A new background method for greenhouse gases flux calculation based in back-trajectories over the Amazon
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The large amount of carbon stored in trees and soils of the Amazon rain forest is under
pressure from land use as well as climate change. Therefore, various efforts to monitor greenhouse
gas exchange between the Amazon forest and the atmosphere are now ongoing, including regular
vertical profile (surface to 4.5 km) greenhouse gas measurements across the Amazon. These profile
measurements can be used to calculate fluxes to and from the rain forest to the atmosphere at
large spatial scales by considering the enhancement or depletion relative to the mole fraction of
air entering the Amazon basin from the Atlantic, providing an important diagnostic of the state,
changes and sensitivities of the forests. Previous studies have estimated greenhouse gas mole fractions
of incoming air (‘background’) as a weighted mean of mole fractions measured at two background
sites, Barbados (Northern Hemisphere) and Ascension (Southern hemisphere) in the Tropical Atlantic,
where the weights were based on sulphur hexafluoride (SF6) measured locally (in the Amazon vertical
profiles) and at the two background sites. However, this method requires the accuracy and precision
of SF6 measurements to be significantly better than 0.1 parts per trillion (picomole mole1), which is
near the limit for the best SF6 measurements and assumes that there are no SF6 sources in the Amazon
basin. We therefore present here an alternative method. Instead of using SF6, we use the geographical
position of each air-mass back-trajectory when it intersects the limit connecting these two sites to
estimate contributions from Barbados versus Ascension. We furthermore extend the approach to
include an observation site further south, Cape Point, South Africa. We evaluate our method using
CO2 vertical profile measurements at a coastal site in Brazil comparing with values obtained using
this method where we find a high correlation (r2 = 0.77). Similarly, we obtain good agreement for CO2
background when comparing our results with those based on SF6, for the period 2010–2011 when
the SF6 measurements had excellent precision and accuracy. We also found high correspondence
between the methods for background values of CO, N2O and CH4. Finally, flux estimates based
on our new method agree well with the CO2 flux estimates for 2010 and 2011 estimated using the SF6-based method. Together, our findings suggest that our trajectory-based method is a robust new
way to derive background air concentrations for the purpose of greenhouse gas flux estimation using
vertical profile data.
Como referenciar
DOMINGUES, LUCAS G.; GATTI, LUCIANA V.; AQUINO, AFONSO; SÁNCHEZ, ALBER; CORREIA, CAIO; GLOOR, MANUEL; PETERS, WOUTER; MILLER, JOHN; TURNBULL, JOCELYN; SANTANA, RICARDO; MARANI, LUCIANO; CÂMARA, GILBERTO; NEVES, RAIANE; CRISPIM, STÉPHANE. A new background method for greenhouse gases flux calculation based in back-trajectories over the Amazon. Atmosphere, v. 11, n. 7, p. 1-8, 2020. DOI: 10.3390/atmos11070734. Disponível em: http://repositorio.ipen.br/handle/123456789/31464. Acesso em: 30 Dec 2025.
Esta referência é gerada automaticamente de acordo com as normas do estilo IPEN/SP (ABNT NBR 6023) e recomenda-se uma verificação final e ajustes caso necessário.