A11C-0121
Secondary Organic Aerosol from Biogenic VOCs over West Africa during AMMA
As part of the international AMMA (African Monsoon Multidisciplinary Analyses) project a large field experiment took place in West Africa during July and August 2006. This involved a number of ground-based facilities and 5 aircraft, including the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146, which was based in Niamey, Niger and made 21 flights. The 146 was equipped with instruments measuring parameters relevant to dynamics, gas phase composition, radiation, aerosols and clouds. The flights made were designed to examine a range of multidisciplinary scientific questions. This paper presents measurements of organic aerosol above subtropical West Africa during the monsoon season using data from the FAAM aircraft. Measurements of biogenic volatile organic compounds (BVOC) at low altitudes over these subtropical forests were made during July and August 2006 mainly above Benin, Nigeria and Niger. In air masses characterised by high BVOC concentrations, data from an Aerodyne Quadrupole Aerosol Mass Spectrometer show an organic aerosol loading of 0.58 μgm-3 over tropical West Africa. In contrast, organic aerosol mass (OM) concentrations were negligible when BVOC concentrations were low. This represents the first regionally averaged assessment of OM in this region during the wet season. This is in good agreement with predictions based on aerosol yields from isoprene and monoterpenes during chamber studies and model predictions based on partitioning schemes, contrasting markedly with the large under representations of OM in similar models when compared with data from mid latitudes.
A11C-0122
Carbonaceous Aerosols in African Dust Over the Caribbean
African Dust (AD) particles transported by the trade winds from the North African desert make their way each year to the Caribbean, particularly during the summer months. Dust, as well as carbonaceous particles, influences the Earth's radiative budget directly by scattering and absorbing solar radiation in the atmosphere and indirectly by affecting cloud formation and, thus, cloud albedo. Yet the underlying physico-chemical processes and the interactions between dust and carbonaceous particles are poorly understood, especially if dust particles are as aged as those that travel from Africa to the Caribbean region. Here we present results on the chemical composition of aerosol samples sampled at several locations in the Caribbean in the presence and absence of African Dust. We performed chemical characterization of fine (Dp < 1.7 μm) and size-resolved samples focusing on the carbonaceous fraction (organic and elemental carbon (OC and EC)), the water-soluble organic carbon (WSOC)), and the water-soluble nitrogen (WSN). The presence of African dust was supported by aerosol optical thickness based on satellite images, results from the air masses backward trajectories calculated with the NOAA HYSPLIT model, the color of the filters after sampling, and chemical composition. Preliminary results showed limited increase in the concentrations of OC during dust events. The size-resolved samples showed three modes for the OC size distributions during the summer period, two in the fine fraction (Dp = 0.40 μm and 1.65 μm) and one in the coarse fraction (Dp = 6.70 μm). OC concentrations were also higher for the fine fraction (fine ~ 0.25 μg/m3 vs coarse 0.15 μg/m3). Additional results regarding OC, WSOC, WSN, and water-soluble ions together with the possible OC sources in the AD samples will be presented.
A11C-0123
Ambient Aerosol in Southeast Asia: High Resolution Aerosol Mass Spectrometer Measurements Over Oil Palm (Elaeis guineensis)
The emission of organic compounds in the troposphere is important factor in the formation of secondary organic aerosol (SOA). A very large proportion of organic material emitted globally is estimated to arise from biogenic sources, with almost half coming from tropical and sub-tropical forests. Preliminary analyses of leave cuvette emission studies suggest that oil palm (Elaeis guineensis) is a significantly larger source of isoprene than tropical forest. Much larger sources of isoprene over oil palm allied with a larger anthropogenic component of local emissions contrast greatly with the remote tropical forest environment and therefore the character of SOA formed may differ significantly. These issues, allied with the high price of palm oil on international markets leading to increased use of land for oil palm production, could give rise to rapidly changing chemical and aerosol regimes in the tropics. It is therefore important to understand the current emissions and composition of organic aerosol over all important land-uses in the tropical environment. This in turn will lead to a greater understanding of the present, and to an improvement in predictive capacity for the future system. To help address these issues, a high resolution time of flight aerosol mass spectrometer (HR-ToF-AMS) was deployed in the Sabahmas (PPB OIL) oil palm plantation near Lahad Datu, in Eastern Sabah, as part of the field component of the Aerosol Coupling in the Earth System (ACES) project, part of the UK NERC APPRAISE program. This project was allied closely with measurements made of similar chemical species and aerosol components at a forest site in the Danum Valley as part of the UK Oxidant and Particle Photochemical Processes above a Southeast Asian tropical rainforest (OP3) project. Measurements of submicron non- refractory aerosol composition are presented along with some preliminary analysis of chemically resolved aerosol fluxes made with a new eddy covariance system, based on the HR-ToF-AMS. The measurements are interpreted in the context of the measurements over tropical rain forest at Danum and aircraft measurements across Sabah.
