Source Of Atmospheric Aerosols Research Articles

Growth of atmospheric nano-particles by heterogeneous nucleation of organic vapor

Abstract. Atmospheric aerosols play critical roles in air quality, public health, and visibility. In addition, they strongly influence climate by scattering solar radiation and by changing the reflectivity and lifetime of clouds. One major but still poorly understood source of atmospheric aerosols is new particle formation, which consists of the formation of thermodynamically stable clusters from trace gas molecules (homogeneous nucleation) followed by growth of these clusters to a detectable size (~3 nm). Because freshly nucleated clusters are most susceptible to loss due to high rate of coagulation with pre-existing aerosol population, the initial growth rate strongly influences the rate of new particle formation and ambient aerosol population. Whereas many field observations and modeling studies indicate that organics enhance the initial growth of the clusters and therefore new particle formation, thermodynamic considerations would suggest that the strong increase of equilibrium vapor concentration due to cluster surface curvature (Kelvin effect) may prevent ambient organics from condensing on these small clusters. Here, the contribution of organics to the initial cluster growth is described as heterogeneous nucleation of organic molecules onto these clusters. We find that the strong gradient in cluster population with respect to its size leads to positive cluster number flux. This positive flux drives the growth of clusters substantially smaller than the Kelvin diameter, conventionally considered the minimum particle size that can be grown through condensation. The conventional approach neglects the contribution from the cluster concentration gradient, and underestimates the cluster survival probabilities by a factor of up to 60 if early growth of clusters is due to both condensation of sulfuric acid and heterogeneous nucleation of organic vapors.

Overview of the meteorology and transport patterns during the DAURE field campaign and their impact to PM observations

The experimental campaign “Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in Spain” (DAURE) took place in a urban (Barcelona city) and a rural (the Montseny Natural Park) Spanish sites. Its main objective was to study the formation and transport processes of particulate matter in the region during winter and summer time. This paper presents a description of the meteorological conditions during the campaign by means of meteorological observations, high-resolution mesoscale meteorological modelling and backward Lagrangian particle dispersion simulations. Modelling results are in agreement with observations and provide a valuable tool for characterizing transport patterns in relation to episodes of air pollution. An objective classification of the synoptic conditions and a classification of the main local dispersion patterns is presented and discussed. Additionally, the measured PM1 and PM10 levels in both urban and rural sites are discussed and related to the meteorological conditions observed.

SO2 oxidation and nucleation studies at near-atmospheric conditions in outdoor smog chamber

Environmental context Nucleation, a fundamental step in atmospheric new-particle formation, is a significant source of atmospheric aerosols. Most laboratory experiments investigate H2SO4 nucleation based on indoor chambers or flow tube reactors, and find discrepancies with field observations. Here a large outdoor smog chamber is used to study the relationship between SO2 and nucleation rates, and demonstrate the importance of aqueous phase oxidation of SO2 by H2O2 and other oxidants. Abstract Particle formation under different initial ambient background conditions was simulated in a dual outdoor smog chamber for the SO2 and O3–SO2 systems with and without sunlight, as well as a propylene–NOx–SO2–sunlight system. An exponential power of 1.37 between nucleation rates at 1nm (J1) and SO2 gas phase concentrations was obtained for the SO2–sunlight system and a minimum of 0.45ppbSO2 is required by this relationship to initiate nucleation (J1 is equal to 1cm–3s–1). An investigation of the O3–SO2–sunlight/dark system showed that the presence of O3 contributed to the particle nucleation and growth at night; however, it only enhanced the particle growth in the daytime when H2SO4 photochemistry was present. In the presence of an OH• scavenger, the O3–SO2 system did not show particle nucleation, suggesting that the scavenger cut off this pathway of SO2 oxidation. A lower nucleation rate and higher particle grow rate were also observed for SO2 oxidation in the presence of propylene and NOx. However a higher SO2 decay rate was obtained for the propylene system especially under high relative humidity, which was not observed in the O3–SO2 system. This suggests that aqueous phase oxidation of SO2 from H2O2, RO2• and other oxidants produced in the propylene–NOx system contribute to the particle growth.

