# Advancements and Prospects of Electronic Nose in Various Applications: A Comprehensive Review
## 3 Application Areas
### Environmental Monitoring  
Electronic noses find applications in various environmental contexts, encompassing several key areas: (i) analysis of air quality parameters, (ii) monitoring water quality, (iii) facilitating process control, (iv) safeguarding worker health, especially in confined industrial environments such as factories and mines, and (v) evaluating the efficiency of odor control systems [29]. In each of these contexts, electronic noses serve as either viable alternatives to or supportive tools alongside traditional analytical methods. In the realm of air quality assessment, for instance, an electronic nose based on metal oxide (MOX) sensors can stand in for gas chromatography to identify and quantify a range of pollutants [106]. Similarly, for process control, where conventional analysis methods can be resource-intensive and time-consuming, an e-nose offers an economical solution. As an illustration, preventing undesired anaerobic processes in a composting facility necessitates measurements of temperature, oxygen levels, pH, and microbial activity [107]. Alternatively, a specialized e-nose tailored to the composting process can yield similar data at reduced costs and complexity, employing a descriptive approach. Beyond acting as complements or substitutes for analytical methods, electronic noses uniquely possess the ability to evaluate and categorize odors, making them essential for quantifying olfactory perceptions. Consequently, appropriate sensing techniques are harnessed to quantitatively assess odors. Indeed, the preservation of workers' health in coal mines stands as a paramount reason that propelled the development of gas sensors. Historically, the coal mining industry faced substantial challenges due to the presence of perilous gases like hydrogen sulfide (H\({}_{2}\)S) and methane (CH\({}_{4}\)) in mine shafts [108]. To address this, ingenious solutions were developed. [PERSON], a Scottish physiologist, introduced the use of canaries as live indicators of gas presence. Canaries, being sensitive to toxic gases, served as early warning systems. If the birds exhibited distress or stopped singing, it signaled the presence of hazardous gases, prompting miners to evacuate [109]. Technological progress spurred the evolution of gas sensors. Dr. [PERSON]'s work in the 1920s involving sensors based on light wave interference demonstrated a pivotal step forward [110]. [PERSON]'s patent for combustion-type sensors in the 1950s further contributed to the field's advancement [110; 111]. The introduction of solid-state metal-oxide gas (SMOX) sensors by [PERSON] in the 1960s marked a transformative milestone [110; 111]. This progression paved the way for the integration of gas sensing technology into broader monitoring systems. Today, electronic noses stand as remarkable embodiments of this evolution. These noses, equipped with sophisticated gas sensors, offer real-time and accurate detection of a diverse range of volatile compounds and gases. For instance, they enable the continuous monitoring of air quality in urban environments, alerting authorities to the presence of pollutants such as nitrogen dioxide (NO\({}_{2}\)), sulfur dioxide (SO\({}_{2}\)), and ozone (O\({}_{3}\)) [112]. A thorough summary of air quality monitoring is meticulously presented in Table 3. Moreover, in industrial zones, electronic noses play a crucial role in identifying noxious emissions emanating from factories and plants, enabling swift intervention to alleviate potential detrimental effects on both human well-being and the ecosystem.