A11C-0124
Aerosol Fluxes over Amazon Rain Forest Measured with the Eddy Covariance Method
We present measurements of vertical aerosol fluxes over the Amazon carried out on top of K34, a 50 meter high tower in the Cuieiras Reserve about 50 km north of Manaus in northern Brazil. The turbulent fluxes were measured with the eddy covariance method. The covariance of vertical wind speed from a sonic anemometer Gill Windmaster and total aerosol number concentration from a condensation particle counter (CPC) TSI 3010 provided the total number flux (diameter >0.01 μm). The covariance of vertical wind speed and size resolved number concentrations from an optical particle counter (OPC) Grimm 1.109 provided size resolved number fluxes in 15 bins from 0.25 μm to 2.5 μm diameter. Additionally fluxes of CO2 and H2O were derived from Li-7500 observations. The observational period, from early March to early August, includes both wet and dry season. OPC fluxes generally show net aerosol deposition both during wet and dry season with the largest downward fluxes during midday. CPC fluxes show different patterns in wet and dry season. During dry season, when number concentrations are higher, downward fluxes clearly dominate. In the wet season however, when number concentrations are lower, our data indicates that upward and downward fluxes are quite evenly distributed during course of a day. On average there is a peak in upward flux during late morning and another peak during the afternoon. Since the OPC fluxes in the same time show net deposition, there is an indication of net source of primary aerosol particles with diameters between 10 and 250 nm emitted from the rain forest. Future data analysis will hopefully shed light on origin and formation mechanism of these particles and thus provide a deeper insight in the rain forest – atmosphere interactions. The aerosol flux measurements were carried out as a part of the AMAZE project in collaboration with University of Sao Paulo, Brazil, and financial support was provided by Swedish International Development Cooperation Agency (SIDA).
A11C-0125
NOCTURNAL BOUNDARY LAYER MEASUREMENTS DURING THE AMAZONIAN AEROSOL CHARACTERIZATION EXPERIMENT (AMAZE)
To characterize the Nocturnal Boundary Layer (NBL) hourly profiles of wind, pressure, temperature, humidity and 5 sizes particles concentration, were made by using tethered balloon at INPA tropical Amazon rainforest Reserve (Cuieiras) 100 km northwest from Manaus city. The measurements were made during the wet season March/2008. The NBL height was 100 to 150m, with a very well mixed layer close to surface associate with temperature inversion. The wind profiles shows a very clear low level in two nights, about 500 to 900 m, and, in general, all nights show an stable and cooler air layer close the surface uncoupled with outer residual boundary layer above. At the site a very clear drainage flow from north quadrant down slope eastward quadrant during very the stable cases. This findings is correlates with particles profiles where was commonly trapped by stable layer presenting high concentrations, for all 5 sizes measured, close to the surface at vegetation level and just above it. All nights presents high humidity with fog formation in three cases, associates with temperature below the 23°C. The wind speed were very low about 0.5 to calm, in generally associate with drainage flow down hill. The NBL dynamics is a discussion issue associate to the aerosol nocturnal mixing in complex terrain with tall vegetation, the currently AMAZE site case.
A11C-0126
Quantifying sulfur acidification mechanisms of Saharan dust aerosols
The Saharan Desert is the worlds largest dust source supplying large quantities of dust to the atmosphere over the subtropical North Atlantic Ocean. The deposition of this dust can promote increased marine primary productivity by providing critical nutrients to the oceans. Iron is one such nutrient since the availability of soluble iron in major ocean regions can limit marine productivity. The amount of soluble iron in dust aerosols can be enhanced by atmospheric acidity. SO2 oxidation has been proposed to be the primary source of dust particle acidification. However, considerable uncertainty exists regarding the reactivity of hydrophobic dust aerosols with acid gases and acid gas precursors hampering efforts to quantify acidification processes in the atmosphere. We utilize oxygen isotopic measurements of sulfate aerosol samples collected during two cruises in the subtropical North Atlantic to quantify the importance of different sulfate formation pathways in this region. We take advantage of the strong pH dependence (pH>5) of the oxidation of dissolved SO2 by ozone to quantify sulfate formation on alkaline dust aerosol. Ozone has an anomalous enrichment in δ17O relative to δ18O, and is quantified with Δ17O (Δ17O = δ17O - 0.5*δ18O). This isotopic anomaly is transferred to sulfate upon oxidation, providing a record of the relative importance of the (high pH) ozone oxidation pathway in sulfate formation. We present measurements of the Δ17O composition of sulfate aerosol collected in the subtropical North Atlantic, and quantify direct oxidation of SO2 on dust aerosol with a photochemical box model containing the oxygen isotopic tracers.
A11C-0127
Following Saharan Dust Outbreak Toward The Amazon Basin
The role of the Amazon rainforest on earth climatic system is well recognized. To keep forest wellbeing and the fragile balance between the rainforest and the atmosphere, the Amazon must contain a satisfactory amount of nutrients to support the plants. The extensive rain and floods wash most of the soluble nutrients from the rainforest soil, leaving behind acidic kaolinite clay or sandy soil, with limited minerals for plant growth. It was suggested that lack of mineral in the soil may be replenished by deposition of Saharan mineral dust. Using remote sensing data (from the A-train satellites constellation) following with in-situ measurements (as part of the AMazonian Aerosol CharacteriZation Experiment (AMZE) campaign), ground-based data (from AErosol RObotic NETwork (AERONET)) and back trajectory calculations, we analyzed Saharan dust transport toward the Amazon basin during the AMZE period (Feb 7 to Mar 14, 2008). Dust mass, sink, vertical distribution and surface wind speeds were analyzed over the Bodele depression (located in Chad), where most of the dust is emitted, along the Atlantic Ocean and near the Brazilian coastline. Using an integrated data analysis approach we followed dust packages from their emission in the Sahara to their sink in the Amazon forest.
