Even at low concentrations, the criteria air pollutant particulate matter (PM) is an environmental and public health hazard. Emissions levels legislated for modern diesel vehicles are so low (~90% lower than 2003) that it has become difficult to accurately measure PM by the regulatory metric: the mass of particles collected on a filter (i.e., the gravimetric method). Additionally, gravimetric analysis cannot measure real-time emission rates, and therefore is unable to characterize high-emitting transient events (e.g., engine starts, stop-and-go driving). By an alternate method, PM can be estimated by measuring the number-weighted particle size distribution (PSD) and calculating mass with a combination of theoretical and empirical constants (e.g., particle effective density). This integrated particle size distribution (IPSD) method is capable of high measurement sensitivity and real-time resolution. Real-time measurements by the IPSD method require fast-sizing spectrometers, such as the TSI Engine Exhaust Particle Sizer (EEPS), which sizes (between 5.6-560 nm) and counts particles based on their electrical mobility. The EEPS utilizes a unipolar charger to quickly charge particles for sizing and counting, however this mechanism has been shown to produce a less predictable charge distribution than bipolar chargers used in Scanning Mobility Particle Sizer (SMPS) systems – the gold standard 'slow-sizing' spectrometer. Several evaluations have shown deficiencies in EEPS PSD measurements due to charging differences (associated with particle morphology) unaccounted for in the transfer function matrix used to calibrate the EEPS. Specifically, the unipolar charger multiply charges a higher percentage of soot agglomerates (fractal-like particles common in diesel engine exhaust) than bipolar chargers. Because inaccurate PSDs are a primary reason for reported discrepancies between IPSD calculated mass and the gravimetric method, it is important to correct this deficiency in EEPS measurements. Recently, TSI has released additional EEPS calibration matrices ('soot' and 'Compact') which have shown better agreement with SMPS measurements under preliminary test conditions. This study further evaluates the performance of these new matrices relative to the original 'Default' matrix for diesel and biodiesel exhaust particles. Steady-state (75% engine load) emissions were generated by a light-duty diesel engine operating on (1) ultra-low sulfur diesel (ULSD) and (2) 100% soybean biodiesel. Raw EEPS data processed with each matrix were compared to simultaneously collected reference measurements from an SMPS. PSDs were evaluated based on their shape – i.e., multimodal fits of geometric mean diameter (GMD) and geometric standard deviation (GSD) – and concentration at peak particle diameter. For both fuels, all measurements agreed well in terms of the shape of the PSD: primary mode (accumulation) GMD ± 10nm, GSD ± 0.3. For ULSD, EEPS Default, Soot, and Compact concentrations were higher than the SMPS by factors of 1.9, 1.3, and 2.5, respectively. For biodiesel, EEPS Default, Soot, and Compact concentrations were higher than the SMPS by factors of 2.1, 1.7, and 2.4, respectively. Based on these results, the Soot matrix produced acceptable agreement between EEPS and SMPS measurements of ULSD exhaust particles. However, based on the factor of ~2 difference observed here, an additional calibration matrix may be necessary for the EEPS to accurately measure biodiesel exhaust particles. The IPSD method for estimating PM mass was applied to available data sets with corresponding gravimetric measurements (one ULSD transient cycle test and the same biodiesel steady-state test used for PSD evaluation). Real-time PSDs from each of the three EEPS matrices were used in combination with three sets of values assumed for size-dependent particle effective density (representing a range of potential conditions), resulting in nine IPSD estimates of PM mass corresponding to each gravimetric sample (one ULSD, one biodiesel). For the transient ULSD test, a widely used effective density distribution for fractal-like soot agglomerates resulted in good agreement between IPSD estimated mass and the gravimetric measurement (within 9% and 6% for Soot and Compact matrices, respectively). For the steady-state biodiesel test, assuming unit density (1g/cm³ for all particles) resulted in good agreement between IPSD estimated mass and the gravimetric measurement (within 7% and 2% for Soot and Compact matrices, respectively). These results support previous findings that the Soot matrix is currently the best available option for measurement of ULSD exhaust particles by the EEPS and that particle effective density distributions similar to the "fractal-like" one used here are an accurate estimate for ULSD exhaust particles under many conditions. However, based on the discrepancies between the EEPS and SMPS measured biodiesel exhaust PSDs observed here, as well as a current lack of information on the effective density of biodiesel exhaust particles, it is clear that additional research is necessary in order to understand the properties of biodiesel exhaust particles, especially as they relate to electrical mobility measurements and IPSD estimation of PM mass.