The relative role of Amazonian and non-Amazonian fires in building up the aerosol optical depth in South America: A five year study (2005–2009)

In South America (SA) biomass burning is the major source of atmospheric aerosols. Fires are mostly registered in the dry season (July–November) and are mainly concentrated in the Amazonia and Cerrado regions. Nonetheless, the growing systematic employment of fires for land clearing and pasture maintenance across the SA continent is introducing other, potentially significant, sources of BB aerosols. This study investigates the relative contributions of different SA biomass burning regions in building up the continental aerosol load. To this purpose, the SA continent is divided into four biomass burning source regions and their impact on the aerosol optical depth (AOD) is evaluated in eight different SA target domains. The dataset used includes multi-year (2005–2009) satellite observations of both aerosol and fires and model-based atmospheric trajectories. The methodology followed couples fire counts and atmospheric transport through the definition of a specific quantity, referred to as ‘fire weighted residence time’ (FWRT), which is used to assess the contribution of the four identified fire source regions to the continental aerosol load.Results show that local fires play an important role in building up the regional aerosols load all over SA. Nevertheless, in some regions, contribution of BB aerosols transported from outside their boundaries is comparable to the local one. The major ‘smoke exporter’ regions are found to be the eastern Brazil and the Amazonia–Cerrado regions. In the dry season, due to the typical continental circulation pattern, the first is estimated to contribute to half of the AOD in Northern Amazonia, Southern Amazonia and Cerrado regions, while over 30% of the AOD in Paraguay and North Argentina derives from the Amazonia–Cerrado fires. Due to the presence of the inter-tropical convergence zone, which decouples wind circulation of the two hemispheres, regions north of the Equator (Venezuela, Guyana, Suriname) are found to receive almost no contribution to the local AOD from fires occurring in the nearby active regions of Amazonia and Caatinga. Similarly, Venezuela fires are shown not to impact the Northern Amazonia AOD. Finally, in excluding the continental fire driver of some AOD enhancements observed in the wet season, this study indirectly points to an important role of aerosol transoceanic transport from Africa.

Identification and quantification of organic aerosol from cooking and other sources in Barcelona using aerosol mass spectrometer data

Abstract. PM1 (particulate matter with an aerodynamic diameter <1 μm) non-refractory components and black carbon were measured continuously together with additional air quality and atmospheric parameters at an urban background site in Barcelona, Spain, during March 2009 (campaign DAURE, Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the western Mediterranean). Positive matrix factorization (PMF) was conducted on the organic aerosol (OA) data matrix measured by an aerosol mass spectrometer, on both unit mass (UMR) and high resolution (HR) data. Five factors or sources could be identified: LV-OOA (low-volatility oxygenated OA), related to regional, aged secondary OA; SV-OOA (semi-volatile oxygenated OA), a fresher oxygenated OA; HOA (hydrocarbon-like OA, related to traffic emissions); BBOA (biomass burning OA) from domestic heating or agricultural biomass burning activities; and COA (cooking OA). LV-OOA contributed 28% to OA, SV-OOA 27%, COA 17%, HOA 16%, and BBOA 11%. The COA HR spectrum contained substantial signal from oxygenated ions (O:C: 0.21) whereas the HR HOA spectrum had almost exclusively contributions from chemically reduced ions (O:C: 0.03). If we assume that the carbon in HOA is fossil while that in COA and BBOA is modern, primary OA in Barcelona contains a surprisingly high fraction (59%) of non-fossil carbon. This paper presents a method for estimating cooking organic aerosol in ambient datasets based on the fractions of organic mass fragments at m/z 55 and 57: their data points fall into a V-shape in a scatter plot, with strongly influenced HOA data aligned to the right arm and strongly influenced COA data points aligned to the left arm. HR data show that this differentiation is mainly driven by the oxygen-containing ions C3H3O+ and C3H5O+, even though their contributions to m/z 55 and 57 are low compared to the reduced ions C4H7+ and C4H9+. A simple estimation method based on the markers m/z 55, 57, and 44 is developed here and allows for a first-order-estimation of COA in urban air. This study emphasizes the importance of cooking activities for ambient air quality and confirms the importance of chemical composition measurements with a high mass and time resolution.