A11C-0128
Mass Spectrometric Analysis of Pristine Aerosol Particles During the wet Season of Amazonia - Detection of Primary Biological Particles?
The contribution of primary biological aerosol (POA) particles to the natural organic aerosol is a subject of current research. Estimations of the POA contribution to the total aerosol particle concentration range between 25 and 80%, depending on location and season. Especially in the tropical rain forest it is expected that POA is a major source of supermicron, possibly also of submicron particles. During AMAZE (Amazonian Aerosol CharacteriZation Experiment), a field project near Manaus, Brazil, in February/March 2008, an Aerodyne ToF-AMS was equipped with a high pressure aerodynamic lens. This high pressure lens (operating pressure 14.6 torr) is designed with the objective to extend the detectable size range of the AMS into the supermicron size range where primary biological particles are expected. Size distribution measured by the AMS were compared with size distribution from an optical particle counter and indicate that the high pressure lens has a 50% cut-off at a vacuum aerodynamic diameter of about 1 μm, but still has significant transmission up to a vacuum aerodynamic diameter of about 2 μm, thus extending the detectable size range of the AMS into the coarse mode. The measuring instruments were situated in a container at ground level. The aerosol was sampled through a 40 m vertical, laminar inlet, which was heated and dried to maintain a relative humidity between 30 and 40%. The inlet was equipped with a 7 μm cut-off cyclone. Size distributions recorded with an optical particle counter parallel to the AMS show that the inlet transmitted aerosol particles up to an optically detected diameter of 10 μm. POA particles like plant fragments, pollen, spores, fungi, viruses etc. contain chemical compounds as proteins, sugars, amino acids, chlorophyll, and cellular material as cellulose. Laboratory experiments have been performed in order to identify typical mass spectral patterns of these compounds. These laboratory data were compared to size resolved particle mass spectra that were obtained during AMAZE. First results indicate that the mass spectra of organic aerosol particle sampled during AMAZE show a size dependence, thereby indicating a size-dependent chemical composition of the aerosol particles. A detailed comparison between the laboratory data and the AMS mass spectra of the fraction of large particles sampled during AMAZE will be presented.
A11C-0129
Analysis of the Organic Fraction of the Amazonian Aerosol Using an Aerosol Mass Spectrometer Coupled With a Thermodenuder
Organic matter dominates the aerosol in the tropical rain forest, but our knowledge and understanding of the
detailed chemical composition is by far not complete. With standard methods like chemical extraction and
analysis of filter samples only a small fraction of the total organic mass can be identified and quantified.
Recently, with new developments in online aerosol measurement techniques such as aerosol mass
spectrometry it has become possible to gain new insights. This is augmented with mathematical extraction
techniques such as positive matrix factorization (PMF).
One recent method that has become very important is the use of thermodenuders to resolve aerosol
components of different volatilities. These heat the aerosol prior to the analysis in order to remove different
fractions of the aerosol composition. Depending on the thermodenuder temperature this method offers the
possibility to remove the total volatile fraction of the aerosol or only a part of it.
During the AMAZE-2008 campaign, taking place from February to March 2008 in the vicinity of Manaus,
Brazil, we operated an Aerodyne High-Resolution ToF-AMS in conjunction with a thermodenuder during part
of the campaign.
We used the AMS for measuring the aerosol chemical composition, switching every 15 minutes between the
thermodenuder and the ambient inlet for comparison of the aerosol in its unchanged state and the aerosol
modified by the thermodenuder.
For most of the time during which the thermodenuder was coupled with the AMS, we operated the
thermodenuder at a temperature of approximately 90°C. At this temperature, only the most volatile
fraction of the organic aerosol was found to be removed. A second, more stable fraction started to evaporate
only at temperatures above 100°C. The inorganic, sulfate-dominated fraction was not affected at
90°C.
This setup provided important insights into the chemical composition of the organic aerosol to be found in the
Amazonian region. Here we present preliminary results of the analysis of the AMS/TD measurement data,
which show that the organic mass fraction of the aerosol is decreased by approximately 50% when it is
sampled through the thermodenuder at 90°C compared to measurements through the ambient
sampling line. Additionally, we present an extended analysis of the organic fragments contributing to the two
fractions, the more volatile and the less volatile organics.
A11C-0130
Characterization of organic aerosol with a high resolution time-of-flight aerosol mass spectrometer during the Amazonian Aerosol Characterization Experiment (AMAZE- 08)
The Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out in the northern Amazon during the wet season (February and March, 2008), provided an opportunity to investigate the chemical and microphysical properties of nearly pure biogenic organic aerosol. The non-refractory components (i.e., ammonium, chloride, nitrate, sulfate, and organic) of submicron particles were analyzed with the Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) to characterize the dynamics of aerosol particles. The non-refractory mass was composed primarily of organic material. At certain times, the organic components were observed to grow in time series, possibly implying the importance of SOA formation from biogenic precursors. Analysis of the high-resolution spectra revealed that the organic material was dominated by oxygenated species. The average ratio of organic matter (OM) to organic carbon (OC) and the atomic ratios of oxygen-to-carbon and hydrogen-to-carbon calculated from the high-resolution spectra were also determined.
