Parameterization of surface resistances to gaseous dry deposition in regional-scale numerical models

Methods for estimating the dry deposition velocities of atmospheric gases in the U.S. and surrounding areas have been improved and incorporated into a revised computer code module for use in numerical models of atmospheric transport and deposition of pollutants over regional scales. The key improvement is the computation of bulk surface resistances along three distinct pathways of mass transfer to sites of deposition at the upper portions of vegetative canopies or structures, the lower portions, and the ground (or water surface). This approach replaces the previous technique of providing simple look-up tables of bulk surface resistances. With the surface resistances divided explicitly into distinct pathways, the bulk surface resistances for a large number of gases in addition to those usually addressed in acid deposition models (SO₂, O₃ NO_x, and HNO₃) can be computed, if estimates of the effective Henry's Law constants and appropriate measures of the chemical reactivity of the various substances are known. This has been accomplished successfully for H₂O₂, HCHO₃ CH₃CHO (to represent other aldehvdes), CH₃O₂H (to represent organic peroxides), CH₃C(O)O₂H, HCOOH (to represent organic acids), NH₃, CH₃C(O)O₂NO₂ and HNO₂. Other factors considered include surface temperature, stomata1 response to environmental parameters, the wetting of surfaces by dew and rain, and the covering of surfaces by snow. Surface emission of gases and variations of uptake characteristics by individual plant species within the landuse types are not considered explicitly.     

Development of a chemical kinetic model for a biosolids fluidized-bed gasifier and the effects of operating parameters on syngas quality

In an effort to decrease the land disposal of sewage sludge biosolids and to recover energy, gasification has become a viable option for the treatment of waste biosolids. The process of gasification involves the drying and devolatilization and partial oxidation of biosolids, followed closely by the reduction of the organic gases and char in a single vessel. The products of gasification include a gaseous fuel composed largely of N₂, H₂O, CO₂, CO, H₂, CH₄, and tars, as well as ash and unburned solid carbon. A mathematical model was developed using published devolatilization, oxidation, and reduction reactions, and calibrated using data from three different experimental studies of laboratory-scale fluidized-bed sewage sludge gasifiers reported in the literature. The model predicts syngas production rate, composition, and temperature as functions of the biosolids composition and feed rate, the air input rate, and gasifier bottom temperature. Several data sets from the three independent literature sources were reserved for model validation, with a focus placed on five species of interest (CO, CO₂, H₂, CH₄, and C₆H₆). The syngas composition predictions from the model compared well with experimental results from the literature. A sensitivity analysis on the most important operating parameters of a gasifier (bed temperature and equivalence ratio) was performed as well, with the results of the analysis offering insight into the operations of a biosolids gasifier.

Implications:

As gasification becomes a more prominent waste disposal option, understanding the effects of feedstock composition and gasifier parameters on the production of syngas (rate and quality) becomes increasingly important. A model has been developed for the gasification of dried sewage sludge that will allow for prediction of changes in syngas quality (and energy recovery from the waste), and should be helpful in assessing the benefits of new gasification projects.     

Study on the removal of elemental mercury from simulated flue gas by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript>/AC at low temperature

Fe₂O₃ and CeO₂ modified activated coke (AC) synthesized by the equivalent-volume impregnation were employed to remove elemental mercury (Hg⁰) from simulated flue gas at a low temperature. Effects of the mass ratio of Fe₂O₃ and CeO₂, reaction temperature, and individual flue gas components including O₂, NO, SO₂, and H₂O (g) on Hg⁰ removal efficiency of impregnated AC were investigated. The samples were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Results showed that with optimal mass percentage of 3 % Fe₂O₃ and 3 % CeO₂ on Fe3Ce3/AC, the Hg⁰ removal efficiency could reach an average of 88.29 % at 110 °C. Besides, it was observed that O₂ and NO exhibited a promotional effect on Hg⁰ removal, H₂O (g) exerted a suppressive effect, and SO₂ showed an insignificant inhibition without O₂ to some extent. The analysis of XPS indicated that the main species of mercury on used Fe3Ce3/AC was HgO, which implied that adsorption and catalytic oxidation were both included in Hg⁰ removal. Furthermore, the lattice oxygen, chemisorbed oxygen, and/or weakly bonded oxygen species made a contribution to Hg⁰ oxidation.     

