Os efeitos dos aerossóis e nuvens sobre o fluxo de CO2 na Amazônia Central e em Rondônia

Abstract

This study examined the effects of changes in net radiation due to aerosols and clouds on the net ecosystem exchange (NEE) in primary forest ecosystems in Rondônia and central Amazonia. Nevertheless it is also evaluated some of the major environmental factors affecting the photosynthetic activity of plants, such as air temperature and relative humidity. A algorithm of clear-sky irradiance was developed and used to determine the relative irradiance (f) which was used to quantify the percentage of solar radiation absorbed and scattered due to aerosols and clouds. The aerosol optical Depth (AOD) measurements were performed with MODIS (onboard TERRA and AQUA satellites), previously validated with AOD measurements from the NASA/AERONET network of sun photometers. The carbon fluxes were measured through eddy-correlation techniques. Two sites were studied: the Biological Reserve of Jaru (located in the region of the arc of deforestation in Rondônia) and the Cuieiras Biological Reserve (located in a preserved region in central Amazonia). In the Jaru Biological Reserve, a 29% increase in carbon uptake (NEE) when the AOD ranged from 0.10 to 1.5 was observed. In the Cuieiras Biological Reserve, this effect is smaller, being ~ 26%. For higher aerosol loading in the atmosphere, with stronger reductions of solar radiation, the photosynthetic process is almost shut down, with NEE values close to zero for very high AOD or high cloud cover. The increase of 29 and 26% of NEE, is attributed to an increase of the diffusion fraction of the solar radiation. Major changes in air temperature and relative humidity explained by the interaction of solar radiation with high aerosol load were also observed at both sites. Considering the long range transport of aerosols, the change in carbon flux may occurs in large areas in Amazonia, changing the potential for forest ecosystems to absorb significant amounts of atmospheric CO2.