A11C-0131
Biological Particle Emissions From a South-East Asian Tropical Rainforest Using a Real- Time Dual Channel UV Fluorescence Bio-Aerosol Spectrometer
Primary biogenic aerosols (PBA) contribute typically up to half of coarse mode particulate loading in tropical
regions (e.g. Elbert et al. 2007). PBA contribute to the spread of genetic material and hence biodiversity
within the biosphere either directly by transport of the organisms or their reproductive components. This
spread via various vectors contributes to disease both animal and plant. Many studies have suggested PBA
might be important for initiation of cloud formation and subsequent precipitation evolution by acting as cloud
condensation nuclei (CCN) or possibly as ice nuclei (IN). This link is inferred from laboratory studies
demonstrating the high activation efficiency of PBA at warm temperatures, coupled with observations that
biological particles are ubiquitous in the atmosphere. Despite more than two hundred years of research, e.g.
Ehrenberg (1830), information on the abundance, composition and more importantly the sources and
heterogeneity of PBA on global scales are still poorly understood.
The first realistic estimates of global average emission rates of PBA based on observations (mainly in
Amazonia) and budget calculations, were provided by Elbert et al. (2007). They demonstrate that fungi, which
have evolved many passive and active spore dispersal mechanisms, contribute a major fraction of the
observed PBA and coarse particulate mass (particles with diameters between 1-10 μ m) in many, but in
particular, tropical regions. Two major classes of fungal spores are commonly identified, these being AAM
and ABM, Acomycota and Basidiomycota respectively (we will adopt the nomenclature used by Elbert et al.
2007, in this study). These species discharge their spores via wet spore active discharge mechanisms.
Elbert et al. (2007) estimate a global average spore emission rate for ABM of ~17-50 Tg yr-1. This
is consistent with observed typical concentrations of ABS which range from ~103 to 104 m-
3; and ~0.1-1 μ g m-3 by mass. The global average abundance and net emission for all
fungal spores is ~1 μ g m-3 and ~50 Tg yr-1. These calculations demonstrate the
potential importance of PBA, and in particular fungal spores, for global budgets of organic aerosols,
particularly in tropical regions, however uncertainties are extremely large, ranging from 50 - 1000 Tg yr-
1.
In this study we use the WIBS-3: a low-cost portable single-particle dual-channel UV fluorescence
spectrometer (Kaye et al., 2008) to investigate the dynamics of PBA in real-time within and above a tropical
forest of 50 m height in Borneo, Malaysia, to estimate net PBA emissions. Different circadian cycles were
observed for bio and non-bio aerosol sources and the factors controlling bioaerosol emissions will be
discussed in detail.
http://strc.herts.ac.uk/pi/proj.html
A11C-0132
Analysis of Chemical Composition of Atmospheric Aerosols Above a South East Asian Rainforest
The tropics emit a huge amount of volatile organic compounds (VOCs) into the Earth's atmosphere. The processes by which these gases are oxidised to form secondary organic aerosol (SOA) are not well understood or quantified. Insight into the origins and properties of these particles can be gained by analysis of their composition. Intensive field measurements were carried out as part of the Oxidant and Particle Photochemical Processes (OP3) and the Aerosol Coupling in the Earth System (ACES) projects in the rainforest in Malaysian Borneo. This is the first campaign of its type in a South East Asian rainforest. We present detailed organic aerosol composition measurements made using an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) at Bukit Atur, a Global Atmosphere Watch site located in the Danum Valley Conservation Area. This is a state-of-the-art field deployable instrument that can provide real time composition, mass loading and aerodynamic particle sizing information. In addition, the mass spectral resolution is sufficient to perform an analysis of the elemental composition of the organic species present. Other tools such as positive matrix factorisation (PMF) have been used to help assess the relative source contributions to the organic aerosol. The aerosol's chemical origins have been further investigated by comparing these spectra to chamber experiments, mass spectral libraries and data from comparable locations in other locations. These data are also being analysed in conjunction with high complexity offline techniques applied to samples collected using filters and a Particle-Into-Liquid Sampler (PILS). Methods used include liquid chromatography and comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry. These techniques provide a more detailed chemical characterisation of the SOA and water soluble organic carbon, allowing direct links back to gas phase precursors.
A11C-0133
Optical Properties Of Mineral Dust Particles Mixed With Black Carbon In Indo-Ganges Basin, Northern India
Among all the aerosol species estimation of radiative forcing of dust particles is most uncertain because of
the difficulties in modeling accurately their optical properties due to our limited knowledge of their mineralogy
and morphology (Sokolik and Toon, 1999). There is large variation in their shapes and mineralogical
composition across the global deserts and the data available is limited. The problem becomes further
complicated when these highly non spherical shaped particles interact with other absorbing particles e. g.