Multiple regression analysis in modeling of columnar ozone in Peninsular Malaysia

This study aimed to predict monthly columnar ozone (O₃) in Peninsular Malaysia by using data on the concentration of environmental pollutants. Data (2003–2008) on five atmospheric pollutant gases (CO₂, O₃, CH₄, NO₂, and H₂O vapor) retrieved from the satellite Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) were employed to develop a model that predicts columnar ozone through multiple linear regression. In the entire period, the pollutants were highly correlated (R?=?0.811 for the southwest monsoon, R?=?0.803 for the northeast monsoon) with predicted columnar ozone. The results of the validation of columnar ozone with column ozone from SCIAMACHY showed a high correlation coefficient (R?=?0.752–0.802), indicating the model’s accuracy and efficiency. Statistical analysis was utilized to determine the effects of each atmospheric pollutant on columnar ozone. A model that can retrieve columnar ozone in Peninsular Malaysia was developed to provide air quality information. These results are encouraging and accurate and can be used in early warning of the population to comply with air quality standards.     

The Effects of Liquid Water Addition In Gas Turbine Combustors

The addition of liquid water, in quantities equivalent to the mass of fuel consumed, exerts thermal and chemical effects upon the combustion process in a gas turbine engine. The thermal influence is produced by the vaporizalion and heating of the water and its vapor. The final temperature is reduced and the concentrations of NO _x , O, OH, CO are lower than standard combustion concentrations. Chemically, the additional H₂O participates in reactions producing the aforementioned species. However, the lower temperature overrides this influence. These effects have been assessed for different fuel states, i.e., for pre-mixed combustion and for liquid fuel undergoing vaporization and mixing.     

Influence of Operating Conditions on the Formation of Heavy Metal Compounds During Incineration

ABSTRACT

The formation of Cr, Pb, and Cd species under various operating conditions in a pilot-scale fluidized-bed incinerator was investigated. Examined were the effects of (1) an organic chloride (PVC) additive, (2) an inorganic chloride (NaCl) additive, and (3) NaNO₃ and PVC additives,

under various operating temperatures. Two-stage modeling was performed to match the actual incineration conditions of the current study.

Thermodynamic equilibrium analysis indicated that Cr₂O₃, PbCl₂, and CdCl₂ were the dominant species of Cr, Pb, and Cd when an organic chloride (PVC) was present, whereas PbO and CdO were the dominant species under the other operating conditions. The XRD analysis identified Cr₂O₃, PbCl₂, and CdCl₂»H₂O as the dominant species of Cr, Pb, and Cd when an organic chloride (PVC) was present, whereas Cr₂O₃, PbO, Pb₂O₃, CdO, and CdCO₃ were identified under the other operating conditions. The sodium contained in the feedstock was shown to react with chlorine to form sodium chloride both in modeling results and by X-ray diffraction (XRD) analysis. The temperature of the operating conditions had little effect on the formation of heavy metal species.     

Absorption cross-sections of atmospheric constituents: NO2, O2, and H2O

Absorption spectroscopy, which is widely used for concentration measurements of tropospheric and stratospheric compounds, requires precise values of the absorption cross-sections of the measured species. NO₂, O₂ and its collision-induced absorption spectrum, and H₂O absorption cross-sections have been measured at temperature and pressure conditions prevailing in the Earth’s atmosphere. Corrections to the generally accepted analysis procedures used to resolve the convolution problem are also proposed.     

