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Browsing by Author "Brito, Joel"

Now showing 1 - 4 of 4
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    Contributions of biomass-burning, urban, and biogenic emissions to the concentrations and light-absorbing properties of particulate matter in central Amazonia during the dry season
    de Sa, Suzane S.; Rizzo, Luciana V.; Palm, Brett B.; Campuzano-Jost, Pedro; Day, Douglas A.; Yee, Lindsay D.; Wernis, Rebecca A.; Isaacman-VanWertz, Gabriel; Brito, Joel; Carbone, Samara; Liu, Yingjun J.; Sedlacek, Arthur; Springston, Stephen R.; Goldstein, Allen H.; Barbosa, Henrique M. J.; Alexander, M. Lizabeth; Artaxo, Paulo; Jimenez, Jose L.; Martin, Scot T. (European Geophysical Union, 2019-06-18)
    Urbanization and deforestation have important impacts on atmospheric particulate matter (PM) over Amazonia. This study presents observations and analysis of PM1 concentration, composition, and optical properties in central Amazonia during the dry season, focusing on the anthropogenic impacts. The primary study site was located 70 km downwind of Manaus, a city of over 2 million people in Brazil, as part of the GoAmazon2014/5 experiment. A high-resolution time-of-flight aerosol mass spectrometer (AMS) provided data on PM1 composition, and aethalometer measurements were used to derive the absorption coefficient b(abs,BrC) of brown carbon (BrC) at 370 nm. Non-refractory PM1 mass concentrations averaged 12.2 mu g m(-3) at the primary study site, dominated by organics (83 %), followed by sulfate (11 %). A decrease in b(abs,BrC) was observed as the mass concentration of nitrogen-containing organic compounds decreased and the organic PM1 O : C ratio increased, suggesting atmospheric bleaching of the BrC components. The organic PM1 was separated into six different classes by positive-matrix factorization (PMF), and the mass absorption efficiency E-abs associated with each factor was estimated through multivariate linear regression of b(abs,BrC) on the factor loadings. The largest E-abs values were associated with urban (2.04 +/- 0.14 m(2) g(-1)) and biomass-burning (0.82 +/- 0.04 to 1.50 +/- 0.07 m(2)g(-1)) sources. Together, these sources contributed at least 80 % of b(abs,BrC) while accounting for 30 % to 40 % of the organic PM1 mass concentration. In addition, a comparison of organic PM1 composition between wet and dry seasons revealed that only part of the 9-fold increase in mass concentration between the seasons can be attributed to biomass burning. Biomass-burning factor loadings increased by 30-fold, elevating its relative contribution to organic PM1 from about 10 % in the wet season to 30 % in the dry season. However, most of the PM1 mass (> 60 %) in both seasons was accounted for by biogenic secondary organic sources, which in turn showed an 8-fold seasonal increase in factor loadings. A combination of decreased wet deposition and increased emissions and oxidant concentrations, as well as a positive feedback on larger mass concentrations are thought to play a role in the observed increases. Furthermore, fuzzy c-means clustering identified three clusters, namely "baseline", "event", and "urban" to represent different pollution influences during the dry season. The baseline cluster, representing the dry season background, was associated with a mean mass concentration of 9 +/- 3 mu g m(-3). This concentration increased on average by 3 mu g m(-3) for both the urban and the event clusters. The event cluster, representing an increased influence of biomass burning and long-range transport of African volcanic emissions, was characterized by remarkably high sulfate concentrations. The urban cluster, representing the influence of Manaus emissions on top of the baseline, was characterized by an organic PM1 composition that differed from the other two clusters. The differences discussed suggest a shift in oxidation pathways as well as an accelerated oxidation cycle due to urban emissions, in agreement with findings for the wet season.
