Multi-wavelength aerosol light absorption measurements in the Amazon rainforest

The most important light-absorbing aerosol is black carbon (BC), which is emitted by incomplete combustion of fossil fuels and biomass. BC is considered the second anthropogenic contributor to global warming. Beyond BC, other aerosols like some organics, dust, and primary biological aerosol particles are able to absorb radiation. In contrast to BC, the light absorption coefficient of these aerosols is wavelength dependent. Therefore, multi-wavelength measurements become important in environments where BC is not the predominant light-absorbing aerosol like in the Amazon. The Amazon Tall Tower Observatory (ATTO) site is located in the remote Amazon rainforest, one of the most pristine continental sites in the world during the wet season. In the dry season, winds coming from the southern hemisphere are loaded with biomass burning aerosol particles originated by farming-related deforestation. BC and aerosol number concentration data from the last two years indicate this is the most polluted period. Two different techniques have been implemented to measure the light absorption at different wavelengths; one of them is the 7-wavelengths Aethalometer, model AE30, an instrument that measures the light attenuation on a filter substrate and requires multiple scattering and filter-loading corrections to retrieve the light absorption coefficient. The other method is an offline technique, the Multi-Wavelength Absorbance Analysis (MWAA), which is able to measure reflectance and absorbance by aerosols collected on a filter and, by means of a radiative model, can retrieve the light absorption coefficient. Filters collected during May-September 2014, comprehending wet-to-dry transition and most of the dry season, were analyzed. The results indicate that the Absorption \uc5ngstr\uf6m Exponent (AAE), a parameter that is directly proportional to the wavelength dependence of the aerosol light absorption, is close to 1.0 during the transition period and slightly decreases in the beginning of the dry season. However, during strong biomass burning episodes in the dry season, the AAE increases significantly, and reaches values higher than 1.3, indicating the presence of wavelength dependent light-absorbing aerosols like organics (brown carbon). The present study is a contribution to the understanding of the optical properties of light-absorbing aerosol particles under pristine and biomass-burning conditions

Measurement report : Long-range transport and the fate of dimethyl sulfide oxidation products in the free troposphere derived from observations at the high-altitude research station Chacaltaya (5240 m a.s.l.) in the Bolivian Andes

Dimethyl sulfide (DMS) is the primary natural contributor to the atmospheric sulfur burden. Observations concerning the fate of DMS oxidation products after long-range transport in the remote free troposphere are, however, sparse. Here we present quantitative chemical ionization mass spectrometric measurements of DMS and its oxidation products sulfuric acid (H2SO4), methanesulfonic acid (MSA), dimethylsulfoxide (DMSO), dimethylsulfone (DMSO2), methanesulfinic acid (MSIA), methyl thioformate (MTF), methanesulfenic acid (MSEA, CH3SOH), and a compound of the likely structure CH3S(O)(2)OOH in the gas phase, as well as measurements of the sulfate and methanesulfonate aerosol mass fractions. The measurements were performed at the Global Atmosphere Watch (GAW) station Chacaltaya in the Bolivian Andes located at 5240 m above sea level (a.s.l.). DMS and DMS oxidation products are brought to the Andean high-altitude station by Pacific air masses during the dry season after convective lifting over the remote Pacific ocean to 6000-8000 m a.s.l. and subsequent longrange transport in the free troposphere (FT). Most of the DMS reaching the station is already converted to the rather unreactive sulfur reservoirs DMSO2 in the gas phase and methanesulfonate (MS-) in the particle phase, which carried nearly equal amounts of sulfur to the station. The particulate sulfate at Chacaltaya is however dominated by regional volcanic emissions during the time of the measurement and not significantly affected by the marine air masses. In one of the FT events, even some DMS was observed next to reactive intermediates such as methyl thioformate, dimethylsulfoxide, and methanesulfinic acid. Also for this event, back trajectory calculations show that the air masses came from above the ocean (distance > 330 km) with no local surface contacts. This study demonstrates the potential impact of marine DMS emissions on the availability of sulfur containing vapors in the remote free troposphere far away from the ocean.Peer reviewe

Global distribution of atmospheric phosphorus sources, concentrations and deposition rates, and anthropogenic impacts

A worldwide compilation of atmospheric total phosphorus (TP) and phosphate (PO4) concentration and deposition flux observations are combined with transport model simulations to derive the global distribution of concentrations and deposition fluxes of TP and PO4. Our results suggest that mineral aerosols are the dominant source of TP on a global scale (82%), with primary biogenic particles (12%) and combustion sources (5%) important in nondusty regions. Globally averaged anthropogenic inputs are estimated to be ~5 and 15% for TP and PO4, respectively, and may contribute as much as 50% to the deposition over the oligotrophic ocean where productivity may be phosphorus-limited. There is a net loss of TP from many (but not all) land ecosystems and a net gain of TP by the oceans (560 Gg P a-1). More measurements of atmospheric TP and PO4 will assist in reducing uncertainties in our understanding of the role that atmospheric phosphorus may play in global biogeochemistry

Biogeochemical cycling of carbon, water, energy, trace gases, and aerosols in Amazonia: The LBA-EUSTACH experiments

