The Amazon tall tower observatory (ATTO) site – Multi-year aerosol observations and scientific key questions

Abstract:

The Amazon tall tower observatory site is located 150 km NE of Manaus in undisturbed rain forest areas. It serves as a remote measurement station in the Amazon forest with continuous aerosol, trace gas, micrometeorological, and ecological measurements. During part of the rainy season, the atmospheric state approximates pre-industrial conditions, in strong contrast to the dry season, which is dominated by significant pollution from deforestation fires and urban emissions.

This presentation will focus on aerosol studies of the past three years. It aims to provide a brief overview of the characteristic seasonality of the aerosol burden at the ATTO site. Moreover, it will discuss the following key questions and current results of the ongoing observations: (i) During the wet season and in the absence of long-range advection of African aerosols, atmospheric conditions at the ATTO site approximate a pristine state, which reveals the genuine contribution of biogenic aerosols. Biogenic particles in the super- and submicron range have been observed and their properties as well as potential sources will be discussed. (ii) In contrast to the classical new particle formation, the occurrence of ultrafine particles is comparably sparse and mainly occurs as short ‘bursts’, indicating a rather localized character. Our current understanding of this phenomenon and its significance for the overall aerosol burden will be addressed. (iii) Aerosol absorptivity is mainly caused by black carbon, however, indications for the presence of other light absorbing aerosol species have been found. Current results on light absorbing aerosol under clean and polluted conditions will be presented. (iv) Aerosol particles at the ATTO site are typically strongly aged and comprise pronounced internal mixtures, with important implications for their properties. Microspectroscopic analysis helps to obtain insights into atmospheric processing and its impact on particle morphology and phase state.