Highly Oxygenated Molecules in the Amazon, Beijing and elsewhere

In a new study, Dr. Haijie Tong and co-authors studied a subset of PM2.5, the so-called highly oxygenated molecules (HOMs) and its relationship with radical yield and aerosol oxidative potential. They analyzed fine particulate matter in the air in multiple locations. This including the highly polluted megacity Bejing and in the pristine rainforest at ATTO. They wanted to get insights into the chemical characteristic and evolutions of these HOM particles. In particular, they wanted to find out more about the potential of HOMs to form free radicals. These are highly reactive species with unpaired electrons.

New Publication: Comparing air pollution in Manaus and at ATTO by identifying aerosols

You have probably heard a lot about air pollution recently, be it because of the massive wildfires in California, smog in India or the diesel emission scandal in Germany. So let’s look into air pollution in the Amazon. Most air pollutants are actually aerosols. Identifying these aerosols and their chemical composition can help us understand where they come from and to what extent certain regions are affected by air pollutions. That is exactly what Li Wu and co-authors did in their new study in the Amazon rainforest.

They collected and analyzed aerosols in two locations: the city of Manaus, a large urban area in Brazil, and the ATTO site in the heart of the forest. The samples were collected during the wet season when ATTO is mainly influenced by air masses from the Atlantic and is located upwind from Manaus. And indeed they found that at ATTO the aerosols are mostly of organic origin, emitted by the forest itself. Additionally, they could identify mineral dust and sea-salt particles. In contrast, they frequently found soot, fly ash and particles containing heavy metals in the samples in Manaus. These are most likely produced by human activities. The good news is that such anthropogenic particles are still largely absent from the atmosphere over the rainforest, showing us that pristine wilderness regions do still exist. That is, at least during the wet season when the winds blow in the “right” direction.

The scientists published the study in Atmospheric Chemistry and Physics (ACP) and is available Open Access here.

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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 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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