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Urbanisation increases aerosol on Amazonian rainforests with negative consequences

A new study warns about the link between urbanization and the climate of the Amazon rainforest, considered as the lung of the planet. The study, published in Nature Communications, shows that urban pollution from Manaus, the populous city in the state of Amazonas, Brazil, causes a sharp increase in aerosol formation in the nearby rainforest and this increase would be higher than previously estimated.

The increase in aerosols, estimated at 60% by scientists of the Fundação de Amparo à Pesquisa do Estado de São Paulo, causes more clouds and rain and changes the levels of photosynthesis of plants. According to the researchers, these results “will make meteorological models more accurate and refine regional and global climate modeling.”

The aerosol is composed of countless tiny solid particles or liquid droplets suspended in the air. It is also naturally present because it is produced by forests (for example, it comes from the formation of pollen, ash or carbon particles from fires), but the “artificial” one is formed by the chemical reactions of the “natural” aerosol with volatile organic compounds (VOCs) or gaseous ones produced by human activities, primarily by the combustion of fossil fuels.

These reactions have a significant effect on the environment: a greater quantity of aerosols in the air means greater absorption of solar radiation and, among other things, a greater quantity of rain.

As Henrique Barbosa, one of the authors of the article, points out, “when levels of sulfur and nitrogen compounds from urban pollution accumulate in the atmosphere, biogenic vapors in the forest oxidize much more rapidly, forming many new aerosols – much more than they would if the process were purely natural.”