Formic acid and nitric acid have been found to contribute to aerosol formation and are key components of acidity in the troposphere. Tropospheric measurements of these species are often limited, resulting in major uncertainties when assessing their effects on the climate. Current global chemistry-transport models significantly under-predict formic acid concentrations, particularly in the mid-to-high latitudes of the Northern Hemisphere. Furthermore, large discrepancies exist in the role played by dinitrogen pentoxide on nitric acid production between two recently documented models assessing the global nitric acid budget. In order to accurately constrain the budget of these acids in the mid-to-high latitudes of the Northern Hemisphere, it is crucial that these uncertainties are addressed. In this work, airborne measurements of formic acid, nitric acid and dinitrogen pentoxide are presented from across different regions of the Northern Hemisphere to investigate direct and indirect sources contributing to the formic acid and nitric acid regional budgets. Measurements were collected using a Chemical Ionisation Mass Spectrometer (CIMS) fitted to the Facility for Atmospheric Airborne Measurements (FAAM) BAe-146 aircraft. Formic acid measurements within the European Arctic during March and July 2012 would indicate ocean sources dominate over terrestrial sources irrespective of seasonality. CH2I2 photolysis and oxidation was hypothesised as a marine source of formic acid. Modelled estimates would indicate the CH2I2 reaction route may represent a significant summer marine source of formic acid within the Fenno-Scandinavian Arctic. Additionally, low altitude aircraft measurements taken within the Fenno-Scandinavian Arctic over regions occupied by wetlands in August 2013 were used to calculate a formic acid surface flux. Results would suggest formic acid emission from wetlands may represent up to 37 times greater than its globally inferred estimate. A flux measurement conducted over a comparable region in September 2013 observed a negative flux, indicating a change of this region from a net source to a net sink of formic acid. The inconsistency of this regional wetland source confirms the need for in-depth studies on formic acid emission from wetlands, in order to better understand its contribution to the regional and global formic acid budget. In a separate study, significant daytime elevations of N2O5 and HNO3 concentrations were observed within identified biomass burning plumes off the eastern coast of Canada. In-plume correlations between N2O5 and HNO3 concentrations observed within these environments suggest N2O5 was acting as additional daytime source of gaseous HNO3 when subjected to photolytically-limited conditions. This result has important implications to ozone production and provides evidence for an additional daytime source of nitric acid, which must be included in chemistry models calculating the global nitric acid budget.

No description available.

I investigated the utility of Br- as a chemical ionization mass spectrometry (CIMS) reagent ion for the detection and measurement of both atmospheric trace gases and aerosol species. The primary goals of this study are to obtain fast, very sensitive measurements of nitrate and sulfate and to ascertain if gas phase PAN and HNO3 could be measured simultaneously with the same chemical ionization scheme. Gas-phase measurements of PAN and nitric acid were conducted and the sensitivities of these measurements to temperature and relative humidity were determined. The potential for measuring aerosol composition by CIMS was assessed by comparison with PILS (particle-into-liquid sampler) measurements.

This study presents airborne measurements of HO2NO2, HCl and SO2 using chemical ionization mass spectrometry (CIMS) during the Intercontinental Chemical Transport Experiment (INTEX) field campaign, an intensive study to characterize the chemical composition of the troposphere in the eastern United States, Mexico City, and the North Pacific which is the outflow region of Asia. The first direct in situ measurements of HO2NO2 were made in the free troposphere over the eastern U.S. during summer 2004. The highest mean mixing ratio of 76 pptv (median = 77 pptv, = 39 pptv) was observed in the altitude range of 8-9 km. Highly constrained steady state calculations of HO2NO2 using measured HOx levels are poorly correlated with observed HO2NO2 in the upper troposphere (8 km < z < 12 km; the median ratio of [HO2NO2]SS-MEA/[HO2NO2]MEA = 2.9). However, steady state HO2NO2 using model-derived HOx shows reasonable agreement with measurements in the free troposphere ([HO2NO2]SS-MEA/[HO2NO2]MEA = 1.3). The vertical distribution of HCl was measured over the north Pacific during May 2006 from the marine boundary layer (MBL) up to lower stratosphere. Recent stratospheric influence in the upper troposphere (8 km < z < 12 km) was efficiently identified from enhanced HCl (up to ~100 pptv) relative to very low background levels (< 2pptv). In the remote MBL, the acidification of seasalt aerosols by HNO3 appeared to be the major source of HCl, with level consistently over 20 pptv (up to 400 pptv). The distribution of SO2 was measured in the outflow region of the eastern U.S. and Asia; two major anthropogenic SO2 source regions. This study presents vertical and horizontal distributions of SO2 and relevant gas phase and aerosol parameters to characterize SO2 transport in the troposphere. SO2 in the boundary layer was efficiently transported to the upper troposphere by deep convection and frontal uplift processes. High SO2 in convective plume in the upper troposphere were strongly correlated with ultrafine aerosols.Conversely, SO2 from frontal uplift shows a strong correlation with non-volatile aerosols. Comparisons of SO2 products from global 3-D chemical transportation models (GEOS-CHEM and MOZART) with observations suggest that sulfur sources are relatively well described but that the oxidation mechanism needs refinement.