From quantum chemical formation free energies to evaporation rates

Abstract. Atmospheric new particle formation is an important source of atmospheric aerosols. Large efforts have been made during the past few years to identify which molecules are behind this phenomenon, but the actual birth mechanism of the particles is not yet well known. Quantum chemical calculations have proven to be a powerful tool to gain new insights into the very first steps of particle formation. In the present study we use formation free energies calculated by quantum chemical methods to estimate the evaporation rates of species from sulfuric acid clusters containing ammonia or dimethylamine. We have found that dimethylamine forms much more stable clusters with sulphuric acid than ammonia does. On the other hand, the existence of a very deep local minimum for clusters with two sulfuric acid molecules and two dimethylamine molecules hinders their growth to larger clusters. These results indicate that other compounds may be needed to make clusters grow to larger sizes (containing more than three sulfuric acid molecules).

Fossil versus contemporary sources of fine elemental and organic carbonaceous particulate matter during the DAURE campaign in Northeast Spain

Abstract. We present results from the international field campaign DAURE (Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the Western Mediterranean), with the objective of apportioning the sources of fine carbonaceous aerosols. Submicron fine particulate matter (PM1) samples were collected during February–March 2009 and July 2009 at an urban background site in Barcelona (BCN) and at a forested regional background site in Montseny (MSY). We present radiocarbon (14C) analysis for elemental and organic carbon (EC and OC) and source apportionment for these data. We combine the results with those from component analysis of aerosol mass spectrometer (AMS) measurements, and compare to levoglucosan-based estimates of biomass burning OC, source apportionment of filter data with inorganic composition + EC + OC, submicron bulk potassium (K) concentrations, and gaseous acetonitrile concentrations. At BCN, 87 % and 91 % of the EC on average, in winter and summer, respectively, had a fossil origin, whereas at MSY these fractions were 66 % and 79 %. The contribution of fossil sources to organic carbon (OC) at BCN was 40 % and 48 %, in winter and summer, respectively, and 31 % and 25 % at MSY. The combination of results obtained using the 14C technique, AMS data, and the correlations between fossil OC and fossil EC imply that the fossil OC at Barcelona is ∼47 % primary whereas at MSY the fossil OC is mainly secondary (∼85 %). Day-to-day variation in total carbonaceous aerosol loading and the relative contributions of different sources predominantly depended on the meteorological transport conditions. The estimated biogenic secondary OC at MSY only increased by ∼40 % compared to the order-of-magnitude increase observed for biogenic volatile organic compounds (VOCs) between winter and summer, which highlights the uncertainties in the estimation of that component. Biomass burning contributions estimated using the 14C technique ranged from similar to slightly higher than when estimated using other techniques, and the different estimations were highly or moderately correlated. Differences can be explained by the contribution of secondary organic matter (not included in the primary biomass burning source estimates), and/or by an overestimation of the biomass burning OC contribution by the 14C technique if the estimated biomass burning EC/OC ratio used for the calculations is too high for this region. Acetonitrile concentrations correlate well with the biomass burning EC determined by 14C. K is a noisy tracer for biomass burning.

Source apportionment of particulate organic compounds in a rural area of Spain by positive matrix factorization

This study was conducted in order to identify possible sources and to estimate their contribution to particulate matter in a rural area. For this purpose, a commonly used receptor model, positive matrix factorization (PMF), was applied to a PM2.5 data set collected in a rural area of Madrid (Spain) between May 2004 and April 2005. A total of eighty nine samples were gathered. Chemical composition of particulate matter including major components, trace elements, total carbon, alkanes, PAHs, alcohols and acids were analyzed to study sources of atmospheric aerosols using the positive matrix factorization model. This work is characterized by including some organic tracers within PMF analysis, through which we can get a more accurate source apportionment. To our knowledge, this is the first work employing organic tracers for source apportionment by PMF model in a rural area of Spain. To assign PMF factor with a possible source, authors have based on the presence of tracer species. PMF apportioned the PM2.5 mass into nine factors. The factors included (1) even n–alcohols/acids factor, (2) n–alkanes factor, (3) secondary nitrate factor, (4) secondary sulfate factor, (5) secondary organic aerosol, (6) palmitic/stearic factor, (7) PAHs factor, (8) crustal factor and (9) low molecular weight alcohols/acids factor. Six of these factors are related to primary emissions and three of them are categorized as secondary aerosol. PMF identified two mixed sources, factor 6 identified as cooking /microbial source and factor 9 identified as a mixed source.

