An international research team has shown that urban pollution from Manaus, Amazonas, Brazil massively increases the formation of secondary organic aerosols over the Amazon rainforest.
The study, which is published in Nature Communications, showed that urban pollution increases the formation of secondary organic aerosols across the Amazon rainforest by an average of 200 percent, with spikes of up to 400 percent.
The team said: “For the first time, we were able to model and predict aerosol levels in the Amazon. Climate models based on the Northern Hemisphere are known not to apply to the Amazon Rainforest. We realized that the numbers derived from other studies didn’t add up. The results of this new study will therefore make meteorological models more accurate and refine regional as well as global climate modelling.”
What are secondary organic aerosols?
An aerosol is fine solid particles or liquid drops suspended in the air. Primary aerosols are produced naturally by forests and include particles such as dust, pollen, ash and carbon, from wildfires, for example.
Secondary organic aerosols are formed by the chemical reactions of these primary aerosols and gaseous precursors or volatile organic compounds (VOCs) which are emitted by forests and human activities, such as the urban pollution caused by burning fossil fuels. The aerosols play a role in the atmosphere’s solar radiation absorption to form rainclouds.
The co-author and professor at IF-USP, Henrique Barbosa, commented: “When levels of sulfur and nitrogen compounds from urban pollution build up in the atmosphere, biogenic vapours in the forest are oxidized much more rapidly, forming many new aerosols – far more than would be the case if the process were purely natural.”
Barbosa added: “The Amazon region is mostly quite pristine and free of pollution. A tiny increase in nitrogen compounds, for example, triggers a huge rise in forest aerosol levels. The disturbance caused by anthropogenic emissions is very violent and affects the climate of the region, the hydrological system and the global climate.”