Browsing by Author "Wang, Jian"

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    Application of biochar to soils may result in plant contamination and human cancer risk due to exposure of polycyclic aromatic hydrocarbons
    Wang, Jian; Xia, Kang; Waigi, Michael Gatheru; Gao, Yanzheng; Odinga, Emmanuel Stephen; Ling, Wanting; Liu, Juan (2018-12)
    Biochars are added to soil to improve agronomic yield. This greenhouse- and field-scale study evaluated poly cyclic aromatic hydrocarbon (PAH) contamination in 35 commercial and laboratory-produced biochars, and assessed the effects of biochar amendment of soils on PAH accumulation in vegetables and the risk for cancer. The total and bioavailable PAH concentrations in biochars varied from 638 to 12,347 mu g/kg and from below the detection limit (BDL) to 2792 mu g/kg, respectively. PAH formation in biochars decreased with increasing production temperature (350-650 degrees C). Root exudates enhanced PAH release from biochars. The total PAH concentrations in eight edible vegetables growing in biochar-amended soil varied according to biochar and vegetables type from BDL to 565 mu g/kg. A health risk assessment framework was integrated with the benzo [a] pyrene toxic equivalency quotient and the incremental lifetime cancer risk (ILCR) to estimate the exposure risk for human beings via ingestion of PAH-contaminated vegetables. The total ILCR for adults was above 10(-6), which suggests a risk to human health from direct exposure to PAHs in vegetables grown in biochar-amended soil. These results demonstrate that biochar application may lead to contamination of plants with PAHs, which represents a risk to human health. The PAH levels in biochars produced using different conditions and/or feed-stocks need to be evaluated and biochars should be pretreated to remove PAHs before their large-scale agronomic application.
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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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    Soil Organic Nitrogen - Investigation of Soil Amino Acids and Proteinaceous Compounds
    Ma, Li (Virginia Tech, 2015-05-01)
    Soil carbon (C) and nitrogen (N) are predominantly in organic form. Proteins/ peptides, as an important organic form of N, constitute a substantial part of soil organic matter. On one hand, proteins/peptides are an important N source for plants and microorganisms, particularly in soils where inorganic N is limited. On the other hand, their stabilization in soils by forming organo-mineral associates or macromolecule complex reduces the C loss as CO2 into the atmosphere. Therefore, studies on the turnover, abundance, composition, and stability of proteins/peptides are of crucial importance to agricultural productivity and environmental sustainability. In the first part of this study, the bioavailability and distribution of amino acids, (building block of proteins/peptides), were investigated, in soils across the North-South and West-East transects of continental United States. The second part of this study aimed to understand the variations of organic C speciation in soils of continental United States. Previous investigations of the interactions between soil minerals and proteins/peptides were mostly limited to batch sorption experiments in labs, seldom of which gave the details at the molecular scales. Therefore, in the third part of this study, the molecular orientation of self-assembled oligopeptides on mineral surfaces was investigated by employing synchrotron based polarization-dependent Near Edge X-ray Adsorption Fine Structure Spectroscopy (NEXAFS) techniques. Specific aims of this study were: 1) to assess potentially bioavailable pool of proteinaceous compounds and the immediately bioavailable pool of free amino acids in surface and subsurface soils of various ecosystems; 2) to evaluate the relationship between environmental factors and levels/composition of the two pools; 3) to investigate the organic C speciation in soils of various land use; and 4) to understand molecular level surface organization of small peptides on mineral surfaces. The levels of free amino acids and hydrolysable amino acids which represent the potentially bioavailable pool of proteinaceous compounds in A-horizon soils were significantly high than in C-horizon soils due to the accumulation of organic matter in surface. On average, free amino acids accounted for less than 4 % of hydrolysable amino acids which represent the total proteinaceous compounds in soils. The composition of free amino acids was significantly different between surface soil and subsurface soil and was significantly influenced by mean annual temperature and precipitation. A relatively uniform composition of hydrolysable amino acids was observed irrespective of a wide range of land use. Significant variations were observed for the levels of free and hydrolysable amino acids along mean annual temperature and precipitation gradients, as well as among vegetation types of continental USA, suggesting levels of free and hydrolysable amino acids were associated with the above-ground biomass and root distribution. Organic C speciation investigation revealed the presence of carboxylic-C (38%), aliphatic-C (~ 22%), aromatic-C (~ 18%), O/N-alkyl-C (~ 16%), and phenolic-C (< 6%). Factors such as temperature and vegetation cover were revealed in this study to account for the fluctuations of the proportions of aromatic-C and phenolic-C, in particular. Phenolic-C may serve as a good indicator for the effect of temperature or vegetation on the composition of SOC. The average composition of soil organic C, over the continental scale, was relatively uniform over various soil ecosystems and between two soil horizons irrespective of surface organic C content. Polarization dependent NEXAFS analysis showed the oligopeptides tend to orient on mineral surface with an average tilt angle of 40 ° between the molecular chain and the mineral surface.
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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.