Characteristics, seasonality and sources of carbonaceous and ionic components in the tropical aerosols from Indian region

Abstract. To better characterize the tropical aerosols in Indian region, PM10 samples collected from Chennai, India (13.04° N; 80.17° E) were analyzed for carbonaceous and water-soluble ionic components. Concentration ranges of elemental carbon (EC) and organic carbon (OC) were 2.4–14 μg m−3 (ave. 6.5 μg m−3) and 3.2–15.6 μg m−3 (ave. 9.1 μg m−3) in winter samples whereas they were 1.1–2.5 μg m−3 (ave. 1.6 μg m−3) and 4.1–17.6 μg m−3 (ave. 9.7 μg m−3) in summer samples, respectively. Concentration of secondary organic carbon (SOC) retrieved from EC-tracer method was 4.6±2.8 μg m−3 in winter and 4.3±2.8 μg m−3 in summer. OC accounted for 38.5±14 % (n = 49) of combined concentrations of carbonaceous and ionic components in PM10. We also found that OC concentrations are generally higher than those of SO42− (8.8±2.5 μg m−3 and 4.1±2.7 μg m−3 in winter and summer, respectively), which was the most abundant ionic species (57 %) followed by NH4+ (15 %) >NO3−>Cl−>K+>Na+> Ca2+>MSA−>Mg2+. The mass fractions of EC, organic matter (OM) and ionic species varied seasonally, following the air mass trajectories and corresponding source strength. Based on mass concentration ratios of selected components and relations of EC and OC to marker species, we found that biofuel/biomass burning is a major source of atmospheric aerosols in South and Southeast Asia. The high concentrations of SOC and WSOC/OC ratios (ave. 0.45; n = 49) as well as good correlations between SOC and WSOC suggest that the secondary production of organic aerosols during long-range atmospheric transport is also significant in this region. This study provides the baseline data of carbonaceous aerosols for southern part of the Indian subcontinent.

On-line measurement of organic aerosol elemental composition based on high resolution aerosol mass spectrometry

Organic matter is a crucial component of atmospheric aerosols. The density, hygroscopicity, and vapor pressure of organic aerosol are closely related to its elemental composition. In this study, a newly-developed elemental analytical method based on high resolution aerosol mass spectrometry was used to measure the elemental compositions of organic aerosols in China, with a high time resolution of 10 minutes. The average composition of organic matter (at%) in PM₁ in summer in Shenzhen was 35.0 C, 53.8 H, 0.9 N and 10.4 O, corresponding to an OM/OC ratio (mass ratio of organic matter to organic carbon) of 1.55; the values for summer in Beijing were 34.8 C, 51.6 H, 0.8 N and 12.7 O, corresponding to an OM/OC ratio of 1.64. The OM/OC ratios correlated strongly with the O/C ratios, indicating that the oxygen content of organic aerosols is a dominant factor in determining the OM/OC ratio. Generally the diurnal variations of the O/C ratios in both Shenzhen and Beijing showed higher values in the daytime and lower values at night, and had three short periods with especially low values: in the morning, at noon, and in the evening. This reflects changes in the relative influence of primary emissions and secondary formation of organic aerosol. Future detailed studies of the O/C ratios of organic aerosols will significantly improve our understanding of the properties and sources of atmospheric aerosols in China.