Black Carbon emitted from pollution sources. The dust from Indian desert, while being transported through
the Indo Gangetic basin during the Pre Monsoon season (March-May), mixes with BC particles present in
large concentration in the region (Tripathi et al., 2005). The accurate estimation of optical properties of these
particles, which could be different from pure dust or BC particles, is important because of their suspected
impact on the development of monsoon (Lau et al, 2006). In this work, we have made an attempt to model the
optical properties of these complicated aerosol systems. We have used dust mineralogical composition
(absorbing and non absorbing) from the recent work of Mishra and Tripathi (2008), who modeled the optical
properties of pure dust particles over Indian desert. Mixing state of the two species i.e. dust and BC is an
important issue (Clarke et al., 2004) while modeling these systems. We consider both external and internal
mixing scenarios while modeling in absence of any observational information. Earlier study on mixing state of
aerosols (assuming them to be spherical in shape), in IGB, have indicated that dust coated with BC is the
most probable scenario for internal mixing (Dey et al., 2008). In the present study, optical properties
(scattering and absorption cross-sections, phase functions and asymmetry parameter) have been modeled
using Discrete Dipole Approximation method (Draine and Flatau, 2004) for a variety of non spherical shapes
such as concentric spheres, spheroids, ellipsoids and layered rectangular bar, and various combinations of
spheres and spheroids attached externally (maximum up to three).
References
Clarke, A. D., et al. (2004), Size distributions and mixtures of dust and black carbon aerosol in Asian outflow:
Physiochemistry and optical properties, J. Geophys. Res., 109, D15S09.
Dey, S., et al. (2008), On the mixing state of aerosols in the Indo-Gangetic basin, northern India, Geophys.
Res. Lett., 35, L03808.
Draine, B. T., and P. J. Flatau (2004), User Guide for the Discrete Dipole Approximation Code DDSCAT 6.1,
http://arxiv.org/abs/astro-ph/0409262v2.
Lau, K. M., et al. (2006), Asian summer monsoon anomalies induced by aerosol direct forcing: the role of the
Tibetan Plateau., J. Climate, 26, 855-864.
Mishra, S. K., and S. N. Tripathi (2008), Modeling optical properties of mineral dust over the
Indian Desert, J. Geophys. Res., accepted.
Sokolik, I. N., and O. B. Toon (1999), Incorporation of mineralogical composition into models of the radiative
properties of mineral aerosol from UV to IR wavelengths, J. Geophys. Res., 104, 9423-
9444.
Tripathi S. N., et al. (2005), Aerosol black carbon radiative forcing at an industrial city in Northern India,
Geophys. Res. Lett., 32(8), L08802.
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A11C-0134
Single Particle Scanning Electron Microscopy Analysis of Wet-Season Aerosol Collected in the Amazonian Tropical Rain Forest (Manaus, Brasil)
Single particle analysis of aerosols particles larger than 0.2 μm diameter was performed on samples collected in the tropical rain forest (Manaus, Brasil) during the AMAZE campaign in February and March 2008. The elemental composition and morphology of the particles were determined using SEM–EDX. The aerosol particles were divided into 10 groups according to their chemical composition and morphology: droplets of organic aerosol (OA), primary biogenic particles with and without OA coatings, other carbonaceous aerosol with and without OA coatings, mineral dust with and without OA coating and sea salt with and without OA coatings were identified as the most abundant aerosol groups. We present size distributions for all particle groups and the abundance of these groups in different size ranges. Due to careful investigation of the samples at a low acceleration voltage for the first time OA droplets and coatings were identified as a significant contribution to wet season aerosol mass collected in the Amazonian tropical rain forest, during single particle SEM analysis. During days with low aerosol loadings, OA droplets typically accounted for >50% of the accumulation mode aerosol, OA droplets with sea salt core (20- 40%), other carbonaceous aerosol (5-10%), mineral dust (5-10%), and primary biogenic particles with and without OA coatings accounted for most of the remainder. Coarse mode particles were dominated by primary biogenic particles with (>50%) and without (~10-20%) OA coatings. Mineral dust (~10- 20%), sea salt (~10%), dust with OA coatings (~10%) and OA droplets (~5%) accounted for most of the remainder. During days with higher particle numbers the relative abundance of other carbonaceous aerosol with (~20%) and without (~10%) OA coatings increased. The high frequency of OA coatings on different particles types has implications for the radiative properties as well as the hygroscopic behavior of wet season aerosol particles. For the first time we investigate the frequency of such coatings on different particle types and for different size ranges.
A11C-0135
Measurements of Primary Biogenic Aerosol Particles with an Ultraviolet Aerodynamic Particle Sizer (UVAPS) During AMAZE-08
Biogenic aerosols are ubiquitous in the Earth's atmosphere and they influence atmospheric chemistry and
physics, the biosphere, climate, and public health. They play an important role in the spread of biological
organisms and reproductive materials, and they can cause or enhance human, animal, and plant diseases.
Moreover, they influence the Earth's energy budget by scattering and absorbing radiation, and they can
initiate the formation of clouds and precipitation as cloud condensation and ice nuclei. The composition,
abundance, and origin of biogenic aerosol particles and components are, however, still not well understood
and poorly quantified. Prominent examples of primary biogenic aerosol particles, which are directly emitted
from the biosphere to the atmosphere, are pollen, bacteria, fungal spores, viruses, and fragments of animals
and plants.
