Urban atmospheric chlorine chemistry : mechanism development, evaluation and implications

textDetailed photochemical modeling is used to guide air quality management activities around the world. These models use condensed chemical mechanisms to describe the multiphase processes that lead to chemical transformations in the atmosphere. Condensed mechanisms have generally not included the reactions of halogens, yet an expanding body of ambient observational evidence indicates that halogen chemistry, particularly chlorine chemistry, can be important in urban environments. This thesis is focused on the development, implementation, and evaluation of condensed chemical mechanisms that incorporate chlorine chemistry pathways. Gas phase reactions involving molecular chlorine and nitryl chloride (ClNO₂), as well as heterogeneous reactions involving particulate chloride species are addressed. The predictions of the modeling work presented here are compared to environmental chamber experiments and field observations.Chemical Engineerin

Secondary organic aerosol reduced by mixture of atmospheric vapours

Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene 'scavenges' hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).Peer reviewe

2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease

The recommendations listed in this document are, whenever possible, evidence based. An extensive evidence review was conducted as the document was compiled through December 2008. Repeated literature searches were performed by the guideline development staff and writing committee members as new issues were considered. New clinical trials published in peer-reviewed journals and articles through December 2011 were also reviewed and incorporated when relevant. Furthermore, because of the extended development time period for this guideline, peer review comments indicated that the sections focused on imaging technologies required additional updating, which occurred during 2011. Therefore, the evidence review for the imaging sections includes published literature through December 2011

Inland Concentrations of Cl2 and ClNO2 in Southeast Texas Suggest Chlorine Chemistry Significantly Contributes to Atmospheric Reactivity

Measurements of molecular chlorine (Cl2), nitryl chloride (ClNO2), and dinitrogen pentoxide (N2O5) were taken as part of the DISCOVER-AQ Texas 2013 campaign with a High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) using iodide (I-) as a reagent ion. ClNO2 concentrations exceeding 50 ppt were regularly detected with peak concentrations typically occurring between 7:00 a.m. and 10:00 am. Hourly averaged Cl2 concentrations peaked daily between 3:00 p.m. and 4:00 p.m., with a 29-day average of 0.9 ± 0.3 (1σ) ppt. A day-time Cl2 source of up to 35 ppt∙h−1 is required to explain these observations, corresponding to a maximum chlorine radical (Cl•) production rate of 70 ppt∙h−1. Modeling of the Cl2 source suggests that it can enhance daily maximum O3 and RO2• concentrations by 8%–10% and 28%–50%, respectively. Modeling of observed ClNO2 assuming a well-mixed nocturnal boundary layer indicates O3 and RO2• enhancements of up to 2.1% and 38%, respectively, with a maximum impact in the early morning. These enhancements affect the formation of secondary organic aerosol and compliance with air quality standards for ozone and particulate matter

Carboxylic acids from limonene oxidation by ozone and hydroxyl radicals: insights into mechanisms derived using a FIGAERO-CIMS

This work presents the results from a flow reactor study on the formation of carboxylic acids from limonene oxidation in the presence of ozone under NOx-free conditions in the dark. A High-Resolution Time-of-Flight acetate Chemical Ionisation Mass Spectrometer (HR-ToF-CIMS) was used in combination with a Filter Inlet for Gases and AEROsols (FIGAERO) to measure the carboxylic acids in the gas and particle phases. The results revealed that limonene oxidation produced large amounts of carboxylic acids which are important contributors to secondary organic aerosol (SOA) formation. The highest 10 acids contributed 56 %–91 % to the total gas-phase signal, and the dominant gas-phase species in most experiments were C8H12O4, C9H14O4, C7H10O4 and C10H16O3. The particle-phase composition was generally more complex than the gas-phase composition, and the highest 10 acids contributed 47 %–92 % to the total signal. The dominant species in the particle phase were C8H12O5, C9H14O5, C9H12O5 and C10H16O4. The measured concentration of dimers bearing at least one carboxylic acid function in the particle phase was very low, indicating that acidic dimers play a minor role in SOA formation via ozone (O3)/hydroxyl (OH) oxidation of limonene. Based on the various experimental conditions, the acidic compositions for all experiments were modelled using descriptions from the Master Chemical Mechanism (MCM). The experiment and model provided a yield of large (C7–C10) carboxylic acid of the order of 10 % (2 %–23 % and 10 %–15 %, respectively). Significant concentrations of 11 acids, from a total of 16 acids, included in the MCM were measured with the CIMS. However, the model predictions were, in some cases, inconsistent with the measurement results, especially regarding the OH dependence. Reaction mechanisms are suggested to fill-in the knowledge gaps. Using the additional mechanisms proposed in this work, nearly 75 % of the observed gas-phase signal in our lowest concentration experiment (8.4 ppb converted, ca. 23 % acid yield) carried out under humid conditions can be understood

