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Search Results: 1 - 10 of 200651 matches for " P. Artaxo "
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Spectral light absorption by ambient aerosols influenced by biomass burning in the Amazon Basin. I: Comparison and field calibration of absorption measurement techniques
O. Schmid,P. Artaxo,W. P. Arnott,D. Chand
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2006,
Abstract: Spectral aerosol light absorption is an important parameter for the assessment of the radiation budget of the atmosphere. Although on-line measurement techniques for aerosol light absorption, such as the Aethalometer and the Particle Soot Absorption Photometer (PSAP), have been available for two decades, they are limited in accuracy and spectral resolution because of the need to deposit the aerosol on a filter substrate before measurement. Recently, a 7-wavelength (λ) Aethalometer became commercially available, which covers the visible (VIS) to near-infrared (NIR) spectral range (λ=450–950 nm), and laboratory calibration studies improved the degree of confidence in these measurement techniques. However, the applicability of the laboratory calibration factors to ambient conditions has not been investigated thoroughly yet. As part of the LBA-SMOCC (Large scale Biosphere atmosphere experiment in Amazonia – SMOke aerosols, Clouds, rainfall and Climate) campaign from September to November 2002 in the Amazon basin we performed an extensive field calibration of a 1-λ PSAP and a 7-λ Aethalometer utilizing a photoacoustic spectrometer (PAS, 532 nm) as reference device. Especially during the dry period of the campaign, the aerosol population was dominated by pyrogenic emissions. The most pronounced artifact of integrating-plate type attenuation techniques (e.g. Aethalometer, PSAP) is due to multiple scattering effects within the filter matrix. For the PSAP, we essentially confirmed the laboratory calibration factor by Bond et al. (1999). On the other hand, for the Aethalometer we found a multiple scattering enhancement of 5.23 (or 4.55, if corrected for aerosol scattering), which is significantly larger than the factors previously reported (~2) for laboratory calibrations. While the exact reason for this discrepancy is unknown, the available data from the present and previous studies suggest aerosol mixing (internal versus external) as a likely cause. For Amazonian aerosol, we found no absorption enhancement due to hygroscopic particle growth in the relative humidity (RH) range between 40% and 80%. However, a substantial bias in PSAP sensitivity that correlated with both RH and temperature (T) was observed for 20%
Spatial variability of the direct radiative forcing of biomass burning aerosols and the effects of land use change in Amazonia
E. T. Sena, P. Artaxo,A. L. Correia
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2013,
Abstract: This paper addresses the Amazonian shortwave radiative budget over cloud-free conditions after considering three aspects of deforestation: (i) the emission of aerosols from biomass burning due to forest fires; (ii) changes in surface albedo after deforestation; and (iii) modifications in the column water vapour amount over deforested areas. Simultaneous Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging SpectroRadiometer (MODIS) were analysed during the peak of the biomass burning seasons (August and September) from 2000 to 2009. A discrete-ordinate radiative transfer (DISORT) code was used to extend instantaneous remote sensing radiative forcing assessments into 24-h averages. The mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season for the 10-yr studied period was 5.6 ± 1.7 W m 2. Furthermore, the spatial distribution of the direct radiative forcing of aerosols over Amazonia was obtained for the biomass burning season of each year. It was observed that for high AOD (larger than 1 at 550 nm) the maximum daily direct aerosol radiative forcing at the TOA may be as high as 20 W m 2 locally. The surface reflectance plays a major role in the aerosol direct radiative effect. The study of the effects of biomass burning aerosols over different surface types shows that the direct radiative forcing is systematically more negative over forest than over savannah-like covered areas. Values of 15.7 ± 2.4 W m 2τ550 nm and 9.3 ± 1.7 W m 2τ550 nm were calculated for the mean daily aerosol forcing efficiencies over forest and savannah-like vegetation respectively. The overall mean annual land use change radiative forcing due to deforestation over the state of Rond nia, Brazil, was determined as 7.3 ± 0.9 W m 2. Biomass burning aerosols impact the radiative budget for approximately two months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo-change is approximately 6 times higher than the impact due to aerosol emissions. The influence of atmospheric water vapour content in the radiative budget was also studied using AERONET column water vapour. It was observed that column water vapour is on average smaller by about 0.35 cm (around 10% of the total column water vapour) over deforested areas compared to forested areas. Our results indicate that this drying contributes to an increase in the shortwave radiative forcing, which varies from 0.4 W m 2 to 1.2 W m 2 depending on the column water vapour content before deforestation. The large radiative forcing values presented in this study point out that deforestation could have strong implications in convection, cloud development and the ratio of direct to diffuse radiation, which impacts carbon uptake by the forest.
