Armistead G. Russell

NARSTO critical review of photochemical models and modeling

Abstract Photochemical air quality models play a central role in both schentific investigation of how pollutants evlove in the atmosphere as well as developing policies to manage air quality. In the past 30 years, these models have evolved from rather crude representations of the physics and chemistry impacting trace species to their current state: comprehensive, but not complete. The evolution has included advancements in not only the level of process descriptions, but also the computational implementation, including numerical methods. As part of the NARSTO Critical Reviews, this article discusses the current strengths and weaknesses of air quality models and the modeling process. Current Eulerian models are found to represent well the primary processes impacting the evolution of trace species in most cases though some exceptions may exist. For example, sub-grid-scale processes, such as concentrated power plant plumes, are treated only approximately. It is not apparent how much such approximations affect their results and the polices based upon those results. A significant weakness has been in how investigators have addressed, and communicated, such uncertainties. Studies find that major uncertainties are due to model inputs, e.g., emissions and meteorology, more so than the model itself. One of the primary weakness identified is in the modeling process, not the models. Evaluation has been limited both due to data constraints. Seldom is there ample observational data to conduct a detailed model intercomparison using consistent data (e.g., the same emissions and meteorology). Further model advancement, and development of greater confidence in the use of models, is hampered by the lack of thorough evaluation and intercomparisons. Model advances are seen in the use of new tools for extending the interpretation of model results, e.g., process and sensitivity analysis, modeling systems to facilitate their use, and extension of model capabilities, e.g., aerosol dynamics capabilities and sub-grid-scale representations. Another possible direction that is the development and widespread use of a community model acting as a platform for multiple groups and agencies to collaborate and progress more rapidly.

Review of recent advances in carbon dioxide separation and capture

This review provides a comprehensive assessment of recently improved carbon dioxide (CO2) separation and capture systems, used in power plants and other industrial processes. Different approaches for CO2 capture are pre-combustion, post-combustion capture, and oxy-combustion systems, which are reviewed, along with their advantages and disadvantages. New technologies and prospective “breakthrough technologies”, for instance: novel solvents, sorbents, and membranes for gas separation are examined. Other technologies including chemical looping technology (reaction between metal oxides and fuels, creating metal particles, carbon dioxide, and water vapor) and cryogenic separation processes (based on different phase change temperatures for various gases to separate them) are reviewed as well. Furthermore, the major CO2 separation technologies, such as absorption (using a liquid solvent to absorb the CO2), adsorption (using solid materials with surface affinity to CO2 molecules), and membranes (using a thin film to selectively permeate gases) are extensively discussed, though issues and technologies related to CO2 transport and storage are not considered in this paper.

Fine Particle Sources and Cardiorespiratory Morbidity: An Application of Chemical Mass Balance and Factor Analytical Source-Apportionment Methods

Background Interest in the health effects of particulate matter (PM) has focused on identifying sources of PM, including biomass burning, power plants, and gasoline and diesel emissions that may be associated with adverse health risks. Few epidemiologic studies, however, have included source-apportionment estimates in their examinations of PM health effects. We analyzed a time-series of chemically speciated PM measurements in Atlanta, Georgia, and conducted an epidemiologic analysis using data from three distinct source-apportionment methods. Objective The key objective of this analysis was to compare epidemiologic findings generated using both factor analysis and mass balance source-apportionment methods. Methods We analyzed data collected between November 1998 and December 2002 using positive-matrix factorization (PMF), modified chemical mass balance (CMB-LGO), and a tracer approach. Emergency department (ED) visits for a combined cardiovascular (CVD) and respiratory disease (RD) group were assessed as end points. We estimated the risk ratio (RR) associated with same day PM concentrations using Poisson generalized linear models. Results There were significant, positive associations between same-day PM2.5 (PM with aero-dynamic diameter ≤ 2.5 μm) concentrations attributed to mobile sources (RR range, 1.018–1.025) and biomass combustion, primarily prescribed forest burning and residential wood combustion, (RR range, 1.024–1.033) source categories and CVD-related ED visits. Associations between the source categories and RD visits were not significant for all models except sulfate-rich secondary PM2.5 (RR range, 1.012–1.020). Generally, the epidemiologic results were robust to the selection of source-apportionment method, with strong agreement between the RR estimates from the PMF and CMB-LGO models, as well as with results from models using single-species tracers as surrogates of the source-apportioned PM2.5 values. Conclusions Despite differences among the source-apportionment methods, these findings suggest that modeled source-apportioned data can produce robust estimates of acute health risk. In Atlanta, there were consistent associations across methods between PM2.5 from mobile sources and biomass burning with both cardiovascular and respiratory ED visits, and between sulfate-rich secondary PM2.5 with respiratory visits.

