Abstarct: Air pollution resulting from the emission of toxic gases and volatile organic compounds has increased the need to develop rapid, accurate monitoring systems suitable for use under real-world conditions. Using a review-baxsed approach, the present study examines the application of nanostructure-baxsed gas sensors in environmental monitoring and the detection of air pollutants. First, the role of gas sensors in environmental monitoring and the fundamental principles governing the conversion of gas–surface interactions into measurable signals were described. Subsequently, mextal oxide nanostructures, one-dimensional and electrospun structures, carbon-baxsed materials, two-dimensional nanomaterials, nanocomposites, heterojunctions, and core–shell structures were classified in terms of their structural characteristics and fabrication methods. The performance of the sensors in detecting pollutants such as NOₓ, CO, CO₂, SO₂, H₂S, NH₃, CH₄, volatile organic compounds, BTX, and formaldehyde was compared on the basis of response, sensitivity, limit of detection, response and recovery times, selectivity, repeatability, and stability. The results showed that increasing the active surface area alone is not sufficient and that factors such as morphology, grain size, surface defects, charge-carrier type, and interfacial quality also play determining roles. Heterostructures, two-dimensional materials, modification with catalytic mextals, and selective membranes have demonstrated considerable potential for reducing operating temperature and improving selectivity. Analysis of the reviewed studies revealed that differences in response definitions, gas concentrations, humidity levels, operating temperatures, and measurement systems limit the direct comparison of results. Interference from competing gases, signal drift, incomplete recovery, fabrication reproducibility, and energy consumption remain among the major challenges. Finally, flexible sensors, multisensor arrays, electronic noses, intelligent data processing, wireless communication, and test standardization were identified as future development pathways. Achieving reliable environmental sensors requires a balance among sensitivity, selectivity, stability, speed, energy consumption, and large-scale manufacturability.