Abstract. Environmental temperature plays a vital role in controlling chemical transformations that lead to the formation of secondary organic aerosol (SOA) and ultimately impact the composition and optical properties of the aerosol particles. In this study, we investigated optical properties of n-dodecane SOA under two temperature conditions: 5 and 25 ∘C. It was shown that low-temperature conditions could enhance the real part of the refractive index (RI) of the SOA at wavelengths of 532 and 375 nm. Mass spectrometry analysis revealed that the molecular composition of n-dodecane SOA was significantly modified by temperature: a large amount of oligomers were formed under low-temperature conditions, which led to higher RI values. These findings will help improve our understanding of the chemical composition and optical properties of SOA under different temperature conditions and will provide one possible explanation for the low visibility in suburban areas during winter.