scholarly journals Aerosol number fluxes over the Amazon rain forest during the wet season

2009 ◽  
Vol 9 (4) ◽  
pp. 17335-17383 ◽  
Author(s):  
L. Ahlm ◽  
E. D. Nilsson ◽  
R. Krejci ◽  
E. M. Mårtensson ◽  
M. Vogt ◽  
...  
Keyword(s):  
Rain Forest ◽  
Friction Velocity ◽  
Aerosol Particles ◽  
Anthropogenic Sources ◽  
Deposition Flux ◽  
Wet Season ◽  
Secondary Aerosol ◽  
Aerosol Emission ◽  
Amazon Rain Forest ◽  
Particle Fluxes

Abstract. Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3·u∗ where u∗ is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, primary aerosol emission had a limited impact on the total aerosol number population in this study, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. It seems that a significant contribution of secondary aerosol particles to the aerosol population is the most reasonable explanation for the net downward flux. This is an indication that secondary aerosol particles may dominate the aerosol number population in the Amazon boundary layer and that the contribution of primary aerosol particles may be low in terms of numbers. However, aerosol flux measurements should be repeated in a more remote area of the Amazon with less influence from anthropogenic sources before any final conclusions may be drawn.

scholarly journals Aerosol number fluxes over the Amazon rain forest during the wet season

2009 ◽  
Vol 9 (24) ◽  
pp. 9381-9400 ◽  
Author(s):  
L. Ahlm ◽  
E. D. Nilsson ◽  
R. Krejci ◽  
E. M. Mårtensson ◽  
M. Vogt ◽  
...  
Keyword(s):  
Rain Forest ◽  
Large Scale ◽  
Friction Velocity ◽  
Aerosol Particles ◽  
Deposition Flux ◽  
Wet Season ◽  
Transfer Velocity ◽  
Aerosol Emission ◽  
Amazon Rain Forest ◽  
Particle Fluxes

Abstract. Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt = 2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.

scholarly journals A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest

2010 ◽  
Vol 10 (6) ◽  
pp. 3063-3079 ◽  
Author(s):  
L. Ahlm ◽  
E. D. Nilsson ◽  
R. Krejci ◽  
E. M. Mårtensson ◽  
M. Vogt ◽  
...  
Keyword(s):  
Rain Forest ◽  
Particle Flux ◽  
Dry Season ◽  
Deposition Flux ◽  
Wet Season ◽  
Transfer Velocity ◽  
Particle Transfer ◽  
Amazon Rain Forest ◽  
Stable Conditions ◽  
Particle Fluxes

Abstract. Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53 m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.

scholarly journals A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest

2009 ◽  
Vol 9 (6) ◽  
pp. 26881-26924
Author(s):  
L. Ahlm ◽  
E. D. Nilsson ◽  
R. Krejci ◽  
E. M. Mårtensson ◽  
M. Vogt ◽  
...  
Keyword(s):  
Dry Deposition ◽  
Rain Forest ◽  
Particle Deposition ◽  
Particle Flux ◽  
Friction Velocity ◽  
Deposition Velocity ◽  
Dry Season ◽  
Wet Season ◽  
Deposition Velocities ◽  
Amazon Rain Forest

Abstract. Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53 m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. The primary goal is to quantify the dry deposition sink and to investigate whether particle deposition velocities change when going from the clean wet season into the more polluted dry season. Furthermore, it is tested whether the rain forest is always a net sink of particles in terms of number concentrations, or if particle emission from the surface under certain circumstances may dominate over the dry deposition sink. The particle deposition velocity vd increased linearly with increasing friction velocity in both seasons and the relations are described by vdd=(2.7 u* −0.2)×10−3 (dry season) and vdw=2.5 u*×10−3 (wet season), where u* is the friction velocity. The fact that the two relations are very similar to each other indicates that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle deposition velocities in this study are low compared to studies over boreal forests. The reason is probably domination of accumulation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. Net particle deposition fluxes prevailed in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of natural biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.

scholarly journals Seasonal variation of ozone deposition to a tropical rain forest in southwest Amazonia