Illness perception and fatigue after myocardial infarction

Treatment of myocardial infarction (MI) has undergone major advances in recent years, including reductions in mortality and hospital stays. To optimize patients’ recovery, secondary preventive strategies are important. However, many patients fail to attend to such programmes. It has been shown that illness perceptions may influence attendance to rehabilitation programmes as well as recovery. Other obstacles are post-MI fatigue and depression. The main focus of the present thesis was to explore illness perception and fatigue after MI. A secondary aim was to investigate the levels of illness perceptions and fatigue and their relationships with demographic/clinical variables, depression, anxiety and health-related quality of life (HRQoL). In Study I, patients’ illness perception of MI was explored. The methodology used was grounded theory (25 informants interviewed). The core categories illness reasoning and trust in oneself vs. trust in others were found to be fundamental in viewing the MI either as an acute isolated heart attack or as a sign of a chronic condition. In Study II, the aim was to gain a deeper understanding of what fatigue means to patients with recent MI and how they managed to deal with the consequences of fatigue. Grounded theory was applied also in this study (19 informants interviewed). A central theme was labelled living with incomprehensible fatigue. This core category was featured by several properties: different kind of tiredness, unrelated to effort, unpredictable occurrence, and unknown cause. In Study III, the incidence of fatigue in 204 consecutive MI patients was examined and compared to reference populations. Gender differences in fatigue were also examined, as well as changes over time and the relationships between fatigue versus clinical and demographic variables and measures of emotional distress. The Hospital Anxiety and Depression Scale (HADS) and the Multidimensional Fatigue Inventory (MFI-20) were used. MI patients reported higher levels of fatigue compared with the general population, depression and fatigue overlapped, but 33% reported fatigue without coexisting depression. No gender differences were found. In Study IV, illness perceptions in 204 consecutive MI patients were examined using the Illness Perception Questionnaire (IPQ-R) and compared to reference populations. Changes in illness perceptions over time were also examined, as well as the relationships between illness perceptions and anxiety/depression (HADS), fatigue (MFI-20), somatic health problems (SHCQ) and HRQoL (SF-36). It was shown that illness perceptions changed over time, from viewing the MI as an acute event to a more chronic condition, and that the beliefs in personal and treatment control of MI decreased. These negative beliefs were associated with fatigue and lowered HRQoL. In conclusion, the studies contribute to our understanding of how patients perceive their MI, and particularly that fatigue is a notable symptom affecting patients´ lives. Individualized secondary preventive strategies could start with identifying patient’s unique illness perception. It is also important to identify patients who are fatigued to provide adequate treatment as well as to prevent progression from fatigue to exhaustion

Composition and Sources of Particulate Matter Measured near Houston, TX: Anthropogenic-Biogenic Interactions

Particulate matter was measured in Conroe, Texas (~60 km north of downtown Houston, Texas) during the September 2013 DISCOVER-AQ campaign to determine the sources of particulate matter in the region. The measurement site is influenced by high biogenic emission rates as well as transport of anthropogenic pollutants from the Houston metropolitan area and is therefore an ideal location to study anthropogenic-biogenic interactions. Data from an Aerosol Chemical Speciation Monitor (ACSM) suggest that on average 64 percent of non-refractory PM1 was organic material, including a high fraction (27%–41%) of organic nitrates. There was little diurnal variation in the concentrations of ammonium sulfate; however, concentrations of organic and organic nitrate aerosol were consistently higher at night than during the day. Potential explanations for the higher organic aerosol loadings at night include changing boundary layer height, increased partitioning to the particle phase at lower temperatures, and differences between daytime and nighttime chemical processes such as nitrate radical chemistry. Positive matrix factorization was applied to the organic aerosol mass spectra measured by the ACSM and three factors were resolved—two factors representing oxygenated organic aerosol and one factor representing hydrocarbon-like organic aerosol. The factors suggest that the measured aerosol was well mixed and highly processed, consistent with the distance from the site to major aerosol sources, as well as the high photochemical activity