To measure the impact of pollution, aircraft will fly 200 hours over the Amazon

Operations are designed to study the impact of the pollution plume emitted by the Manaus metropolitan region on such things as atmospheric chemistry and cloud formation.

By Karina Toledo, in Washington, DC

Agência FAPESP – In order to study what happens to the pollution plume emitted by the metropolitan region of Manaus (AM) – discovering where the particles go, how they interact with compounds emitted by the tropical rainforest, and how they affect cloud properties in the region –, two research aircraft equipped with state-of-the-art instruments will fly nearly 200 hours over the Amazon during 2014.

Two intensive operational periods of data collection have already been conducted under the scope of the scientific initiative Green Ocean Amazon (GOAmazon): the first during the wet season from February to March, and the second during the dry season from September to October.

Some preliminary results were presented October 28-29, 2014 in Washington, DC during the symposium FAPESP-U.S. Collaborative Research on the Amazon.

“More than 50 researchers are studying the effects of pollution and anthropogenic activities on aspects such as atmospheric chemistry, cloud microphysics and ecosystem function. The ultimate goal of GOAmazon is to estimate future changes in the radiative balance, energy distributions, regional climate, and feedbacks to global climate,” explained Scot T. Martin, a researcher from Harvard University.

The GOAmazon initiative is funded by the U.S. Department of Energy (DOE), FAPESP, and the Amazonas Research Foundation (FEPEAM) among other partners (read more about it at: http://agencia.fapesp.br/18803).

According to Martin, the city of Manaus and its surrounding area constitutes a giant open-air laboratory for this type of investigation. This is because the Amazonas capital, which has several thermoelectric plants, nearly 2 million inhabitants and 600,000 automobiles, is surrounded by 2,000 kilometers (km) of pristine tropical rainforest. During the wet season, the particulate load in the region is as low as that of pre-industrial times.

The first air operation, conducted during the wet season and financed by DOE, included deployment of the U.S. Gulfstream-1 aircraft (G-1), owned by Pacific Northwest Laboratory (PNNL).

The second operation, which took place from September to October, included, in addition to the G-1, the German aircraft known as HALO (High Altitude and Long Range Research Aircraft), capable of flying at altitudes of up to 15,000 km, with a flight range of seven hours.

HALO is managed by a research consortium made up of the German Center for Aeronautics and Space Research (DLR), the Max Planck Institute (MPI) and the German Research Foundation (DFG). Its participation in GOAmazon was made possible through the project Acridicon-Chuva (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems), led by Luiz Augusto Toledo Machado from the National Institute for Space Research (INPE).

Differences in the clouds

The two aircraft left from the Manaus airport and accompanied the pollution plume as carried by the wind. The flight plan was made to allow the collection of data from both inside and outside the plume for purposes of data comparison.

As Jian Wang, a researcher from the DOE’s Brookhaven National Laboratory explained, the flights measured concentrations of trace gases such as nitric oxide, nitrogen dioxide, ozone, carbon dioxide, methane and volatile organic compounds such as isoprene and terpene.

They also measured the properties of aerosols, such as chemical composition, concentration per cubic centimeter (cm³), particle size, and optical properties (solar radiation absorption or reflection). In addition, they measured cloud properties, such as droplet size, total water content and its percentage as liquid water and ice.

“During the wet season, we could see that the plume is well-defined. The number of solid particles inside the pollution plume is 100 times greater compared to those outside the plume. There are 300 particles per cm³ outside the plume and 30,000 inside it. This means that the cloud that is going to form in each case is very different,” Martin explained.

The Harvard researcher explained that the aerosol particles function as water vapor condensation nuclei present in the atmosphere, enabling the formation of droplets.

“There is a fixed amount of water that, in the case of the plume, will be divided into a much larger number of nuclei. Therefore, the droplets that form are smaller and precipitation becomes more difficult,” Martin explained.

According to the researcher, the chemical composition of the particles is also very different. Inside the plume, the number of sulfates and nitrates is larger, which could have an impact on public health and on cloud formation.

“These sulfate and nitrate particles attract more water than organic particles and this also alters cloud development,” he said.

Investigating the processes of precipitation

In his presentation, Machado showed data from the air measurements taken by HALO aircraft. Unlike what was noted with the G-1 during the wet season, the researcher explained, the Manaus plume during the dry season is less defined because it mixes with emissions from biomass burning.

“The data are still being processed so we have only some of the quick analyses conducted during the operation to be sure that the instruments were working properly and to help plan the flights. But we can already see that the potential from this operation is enormous,” Machado said.

According to the INPE researcher, the German aircraft is equipped with state-of-the-art instrumentation tested for the first time in Manaus. The operation cost nearly €4 million. The aircraft’s value is estimated at €90 million.

The objectives of the project led by Machado include understanding the interaction between aerosols and precipitation in polluted and clean conditions, studying the vertical structure of atmospheric chemistry, and understanding the differences between clouds in forested and deforested areas.

Some of the flights conducted during the dry season were made using two aircraft that followed the same trajectory at different altitudes, measuring properties of cloud microphysics to enable comparisons, explained Machado.

According to the INPE researcher, this would not have been possible with just one aircraft flying at different altitudes at different times because the life of these clouds is short, lasting only about 20 minutes.

“Something that we already knew, but that was clearly confirmed during these operations, is that polluted regions present high concentrations of small droplets, and clean regions have low concentrations of large droplets. In the case of clean clouds, this droplet concentration decreases from the bottom to the top of the cloud, while in the polluted cloud it is more homogenous,” he explained.

In an interview with Agência FAPESP, Paulo Artaxo, professor at the Physics Institute of the University of São Paulo (IF-USP), and one of the creators of GOAmazon along with Martin, said that the presence of solid nitrate particles inside what is known as deep convective clouds, that reach as high as 18 km, was something that surprised researchers.

“Nitrate is a highly soluble compound. The big question is: how can it be present in aerosol form and not adsorbed by the water in the clouds? We still do not know the mechanisms that govern the formation of these particles inside the deep convective clouds, but this will be the subject of intense study over the coming year,” Artaxo said.

One of the hypotheses, added the USP researcher, is that nitrate is related to a phenomenon known as cloud invigoration, or reinforcement of cloud structures, seen in tropical regions all over the world.

“In pollution-free conditions, the clouds in the Amazon region present a maximum height of 3-4 km. But in the presence of large quantities of aerosol particles, the clouds acquire unusual growth intensity, which alters the entire balance of solar radiation, the hydrological cycle and the thermodynamic properties of the atmosphere,” Artaxo said.

Scientists are beginning to analyze the data collected by the aircraft and will add it to measurements being carried out at the various ground-based research sites of the GOAmazon project, scheduled to be in operation through December 2015.