Predicting Extents of Mercury Oxidation in Coal-Derived Flue Gases

Abstract

The proposed mercury (Hg) oxidation mechanism consists of a 168-step gas phase mechanism that accounts for interaction among all important flue gas species and a heterogeneous oxidation mechanism on unburned carbon (UBC) particles, similar to established chemistry for dioxin production under comparable conditions. The mechanism was incorporated into a gas cleaning system simulator to predict the proportions of elemental and oxidized Hg species in the flue gases, given relevant coal properties (C/H/O/N/S/Cl/Hg), flue gas composition (O₂, H₂O, HCl), emissions (NO_X, SO_X, CO), the recovery of fly ash, fly ash loss-on-ignition (LOI), and a thermal history. Predictions are validated without parameter adjustments against datasets from lab-scale and from pilot-scale coal furnaces at 1 and 29 MW_t. Collectively, the evaluations cover 16 coals representing ranks from sub-bituminous through high-volatile bituminous, including cases with Cl₂ and CaCl₂ injection. The predictions are, therefore, validated over virtually the entire domain of Cl-species concentrations and UBC levels of commercial interest. Additional predictions identify the most important operating conditions in the furnace and gas cleaning system, including stoichiometric ratio, NO_X, LOI, and residence time, as well as the most important coal properties, including coal-Cl.     

Fine particulate speciation profile and emission factor of municipal solid waste incinerator established by dilution sampling method

In this study, fine particulate matter (PM_2.5) emitted from a municipal solid waste incinerator (MSWI) was collected using dilution sampling method. Chemical compositions of the collected PM_2.5 samples, including carbon content, metal elements, and water-soluble ions, were analyzed. Traditional in-stack hot sampling was simultaneously conducted to compare the influences of dilution on PM_2.5 emissions and the characteristics of the bonded chemical species. The results, established by a dilution sampling method, show that PM_2.5 and total particulate matter (TPM) emission factors were 61.6 ± 4.52 and 66.1 ± 5.27 g ton-waste^?1, respectively. The average ratio of PM_2.5/TPM is 0.93, indicating that more than 90% of PM emission from the MSWI was fine particulate. The major chemical species in PM_2.5 included organic carbon (OC), Cl^?, NH₄⁺, elemental carbon (EC) and Si, which account for 69.7% of PM_2.5 mass. OC was from the unburned carbon in the exhaust, which adsorbed onto the particulate during the cooling process. High Cl^? emission is primarily attributable to wastes containing plastic bags made of polyvinyl chloride, salt in kitchen refuse and waste biomass, and so on. Minor species that account for 0.01–1% of PM_2.5 mass included SO₄^2-, K⁺, Na, K, NO₃^?, Al, Ca²⁺, Zn, Ca, Cu, Fe, Pb, and Mg. The mean ratio of dilution method/in-stack hot method was 0.454. The contents of water-soluble ions (Cl^?, SO₄^2-, NO₃^?) were significantly enriched in PM_2.5 via gas-to-particle conversion in the dilution process. Results indicate that in-stack hot sampling would underestimate levels of these species in PM_2.5.

Implications: PM_2.5 samples from a municipal solid waste incinerator (MSWI) were collected simultaneously by a dilution sampling technique and a traditional in-stack method. PM_2.5 emission factors and chemical speciation profiles were established. Dilution sampling provides more reliable data than in-stack hot sampling. The results can be applied to estimate the PM_2.5 emission inventories of MSWI, and the source profile can be used for contribution estimate of chemical mass balance modeling.     

Dissociation of Sulfur Hexafluoride Tracer Gas in the Presence of an Indoor Combustion Source

ABSTRACT

As an odorless, nontoxic, and inert compound, sulfur hexafluoride (SF₆) is one of the most widely used tracer gases in indoor air quality studies in both controlled and uncontrolled environments. This compound may be subject to reactions with water vapor under elevated temperature to form acidic inorganic compounds such as HF and H₂SO₄. Thus, in the presence of unvented combustion sources such as kerosene heaters, natural gas heaters, gas log fireplaces, candles, and lamps, the SF₆ dissociation may interfere with measurements of the emissions from these sources. Tests were conducted in a research house with a vent-free natural gas heater to investigate these potential interferences. It was observed that the heater operation caused about a 5% reduction of SF₆ concentration, which can be an error source for the ventilation rate measurement and consequently the estimated pollutant emission rates. Further analysis indicates that this error can be much greater than the observed 5% under certain test conditions because it is a function of the ventilation flow rate. Reducing the tracer gas concentration has no effect on this error. A simple theoretical model is proposed to estimate the magnitude of this error.