An existing method for the measurement of atmospheric gaseous species was modified to collect data on aerosol concentrations. Data from biomass burning events in different regions (Canada, the Arctic and California) were collected during April to July, 2008 and the concentrations and evolution of secondary organic aerosols were discussed. And finally, data on the light absorbing properties of water soluble organic aerosols were collected in Atlanta, GA and compared with filter data for the same properties. The results presented in this thesis showed that a negative ion chemical ionization mass spectrometer (CIMS), can be modified by the addition of a thermally denuded inlet to measure aerosol phase sulfuric acid. This system can also be used to measure other aerosol phase organic acids. In the biomass burning plumes studied in the second part, no clear indication of formation of secondary aerosol or gaseous species was observed, except for peroxyacetyl nitrate (PAN). Filter data collected from FRM sites in the Southeastern U.S. showed that biomass burning is the most dominant source of water soluble light absorbing carbonaceous aerosol in this region. The data from a study in Atlanta, GA showed that the online PILS-LWCC-WSOC system might be used for measurements of light absorbing properties of aerosols and WSOC.

No description available.

Compostos de amônio quaternário (QACs) têm sido amplamente utilizados como desinfetantes e antissépticos, sendo essenciais na prevenção e controle de infecções bacterianas na medicina humana e veterinária. Embora patógenos prioritários multirresistentes têm sido muito bem caracterizados quanto ao perfil de suscetibilidade e contexto genético da resistência aos antibióticos, dados de resistência aos QACs são limitados. Assim, o objetivo do presente estudo foi avaliar a atividade in vitro dos QACs de uso doméstico e hospitalar [cloreto de benzalcônio (BAC), cloreto de cetilpiridinio (CPC) e brometo de cetiltrimetilamônio (CTAB)], contra patógenos prioritários multirresistentes, identificando os principais genes de resistência associados. Foram estudadas 100 cepas multirresistentes previamente sequenciados usando as plataformas Illumina MiSeq e NextSeq representativas de diferentes hospedeiros (humanos e animais) e fontes (ambientes e alimentos). As cepas foram identificadas como Klebsiella pneumoniae (n= 24), Escherichia coli (n= 30); Pseudomonas aeruginosa (n= 10), Enterobacter spp, (n= 8), Acinetobacter baumannii (n= 11) e Salmonella spp. (n= 17). Genes de resistência aos QACs foram identificados in silico através do alinhamento dos contigs obtidos de cada cepa sequenciada com genes de referência obtidos do GenBank, utilizando o programa Geneious versão 8 (Biomatters Ltd). A identidade de cada gene foi analisada utilizando o programa BLASTx, no qual um critério baseado em &#8805;90% identidade resultou na identificação dos genes mdfA (77%), qacE (44%), qacE&#916;1 (43%), sugE(c) (29%), emrE (21%), qacA (19%), sugE(p) (5%), qacF (7%), qacH (7%) e qacL (7%) em 85 cepas; enquanto que 15 cepas não possuíam nenhum gene de resistência aos QACs. A concentração inibitória mínima (CIM) dos QACs para as 100 cepas foi determinada pelo método de microdiluição em caldo. Os resultados sugeriram que a resistência em patógenos prioritários circulando na interface humano-ambiente-animal não é restrita aos antibióticos, uma vez que a elevada ocorrência de genes qacE, qacE&#916;1 e mdfA poderia estar associada com uma redução da suscetibilidade para QACs. Consequentemente, a resistência aos QACs poderia também contribuir para a persistência e adaptação destes patógenos nos seres humanos e outros animais, assim como em ambientes impactados antropogenicamente. / Quaternary ammonium compounds (QACs) have been widely used as disinfectants and antiseptics, being applied as essential compounds in the prevention and control of bacterial infections in human-and veterinary hospital medicine. Although multiresistant priority pathogens have been well characterized with respect to their susceptibility profile and their genetic context of resistance for antibiotics, studies of resistance to QACs are limited. Thus, the objective of the present study was to evaluate the in vitro activity of QACs [(benzalkonium chloride (BAC), cetylpyridinium chloride (CPC) and cetyltrimethylammonium bromide (CTAB)] for household and hospital use against multiresistant priority pathogens, identifying the main resistance genes associated. A hundred multiresistant isolates (previously sequenced using the Illumina MiSeq and NextSeq platforms), representative of different hosts (humans and animals) and sources (environment and food) were studied. Isolates were identified as Klebsiella pneumoniae (n=24), Escherichia coli (n=30), Pseudomonas aeruginosa (n=10), Enterobacter spp. (n=8), Acinetobacter baumannii (n=11) and Salmonella spp. (n=17). In silico analysis for identification of genes conferring resistance to QACs were performed by aligning the contigs obtained from the strains with reference genes deposited in GenBank, using the Geneious version program (Biomatters Ltd). Similarities were analyzed using the BLASTx online program, considering the alignment criteria based on &#8805; 90% identity. The result of these analysis revealed the presence of the following QAC genes: mdfA (77%), qacE (44%), qacE&#916;1 (43%), sugE(c) (29%), emrE (21%), qacA (19%), sugE (p) (5%), qacF (7%), qacH (7%) e qacL (7%); while 15 strains showed no resistance genes for QACs. Determination of QACs minimum inhibitory concentration (MIC) for the 100 isolates, by the broth microdilution method. These results suggest that resistance to QACs in priority pathogens, circulating at the human-environment-animal interface, is not restricted to antibiotics, since the high occurrence of genes qacE, qacE&#916;1 and mdfA were associated with a reduced susceptibility to QACs. Consequently, resistance to QACs could also contribute to the persistence and adaptation of these pathogens in humans and othes animals, as well as in anthropogenically impacted environments.

