# Research on Soil Pesticide Residue Detection Using an Electronic Nose Based on Hybrid Models
## 1 Introduction  
Pesticides play an important role in modern agricultural production, as they are the main way to reduce agricultural product losses, solve the problems of plant diseases and pests, and increase yields [1]. However, only about 30% of pesticides can effectively exert their effects [2, 3]. Pesticides that are not effectively utilized enter the environment. Although they undergo varying degrees of degradation or migration under natural conditions, soils that have been contaminated for a long time face problems such as acidification, nutrient loss, a decrease in porosity [4, 5]. Research has shown that the pesticide content in plant roots, stems, and leaves increases with the increase of a pesticide residue's concentration in the soil [6, 7]. Pesticides in these plants ultimately cause harm to human beings through the material cycle of the ecosystem [8]. Pesticidesides in soil can be released into the atmosphere as volatile organic compounds (VOCs). This is mainly because pesticides are volatile by nature, allowing them to transition directly from a liquid or solid to a gaseous form. Under the influence of sunlight, they decompose into smaller molecules or VOCs. Moreover, soil microorganisms can convert pesticides into VOCs through biodegradation [9]. The early detection of soil pollution is of great significance for soil protection and human safety. And the remediation methods used for different types of pesticide pollution vary, so it is crucial to accurately identify the types of residual pesticides in the soil [10, 11, 12]. At present, chromatography, mass spectrometry, and spectroscopy are the most mature methods for detecting pesticide residues, with advantages such as their high sensitivity, wide detection range, and strong reliability [13]. However, these methods rely on largeinstruments, which are expensive and costly, making it difficult to conduct on-site testing. In addition, sample preprocessing is cumbersome and time-consuming, requiring professional technical personnel to perform it. These defects make it difficult for them to achieve fast and real-time detection and limit their widespread use. The chemicals used for pretreatment before testing may also cause environmental pollution [14]. Therefore, it is necessary to continue to develop new, fast, accurate, easy-to-operate, and low-cost pesticide residue detection methods to meet practical needs and minimize negative impacts on the environment. An electronic nose is a device that simulates mammalian olfactory organs' ability to identify odors [15]. Compared with traditional methods, electronic noses have the advantages of having a small size, no sample pretreatment, a fast detection speed, being non-destructive, and having environmental protection. Therefore, they are widely used in various fields such as the food industry [16], chemical industry [17] and medical field [18]. In recent years, electronic noses have also received increasing attention in the field of soil information detection. For example, in order to solve problems such as time-consuming, laborious, and complex operations in traditional soil nutrient testing, [PERSON] et al. [19] developed an electronic nose that detects volatile organic compounds to monitor the soil's status, successfully classifying soils with different organic matter contents using PCA. [PERSON] et al. [20] used electronic nose technology to measure the volatile organic compounds released by soil microorganisms and calculate their activity. [PERSON] et al. [21] measured the volatile organic compounds released by soil microorganisms and calculated their activity using electronic nose technology. [PERSON] et al. [22] successfully differentiated the gasoline and diesel pollution levels in soil using electronic nose technology, PCA, and an ANN. At present, studies have applied electronic nose systems for the detection of pesticide residues in soil. [PERSON] et al. [23], inspired by bionics, proposed a biomimetic strategy for detecting unknown pesticide residues in soil using electronic noses.