During the AMazonian Aerosol CharacteriZation Experiment (AMAZE-08) a large number
of aerosol and gas-phase measurements were taken on a remote site close to Manaus, Brazil, during a
period of five weeks in February and March 2008. The presented study is focused on data from an ultraviolet
aerodynamic particle sizer (UVAPS, TSI inc.) that has been deployed for the first time in Amazonia. In this
instrument, particle counting and aerodynamic sizing over the range of 0.5-20 μm are complemented by
the measurement of UV fluorescence at 355 nm (excitation) and 420-575 nm (emission), respectively.
Fluorescence at these wavelengths is characteristic for reduced pyridine nucleotides (e.g., NAD(P)H) and for
riboflavin, which are specific for living cells. Thus particles exhibiting fluorescence signals can be regarded as
'viable aerosols' or 'fluorescent bioparticles' (FBAP), and their concentration can be considered as lower limit
for the actual abundance of primary biogenic aerosol particles.
First data analyses show a pronounced peak of FBAP at diameters around 2-3 μm. In this size range the
biogenic particle fraction was generally higher than 50 %. Additionally, bursts of FBAP have been observed
nearly every day just before sunrise. During these periods the coarse (super-micron) aerosol consisted
almost completely of fluorescent bioparticles.
A11C-0136
Using Multi-Isotope Tracer Methods to Understand the Sources of Nitrate in Aerosols, Fog and River Water in Podocarpus National Forest, Ecuador
The eastern slopes of the Andean rainforests of Ecuador possess some of the highest plant biodiversity found on the planet; however, these ecosystems are in jeopardy because region is experiences one of the highest deforestation rates in South America. This rainforest characterized by high acidity and low nutrient soils and experiences natural process which are both destabilizing and stabilizing to biodiversity rendering this a unique, though sensitive environment. There is increased concern that anthropogenic activities especially biomass burning are affecting the rainforests and could lead to higher extinction rates, changes in the biodiversity and far reaching effects on the global troposphere. Measurements of nitrate and sulfate in rain and fog water have shown periods of elevated concentrations in the Podocarpus National Park near Loja, Ecuador. These high episodes contribute to annual deposition rates that are comparable to polluted regions of North America and Europe. Significant anthropogenic sources such as large scale industry or a major city, near this forest are lacking. It is believed that the majority of the nitrate and sulfate pollution is due to the large amount of biomass burning during the dry season in the Amazon Basin. In recent years it has been shown that large amount of dust is transported across the Atlantic from Africa which reaches South America. Concentration measurements do not elucidate the source of high nitrate and sulfate pollution; however, by measuring all three stable isotopes of oxygen in nitrate and sulfate from fog and river water provides a new way to examine the impacts of biomass burning on the region. By using stable isotope techniques atmospheric nitrate and sulfate can be resolved from terrestrial sources. This provides a unique way to trace the contributions from the biomass burning and farming sources. Current research at the field station, Estación Científica San Francisco in the Podocarpus National Forest monitors sulfate and nitrate concentrations in rain and fog water by standard methods to investigate water and nutrient pathways along with data from satellite and ground based remote sensing, observations and numerical models. We hope to pair this with a multi-isotope tracer method and NOAA Hysplit Back trajectories, and satellite imagery for information about the number of fires burning in the region to help identify sources of the high nitrate deposition.
A11C-0137
Global impacts of South Asian outflow of organic carbon aerosol in spring
We analyze features of atmospheric circulation and transport of organic carbon (OC) aerosol emitted in South Asia using the global 3-D chemical transport model GEOS-Chem driven by the assimilated meteorological data. Strong deep convections over South Asia and the northeastward transport associated with the Western Pacific subtropical high favor the South Asian outflow of OC in March-May when biomass burning emissions are the largest in a year. Concentrations of OC in the free troposphere (FT) over eastern China are found to peak simultaneously with those in South Asia in spring. Model results show that in spring OC emitted in South Asia contributes to 5-50% of surface-layer OC mass in southern China, while the fraction of OC lifted to the FT undergoes intercontinental transport. At 500 hPa , South Asian outflow of OC accounts for about 40-80%, 40-60%, and 30-50% of OC concentrations, respectively, over eastern China, the United States, and Europe. As compared with the measured high OC values over eastern Asia during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia), model predictions of OC concentrations in the FT exhibit a low bias. Sensitivity studies are performed to identify the uncertainties associated with the simulation of emission, transport and deposition of OC from South Asia.
A11C-0138
The Climate Effects Of Seasonally Varying Tropical Carbonaceous Aerosols
Biomass-burning emitted carbonaceous aerosols (BBCA) in the tropical region play an important role in the earth's radiation budget and hydrological cycle by absorbing and scattering sunlight and by acting as condensation nuclei for clouds. Due to the characteristics of their sources, the appearance of BBCA and thus their radiative forcing has a very strong seasonality. The climate effects of this type of seasonal aerosol forcing are not fully understood. In this study, the climate impact of strong periodic emissions of BBCA has been examined by using a three-dimensional interactive aerosol-climate system model developed based on the Community Atmospheric Model (CAM3) of NCAR. The aerosol module of this model describes size and mixing-state dependent physiochemical and radiative processes of seven aerosol modes using a two-moment scheme, including major anthropogenic aerosol constituents of sulfate, BC, and OC as well as their mixtures. The biomass burning emissions of carbonaceous aerosols were prepared based on the Global Emissions Inventory Activity (GEIA) monthly biomass burning black carbon data (http://www.geiacenter.org). The climate effect of seasonality of tropical carbonaceous aerosol forcing is derived by comparing modeled results of two 60-year integrations (driven by a slab ocean model) respectively using the constant and seasonal emissions of carbonaceous aerosols. We will discuss the difference in the BBCA-climate interaction caused by the seasonality of biomass-burning carbonaceous emissions, and the changes in the source and sink of aerosols as well as the transformation of their radiative and hygroscopic properties due to the seasonal emissions.