Oxidation of ketone groups in transported biomass burning aerosol from the 2008 Northern California Lightning Series fires

Submicron particles were collected from June to September 2008 in La Jolla, California to investigate the composition and sources of atmospheric aerosol in an anthropogenically-influenced coastal site. Factor analysis of aerosol mass spectrometry (AMS) and Fourier transform infrared (FTIR) spectroscopy measurements revealed that the two largest sources of submicron organic mass (OM) at the sampling site were (1) fossil fuel combustion associated with ship and diesel truck emissions near the ports of Los Angeles and Long Beach and (2) aged smoke from large wildfires burning in central and northern California. During non-fire periods, fossil fuel combustion contributed up to 95% of FTIR OM, correlated to sulfur, and consisted mostly of alkane (86%) and carboxylic acid groups (9%). During fire periods, biomass burning contributed up to 74% of FTIR OM, consisted mostly of alkane (48%), ketone (25%), and carboxylic acid groups (17%), and correlated to AMS-derived factors resembling brush fire smoke, wood smoldering and flaming particles, and biogenic secondary organic aerosol. The two AMS-derived biomass burning factors were identified as oxygenated and hydrocarbon biomass burning aerosol on the basis of spectral similarities to smoldering and flaming smoke particles, respectively. In addition, the ratio of oxygenated to hydrocarbon biomass burning OM shows a clear diurnal trend with an afternoon peak, consistent with photochemical oxidation. Back trajectory analysis indicates that 2–4-day old forest fire emissions include substantial ketone groups, which have both lower O/C and lower m/ z 44/OM fraction than carboxylic acid groups. Air masses with more than 4-day old emissions have higher carboxylic acid/ketone group ratios, showing that atmospheric processing of these ketone-containing organic aerosol particles results in increased m/ z 44 and O/C. These observations may provide functionally-specific evidence for the type of chemical processing that is responsible for biomass burning particle composition in the atmosphere.

A review of natural aerosol interactions and feedbacks within the Earth system

Abstract. The natural environment is a major source of atmospheric aerosols, including dust, secondary organic material from terrestrial biogenic emissions, carbonaceous particles from wildfires, and sulphate from marine phytoplankton dimethyl sulphide emissions. These aerosols also have a significant effect on many components of the Earth system such as the atmospheric radiative balance and photosynthetically available radiation entering the biosphere, the supply of nutrients to the ocean, and the albedo of snow and ice. The physical and biological systems that produce these aerosols can be highly susceptible to modification due to climate change so there is the potential for important climate feedbacks. We review the impact of these natural systems on atmospheric aerosol based on observations and models, including the potential for long term changes in emissions and the feedbacks on climate. The number of drivers of change is very large and the various systems are strongly coupled. There have therefore been very few studies that integrate the various effects to estimate climate feedback factors. Nevertheless, available observations and model studies suggest that the regional radiative perturbations are potentially several Watts per square metre due to changes in these natural aerosol emissions in a future climate. Taking into account only the direct radiative effect of changes in the atmospheric burden of natural aerosols, and neglecting potentially large effects on other parts of the Earth system, a global mean radiative perturbation approaching 1 W m−2 is possible by the end of the century. The level of scientific understanding of the climate drivers, interactions and impacts is very low.

Kinetic modeling of nucleation experiments involving SO<sub>2</sub> and OH: new insights into the underlying nucleation mechanisms

Abstract. Nucleation is an important source of atmospheric aerosols which have significant climatic and health implications. Despite intensive theoretical and field studies over the past decades, the dominant nucleation mechanism in the lower troposphere remains to be mysterious. Several recent laboratory studies on atmospheric nucleation may shed light on this important problem. However, the most interesting finding from those studies was based on the derived H2SO4 concentration whose accuracy has not yet been evaluated by any other means. Moreover, the threshold H2SO4 concentration needed to reach the same degree of nucleation reported by two separate nucleation studies varies by about one order of magnitude. In this study, we apply a recently updated kinetic nucleation model to study the nucleation phenomena observed in those recent experiments. We show that the H2SO4 concentration can be estimated with a higher level of accuracy with the kinetic model by constraining the simulated particle size distributions with observed ones. We find that the required H2SO4 concentrations to achieve the best agreement between modeling and measurements are a factor of ~2 to 4 higher than reported in those experiments. More importantly, by comparing the derived thermodynamic properties associated with the nucleation process, we conclude that different unknown species may participate in the two separate nucleation experimental studies, which may explain the large difference in the reported threshold H2SO4 concentration. Although the unknown species involved has yet to be identified, the derived values of thermodynamic properties can serve as a valuable guideline for the search of their chemical identities using advanced quantum-chemical approaches.