The biogeochemical cycling of carbon, water, energy, aerosols, and trace gases in the Amazon Basin was investigated in the project European Studies on Trace Gases and Atmospheric Chemistry as a Contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). We present an overview of the design of the project, the measurement sites and methods, and the meteorological conditions during the experiment. The main results from LBA-EUSTACH are: Eddy correlation studies in three regions of the Amazon Basin consistently show a large net carbon sink in the undisturbed rain forest. Nitrogen emitted by forest soils is subject to chemical cycling within the canopy space, which results in re-uptake of a large fraction of soil-derived NOx by the vegetation. The forest vegetation is both a sink and a source of volatile organic compounds, with net deposition being particularly important for partially oxidized organics. Concentrations of aerosol and cloud condensation nuclei (CCN) are highly seasonal, with a pronounced maximum in the dry (burning) season. High CCN concentrations from biomass burning have a pronounced impact on cloud microphysics, rainfall production mechanisms, and probably on large-scale climate dynamics. Copyright 2002 by the American Geophysical Union

Oxidized organic molecules in the tropical free troposphere over Amazonia

Peer reviewe

Biosphere-atmosphere interactions

The contemporary atmosphere was created as a result of biological activity some two billion years ago. To this day, its natural composition is supported and modified, mostly through biological processes of trace gas production and destruction, while also involving physical and chemical degradation processes. The biosphere has a major influence on present environmental conditions, both on a regional and global scale. One of the bestdocumented and most important indicators of global change is the progressive increase of a number of trace gases in the atmosphere, among them carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), all of which are of biospheric origin. There is considerable uncertainty, however, regarding the processes that determine the concentration and distribution of trace gases and aerosols in the atmosphere and the causes and consequences of atmospheric change (Andreae and Schimel 1989). To improve our understanding IGAC created an environment for multi-disciplinary collaboration among biologists, chemists, and atmospheric scientists. This was essential to develop analytical methods, to characterise ecosystems, to investigate physiological controls, to develop and validate micrometeorological theory, and to design and develop diagnostic and predictive models (Matson and Ojima 1990)

Biosphere-Atmosphere Interactions

The contemporary atmosphere was created as a result of biological activity some two billion years ago. To this day, its natural composition is supported and modified, mostly through biological processes of trace gas production and destruction, while also involving physical and chemical degradation processes. The biosphere has a major influence on present environmental conditions, both on a regional and global scale. One of the bestdocumented and most important indicators of global change is the progressive increase of a number of trace gases in the atmosphere, among them carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), all of which are of biospheric origin. There is considerable uncertainty, however, regarding the processes that determine the concentration and distribution of trace gases and aerosols in the atmosphere and the causes and consequences of atmospheric change (Andreae and Schimel 1989). To improve our understanding IGAC created an environment for multi-disciplinary collaboration among biologists, chemists, and atmospheric scientists. This was essential to develop analytical methods, to characterise ecosystems, to investigate physiological controls, to develop and validate micrometeorological theory, and to design and develop diagnostic and predictive models (Matson and Ojima 1990)

The SALTENA Experiment: Comprehensive Observations of Aerosol Sources, Formation, and Processes in the South American Andes

International audienceThis paper presents an introduction to the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5,240 m MSL in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4,000 m MSL) and La Paz (3,600 m MSL). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, airmass origin, and boundary layer-free troposphere interactions during the campaign using a 6-month high-resolution Weather Research and Forecasting (WRF) simulation coupled with Flexible Particle dispersion model (FLEXPART). We then show some of the research highlights from the campaign, including (i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz-El Alto, (ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, (iii) the characterization of the compounds involved in new particle formation, and (iv) the identification of long-range-transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere

A new methodology to assess the performance and uncertainty of source apportionment models II: The results of two European intercomparison exercises

The performance and the uncertainty of receptor models (RMs) were assessed in intercomparison exercises employing real-world and synthetic input datasets. To that end, the results obtained by different practitioners using ten different RMs were compared with a reference. In order to explain the differences in the performances and uncertainties of the different approaches, the apportioned mass, the number of sources, the chemical profiles, the contribution-to-species and the time trends of the sources were all evaluated using the methodology described in Belis et al. (2015). In this study, 87% of the 344 source contribution estimates (SCEs) reported by participants in 47 different source apportionment model results met the 50% standard uncertainty quality objective established for the performance test. In addition, 68% of the SCE uncertainties reported in the results were coherent with the analytical uncertainties in the input data. The most used models, EPA-PMF v.3, PMF2 and EPA-CMB 8.2, presented quite satisfactory performances in the estimation of SCEs while unconstrained models, that do not account for the uncertainty in the input data (e.g. APCS and FA-MLRA), showed below average performance. Sources with well-defined chemical profiles and seasonal time trends, that make appreciable contributions (>10%), were those better quantified by the models while those with contributions to the PM mass close to 1% represented a challenge. The results of the assessment indicate that RMs are capable of estimating the contribution of the major pollution source categories over a given time window with a level of accuracy that is in line with the needs of air quality management.JRC.H.2-Air and Climat