Category: Publications

New Publication: Aerosol composition and cloud dynamics

The properties and dynamics of clouds are strongly dependent on the types and amounts of aerosol particles in the atmosphere. They act as so-called cloud condensation nuclei as they initiate the formation of cloud droplets. Therefore, it is crucial to gain a sound understanding of the emission patterns, properties, and seasonal variability of aerosols in relation to the cloud life cycles. In order to achieve this goal, our aerosol group was able to record such data at ATTO. Over the course of a full year, they continuously measured aerosols and their properties in the atmosphere at the 80 m tower. Thus, they created the first such long-term record in the Amazon.

The results of the study were published in two parts; the first was released in 2016 and focused on the parameterization of the aerosol properties. This provides the scientific community with input for models to better predict atmospheric cycling and future climate. Because clouds are such a vital and highly complex component of the climate system, it is important for models to get them “right” in order to make reliable predictions.

In this newly published second part of the study, the authors focused on defining the most distinctive states of aerosol composition and associated cloud formation conditions in the ATTO region. They distinguished between four separate regimes that alternate throughout the year. For example, they discovered that the atmosphere is practically pristine during certain episodes in the wet season (from March to May), with no detectable influence of pollution. However, throughout the rest of the year, “foreign” aerosols arrive at the site in varying amounts. They include natural aerosol particles such as Saharan dust, but also pollutants such as smoke from biomass burning (wildfires and much more often deforestation fires) within the Amazon or even in Africa.

Part 1 and Part 2 of this study were published by first author Mira Pöhlker in Atmospheric Chemistry and Physics (ACP) Issues 16 and 18. They are available Open Access and thus freely available for everyone.

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New publication: African volcanic emissions reach Amazon

The long-range transport of particles, such as sulfate, across the Atlantic to the Amazon rainforest can help to better understand atmospheric cycling. A good opportunity for that arose in 2014. Some of the most active volcanoes worldwide, the Nyamuragira and Mount Nyiragongo volcanoes in Congo in Central Africa, erupted violently.

Satelite image of the eruption plumes of Nyamuragira and Nyiragongo volcanoes in Congo. © NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey (USGS)

During this eruption, they emitted a lot of sulfur dioxide (SO2) into the atmosphere. This gas that is later converted to sulfate particles by oxidation. Usually, these particles are diluted in the atmosphere as they mix with other particles. It thus becomes difficult to distinguish them far away from their source. However, the emissions of 2014 were so strong that the sulfate particles originating from the volcanic gas were observed over the Amazon rainforest by ground-based instruments at our ATTO site (specifically at the 80 m tall triangular mast) and by aircraft measurements (during the ACRIDICON-CHUVA campaign). This observation is now being used by ATTO scientists as a case study to understand how gas and particle emissions from Africa are transported over the Atlantic Ocean and reach the Amazon Basin.

For scale, the volcanoes in Congo are almost 10,000 km away from ATTO, and it took the particles around 2 weeks to bridge that distance!

Map of sulfur dioxide plumes emitted from the Nyamuragira volcano and the modeled trajectories of the air masses moving across the Atlantic towards the Amazon. © Saturno et al. (2018)

The full study was just published in Atmospheric Chemistry and Physics (ACP) Issue 18 by first author Jorge Saturno. It is available Open Access and thus freely available for everyone.

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New publication on aerosols in the Amazon

Scientists from our Aerosol group published a new “Long-term study on coarse mode aerosols in the Amazon rainforest with the frequent intrusion of Saharan dust plumes”.

They analyzed the coarse fraction of aerosols (those that are at least 1 micrometer in diameter) every 5 minutes for over 3 years and were surprised to find that over this period the size and abundance of these “large” aerosol particles remained fairly constant. In contrast, the smaller aerosols are heavily influenced by the seasonal occurrence of smoke from fires. This coarse fraction, however, is mainly comprised of aerosols derived from the rainforest itself (such as pollen). That pattern only changes during the wet season (December through April), when Saharan dust, sea salt particles from the Atlantic and smoke from fires in Africa episodically make their way to the Amazon. Especially in February and March, pulses of African aerosols become so frequent they are the norm rather than the exception. Our scientists then used these data to estimate how much dust is deposited in the ATTO region each year: 5-10 kg per hectare, or 0.5-1 g per square meter.

You can read the full study by lead author Daniel Moran-Zuloaga in Atmospheric Chemistry and Physics Issue 18. It is published Open Access and thus freely available online. The data set is also available for further analysis (see publication for details)!

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