigating botanical biofilter systems applied in both indoor and outdoor environments. To this end, this review aims to offer a foundational understanding of state-of-the-art technologies and materials employed in air purification. It provides information on the types of experiments that can be conducted to evaluate performance, identifying strategies for field experiments (detailing instruments and sensors used), laboratory tests (highlighting which analyses are performed and how), and modeling software for system simulation. By addressing these aspects, this review seeks to enhance the design, implementation, and effectiveness of green systems in mitigating urban air pollution.