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The inhabitants of the municipality of São Francisco de Assis, in the center of Rio Grande do Sul, reported the occurrence of black rain in the town during the weekend. Rainwater accumulated in buckets and other objects turned black in color. The black rain images were featured by MetSul meteorologist Estael Sias at SBT Rio Grande First Edition as part of Our Climate.
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The rain occurred at a time when there was a large amount of smoke over Rio Grande do Sul, which significantly changed the color of the sky on Friday in many cities of the state of Rio Grande do Sul to offer the perspective that the weather was cloudy. or cloudy even though the satellites showed no clouds. Due to a jet stream (wind), at about 1,500 meters of altitude, the smoke from the fires in the Amazon region, in the Pantanal and in neighboring countries was transported to Rio Grande do Sul.
With the weekend’s rainfall, associated with a frontal system over the State, the particulate material precipitated over Rio Grande do Sul. The rain has the effect of “cleaning” the atmosphere, which explains the quality of the air in a polluted city improves much after record rainfall. The particulate matter suspended in the atmosphere, and in the case of burning is soot or the so-called black carbon (soot) from the burning of biomass, ended up precipitating together with the rain.
In recent days, MetSul Meteorologia had been receiving reports from Porto Alegre and other cities with dark rainfall. An employee of a swimming pool treatment company had told us about the change in the color of the water he observed. This meant that in the last week we collected rainwater in a simple domestic experiment, in a clean object and placed in a point free of any contamination, to check if there was any contamination and the result was small black dots mixed in the rainwater .
MetSul
It is not a new fact, however, the occurrence of black rain, despite indicating a situation of great presence of aerosols in the atmosphere and reflecting a serious environmental situation. Last year, the cities of Rio Grande do Sul and São Paulo registered black rains. In the case of São Paulo, the university’s chemical analyzes showed that black rain was the result of fires.
In 2010, another year of many fires, MetSul Meteorologia recorded in photographs that many cars parked in Porto Alegre had soot on their surfaces after a rainy day with smoke in the atmosphere.
MetSul
MetSul anticipates that the advance of tropical heat will maintain a large flow of smoke to southern Brazil and São Paulo, reaching the coast of Rio de Janeiro for the rest of the week.
As expected the rain associated with the advance of warm air from the North between this Tuesday and Wednesday, but, especially on Wednesday, with the presence of a lot of smoke in the atmosphere, the precipitation of black carbon can occur again.
Black carbon, environment and climate
Studies show that the presence of soot from burning in the atmosphere can interfere with the appearance of rain, melt glaciers and impact global warming. A team led by Newton de Magalhães Neto, from the State University of Rio de Janeiro (UERJ), modeled the possible effect that biomass burning in the Amazon basin could have on the Bolivian Zongo glacier, using data collected between 2000 and 2016 about fire episodes. , movements of smoke columns, precipitation and melting of glaciers.
The researchers found that aerosols from biomass burning, such as black carbon, can be carried by the wind to tropical Andean glaciers. There, they settle in the snow and have the potential to increase glacier melt, because the snow is darkened by black carbon or dust particles and therefore reflects less light (less albedo).
One of the main components of soot, black carbon is the component of particulate material that absorbs solar energy. The amount of energy stored in the atmosphere is measured in watts per square meter of the Earth’s surface and a 2013 study estimated the effect of black carbon at 1.1 watts per square meter per year, second only to carbon dioxide. which is responsible for 1.56 watts per square meter.
In other words, black carbon is the second largest contributor to climate change after CO2, the study noted. Unlike CO2, which can remain in the atmosphere for hundreds or thousands of years, black carbon, as a particle, remains in the atmosphere for only days or weeks before returning to earth in rain or snow.
Black carbon, like all particles in the atmosphere, also affects the reflectivity, stability, and duration of clouds and alters precipitation. Depending on the amount of soot in the air and the layer of the atmosphere in which the black carbon is found, it has different effects. If it absorbs heat at the level where clouds form, they tend to evaporate. When it is above the lower stratocumulus clouds that block the sun, the carbon stabilizes them and thus has a cooling effect.
Since black carbon interacts with other components of particulate matter, such as sulfates and nitrates that reflect sunlight and cool the atmosphere, scientists don’t know exactly how much black carbon can influence over time, but Brazilian studies show that the smoke interferes in the rain formation process in the Amazon with a reducing effect.
Among the studies on soot from burning, one showed that incomplete burning of wood from trees results in the production of black carbon that reaches the waters of the Amazon River in the form of carbon and soot and ends up being transported to the Atlantic Ocean as dissolved organic carbon.
An international group of researchers quantified and characterized for the first time the black carbon that flows through the Amazon River in a study published in the journal Nature Communications, which showed that most of this material transferred to the ocean is “young”, suggesting that it was produced by burning in the forest.
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