This work presents the development of a laser-induced fluorescence technique to measure atmospheric formaldehyde. In conjunction with the technique, the design of a compact, narrow linewidth, etalon-tuned titanium:sapphire laser cavity which is pumped by the second harmonic of a kilohertz Nd:YAG laser is also presented. The fundamental tunable range is from 690-1100 nm depending on mirror reflectivities and optics kit used. The conversion efficiency is at least 25% for the fundamental, and 2-3% for intracavity frequency doubling from 3.5-4W 532 nm pump power. The linewidth is < 0.1 cm-1, and the pulsewidth is 18 nsec. Also presented are observations of gas-phase sulfuric acid from the NEAQS-ITCT 2K4 (New England Air Quality Study Intercontinental Transport and Chemical Transformation) field campaign in July and August 2004. Sulfuric acid values are reported for a polluted environment and possible nucleation events as well as particle growth within the boundary layer are explored. Sulfate production rates via gas phase oxidation of sulfur dioxide are also reported. This analysis allows an important test of our ability to predict sulfuric acid concentration and probe its use as a fast time response photochemical tracer for the hydroxyl radical, OH. In comparison, the NASA time-dependent photochemical box model is used to calculate OH concentration. Nighttime H2SO4 values are examined to test our understanding of nocturnal OH levels and oxidation processes. In comparison, sulfuric acid from a large ground based mission in Tecámac, México (near the northern boundary of Mexico City) during MIRAGE-Mex field campaign (March 2006) is presented. The observations in conjunction with the NASA LARc Photochemical box model are used to explore ozone production, nitrate and sulfate formation, and radical levels and radical production rates during the day. The one minute observations of sulfuric acid, sulfur dioxide, and aerosol surface area were again used to calculate OH levels assuming steady state, and are in good agreement with observations of OH (R2 = 0.7). Photochemical activity is found to be a maximum during the morning hours, as seen in ozone and nitrate formation.

Halogen chemistry plays an important role in spring time ozone and mercury depletion events (ODEs and MDEs) and may efficiently oxidize hydrocarbons such as the important greenhouse gas methane (CH4) in the polar marine boundary layer. This thesis presents a detailed study of bromine and chlorine chemistry in the Arctic boundary layer based on measurements of bromine and chlorine containing species using chemical ionization mass spectrometry (CIMS). The capability of CIMS to accurately measure bromine oxide (BrO) was demonstrated. The first direct measurements of hypobromous acid (HOBr) were achieved. Conditions that likely favor bromine activation (e.g. high wind speeds) was presented. To advance the understanding of bromine recycling, a time dependent model was built to simulate the bromine speciation. Unexpected high levels of molecular chlorine (Cl2) were observed at Barrow, AK, which had a large impact on methane oxidation and could contribute to ozone loss and mercury oxidation at Barrow, AK. Moreover, BrO levels observed at Summit, Greenland did not explain the under prediction of hydroxyl radical (OH). However, the enhanced OH was found to be coincident with elevated reactive gaseous mercury (RGM). In addition, airborne BrO measurements were found to be generally consistent with airborne observations of soluble bromide based on the response factors of mist chamber to the bromine species and bromine chemical mechanisms.

The hydrolysis reaction of N2O5 was investigated at room temperature on two aerosol types using a flow tube coupled to a newly built Chemical Ionization Mass Spectrometer (CIMS). This instrument was fully constructed and optimized during this research period, as well as employed to conduct one of two aerosol studies. The first examined the reaction on ammonium bisulphate aerosols using a new ion detection method, I-•N2O5 cluster formation, which proved to be highly advantageous over the common approach of dissociative charge transfer, yielding a sensitivity for I-•N2O5 of 0.024 Hz/pptv. The uptake coefficients at 30% and 50% relative humidity were 0.0067 ± 0.0002 and 0.0120 ±0.0014, respectively. The second study was performed using a different CIMS previously assembled in the laboratory. In this case, the reaction was investigated on secondary organic aerosols produced through the ozonolysis of α-pinene, and resulted in an uptake coefficient of 8.5x10-5 ± 7x10-6 at 0% relative humidity.