Long-term study on coarse mode aerosols in the Amazon rain forest with the frequent intrusion of Saharan dust plumes

Abstract

In the Amazonian atmosphere, the aerosol coarse mode comprises a complex, diverse, and variable mixture of bioaerosols emitted from the rain forest ecosystem, longrange transported Saharan dust (we use Sahara as shorthand for the dust source regions in Africa north of the Equator), marine aerosols from the Atlantic Ocean, and coarse smoke particles from deforestation fires. For the rain forest, the coarse mode particles are of significance with respect to biogeochemical and hydrological cycling, as well as ecology and biogeography. However, knowledge on the physicochemical and biological properties as well as the ecological role of the Amazonian coarse mode is still sparse. This study presents results from multi-year coarse mode measure-ments at the remote Amazon Tall Tower Observatory (ATTO) site. It combines online aerosol observations, selected remote sensing and modeling results, as well as dedicated coarse mode sampling and analysis. The focal points of this study are a systematic characterization of aerosol coarse mode abundance and properties in the Amazonian atmosphere as well as a detailed analysis of the frequent, pulse-wise intrusion of African long-range transport (LRT) aerosols (comprising Saharan dust and African biomass burning smoke) into the Amazon Basin.We find that, on a multi-year time scale, the Amazonian coarse mode maintains remarkably constant concentration levels (with 0.4 cm −3 and 4.0 µg m −3 in the wet vs. 1.2 cm −3

Land cover and its transformation in the backward trajectory footprint region of the Amazon Tall Tower Observatory

“…7 illustrates the pronounced northwest-to-southeast gradient, with the northwest being mostly unperturbed and the southeast being subject to intense, large-scale deforestation and land use change (Davidson et al, 2012). Within this gradient, the forest loss data emphasize the geographic extent of the so-called arc of deforestation at the southern and southeastern margins of the Amazon forest, which has been an active frontier of total forest loss (Morton et al, 2006). The arc of deforestation spans from southern Pará and Maranhão in the southeast over Mato Grosso and Rondônia in the south to Acre in the southwest of the basin.…”

Black and brown carbon over central Amazonia: long-term aerosol measurements at the ATTO site

“…The SP2 uses a highintensity Nd:YAG laser beam (1 MW cm −2 , λ = 1064 nm) to irradiate aerosol particles that are provided by an air jet at 90 • , with a flow rate of 0.12 L min −1 . All particles scatter the light from the laser beam and some of them, which are able to absorb radiation at the given wavelength (e.g., rBC), will incandesce and vaporize at high temperatures (Moteki and Kondo, 2008;Stephens et al, 2003). Four avalanche photo-diode (APD) detectors are installed in the instrument to measure (a) scattering, (b) broadband incandescence (350-800 nm), (c) narrowband incandescence (630-880 nm), and (d) scattering with a split detector.…”

Influx of African biomass burning aerosol during the Amazonian dry season through layered transatlantic transport of black carbon-rich smoke

“…The large-scale trade wind circulation over the tropical Atlantic region is defined by the position of the 470 intertropical convergence zone (ITCZ), which oscillates north-southwards over the year. The ITCZ movement is a main factor of the pronounced aerosol seasonality in the central Amazon Martin et al, 2010;Moran-Zuloaga et al, 2018;Pöhlker et al, 2019Pöhlker et al, , 2018Saturno et al, 2018b). Based on BTs, which reflect the large-scale trade wind circulation patterns, we investigated the origin and age of the UPL up to 10 days prior to its observation.…”

“…Various observational results underline that the long-range transport (LRT) of (long-lived) 110 species from Africa plays a major role for the Amazonian atmospheric composition. For instance, the plume-wise LRT of African dust and smoke during the Amazonian wet season has been well documented (Talbot et al, 1990;Swap et al, 1992;Ansmann et al, 2009;Baars et al, 2011;Wang et al, 2016;Moran-Zuloaga et al, 2018). Moreover, the arrival of a plume of remarkably sulfur-rich aerosol particles in the central Amazon in September 2014 has been traced back to the LRT of volcanogenic emissions from east-115 ern Congo (Saturno et al, 2018a).…”