A11C-0139
Size-resolved measurements of cloud condensation nuclei (CCN) during the wet season in Amazonia
Aerosol particles that serve as cloud condensation nuclei (CCN) are of central importance for several aspects of the climate system, especially the formation of cloud and precipitation, and for the Earth's radiative balance. The CCN activity and its relation to other properties of aerosol particles from different sources and regions, are, however, not yet well characterized (Vestin, et al. 2007; Andreae and Rosenfeld 2008). In this study we have determined CCN properties during the AMAZE-08 (Amazonian Aerosol Characterization Experiment) campaign over the Amazonian rainforest north-west of Manaus, Brazil (2.594541 S, 60.209289 W; 14 February to 14 March 2008). CCN efficiency spectra and concentrations were measured as a function of dry aerosol particle diameter (20-300 nm) and water vapor supersaturation (S = 0.095-0.82%) using a continuous flow CCN counter setup as described by Rose, et al., 2008. The average CCN activation diameters of the dry aerosol particles were in the range of 60-200 nm for this range of supersaturations. These values are about 50-70% higher than those of pure ammonium sulfate and correspond to effective hygroscopicity parameters κ in the range of 0.1–0.2, which is lower than what has been reported for other continental environments (Petters and Kreidenweis 2007; Andreae and Rosenfeld 2008; Pöschl et al., 2008). Depending on supersaturation, the CCN concentrations were in the range of 20-120 cm-3. The online CCN measurements were complemented by experiments with a filter based differential hygroscopicity analyzer (FDHA). Key results and implications will be presented and discussed. References: Andreae, M. O. and D. Rosenfeld (2008). "Aerosol-cloud-precipitation interactions. Part 1. The nature and sources of cloud-active aerosols." Earth-Science Reviews 89(1-2): 13-41. Petters, M. D. and S. M. Kreidenweis (2007). "A single parameter representation of hygroscopic growth and cloud condensation nucleus activity." Atmospheric Chemistry and Physics 7(8): 1961-1971. Pöschl, U., Rose, D., and Andreae, M. O.: Climatologies of Cloud-related Aerosols: Part 2: Particle Hygroscopicity and Cloud Condensation Nuclei Activity, Clouds in the Perturbed Climate System: Their Relationship to Energy Balance, Atmospheric Dynamics, and Precipitation. Strüngmann Forum Report, Vol. 2, edited by: Heintzenberg, J., and Charlson, R. J., The MIT Press, Cambridge, MA, 2008. Rose, D., S. S. Gunthe, et al. (2008). "Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment." Atmospheric Chemistry and Physics 8(5): 1153-1179. Vestin, A., J. Rissler, et al. (2007). "Cloud-nucleating properties of the Amazonian biomass burning aerosol: Cloud condensation nuclei measurements and modeling." Journal of Geophysical Research-Atmospheres 112(D14).
A11C-0140
Global estimation of above-cloud aerosols using spaceborne LIDAR
Estimates of global mean direct climate forcing by absorbing aerosols located above boundary layer clouds are large, uncertain, and almost entirely unconstrained by observations. Spaceborne lidar offers a new opportunity of estimating the aerosols at global scale. Here we use two recently available techniques quantifying the above-cloud aerosols using liquid water clouds as lidar targets from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) [Chand et al., 2008]. Both methods can quantify aerosols above clouds and are based on their self-calibrating techniques. We used one year of global data between 70N-70S to show that day time calibration constants are different than night time calibrations constants. A clear latitudinal dependence is observed in the calibrations constants in CALIPSO observations. Using these 'self-calibration' constants, aerosol optical depth (AOD) and angstrom exponent (AE) of 'above- cloud' aerosols are quantified. Biomass burning is a major source of fine mode aerosols in different regions of world. For example, it is observed that June is the onset of the biomass burning fires in Southern Africa, peaking in August and September and then slowly decreasing until November, with a corresponding signature in aerosol optical depth. Layers with aerosol optical depth greater than 0.3 are commonly observed up to several thousand kilometers away from Africa over the Atlantic Ocean. The 'above-cloud' AOD as high as 1.5 is observed in the peak months. Despite of large variations is AOD, mean AE of these aerosols is about 1.6, without any systematic variability away from the source region. The results estimating the aerosols above clouds, including other regions at global scale, will be presented in the AGU meeting. Chand, D., T. L. Anderson, R. Wood, R. J. Charlson, Y. Hu, Z. Liu, and M. Vaughan (2008), Quantifying above-cloud aerosol using spaceborne lidar for improved understanding of cloudy-sky direct climate forcing, J. Geophys. Res., 113, D13206, doi:10.1029/2007JD009433.
