Abstract
The 2020 biomass burning season in Brazil was marked by an unprecedented amount of fire counts across the Pantanal biome, which led to high levels of air pollution within the biome and downwind areas. Large amount of fire counts was also detected in the Amazon Forest during 2020 compared with the recent years. However, the contribution of Pantanal fire emissions to the regional smoke plume was speculated to rival the contribution of fire emissions from Amazon. Aiming to contextualise the 2020 biomass burning season focusing on the unprecedented role of Pantanal, the present study's main goal is to analyse the recent biomass burning seasons in Brazil looking at the fire counts, the regional smoke plume and its impact on surface solar radiation (SSR). The focus is on the biomes most affected by the recent biomass burning events, Amazon forest, Cerrado and especially Pantanal. To characterise the regional smoke plume we analysed aerosol optical depth, single scattering albedo and its impact on the solar radiation reaching the surface. The influence of interannual variability of the wind at 850 hPa on the transport of the regional smoke plumes was also explored. In 2020, the regional smoke plume covered an area well above 6 million km2, the largest area in the last six years, but equivalent to the observed in a more remote past, as in 2007 and 2010. However, from the point of view of Pantanal, 2020 was an unprecedented year, not due to the amount of smoke over the biome, but regarding the biome contribution to the regional smoke plume. The number of fire counts was 3.4 times higher than the mean value considering the period from 2003 to 2020. The entire biome was continuously covered by a thick smoke layer from September to October, which resulted in a monthly mean deficit of surface solar radiation up to 300 Wm−2. Additionally, the 2020 regional smoke plume presented higher optical absorption when compared with the recent years plumes, which could be related to the Pantanal larger fire emission. However, current knowledge on optical and radiative properties of smoke aerosols from Pantanal is limited compared to the one resultant from Amazon and Cerrado fire emissions, which prevent a definitive conclusion.
Highlights
In South America, the regional biomass burning smoke plume is the most important signature of anthropogenic activities from the point of view of injection of pollutants into the atmosphere at continental scale during the dry season (Prins and Menzel, 1992, Artaxo et al, 1998, Freitas et al, 2004, Longo et al, 2007)
To what extent the 2020 biomass burning season and the produced Regional Smoke Plume (RSP) surpassed the previous recent years? Was there an unprecedented signature of Pantanal biome biomass burning season in the 2020 RSP? These are some of the questions that the present analysis addressed in order to contextualise the 2020 biomass 45 burning season and explore the role of Pantanal biome regarding the RSP dimension, loading and impact on surface solar radiation
An interesting aspect to point out is that, for the Cerrado biome, the years of 2017 and 2020 presented the highest amount of solar radiation at the surface, fire counts were among the highest observed values for these particular years. This multiyear analysis across the 3 biomes definitely revealed that Pantanal signature is the main highlight aspect in the context of 2020 regional smoke plume, since the number of fire counts 145 and aerosol optical depth (AOD) dramatically increased in this biome, compared to the previous years, especially in September and October
Summary
In South America, the regional biomass burning smoke plume is the most important signature of anthropogenic activities from the point of view of injection of pollutants into the atmosphere at continental scale during the dry season (Prins and Menzel, 1992, Artaxo et al, 1998, Freitas et al, 2004, Longo et al, 2007). The article is organised as follow: Section 2 presents a brief description of the study region, a summary of the data used and the methods adopted; Section 3 presents the results divided in 3 sub-sections: Sub-section 3.1 analyzes the intraseasonal and interannual variability of fire counts, aerosol optical depth (AOD) at 550 nm, downward solar radiation at the surface for the three main biomes Amazon tropical rainforest, Cerrado ecosystem, and Pantanal, for the last six years. Being typically the 105 peak of the biomass burning season in Brazil, September was selected to carry on a more comprehensive geographical and interannual analysis of the features and the impact of the regional smoke plume from the last six years, including the analysis of the downward solar radiation at the surface. Extending further in the past (2003-2020), an interannual analysis of total fire counts, mean AOD at 550 nm and downward solar radiation at the surface over Pantanal was carried out focusing on the biomass burning season months, the same months as before
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