Aerosol and precipitation chemistry measurements in a remote site in Central Amazonia: the role of biogenic contribution
T. Pauliquevis, L. L. Lara, M. L. Antunes,P. Artaxo
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: In this analysis a 3.5 years data set of aerosol and precipitation chemistry, obtained in a remote site in Central Amazonia (Balbina, (1°55' S, 59°29' W, 174 m a.s.l.), about 200 km north of Manaus) is discussed. Aerosols were sampled using stacked filter units (SFU), which separate fine (d < 2.5 μm) and coarse mode (2.5 μm < d < 10.0 μm) aerosol particles. Filters were analyzed for particulate mass (PM), Equivalent Black Carbon (BCE) and elemental composition by Particle Induced X-Ray Emission (PIXE). Rainwater samples were collected using a wet-only sampler and samples were analyzed for pH and ionic composition, which was determined using ionic chromatography (IC). Natural sources dominated the aerosol mass during the wet season, when it was predominantly of natural biogenic origin mostly in the coarse mode, which comprised up to 81% of PM10. Biogenic aerosol from both primary emissions and secondary organic aerosol dominates the fine mode in the wet season, with very low concentrations (average 2.2 μg m-3). Soil dust was responsible for a minor fraction of the aerosol mass (less than 17%). Sudden increases in the concentration of elements as Al, Ti and Fe were also observed, both in fine and coarse mode (mostly during the April-may months), which we attribute to episodes of Saharan dust transport. During the dry periods, a significant contribution to the fine aerosols loading was observed, due to the large-scale transport of smoke from biomass burning in other portions of the Amazon basin. This contribution is associated with the enhancement of the concentration of S, K, Zn and BCE. Chlorine, which is commonly associated to sea salt and also to biomass burning emissions, presented higher concentration not only during the dry season but also for the April–June months, due to the establishment of more favorable meteorological conditions to the transport of Atlantic air masses to Central Amazonia. The chemical composition of rainwater was similar to those ones observed in other remote sites in tropical forests. The volume-weighted mean (VWM) pH was 4.90. The most important contribution to acidity was from weak organic acids. The organic acidity was predominantly associated with the presence of acetic acid instead of formic acid, which is more often observed in pristine tropical areas. Wet deposition rates for major species did not differ significantly between dry and wet season, except for NH4+, citrate and acetate, which had smaller deposition rates during dry season. While biomass burning emissions were clearly identified in the aerosol component, it did not present a clear signature in rainwater. The biogenic component and the long-range transport of sea salt were observed both in aerosols and rainwater composition. The results shown here indicate that in Central Amazonia it is still possible to observe quite pristine atmospheric conditions, relatively free of anthropogenic influences.
Long term measurements of the elemental composition and optical properties of aerosols in Amazonia
Arana A. A.,Artaxo P.,Rizzo L. V.,Bastos W.
