Conifer leaf wax acts as a source of secondary fatty alcohols in atmospheric aerosols

Abstract. Fatty alcohols (FAs) are major components of plant leaf surface lipids emitted into the atmosphere as primary biological aerosol particles (PBAPs). FAs in the atmosphere can act as ice-nucleating particles to form clouds that affect climate through radiative forcing and precipitation processes. Secondary FAs (SFAs) in plant waxes can act as tracers for PBAPs. However, the specific plant species that contribute to the atmospheric emissions of SFAs, as well as the factors controlling the SFA amount of atmospheric SFA emissions, remain poorly understood. In this study, we collected size-segregated aerosols and leaf samples from various plant species from a cool-temperate forest site in Hokkaido, northern Japan, during different seasons. n-nonacosan-10-ol was the most abundant SFA in the aerosols, which resided mostly in the supermicrometer size range, with the maximum concentration observed in spring. Among all plant leaves examined, n-nonacosan-10-ol was identified only in coniferous leaf samples. The mass of n-nonacosan-10-ol per leaf exhibited a seasonal trend similar to that of the aerosol SFA concentrations. Our results suggested that the amount of n-nonacosan-10-ol in aerosols was primarily controlled by the number of n-nonacosan-10-ol coniferous trees, which was determined by the phenology. Overall, our findings suggest n-nonacosan-10-ol can be used as a tracer compound for PBAPs originating from conifer leaf wax, which can be used to estimate the atmospheric emission flux of PBAPs on a global scale.