Electron beam lithography (EBL) has become a popular means to prepare a wide variety of nano-arrays for numerous studies and applications, including photonics and sensors. Their fabrications and characterizations are costly and time consuming, underscoring the importance of developing effective tools to rapidly study their physicochemical stabilities and properties over time. In this study, we characterized EBL-fabricated single silver nanoparticle (Ag NP) arrays over their 12-week exposure to ambient conditions using SEM/EDS, AFM and dark-field optical microscopy and spectroscopy (DFOMS). We found that chemical compositions, structural morphologies and plasmonic optical properties of single NPs altered drastically over the exposure. Single cuboid and triangular-prism Ag NPs degraded at rates of (0.74 ± 0.02) and (0.66 ± 0.02) per week, and their localized surface plasmon resonance (LSPR) spectra showed striking blue-shifts (171 ± 25 and 203 ± 35 nm) over the 12-week exposure, respectively. Plasmonic colors of single NPs changed distinctively from red to green over the 12-week exposure. The LSPR spectra of individual NPs in each array were acquired simultaneously and correlated specifically with their SEM and AFM images, demonstrating that DFOMS can serve as high-throughput, ultrasensitive and non-invasive means to characterize chemical, structural and optical properties of nano-arrays in situ in real time at single-NP resolution.