2007 ◽  
Vol 7 (20) ◽  
pp. 5415-5435 ◽  
Author(s):  
U. Rummel ◽  
C. Ammann ◽  
G. A. Kirkman ◽  
M. A. L. Moura ◽  
T. Foken ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Rain Forest ◽  
Deposition Velocity ◽  
Dry Season ◽  
Stomatal Aperture ◽  
Specific Humidity ◽  
Deposition Flux ◽  
Diel Variation ◽  
Wet Season ◽  
Ozone Deposition

Abstract. Within the project EUropean Studies on Trace gases and Atmospheric CHemistry as a contribution to Large-scale Biosphere-atmosphere experiment in Amazonia (LBA-EUSTACH), we performed tower-based eddy covariance measurements of O3 flux above an Amazonian primary rain forest at the end of the wet and dry season. Ozone deposition revealed distinct seasonal differences in the magnitude and diel variation. In the wet season, the rain forest was an effective O3 sink with a mean daytime (midday) maximum deposition velocity of 2.3 cm s−1, and a corresponding O3 flux of −11 nmol m−2 s−1. At the end of the dry season, the ozone mixing ratio was about four times higher (up to maximum values of 80 ppb) than in the wet season, as a consequence of strong regional biomass burning activity. However, the typical maximum daytime deposition flux was very similar to the wet season. This results from a strong limitation of daytime O3 deposition due to reduced plant stomatal aperture as a response to large values of the specific humidity deficit. As a result, the average midday deposition velocity in the dry burning season was only 0.5 cm s−1. The large diel ozone variation caused large canopy storage effects that masked the true diel variation of ozone deposition mechanisms in the measured eddy covariance flux, and for which corrections had to be made. In general, stomatal aperture was sufficient to explain the largest part of daytime ozone deposition. However, during nighttime, chemical reaction with nitrogen monoxide (NO) was found to contribute substantially to the O3 sink in the rain forest canopy. Further contributions were from non-stomatal plant uptake and other processes that could not be clearly identified. Measurements, made simultaneously on a 22 years old cattle pasture enabled the spatially and temporally direct comparison of O3 dry deposition values from this site with typical vegetation cover of deforested land in southwest Amazonia to the results from the primary rain forest. The mean ozone deposition to the pasture was found to be systematically lower than that to the forest by 30% in the wet and 18% in the dry season.

scholarly journals African volcanic emissions influencing atmospheric aerosol particles over the Amazon rain forest

2017 ◽  
Author(s):  
Jorge Saturno ◽  
Florian Ditas ◽  
Marloes Penning de Vries ◽  
Bruna A. Holanda ◽  
Mira L. Pöhlker ◽  
...  
Keyword(s):  
Rain Forest ◽  
Amazon Basin ◽  
Dimethyl Sulfide ◽  
Aerosol Particles ◽  
Amazon Region ◽  
Volcanic Emissions ◽  
Airborne Measurements ◽  
Amazon Rain Forest ◽  
Sulfur Emissions

Abstract. Long-range transport (LRT) plays an important role in the Amazon rain forest by bringing in different primary and secondary aerosol particles from distant sources. The atmospheric oxidation of dimethyl sulfide (DMS), emitted from marine plankton, is considered an important sulfate source over the Amazon rain forest, with a lesser contribution from terrestrial soil and vegetation sulfur emissions. Volcanic sulfur emissions from Africa could be a source of particulate sulfate to the Amazonian atmosphere upon transatlantic transport but no observations have been published. By using satellite observations, together with ground‑based and airborne aerosol particle observations, this paper provides evidence of the influence that volcanic emissions have on the aerosol properties that have been observed in central Amazonia. Under the volcanic influence, sulfate mass concentrations reached up to 3.6 µg m−3 (hourly mean) at ground level, the highest value ever reported in the Amazon region. The hygroscopicity parameter was higher than the characteristic dry-season average, reaching a maximum of 0.36 for accumulation mode aerosol particles. Airborne measurements and satellite data indicated the transport of two different volcanic plumes reaching the Amazon Basin in September 2014 with a sulfate-enhanced layer at an altitude between 4 and 5 km. These observations show that remote volcanic sources can episodically affect the aerosol cycling over the Amazon rain forest and perturb the background conditions. Further studies should address the long-term effect of volcanogenic aerosol particles over the Amazon Basin by running long-term and intensive field measurements in the Amazon region and by monitoring African emissions and their transatlantic transport.