Amine-based CO2 capture technology development from the beginning of 2013-a review.

It is generally accepted by the scientific community that anthropogenic CO2 emissions are leading to global climate change, notably an increase in global temperatures commonly referred to as global warming. The primary source of anthropogenic CO2 emissions is the combustion of fossil fuels for energy. As societys demand for energy increases and more CO2 is produced, it becomes imperative to decrease the amount emitted to the atmosphere. One promising approach to do this is to capture CO2 at the effluent of the combustion site, namely, power plants, in a process called postcombustion CO2 capture. Technologies to achieve this are heavily researched due in large part to the intuitive nature of removing CO2 from the stack gas and the ease in retrofitting existing CO2 sources with these technologies. As such, several reviews have been written on postcombustion CO2 capture. However, it is a fast-developing field, and the most recent review papers already do not include the state-of-the-art research. Notable among CO2 capture technologies are amine-based technologies. Amines are well-known for their reversible reactions with CO2, which make them ideal for the separation of CO2 from many CO2-containing gases, including flue gas. For this reason, this review will cover amine-based technology developed and published in and after the year 2013.

Mathematical modeling of the formation and transport of ammonium nitrate aerosol

A mathematical model describing the transport and formation of aerosol NH_4NO_3 is presented. Based on a vertically resolved Lagrangian trajectory formulation incorporating gas phase kinetics, NH_4NO_3 concentrations are computed at thermodynamic equilibrium with precursor HNO_3 vapor and NH_3 concentrations. Sensitivity analysis shows that NH_4NO_3 concentration predictions are strongly influenced by ambient temperature and NH_3 levels. A brief description of the NH_3 emissions inventory used in this study is included to indicate the important sources. The model was tested by comparison to ambient NH_3, NH_4+ and NO_3− concentrations measured at El Monte, California during June 1974. Model results compare favorably with the ambient measurements and are used to explain trends in those measurements. An early morning nitrate peak develops as HNO_3 produced soon after sunrise reacts with NH_3 accumulated overnight. A second peak in nitrate concentration is predicted and observed at El Monte later in the day. Potential applications of this model to control strategy decisions and to study the fate of NO_x are discussed.

Total reactive nitrogen (NO y ) as an indicator of the sensitivity of ozone to reductions in hydrocarbon and NO x emissions

For areas in the United States not meeting the federal air quality standard for ozone, an issue of continuing controversy is the emphasis to be placed on controlling nitrogen oxides (NOx) in addition to emissions of reactive organic gases (ROG). To assess conditions under which ROG or NOx controls would be most effective, we have analyzed predictions from four studies that represent different locations and meteorological conditions, distinct chemical inputs, e.g., with or without significant biogenic emissions, and different air quality models. A consistent association is found between the sensitivity of ozone to reductions in ROG versus NOx emissions and the simulated total reactive nitrogen (NOy) at the time and place of peak ozone. In the studies examined, ozone was predicted to be reduced most effectively by ROG controls at locations where NOy concentrations exceeded a threshhold value falling in the range of 10 to 25 ppb, whereas NOx controls were predicted to be more effective where NOy concentrations were below that threshhold. The NOy level explains much of the difference in ozone sensitivity at different locations and provides a basis for comparison of predicted sensitivity from different models. In contrast, the morning concentration ratio of ROG to NOx that has been used in the past is a less reliable indicator of O3 sensitivity. Measurement of NOy concentrations along with ozone would assist in empirical testing of model predictions of responses to emission reductions.

