Air quality monitoring has historically relied on fixed regulatory-grade stations designed to provide high-precision and standardised measurements of atmospheric pollutants. These stations are typically equipped with reference analysers based on gravimetric methods for particulate matter, chemiluminescence techniques for nitrogen oxides, UV photometric analysers for ozone, and beta attenuation monitors for con-tinuous particulate measurement. The operation and calibration of these instruments are conducted under interna-tionally recognised quality assurance frameworks such as ISO/IEC 17025, which ensures measurement traceability, reliability, and inter-laboratory comparability (ISO, 2017). Fixed monitoring stations play a central role in regulatory compliance, long-term en-vironmental assessment, and epidemiological studies, forming the backbone of national air quality surveillance networks (European Environment Agency, 2019; Snyder et al., 2013). Despite their robustness and scientific reliability, fixed monitoring systems present structural limitations. Their installation requires significant infrastructure, technical expertise, and financial investment. Moreover, because they are geographically static and typically sparsely distributed, they may not adequately capture fine-scale spatial heterogeneity in urban pollution patterns, particularly in areas affected by traffic con-gestion, industrial activities, or complex urban morphology (Apte et al., 2017). These limitations have motivated the exploration of complementary monitoring approaches.

Traditionally, air quality monitoring has depended on stationary regulatory-grade stations that deliver highly accurate and standardized measurements of airborne pollutants. These facilities typically use reference analyzers that employ gravimetric methods for particulate matter, chemiluminescence for nitrogen oxides, UV photometric analysis for ozone, and beta attenuation monitoring for ongoing particulate measurement. These instruments operate and undergo calibration according to internationally recognized quality assurance standards like ISO/IEC 17025, which guarantees measurement traceability, dependability, and consistency between laboratories (ISO, 2017). Stationary monitoring stations serve as essential components for regulatory compliance, long-term environmental evaluation, and epidemiological research, creating the foundation of national air quality monitoring networks (European Environment Agency, 2019; Snyder et al., 2013). While these fixed monitoring systems offer durability and scientific credibility, they come with inherent structural constraints. Setting them up demands substantial infrastructure, specialized technical knowledge, and considerable financial resources. Additionally, since they remain in fixed locations and are usually spread far apart, they often fail to detect detailed spatial variations in urban pollution distribution, especially in zones influenced by traffic bottlenecks, industrial operations, or complicated urban layouts (Apte et al., 2017). These constraints have sparked interest in developing additional monitoring methods.