scholarly journals Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

2017 ◽  
Author(s):  
Jorge Saturno ◽  
Bruna A. Holanda ◽  
Christopher Pöhlker ◽  
Florian Ditas ◽  
Qiaoqiao Wang ◽  
...  
Keyword(s):  
El Niño ◽  
Light Absorption ◽  
Rain Forest ◽  
El Nino ◽  
Aerosol Particles ◽  
Wavelength Dependence ◽  
Brown Carbon ◽  
Amazon Rain Forest ◽  
Central Amazonia ◽  
Measurement Period

Abstract. The Amazon rain forest is considered a very sensitive ecosystem that could be significantly affected by a changing climate. It is still one of the few places on Earth where the atmosphere in the continent approaches near-pristine conditions for some periods of the year. The Amazon Tall Tower Observatory (ATTO) has been built in central Amazonia to monitor the atmospheric and forest ecosystem conditions. The atmospheric conditions at the ATTO site oscillate between biogenic and biomass burning (BB) dominated states. By using a comprehensive ground-based aerosol measurement setup, we studied the physical and chemical properties of aerosol particles at the ATTO site. This paper presents results from 2012 to 2017, with special focus on light absorbing aerosol particles. The aerosol absorption wavelength dependence (expressed as the absorption Ångström exponent, åabs) was usually below 1.0 and increased during the presence of smoke transported from fires in the southern and eastern regions of the Amazon or advected from savanna fires in Africa. In this study, the brown carbon (BrC) contribution to light absorption at 370 nm was obtained by calculating the theoretical wavelength dependence of åabs (WDA). Our calculations resulted in BrC contributions of 17–29 % (25th and 75th percentiles) to total light absorption at 370 nm (σap 370) during the measurement period (2012–2017). The BrC contribution increased up to 27–47 % during fire events occurring under the influence of El Niño, between September and November 2015. An extended time series of ATTO and ZF2 (another Amazon rain forest sampling site) data showed enhanced light scattering and absorption coefficients during El Niño periods in 2009 and 2015. Long-range transport (LRT) aerosol particles that reached the central Amazon Basin from Africa or from southern Amazon exhibited a wide range of black carbon (BC) to carbon monoxide (CO) enhancement ratios (ERBC) (between 4 and 15 ng m−3 ppb−1) reflecting the variability of fuels, combustion phase, and removal processes in the atmosphere. Higher ERBC were measured during the dry season when we observed values up to 15 ng m−3 ppb−1, which were related to the lowest single scattering albedo (ω0) measured during the studied period, (0.86–0.93). A parameterization of åabs as a function of the BC to OA mass ratio was investigated and was found applicable to tropical forest emissions but further investigation is required, especially by segregating fuel types. Additionally, important enhancements of the BC mass absorption cross‑section (αabs) were found over the measurement period. This enhancement could be linked to heavy coating of the BC aerosol particles. In the future, the BC mixing state should be systematically investigated by using different instrumental approaches.

scholarly journals Seasonal variation of ozone deposition to a tropical rain forest in southwest Amazonia

2007 ◽  
Vol 7 (3) ◽  
pp. 7399-7450 ◽  
Author(s):  
U. Rummel ◽  
C. Ammann ◽  
G. A. Kirkman ◽  
M. A. L. Moura ◽  
T. Foken ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Rain Forest ◽  
Deposition Velocity ◽  
Dry Season ◽  
Stomatal Aperture ◽  
Specific Humidity ◽  
Deposition Flux ◽  
Diel Variation ◽  
Wet Season ◽  
Ozone Deposition