E3S Web of Conferences , 2013, DOI: 10.1051/e3sconf/20130103005
Abstract: Aerosols are being collected and analyzed for trace elements in two sites in Amazonia since January 2008. On eof the site, Manaus is located in a very pristine area in Central Amazonia. The site is nt affected directly by any urban plume for thousands of kilometers. A second site is located in Porto Velho, in a region with heavy land use change and deforestation. Optical properties (light scattering ad absorption) are also being measured in order to study the climatic impact of aerosols. It was observed a clear seasonal pattern for both sites, with higher concentrations in the dry season. But the difference in seasonal concentrations observed for Porto Velho is much larger due to stronger anthropogenic influences. In Manaus during the wet season, very low concentrations of heavy metals, maybe the smallest measured in continental regions are reported. Positive Matrix Factorization (PMF) was used to separate the different aerosol components. In general, for fine and coarse mode and wet and dry season, 3 aerosol components could be observed: 1) Natural biogenic aerosol; 2) biomass burning component; 3) Soil dust both locally and long range transported Sahara dust
Aerosol and precipitation chemistry in a remote site in Central Amazonia: the role of biogenic contribution
T. Pauliquevis,L. L. Lara,M. L. Antunes,P. Artaxo
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: A long-term (2–3 years) measurement of aerosol and precipitation chemistry was carried out in a remote site in Central Amazonia, Balbina, (1°55' S, 59°29' W, 174 m above sea level), about 200 km north of Manaus city. Aerosols were sampled using stacked filter units (SFU), which separate fine (d<2.5 μm) and coarse mode (2.5 μm
Synergetic measurements of aerosols over S o Paulo, Brazil using LIDAR, sunphotometer and satellite data during the dry season
E. Landulfo,A. Papayannis,P. Artaxo,A. D. A. Castanho
Atmospheric Chemistry and Physics Discussions , 2003,
Abstract: A backscattering LIDAR system, the first of this kind in Brazil, has been set-up in a suburban area in the city of S o Paulo (23° 33' S, 46° 44' W) to provide the vertical profile of the aerosol backscatter coefficient at 532 nm up to an altitude of 4–6 km above sea level (a.s.l.). The measurements have been carried out during the second half of the so-called Brazilian dry season, September and October 2001 and during the first half of the dry season in August and September 2002. The LIDAR data are presented and analysed in synergy with aerosol optical thickness (AOT) measurements obtained by a CIMEL sun-tracking photometer in the visible spectral region and with satellite measurements obtained by the MODIS sensor. This synergetic approach has been used, not only to validate the LIDAR data, but also to derive a typical value (45 sr) of the so-called extinction-to-backscatter ratio (LIDAR ratio) during the dry season. The satellite data analysis offers additional information on the spatial distribution of aerosols over Brazil including the determination of aerosol source regions over the country. The LIDAR data were also used to retrieve the Planetary Boundary Layer (PBL) height, aerosol layering and the structure of the lower troposphere over the city of S o Paulo. These first LIDAR measurements over the city of S o Paulo during the dry season showed a significant variability of the AOT in the lower troposphere (0.5–5 km) at 532 nm. It was also found that the aerosol load is maximized in the 1–3 km height region, although up to 3 km thick aerosol layers were also detected in the 2.5–5.5 km region in certain cases. Three-dimensional 96-hours air mass back-trajectory analysis was also performed in selected cases to determine the source regions of aerosols around S o Paulo during the dry season.
The Tropical Forest and Fire Emissions Experiment: overview and airborne fire emission factor measurements
R. J. Yokelson,T. Karl,P. Artaxo,D. R. Blake
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2007,
Abstract: The Tropical Forest and Fire Emissions Experiment (TROFFEE) used laboratory measurements followed by airborne and ground based field campaigns during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. The airborne campaign used an Embraer 110B aircraft outfitted with whole air sampling in canisters, mass-calibrated nephelometry, ozone by UV absorbance, Fourier transform infrared spectroscopy (FTIR), and proton-transfer mass spectrometry (PTR-MS) to measure PM10, O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC). The Brazilian smoke/haze layers extended to 2–3 km altitude, which is much lower than the 5–6 km observed at the same latitude, time of year, and local time in Africa in 2000. Emission factors (EF) were computed for the 19 tropical deforestation fires sampled and they largely compare well to previous work. However, the TROFFEE EF are mostly based on a much larger number of samples than previously available and they also include results for significant emissions not previously reported such as: nitrous acid, acrylonitrile, pyrrole, methylvinylketone, methacrolein, crotonaldehyde, methylethylketone, methylpropanal, "acetol plus methylacetate," furaldehydes, dimethylsulfide, and C1-C4 alkyl nitrates. Thus, we recommend these EF for all tropical deforestation fires. The NMOC emissions were ~80% reactive, oxygenated volatile organic compounds (OVOC). Our EF for PM10 (17.8±4 g/kg) is ~25% higher than previously reported for tropical forest fires and may reflect a trend towards, and sampling of, larger fires than in earlier studies. A large fraction of the total burning for 2004 likely occurred during a two-week period of very low humidity. The combined output of these fires created a massive "mega-plume" >500 km across that we sampled on 8 September. The mega-plume contained high PM10 and 10–50 ppbv of many reactive species such as O3, NH3, NO2, CH3OH, and organic acids. This is an intense and globally important chemical processing environment that is still poorly understood. The mega-plume or "white ocean" of smoke covered a large area in Brazil, Bolivia, and Paraguay for about one month. The smoke was transported >2000 km to the southeast while remaining concentrated enough to cause a 3–4-fold increase in aerosol loading in the S o Paulo area for several days.