The second type of interference comes from the primary and secondary products of the SF₆ dissociation, mainly H₂SO₄, SO₂, HF, and fine particulate matter (PM). In the presence of ~5 ppm SF₆, the total airborne concentrations of these species increased by a factor of 4-10. The tests were performed at relatively high SF₆ concentrations, which is necessary to determine the interferences quantitatively. The second type of interference can be significantly reduced if the SF₆ concentration is kept at a low ppb level.     

Application of Artificial Neural Networks to Modeling and Prediction of Ambient Ozone Concentrations

ABSTRACT

The deterministic modeling of ambient O₃ concentrations is difficult because of the complexity of the atmospheric system in terms of the number of chemical species; the availability of accurate, time-resolved emissions data; and the required rate constants. However, other complex systems have been successfully approximated using artificial neural networks (ANNs). In this paper, ANNs are used to model and predict ambient O₃ concentrations based on a limited number of measured hydrocarbon species, NO_x compounds, temperature, and radiant energy. In order to examine the utility of these approaches, data from the Coastal Oxidant Assessment for Southeast Texas (COAST) program in Houston, TX, have been used. In this study, 53 hydrocarbon compounds, along with O₃, nitrogen oxides, and meteorological data were continuously measured during summer 1993. Steady-state ANN models were developed to examine the ability of these models to predict current O₃ concentrations from measured VOC and NO concentrations. To predict the future concentrations of O₃, dynamic models were also explored and were used for extraction of chemical information such as reactivity estimations for the VOC species.

The steady-state model produced an approximation of O₃ data and demonstrated the functional relationship between O₃ and VOC-NO_x concentrations. The dynamic models were able to the adequately predict the O₃ concentration and behavior of VOC-NO_x-O₃ system a number of hourly intervals into the future. For 3 hr into the future, O₃ concentration could be predicted with a root-mean squared error (RMSE) of 8.21 ppb. Extending the models further in time led to an RMSE of 11.46 ppb for 5-hr-ahead values. This prediction capability could be useful in determining when control actions are needed to maintain measured concentrations within acceptable value ranges.     

The Use of Ambient Measurements To Identify which Precursor Species Limit Aerosol Nitrate Formation

ABSTRACT

A thermodynamic equilibrium model was used to investigate the response of aerosol NO₃ to changes in concentrations of HNO₃, NH₃, and H₂SO₄. Over a range of temperatures and relative humidities (RHs), two parameters provided sufficient information for indicating the qualitative response of aerosol NO₃. The first was the excess of aerosol NH₄ ⁺ plus gas-phase NH₃ over the sum of HNO₃, particulate NO₃, and particulate SO₄ ^2- concentrations. The second was the ratio of particulate to total NO₃ concentrations. Computation of these quantities from ambient measurements provides a means to rapidly analyze large numbers of samples and identify cases in which inorganic aerosol NO₃ formation is limited by the availability of NH₃. Example calculations are presented using data from three field studies. The predictions of the indicator variables and the equilibrium model are compared.     

应用神经网络方法优化垃圾焚烧模拟灰渣熔点的预测

采用SiO₂、Al₂O₃、CaO、Na₂CO₃、NaCl和Fe₂O₃等物质来模拟垃圾焚烧的真实灰渣组成,通过实验测定模拟灰渣熔点,建立神经网络模型进行熔点预测,由预测结果来指导进一步实验,得到修正的模型,最终预测出的半球温度（HT）平均误差低于5%。     

Analysis of Kraft-Mill,Sulfur-Containing Gases with GLC lonization Detectors

The technique includes the use of two chromatographic columns in series to separate O₂, N₂, CO, CO₂, H₂O, H₂S, SO₂ and CH₃SH. Column 1, containing Triton 45 on Chromosorb, separates H₂O, H₂S, SO₂ and CH₃SH. Column 2, packed with Molecular Sieve, separates O₂, N₂, CO and CO₂. The conditions required to obtain adequate sensitivity and separation are discussed.     