Abstract. Within the project EUropean Studies on Trace gases and Atmospheric CHemistry as a contribution to Large-scale Biosphere–atmosphere experiment in Amazonia (LBA-EUSTACH), we performed tower-based eddy covariance measurements of O3 flux above an Amazonian primary rain forest at the end of the wet and dry seasons. Ozone deposition revealed distinct seasonal differences in the magnitude and diel variation. In the wet season, the rain forest was an effective O3 sink with a mean daytime (midday) maximum deposition velocity of 2.3 cm s−1, and a corresponding O3 flux of –11 nmol m−2 s−1. At the end of the dry season, the ozone mixing ratio was about four times higher (up to maximum values of 80 ppb) than in the wet season, as a consequence of strong regional biomass burning activity. However, the typical maximum daytime deposition flux was very similar to the wet season. This results from a strong limitation of daytime O3 deposition due to reduced plant stomatal aperture as a response to large values of the specific humidity deficit. As a result, the average midday deposition velocity in the dry burning season was only 0.5 cm s−1. The large diel ozone variation caused large canopy storage effects that masked the true diel variation of ozone deposition mechanisms in the measured eddy covariance flux, and for which corrections had to be made. In general, stomatal aperture was sufficient to explain the largest part of daytime ozone deposition. However, during nighttime, chemical reaction with nitrogen monoxide (NO) was found to contribute substantially to the O3 sink in the rain forest canopy. Further contributions were from non-stomatal plant uptake and other processes that could not be clearly identified. Measurements, made simultaneously on a 22 years old cattle pasture enabled the spatially and temporally direct comparison of O3 dry deposition values from this site with typical vegetation cover of deforested land in southwest Amazonia to the results from the primary rain forest. The mean ozone deposition to the pasture was found to be systematically lower than that to the forest by 30% in the wet and 18% in the dry season.

scholarly journals Emission and deposition of accumulation and coarse mode particles in the Amazon basin

2010 ◽  
Vol 10 (6) ◽  
pp. 14013-14052
Author(s):  
L. Ahlm ◽  
R. Krejci ◽  
E. D. Nilsson ◽  
E. M. Mårtensson ◽  
M. Vogt ◽  
...  
Keyword(s):  
Wind Speed ◽  
Amazon Basin ◽  
Horizontal Wind ◽  
Anthropogenic Influence ◽  
Wet Season ◽  
Horizontal Wind Speed ◽  
Aerosol Emission ◽  
Diameter Range ◽  
Emission Fluxes ◽  
Particle Fluxes

Abstract. Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, pointed downward in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net emission fluxes dominated. However, in wind sectors associated with higher anthropogenic influence, net deposition fluxes dominated. The net emission fluxes were interpreted as primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and these emissions were best correlated with horizontal wind speed by the equation log10F=0.47·U+2.26 where F is the emission number flux of 0.5–2.5 μm particles [m−2s−1] and U is the horizontal wind speed [ms−1] at the top of the tower.

scholarly journals Bioaerosols in the Amazon rain forest: temporal variations and vertical profiles of Eukarya, Bacteria, and Archaea

2021 ◽  
Vol 18 (17) ◽  
pp. 4873-4887
Author(s):  
Maria Prass ◽  
Meinrat O. Andreae ◽  
Alessandro C. de Araùjo ◽  
Paulo Artaxo ◽  
Florian Ditas ◽  
...  
Keyword(s):  
Rain Forest ◽  
Staining Technique ◽  
Temporal Variations ◽  
Vertical Profiles ◽  
Wet Season ◽  
Model Studies ◽  
Amazon Rain Forest ◽  
Low Concentrations ◽  
Steep Decrease ◽  
Biogenic Aerosols

Abstract. The Amazon rain forest plays a major role in global hydrological cycling, and biogenic aerosols are likely to influence the formation of clouds and precipitation. Information about the sources and altitude profiles of primary biological aerosol particles, however, is sparse. We used fluorescence in situ hybridization (FISH), a molecular biological staining technique largely unexplored in aerosol research, to investigate the sources and spatiotemporal distribution of Amazonian bioaerosols on the domain level. We found wet season bioaerosol number concentrations in the range of 1–5 × 105 m−3 accounting for > 70 % of the coarse mode aerosol. Eukaryotic and bacterial particles predominated, with fractions of ∼ 56 % and ∼ 26 % of the intact airborne cells. Archaea occurred at very low concentrations. Vertical profiles exhibit a steep decrease in bioaerosol numbers from the understory to 325 m height on the Amazon Tall Tower Observatory (ATTO), with a stronger decrease in Eukarya compared to Bacteria. Considering earlier investigations, our results can be regarded as representative for near-pristine Amazonian wet season conditions. The observed concentrations and profiles provide new insights into the sources and dispersion of different types of Amazonian bioaerosols as a solid basis for model studies on biosphere–atmosphere interactions such as bioprecipitation cycling.

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