The effect of atmospheric aerosol particles and clouds on net ecosystem exchange in the Amazon

Abstract

Abstract. Carbon cycling in the Amazon is closely linked to atmospheric processes and climate in the region as a consequence of the strong coupling between the atmosphere and biosphere. This work examines the effects of changes in net radiation due to atmospheric aerosol particles and clouds on the net ecosystem exchange (NEE) of CO 2 in the Amazon region. Some of the major environmental factors affecting the photosynthetic activity of plants, such as air temperature and relative humidity, were also examined. An algorithm for clear-sky irradiance was developed and used to determine the relative irradiance, f , which quantifies the percentage of solar radiation absorbed and scattered due to atmospheric aerosol particles and clouds. Aerosol optical depth (AOD) was calculated from irradiances measured with the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor, onboard the Terra and Aqua satellites, and was validated with ground-based AOD measurements from AERONET (Aerosol Robotic Network) sun photometers. Carbon fluxes were measured using eddy covariance technique at the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) flux towers. Two sites were studied: the Jaru Biological Reserve (RBJ), located in Rondonia, and the Cuieiras Biological Reserve at the K34 LBA tower (located in a preserved region in the central Amazon). Analysis was performed continuously from 1999 to 2009 at K34 and from 1999 to 2002 at RBJ, and includes wet, dry and transition seasons. In the Jaru Biological Reserve, a 29 % increase in carbon uptake (NEE) was observed when the AOD ranged from 0.10 to 1.5 at 550 nm. In the Cuieiras Biological Reserve, the aerosol effect on NEE was smaller, accounting for an approximate 20 % increase in NEE. High aerosol loading (AOD above 3 at 550 nm) or high cloud cover leads to reductions in solar flux and strong decreases in photosynthesis up to the point where NEE approaches zero. The observed increase in NEE is attributed to an enhancement (∼ 50 %) in the diffuse fraction of photosynthetic active radiation (PAR). The enhancement in diffuse PAR can be done through increases in aerosols and/or clouds. In the present study, it was not possible to separate these two components. Significant changes in air temperature and relative humidity resulting from changes in solar radiation fluxes under high aerosol loading were also observed at both sites. Considering the long-range transport of aerosols in the Amazon, the observed changes in NEE for these two sites may occur over large areas in the Amazon, significantly altering the carbon balance in the largest rainforest in the world.

Particulate matter air pollution may offset ozone damage to global crop production

“…1. The enhancing effect of aerosol diffuse light on plant productivity, related by AOD, has also been observed by Cirino et al (2014) and Strada et al (2015). However, these relationships are not easily translatable to DF and RUE values, and it is difficult to remove the impacts of clouds from such observations.…”

Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region

“…For the same sites, we also present in Table 3 the NEE from the DIR+DIF experiment for September 2010. For example, measurements taken at the Jaru Reserve (the same site used by Grace et al, 1995) and at a grass plot (Fazenda Nossa Senhora ( (Von Randow et al, 2004) and Cuieras (Cirino et al, 2014) reserves, respectively, due to differences in the physiology of the forest and possibly the topography in the two sites. There were even more significant differences between the maximum values of carbon uptake between the two sites, which were around −17.5 and −20 µmolC m −2 s −1 under biomass burning and cloudy sky conditions at the Jaru and Cuieras reserves, respectively, and −18 µmolC m −2 s −1 under clean skies in both sites.…”

The status and challenge of global fire modelling

“…Through their impacts on ozone, and as a source of CO and volatile organic compounds, fires also affect the atmospheric abundance of the OH radical, which determines the atmospheric lifetime of the greenhouse gas methane (Bousquet et al, 2006). In addition, ozone produced from fires is directly harmful to plants, reducing photosynthesis (Pacifico et al, 2015) and fire-emitted aerosol can shift the balance between diffuse and direct radiation (Mercado et al, 2009;Cirino et al, 2014). Deposition of fire-produced N (Chen et al, 2010) and P aerosols can enhance productivity in nutrient-limited ecosystems.…”