Properties of aged forest fire plumes after intercontinental transport across the Atlantic Ocean

Abstract

During the ICARTT study in summer 2004, measurements on the intercontinental transport of aerosols from biogenic and anthropogenic origin were performed at the European west coast as a part of the ICARTT-ITOP study (Intercontinental Transport of Ozone and Precursors). During the study the German Falcon 20 research aircraft was operating from an airport north of Paris. The aircraft was equipped with extensive in-situ aerosol and trace gas instrumentation. Additionally, a ground-based aerosol lidar at Palaiseau south of Paris monitored the vertical structure of the atmosphere. Trajectory analyses permitted the identification of the plume origin for several case events. During the ITOP activities in summer 2004, forest fire plumes from Canada and Alaska were transported very frequently in the free troposphere across the Northern Atlantic and probed by the Falcon and by the lidar. Physico-chemical properties of the forest fire plumes showed a strong absorption signal in the visible spectral range, the complete absence of nucleation mode particles, an almost depleted Aitken mode and an enhanced accumulation mode compared to the undisturbed background aerosol. Volatility analyses of Aitken and accumulation mode particles indicated the influence of ageing processes on the aerosol properties. It turned out that the accumulation mode aerosol inside these forest fire plumes was completely internally mixed with nonvolatile cores, while in the undisturbed background aerosol a considerable fraction of entirely volatile particles was found even in the accumulation mode. The forest fire plumes also showed enhanced CO mixing ratios. An overview over the aerosol properties as a function of the plume age will be given based on a large set of investigated plume events.