Unexpected Epoxide Formation in the Gas-Phase Photooxidation of Isoprene

Emissions of nonmethane hydrocarbon compounds to the atmosphere from the biosphere exceed those from anthropogenic activity. Isoprene, a five-carbon diene, contributes more than 40% of these emissions. Once emitted to the atmosphere, isoprene is rapidly oxidized by the hydroxyl radical OH. We report here that under pristine conditions isoprene is oxidized primarily to hydroxyhydroperoxides. Further oxidation of these hydroxyhydroperoxides by OH leads efficiently to the formation of dihydroxyepoxides and OH reformation. Global simulations show an enormous flux--nearly 100 teragrams of carbon per year--of these epoxides to the atmosphere. The discovery of these highly soluble epoxides provides a missing link tying the gas-phase degradation of isoprene to the observed formation of organic aerosols.

Convective aerosol fluxes near the ground surface

1. The asymptotics for mass concentration of finely dispersed aerosol and estimates of hydrodynamic parameters in the viscous thermal boundary layer near the ground surface were obtained on the basis of field measurements in the Caspian desert. The dynamic velocity and temperature drop in the thermal boundary layer are external parameters of the problem considered. The underlying surface, which can emit particles into the atmosphere under specific conditions, is one of the atmospheric aerosol sources. Experimental data and theoretical estimates show that separation of particles from the surface can be related to turbulent stresses induced by velocity shear in the boundary layer over the underlying surface. It occurs when dynamic velocity u ∗ reaches a critical value of ~20‐30 cm/s (see [1] and references in this publication). The dynamic velocity (friction velocity) u ∗ = 〈 u ' v ' 〉 1/2 proportional to turbulent velocity pulsations determines the thickness δ ∗ of the viscous boundary layer near the underlying (smooth) surface, δ ∗ ~ , ν ≈ 0.13 cm 2 /s is the kinematic viscosity of air. The value of δ ∗ is of the order of 100 µ m for the values of u ∗ given here. Particles with sizes exceeding this value can be separated from the boundary layer depending on the degree of cohesion with the underlying surface and their mass. A different situation is related to small sand and dust particles whose size D is significantly smaller than δ ∗ ( D ~ 0.1– 10 µ m). They are completely located in the viscous boundary layer, where turbulent stresses of the wind velocity decrease sharply and cannot overcome the cohesion force between particles. However, the experiν u * mental data provide evidence that particles with an even sum-micrometer size of the ground origin are found in the atmosphere. Several mechanisms exist that explain the appearance of small submicrometer sand and dust particles in the atmosphere. The most known among them are the saltation mechanism when particles of 100 µ m in size separated from the ground release smaller particles during the impact when they fall onto the surface; another mechanism is related to electrization of particles [2]. The former of these mechanisms is directly related to the influence of sufficiently strong turbulent velocity pulsations on the particles of medium size, which appear only when the mean wind velocity reaches sufficiently high values (~10 m/s) in the upper part of the surface boundary layer. However, the amount of small particles in the atmosphere and conditions of their appearance indicate that their ascent can also occur during period that can be characterized as calm weather and when the wind force is obviously insufficient for the formation of strong shear turbulence over the underlying surface [3].

Possible sources of atmospheric aerosol during 2005/06 Harmattan season at Kwabenya (Ghana)

Principal component analysis has been used to characterize and model aerosol particulate matter collected during the 2005/06 harmattan period. Species parameters determined by gravimetric, energy dispersive X-rays fluorescence (EDXRF) and reflectometric techniques were mass, elemental and black carbon concentrations. More than 26 elements were identified in the aerosol samples, but only 17 were used for the coarse fraction and 7 for the fine fraction models, because of detection limitation or missing values. The coarse fraction contained over 90 % of the mass, but the fine particle fraction has higher contribution of black carbon particles than the coarse fraction. Two source profiles were identified in the fine fraction of the aerosol and four source profiles in the coarse fraction. The experimental and modeled particulate mass correlated well, with 0.93 ≤ R2 ≤ 0.95. Journal of Applied Science and Technology Vol. 13 (1 & 2) 2008: pp. 55-63