The Tropical Forest and fire emissions experiment: overview and airborne fire emission factor measurements
R. J. Yokelson,T. Karl,P. Artaxo,D. R. Blake
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: The Tropical Forest and Fire Emissions Experiment (TROFFEE) used laboratory measurements followed by airborne and ground based field campaigns during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. The airborne campaign used an Embraer 110B aircraft outfitted with whole air sampling in canisters, mass-calibrated nephelometry, ozone by uv absorbance, Fourier transform infrared spectroscopy (FTIR), and proton-transfer mass spectrometry (PTR-MS) to measure PM10, O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC). The Brazilian smoke/haze layers extended to 2–3 km altitude, which is much lower than the 5–6 km observed at the same latitude, time of year, and local time in Africa in 2000. Emission factors (EF) were computed for the 19 tropical deforestation fires sampled and they largely compare well to previous work. However, the TROFFEE EF are mostly based on a much larger number of samples than previously available and they also include results for significant emissions not previously reported such as: nitrous acid, acrylonitrile, pyrrole, methylvinylketone, methacrolein, crotonaldehyde, methylethylketone, methylpropanal, "acetol plus methylacetate," furaldehydes, dimethylsulfide, and C1-C4 alkyl nitrates. Thus, we recommend these EF for all tropical deforestation fires. The NMOC emissions were ~80% reactive, oxygenated volatile organic compounds (OVOC). Our EF for PM10 (17.8±4 g/kg) is ~25% higher than previously reported for tropical forest fires and may reflect a trend towards, and sampling of, larger fires than in earlier studies. A large fraction of the total burning for 2004 likely occurred during a two-week period of very low humidity. The combined output of these fires created a massive "mega-plume" >500 km across that we sampled on September 8. The mega-plume contained high PM10 and 10–50 ppbv of many reactive species such as O3, NH3, NO2, CH3OH, and organic acids. This is an intense and globally important chemical processing environment that is still poorly understood. The mega-plume or "white ocean" of smoke covered a large area in Brazil, Bolivia, and Paraguay for about one month. The smoke was transported >2000 km to the southeast while remaining concentrated enough to cause a 3-4-fold increase in aerosol loading in the S o Paulo area for several days.
Rapid formation of isoprene photo-oxidation products observed in Amazonia
T. Karl,A. Guenther,A. Turnipseed,P. Artaxo
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian aerosol characterization experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. A recently suggested novel pathway for isoprene peroxy radicals could explain the observed discrepancy and reconcile the rapid formation of these VOCs. Furthermore, if generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in substantial underestimates of modelled OH reactivity that could explain a major fraction of the missing OH sink over forests which has previously been attributed to a missing source of primary biogenic VOCs.
Transport of Saharan dust from the Bodélé Depression to the Amazon Basin: a case study
Y. Ben-Ami,I. Koren,Y. Rudich,P. Artaxo
Atmospheric Chemistry and Physics Discussions , 2010,
Abstract: Through long-range transport of dust, the Sahara desert supplies essential minerals to the Amazon rain forest. Since Saharan dust reaches South America mostly during the Northern Hemisphere winter, the dust sources active during winter are the main contributors to the forest. Given that the Bodélé depression area in Southwestern Chad is the main winter dust source, a close link is expected between the Bodélé emission patterns and volumes and the mineral supply flux to the Amazon. Until now, the particular link between the Bodélé and the Amazon forest was based on sparse satellite measurements and modeling studies. In this study, we combine a detailed analysis of space-borne and ground data with reanalysis model data and surface measurements taken in the Central Amazon during the Amazonian Aerosol Characterization Experiment (AMAZE-08) in order to explore the validity and the nature of the proposed link between the Bodélé depression and the Amazon forest. This case study follows the dust events of 11–16 and 18–27 February 2008, from the emission in the Bodélé over West Africa, the crossing of the Atlantic Ocean, to the observed effects above the Amazon canopy about 10 days after the emission. The dust was lifted by surface winds stronger than 14 m s 1, usually starting early in the morning. The lofted dust mixed with biomass burning aerosols over Nigeria, was transported over the Atlantic Ocean, and arrived over the South American continent. The top of the aerosol layer reached above 3 km, and the bottom merged with the marine boundary layer. The arrival of the dusty air parcel over the Amazon forest increased the average concentration of aerosol crustal elements by an order of magnitude.
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