FTIR gas-phase kinetic study on the reactions of some acrylate esters with OH radicals and Cl atoms

Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298?±?2 K) and atmospheric pressure (708?±?8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm³ molecule^?1 s^?1): (3.27?±?0.33)?×?10^?11 and (4.43?±?0.42)?×?10^?11, for CH₃CH═CHC(O)OCH₃ and (CH₃)₂CH═CHC(O)OCH_3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N₂ and air were used as the bath gases. The following rate coefficients were obtained (in cm³ molecule^?1 s^?1): k₃ (CH₂═CHC(O)O(CH₂)₅CH₃?+?Cl)?=?(3.31?±?0.31)?×?10^?10, k₄(CH₂═CHC(O)OCH₂CH(CH₂CH₃)(CH₂)₃CH₃?+?Cl)?=?(3.46?±?0.31)?×?10^?10, k₅(CH₂═CHC(O)O(CH₂)₅CH₃?+?OH)?=?(2.28?±?0.23)?×?10^?11, and k₆(CH₂═CHC(O)OCH₂CH(CH₂CH₃)(CH₂)₃CH₃?+?OH)?=?(2.74?±?0.26)?×?10^?11. The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in –C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming.     

Correction in aerosol mass concentration measurements with humidity difference between ambient and instrumental conditions

The influence of humidity is considered on the concentration of the suspended particulate matter (SPM) measured with a β-ray counter. The humidity condition inside a small observatory where the counter is located is, in general, different from the ambient condition outside the observatory. From the measured values, the ambient SPM concentration is derived considering the hygroscopic effect of common aerosol species of sea salt (SS), (NH₄)₂SO₄, NH₄NO₃ and NaNO₃. In a case study conducted during September 2005, temperature and humidity were measured both inside and outside the observatory. The average value of the relative humidity is 48% for inside and 78% for outside, resulting in approximately 53% larger SPM mass concentration after the correction. Accordingly, the value of mass extinction efficiency, which is given by the ratio between the optically measured extinction coefficient and the mass concentration, becomes lower after the correction.     

Responses of CH(4), CO(2) and N(2)O fluxes to increasing nitrogen deposition in alpine grassland of the Tianshan Mountains

To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH₄, CO₂ and N₂O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH₄ uptake, CO₂ and N₂O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO₂ and N₂O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO₂ and N₂O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO₂ and N₂O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers.     

Effect of bulking agents on maturity and gaseous emissions during kitchen waste composting

This study investigated the effect of bulking agents on the maturity and gaseous emissions of composting kitchen waste. Three different bulking agents (cornstalks, sawdust, and spent mushroom substrate) were used to compost kitchen waste under aerobic conditions in 60-L reactors for a 28-d period. A control treatment was also studied using kitchen waste without a bulking agent. During the experiment, maturity indexes such as temperature, pH value, C/N ratio, and germination index were determined, and continuous measurements of leachate and gaseous emissions (CH₄, N₂O, and NH₃) were taken. The results showed that all of the composts with bulking agents reached the required maturity standard, and the addition of spent mushroom substrate gave the highest maturity (C/N ratio decreased from 23 to 16 and germination index increased from 53% to 111%). The bulking agents also reduced leachate production and CH₄ and N₂O emissions, but had little impact on NH₃ emissions. Composting with sawdust as a bulking agent was found to emit less total greenhouse gas (33 kg CO₂-eq t⁻¹ dry matter) than the other treatments.     

The influence of forest fires on CO, HCN, C2H6, and C2H2 over northern Japan measured by infrared solar spectroscopy

Total column abundances of CO, HCN, C₂H₆, and C₂H₂ have been retrieved from infrared solar spectra observed at Moshiri (44.4°N) and Rikubetsu (43.5°N) in northern Japan from 1997 to 2005. The spectra were recorded with high spectral resolution ground-based Fourier transform infrared (FTIR) spectrometers and total column abundances were calculated by SFIT1 version 1.09e. Deviations of these species relative to their seasonal mean values (ΔCO, ΔHCN, ΔC₂H₆, and ΔC₂H₂) were derived, which showed short-time enhancements in 1998, 2002, and 2003. Good correlations among ΔCO, ΔHCN, ΔC₂H₆, and ΔC₂H₂ in a few months of each year were seen. Since the number of forest fires in Siberia had large enhancements in 1998, 2002, and 2003, trajectory analyses were performed in order to assess the influence of forest fires and it was confirmed that air masses passing over the location of burning points in Siberia reached Moshiri and Rikubetsu. This paper shows that enhancements of these species were driven by biomass burning in Siberia.