Difference in Lipid Composition of Urban Aerosols between Day and Night

Abstract

In the course of a study to reveal a diurnal variation in organic components of aerosols, size-separated aerosol samples were collected during the daytime (10 : 30 — 17 : 10) and nighttime (20 : 30 — 6 : 30) in summer. The samples were analyzed for aliphatic hydrocarbons and fatty alcohols. Most aliphatic hydrocarbons in both the day and night samples were anthropogenic in origin. Contributions of diesel and gasoline engine exhausts were obvious in the day and night samples, respectively. Fatty alcohols had a natural origin. Epicuticular waxes of plants and soil were the major source materials for the >C₂₂-alcohols. Source materials for the >C₂₀-alcohols could not be identified. There was a difference in the relative contribution of these materials between day and night. A great difference was also observed in the atmospheric concentrations of aliphatic hydrocarbons and fatty alcohols between the day and night samples. The day sample showed high concentrations of these compounds in large particle size ranges. In the small particle size range (<0.8 μm), the night sample was above the day sample in the concentrations of the >C₂₂-alcohols and natural source-derived hydrocarbons. Some factors governing these variations were discussed.