A11C-0141
The Behavior of the Nitrogen Dioxide, Total Peroxy Nitrates, and Total Alkyl Nitrates in the Borneo Forest During 2008 OP3 campaign
The production of secondary organic aerosols due to the oxidation of biogenic volatile organic compounds, is controlled by NOx and its reservoir concentrations. The mixing ratios of NO2, RO2NO2 and RONO2 were measured as part of the multi-investigator study, OP3, which took place in the Borneo forest (Malaysia) in July 2008. Ten hertz NO2 measurements allow to use the eddy covariance technique to determine NO2 fluxes. NO2, RO2NO2 and RONO2 show diurnal behavior with very low concentration (NO2 below 1 ppbv for almost all the campaign), although it is greater during nights than during days. The implications of these observations and their impact on secondary aerosols production will be discussed.
A11C-0142
Ice Nuclei Measurements From AMAZE-08
The Amazon Basin is the largest intact tropical forest in the world, covering four million square kilometers. With large emissions of gases and particulate matter, this ecosystem plays an important role in the global atmosphere. Assessing gaseous and particulate emissions from the Amazon Basin and the climatic effects of these emissions has been the focus of several major field campaigns. However, until recently there have been no measurements aimed at characterizing ice nuclei (IN) in this region. Such measurements are critical for understanding cloud and precipitation processes. In this paper, we present recent ice nuclei measurements from the AMazonian Aerosol characteriZation Experiment 2008 (AMAZE-08). These data were collected during the rainy season at the Instituto Nacional de Pesquisas da Amazonia TT34 tower northeast of Manaus, Brazil. Results are presented for ice nuclei number concentration and elemental composition collected using the Colorado State University Continuous Flow ice thermal Diffusion Chamber (CFDC). The data suggest that, like many regions of the world, IN concentrations are largely controlled by the presence of desert dust, in this case transported from Africa. However, carbonaceous particles also made up a significant fraction of IN. Based on complementary aerosol composition measurements, we consider possible sources of this carbonaceous fraction.
A11C-0143
Retrieval of Aerosol Single-Scattering Albedo over North Africa via Critical Reflectance
A significant source of uncertainty in the determination of global direct radiative forcing is the uncertainty in the direct forcing over land. An accurate determination of this forcing is dependent upon the availability of reliable information on aerosol absorption. Over ocean, aerosols cause a cooling at the top-of-the- atmosphere; over land, the sign of the aerosol direct effect depends on whether the aerosol is effectively brighter or darker than the underlying surface. Obtaining aerosol absorption information over land is possible using space-based sensors; however, it is complicated due to the sometimes large and spatially-varying surface signal, especially over bright desert surfaces. The aerosol critical reflectance is one parameter that can be used to determine aerosol absorption by deriving it with respect to the underlying surface properties. We estimate aerosol critical reflectance over North Africa, a source region for absorbing mineral dust and biomass burning aerosol species, using MODIS Level 1B reflectance data. Unlike single-image over-desert aerosol retrieval methods, which rely on a minimum top-of-atmosphere reflectance for information about the surface, the critical reflectance method compares two MODIS images with different aerosol loading and the same solar and viewing geometry, 16- days apart, to derive the aerosol critical reflectance. Comparisons of the critical reflectance on coincident 16- day image pairs yield basic information about the aerosol chemistry; we find a positive correlation between spectral dependence of critical reflectance and near-IR path radiance for dust, while a negative spectral dependence of critical reflectance in the visible channels indicates biomass burning aerosol. We then use this information to relate the aerosol critical reflectance to single-scattering albedo (SSA) via a DISORT-type radiative transfer code. Aerosol SSA and size estimates are compared to observations from AERONET and in situ data obtained as a part of the Dust and Biomass Experiment (DABEX) and the Langley Aerosol Research Group Experiment (LARGE), components of the African Monsoon Multidisciplinary Analyses (AMMA) campaign, during 2006. Sensitivity of the critical reflectance to assumed size distributions is also examined, and limitations of the method explored.
A11C-0144
Aerosol Data Assimilation With the Southern Hemispheric CCATT-BRAMS Atmospheric Model With Focus on Fire Emissions
This paper presents the new aerosol data assimilation system of the numerical model CCATT-BRAMS (Coupled Chemistry-Aerosol-Tracer Transport model coupled to the Brazilian developments on the Regional Atmospheric Modeling System (BRAMS)) of INPE. The assimilation system is being developed to improve model simulations of air pollution sources, mainly from fires, and their dispersion in the atmosphere over South America and the South Atlantic. By these means model results are corrected with observational data in an objective and consistent way. Specifically, the three dimensional variational assimilation technique (3- DVAR) is used to assimilate Aerosol Optical Depth (AOD) columns of the Moderate Resolution Imaging Spectroradiometer (MODIS), and in-situ observations from the AERONET (AERosol Robotic NETwork) into CCATT-BRAMS. These model results enriched by data assimilation (i) allow for studies of fire aerosol and tracer formation and transport in the southern hemisphere, and will contribute to an enhanced performance of the operational chemical weather forecast by CPTEC/INPE, and (ii) allow to gain more knowledge about possible improvements for model studies with chemistry at climatological time scales. First validation results of this new system will be presented.