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    Secondary organic aerosol formation from ambient air in an oxidation flow reactor in central Amazonia
    Palm, Brett B.; de Sa, Suzane S.; Day, Douglas A.; Campuzano-Jost, Pedro; Hu, Weiwei; Seco, Roger; Sjostedt, Steven J.; Park, Jeong-Hoo; Guenther, Alex B.; Kim, Saewung; Brito, Joel; Wurm, Florian; Artaxo, Paulo; Thalman, Ryan; Wang, Jian; Yee, Lindsay D.; Wernis, Rebecca A.; Isaacman-VanWertz, Gabriel; Goldstein, Allen H.; Liu, Yingjun; Springston, Stephen R.; Souza, Rodrigo; Newburn, Matt K.; Alexander, M. Lizabeth; Martin, Scot T.; Jimenez, Jose L. (European Geophysical Union, 2018-01-17)
    Secondary organic aerosol (SOA) formation from ambient air was studied using an oxidation flow reactor (OFR) coupled to an aerosol mass spectrometer (AMS) during both the wet and dry seasons at the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) field campaign. Measurements were made at two sites downwind of the city of Manaus, Brazil. Ambient air was oxidized in the OFR using variable concentrations of either OH or O-3, over ranges from hours to days (O-3) or weeks (OH) of equivalent atmospheric aging. The amount of SOA formed in the OFR ranged from 0 to as much as 10 mu g m(-3), depending on the amount of SOA precursor gases in ambient air. Typically, more SOA was formed during nighttime than daytime, and more from OH than from O-3 oxidation. SOA yields of individual organic precursors under OFR conditions were measured by standard addition into ambient air and were confirmed to be consistent with published environmental chamber-derived SOA yields. Positive matrix factorization of organic aerosol (OA) after OH oxidation showed formation of typical oxidized OA factors and a loss of primary OA factors as OH aging increased. After OH oxidation in the OFR, the hygroscopicity of the OA increased with increasing elemental O : C up to O : C similar to 1.0, and then decreased as O : C increased further. Possible reasons for this decrease are discussed. The measured SOA formation was compared to the amount predicted from the concentrations of measured ambient SOA precursors and their SOA yields. While measured ambient precursors were sufficient to explain the amount of SOA formed from O-3, they could only explain 10-50% of the SOA formed from OH. This is consistent with previous OFR studies, which showed that typically unmeasured semivolatile and intermediate volatility gases (that tend to lack C=C bonds) are present in ambient air and can explain such additional SOA formation. To investigate the sources of the unmeasured SOA-forming gases during this campaign, multilinear regression analysis was performed between measured SOA formation and the concentration of gas-phase tracers representing different precursor sources. The majority of SOA-forming gases present during both seasons were of biogenic origin. Urban sources also contributed substantially in both seasons, while biomass burning sources were more important during the dry season. This study enables a better understanding of SOA formation in environments with diverse emission sources.
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    Urban influence on the concentration and composition of submicron particulate matter in central Amazonia
    de Sa, Suzane S.; Palm, Brett B.; Campuzano-Jost, Pedro; Day, Douglas A.; Hu, Weiwei; Isaacman-VanWertz, Gabriel; Yee, Lindsay D.; Brito, Joel; Carbone, Samara; Ribeiro, Igor O.; Cirino, Glauber G.; Liu, Yingjun; Thalman, Ryan; Sedlacek, Arthur; Funk, Aaron; Schumacher, Courtney; Shilling, John E.; Schneider, Johannes; Artaxo, Paulo; Goldstein, Allen H.; Souza, Rodrigo A. F.; Wang, Jian; McKinney, Karena A.; Barbosa, Henrique M. J.; Alexander, M. Lizabeth; Jimenez, Jose L.; Martin, Scot T. (European Geophysical Union, 2018-08-23)