Emission factors of particulate matter and elemental carbon for crop residues and coals burned in typical household stoves in China

Both particulate matter (PM) and black carbon (BC) impact climate change and human health. Uncertainties in emission inventories of PM and BC are partially due to large variation of measured emission factors (EFs) and lack of EFs from developing countries. Although there is a debate whether thermal-optically measured elemental carbon (EC) may be referred to as BC, EC is often treated as the same mass of BC. In this study, EFs of PM (EF(PM)) and EC (EF(EC)) for 9 crop residues and 5 coals were measured in actual rural cooking and coal stoves using the carbon mass balance method. The dependence of the EFs on fuel properties and combustion conditions was investigated. It was found that the mean EF(PM) were 8.19 ± 4.27 and 3.17 ± 4.67 g/kg and the mean EF(EC) were 1.38 ± 0.70 and 0.23 ± 0.36 g/kg for crop residues and coals, respectively. PM with size less than 10 μm (PM(10)) from crop residues were dominated by particles of aerodynamic size ranging from 0.7 to 2.1 μm, while the most abundant size ranges of PM(10) from coals were either from 0.7 to 2.1 μm or less than 0.7 μm. Of various fuel properties and combustion conditions tested, fuel moisture and modified combustion efficiency (MCE) were the most critical factors affecting EF(PM) and EF(EC) for crop residues. For coal combustion, EF(PM) were primarily affected by MCE and volatile matter, whereas EF(EC) were significantly influenced by ash content, volatile matter, heat value, and MCE. It was also found that EC emissions were significantly correlated with emissions of PM with size less than 0.4 μm.

A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations.

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

Mesoporous amine-modified SiO2 aerogel: a potential CO2 sorbent

An amine-modified SiO2 aerogel (AMSA) was prepared using the sol–gel method and supercritical drying technology. CO2 adsorption tests were conducted under different conditions. High adsorption capacities were achieved in the presence of water vapor, with the highest CO2 adsorption capacity of 6.97 mmol/g-sorbent at 25 °C. A novel adsorption mechanism associated with the CO2 sorption process is proposed. The test results indicate that AMSA is a promising CO2 adsorbent.

AMMONIA AND NITRIC ACID CONCENTRATIONS IN EQUILIBRIUM WITH ATMOSPHERIC AEROSOLS: EXPERIMENT VS THEORY

The equilibrium between gaseous ammonia, nitric acid, and aerosol nitrate is discussed on the basis of a recent field experiment in southern California. Comparison is drawn between theoretical equilibrium calculations and simultaneous measurements of nitric acid, ammonia, ammonium ion, nitrate ion, sulfate ion, other ionic species, temperature and dewpoint. Particulate and gaseous pollutant concentrations at some inland sampling sites are readily explained if the aerosol is assumed to exist as an external mixture with all particulate nitrate and ammonium available to form pure NH_4NO_3. At other monitoring sites, especially near the coast, aerosol nitrate is found in the presence of NH_3 and HNO_3 concentrations that thermodynamic calculations show are too low to produce pure NH_4NO_3. This can be explained when the amount of aerosol nitrate that can be derived from reaction of nitric acid with sea salt and soil dust is taken into account. A calculation approach that accounts for the presence of mixed sulfate and nitrate salts improves the agreement between predicted and observed pollutant concentrations in the majority of cases studied. Uncertainties in these calculations arise from a number of sources including the thermodynamic quantities, and the effect of these uncertainties on the comparison between theory and experiment is discussed.