Made available in DSpace on 2016-06-02T19:56:59Z (GMT). No. of bitstreams: 1 6695.pdf: 5587762 bytes, checksum: 18422df241d7678995fda12c8a8bf70f (MD5) Previous issue date: 2015-01-23 / Universidade Federal de Sao Carlos / Human exposure to nanoparticles is increasingly becoming a concern, including in the workplace, due to urban and industrial development and the increasing use of motor vehicles. Filtration using fibrous filters is among the various options that can be used to provide efficient elimination of particles. It is known that there has been little research concerning the removal of nanoparticles using these filtration media. The aim of this study was to characterize, evaluate the efficiency and analyze the influence of filtration area on the efficiencies of the filter media HEPA (high efficiency particulate air), glass, micro-quartz, and polyester (300 g/m2) for the removal of nanoparticles. The filtration area was analyzed because is not possible in general to do the experimental testes in laboratory with large filtration area. The evaluation of the filter media depend on the structure of the filters (fiber diameter, thickness, and permeability), the operating conditions (superficial velocity and filtration area), and the characteristics of the filtered aerosols (density and size distribution). The characterization was used to evaluate the filter media and explain some results. Thickness, fiber diameter and permeability are examples of characterization parameters. The experimental setup was used in experimental tests of permeability and efficiency for the 5.3 and 40.7 cm2 filtration areas. A solution of 5 g/L sodium chloride (NaCl) was used to generate the nanoparticles in the filtration tests and a constant superficial velocity of 0.05 m/s. Particles were counted before and after passing through the filter media at the beginning of filtration using the electrical mobility technique. At the end of the filtration (one hour), the particles were again counted before and after the filters (in triplicate). The permeability constants of the HEPA, glass, and micro-quartz filters were the lower and they are influenced by the filtration area, while a much higher value was obtained for the polyester filter and showed no significant variation using different filtration area. Altogether, all the filter media were highly efficient in removing nanoparticles during approximately 2 hours of filtration, with the exception of the polyester filter, for which the efficiency decreased with increasing particle diameter. / Há uma grande preocupação com a exposição de pessoas às partículas nanométricas presentes no ar, até mesmo no ambiente de trabalho. Isto se deve ao desenvolvimento urbano, industrial e o crescente uso de veículos motorizados. Uma das soluções que vem sendo muito utilizadas ultimamente é o processo de filtração utilizando filtros fibrosos. Como há poucas pesquisas sobre o comportamento desses filtros na remoção de nanopartículas, o objetivo desse estudo foi caracterizar, avaliar a eficiência e verificar se o tamanho da área de filtração influencia no desempenho de meios filtrantes HEPA (High Efficiency Particulate Air Filter), de Vidro, de Micro Quartzo e de Poliéster na remoção de nanopartículas. A área de filtração foi avaliada uma vez que em testes laboratoriais nem sempre são possíveis grandes áreas de filtração para avaliação do desempenho de meios filtrantes. O desempenho de um meio filtrante depende da estrutura dos filtros (espessura, porosidade, diâmetro das fibras), das condições operacionais (velocidade de filtração e área de filtração) e das características do material particulado (densidade, tamanho da partícula e distribuição). A caracterização foi utilizada para avaliar os meios filtrantes e justificar possíveis resultados, entre ela está a espessura, o diâmetro das fibras e a permeabilidade. O sistema experimental foi utilizado tanto para a realização de experimentos de permeabilidade como para experimentos de eficiência com áreas de filtração iguais a 5,3cm2 e 40,7 cm2. Nos testes de eficiência foram utilizados uma solução de 5 g/L de cloreto de sódio para geração de partículas e velocidade constante de 5 cm/s. A contagem das partículas antes e após a passagem pelo meio filtrante era feita em triplicata no tempo zero e também depois de uma hora de filtração utilizando a técnica de mobilidade elétrica. Os meios filtrantes HEPA, de Vidro e de Quartzo apresentaram as menores constantes de permeabilidade e os valores foram ligeiramente influenciados pela área de filtração. Já o filtro de Poliéster foi o mais permeável e não apresentou variação significativa com a área de filtração. De uma forma geral, todos os meios filtrantes foram muito eficientes na remoção de nanopartículas durante duas horas de filtração aproximadamente, com exceção do filtro de Poliéster para o qual a eficiência decaiu com o aumento do tamanho das partículas.

No description available.