    An understanding of how anthropogenic emissions affect the concentrations and composition of airborne particulate matter (PM) is fundamental to quantifying the influence of human activities on climate and air quality. The central Amazon Basin, especially around the city of Manaus, Brazil, has experienced rapid changes in the past decades due to ongoing urbanization. Herein, changes in the concentration and composition of submicron PM due to pollution downwind of the Manaus metropolitan region are reported as part of the GoAmazon2014/5 experiment. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a suite of other gas-and particle-phase instruments were deployed at the "T3" research site, 70 km downwind of Manaus, during the wet season. At this site, organic components represented 79 +/- 7% of the non-refractory PM1 mass concentration on average, which was in the same range as several upwind sites. However, the organic PM1 was considerably more oxidized at T3 compared to upwind measurements. Positive-matrix factorization (PMF) was applied to the time series of organic mass spectra collected at the T3 site, yielding three factors representing secondary processes (73 +/- 15% of total organic mass concentration) and three factors representing primary anthropogenic emissions (27 +/- 15 %). Fuzzy c-means clustering (FCM) was applied to the afternoon time series of concentrations of NOy, ozone, total particle number, black carbon, and sulfate. Four clusters were identified and characterized by distinct air mass origins and particle compositions. Two clusters, Bkgd-1 and Bkgd2, were associated with background conditions. Bkgd-1 appeared to represent near-field atmospheric PM production and oxidation of a day or less. Bkgd-2 appeared to represent material transported and oxidized for two or more days, often with out-of-basin contributions. Two other clusters, Pol-1 and Pol-2, represented the Manaus influence, one apparently associated with the northern region of Manaus and the other with the southern region of the city. A composite of the PMF and FCM analyses provided insights into the anthropogenic effects on PM concentration and composition. The increase in mass concentration of submicron PM ranged from 25% to 200% under polluted compared with background conditions, including contributions from both primary and secondary PM. Furthermore, a comparison of PMF factor loadings for different clusters suggested a shift in the pathways of PM production under polluted conditions. Nitrogen oxides may have played a critical role in these shifts. Increased concentrations of nitrogen oxides can shift pathways of PM production from HO2-dominant to NO-dominant as well as increase the concentrations of oxidants in the atmosphere. Consequently, the oxidation of biogenic and anthropogenic precursor gases as well as the oxidative processing of preexisting atmospheric PM can be accelerated. This combined set of results demonstrates the susceptibility of atmospheric chemistry, air quality, and associated climate forcing to anthropogenic perturbations over tropical forests.
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    Urban pollution greatly enhances formation of natural aerosols over the Amazon rainforest
    Shrivastava, Manish; Andreae, Meinrat O.; Artaxo, Paulo; Barbosa, Henrique M. J.; Berg, Larry K.; Brito, Joel; Ching, Joseph; Easter, Richard C.; Fan, Jiwen; Fast, Jerome D.; Feng, Zhe; Fuentes, Jose D.; Glasius, Marianne; Goldstein, Allen H.; Alves, Eliane Gomes; Gomes, Helber; Gu, Dasa; Guenther, Alex; Jathar, Shantanu H.; Kim, Saewung; Liu, Ying; Lou, Sijia; Martin, Scot T.; McNeill, V. Faye; Medeiros, Adan; de Sa, Suzane S.; Shilling, John E.; Springston, Stephen R.; Souza, R. A. F.; Thornton, Joel A.; Isaacman-VanWertz, Gabriel; Yee, Lindsay D.; Ynoue, Rita; Zaveri, Rahul A.; Zelenyuk, Alla; Zhao, Chun (Springer Nature, 2019-03-05)
    One of the least understood aspects in atmospheric chemistry is how urban emissions influence the formation of natural organic aerosols, which affect Earth's energy budget. The Amazon rainforest, during its wet season, is one of the few remaining places on Earth where atmospheric chemistry transitions between preindustrial and urban-influenced conditions. Here, we integrate insights from several laboratory measurements and simulate the formation of secondary organic aerosols (SOA) in the Amazon using a high-resolution chemical transport model. Simulations show that emissions of nitrogen-oxides from Manaus, a city of similar to 2 million people, greatly enhance production of biogenic SOA by 60-200% on average with peak enhancements of 400%, through the increased oxidation of gas-phase organic carbon emitted by the forests. Simulated enhancements agree with aircraft measurements, and are much larger than those reported over other locations. The implication is that increasing anthropogenic emissions in the future might substantially enhance biogenic SOA in pristine locations like the Amazon.