Long-range transport of aerosols from agriculture crop residue burning in Indo-Gangetic Plains—A study using LIDAR, ground measurements and satellite data

Agriculture crop residue burning in tropics is an important source of atmospheric aerosols and monitoring their long-range transport is an important element in climate change studies. Synchronous measurements using micro-pulsed lidar, MICROTOPS-II sun photometer, multi-filter rotating shadow band radiometer (MFRSR) on aerosol optical depth and ground reaching solar irradiance were carried at an urban location in central region of India. Aerosol backscatter profiles obtained from micro-pulse lidar showed elevated aerosol layers up to ∼3 km on certain days during October 2007. Satellite data observations on aerosol properties suggested transport of particles from agriculture crop residue burning in Indo-Gangetic Plains over large regions. Radiative forcing of aerosols estimated from SBDART model with input information on aerosol chemical properties, aerosol optical depth and single scattering albedo and broadband solar irradiance measurements using MFRSR showed good correlation ( R=0.98).

Clearing enhances dust devil formation

In the southwest of Western Australia, the large scale replacement of native perennial vegetation with agriculture based on winter growing annual species leads to a significant change in the surface albedo and roughness. Whilst the redistribution of the surface energy balance impacts on cloud climatology, the reduced roughness of the agricultural area has enhanced the injection of aerosols into the atmosphere through the increased potential for dust devils. Although the native vegetation experiences a higher sensible heat flux, it is the reduced frictional drag of the cleared agricultural lands that enhances the potential for dust devil formation and thus provides an additional source of atmospheric aerosols.

Interannual variability in global biomass burning emissions from 1997 to 2004

Abstract. Biomass burning represents an important source of atmospheric aerosols and greenhouse gases, yet little is known about its interannual variability or the underlying mechanisms regulating this variability at continental to global scales. Here we investigated fire emissions during the 8 year period from 1997 to 2004 using satellite data and the CASA biogeochemical model. Burned area from 2001–2004 was derived using newly available active fire and 500 m. burned area datasets from MODIS following the approach described by Giglio et al. (2006). ATSR and VIRS satellite data were used to extend the burned area time series back in time through 1997. In our analysis we estimated fuel loads, including organic soil layer and peatland fuels, and the net flux from terrestrial ecosystems as the balance between net primary production (NPP), heterotrophic respiration (Rh), and biomass burning, using time varying inputs of precipitation (PPT), temperature, solar radiation, and satellite-derived fractional absorbed photosynthetically active radiation (fAPAR). For the 1997–2004 period, we found that on average approximately 58 Pg C year−1 was fixed by plants as NPP, and approximately 95% of this was returned back to the atmosphere via Rh. Another 4%, or 2.5 Pg C year−1 was emitted by biomass burning; the remainder consisted of losses from fuel wood collection and subsequent burning. At a global scale, burned area and total fire emissions were largely decoupled from year to year. Total carbon emissions tracked burning in forested areas (including deforestation fires in the tropics), whereas burned area was largely controlled by savanna fires that responded to different environmental and human factors. Biomass burning emissions showed large interannual variability with a range of more than 1 Pg C year−1, with a maximum in 1998 (3.2 Pg C year−1) and a minimum in 2000 (2.0 Pg C year−1).

Significance of atmospheric deposition to freshwater ecosystems in the southern Iberian Peninsula

SUMMARY The Iberian Peninsula is close to the Saharan Desert, which is the biggest source of atmospheric aerosols of the World. Currently, it is recognized that atmospheric deposition of aerosols over ecosystems is a significant source not only of elements with gaseous phases but also of rock-derived ones. In the last years we have been quantifying the atmospheric flux of elements and substances of biogeochemical interest on the aquatic ecosystems of the South Iberian Peninsula, and their impact on their functioning and structure. The results we are obtaining indicate that atmospheric contribution of P and Ca are essential to explain the functioning of high mountain lakes, and that atmospheric input of organic matter partially supports the pelagic food web of these ecosystems. In this article we offer a summary of some of the results obtained to date.