Effects of driving conditions on secondary aerosol formation from a GDI vehicle using an oxidation flow reactor

A comprehensive study on the effects of photochemical aging on exhaust emissions from a vehicle equipped with a gasoline direct injection engine when operated over seven different driving cycles was assessed using an oxidation flow reactor. Both primary emissions and secondary aerosol production were measured over the Federal Test Procedure (FTP), LA92, New European Driving Cycle (NEDC), US06, and the Highway Fuel Economy Test (HWFET), as well as over two real-world cycles developed by the California Department of Transportation (Caltrans) mimicking typical highway driving conditions. We showed that the emissions of primary particles were largely depended on cold-start conditions and acceleration events. Secondary organic aerosol (SOA) formation also exhibited strong dependence on the cold-start cycles and correlated well with SOA precursor emissions (i.e., non-methane hydrocarbons, NMHC) during both cold-start and hot-start cycles (correlation coefficients 0.95–0.99), with overall emissions of ∼68–94 mg SOA per g NMHC. SOA formation significantly dropped during the hot-running phases of the cycles, with simultaneous increases in nitrate and ammonium formation as a result of the higher nitrogen oxide (NOx) and ammonia emissions. Our findings suggest that more SOA will be produced during congested, slow speed, and braking events in highways.acceptedVersionPeer reviewe

Anthropogenic Impacts on Air Pollution - From Primary Marine Emissions to Secondary Organic Aerosol Formation

Anthropogenic air pollution consists of primary and secondary pollutants resulted from human activities. It is related to different environmental and health issues such as climate change, visibility and respiratory diseases.The maritime transport is an important source of anthropogenic primary air pollution. Natural gas (NG) vessels have become more widely used due to the more stringent emission regulations; however, emission data from NG maritime operations is still limited. This thesis conducted a comprehensive analysis on the air quality, health effects and climate change impacts of switching from diesel to NG. Results showed that PM2.5, NOx, CO2 were reduced by about 93%, 92% and 18%, respectively. However, HCHO and CH4 increased several-fold. A health risk assessment showed the diesel plume increased long-term health risk and the NG plume increased short-term health risk. A global warming potential (GWP) analysis was performed and revealed that the average NG exhaust GWP was increased by 38%. Mitigation strategies for further reducing pollutants from NG exhaust are discussed and showed potential for reducing short-term health and climate impacts.Anthropogenic secondary organic aerosol (SOA) is formed from the oxidation of volatile organic compounds (VOCs) such as aromatics and is critically impacted by NOx. Global transport models use the SOA parameters from the two major chemical pathways, RO2+NO and RO2+HO2 and the branching ratio of RO2+NO pathway (β), to predict SOA formation. This thesis attempted to improve the model prediction by experimentally investigating the SOA formation from those pathways with a novel approach of maintaining β constant throughout chamber experiments. At low-NOx conditions, multiple SOA yield curves were observed. The yield increased with HO2/RO¬2, indicating the contribution of RO2+RO2 pathway. The GEOS-Chem model showed that for the regions with high aromatic emissions but lower HO2/RO¬2, aromatic SOA was overestimated by up to 100%. At high-NOx conditions, SOA parameters were developed when controlling β at one during the chamber experiments to simulate the RO2+NO pathway without significant contribution from the other pathways. The global surface β was modelled using GEOS-Chem and four β scenarios were observed. SOA formation was investigated when simulating the daytime β profiles for those scenarios

Secondary Organic and Inorganic Aerosol Formation from a GDI Vehicle under Different Driving Conditions

This study investigated the primary emissions and secondary aerosol formation from a gasoline direct injection (GDI) passenger car when operated over different legislative and real-world driving cycles on a chassis dynamometer. Diluted vehicle exhaust was photooxidized in a 30 m3 environmental chamber. Results showed elevated gaseous and particulate emissions for the cold-start cycles and higher secondary organic aerosol (SOA) formation, suggesting that cold-start condition will generate higher concentrations of SOA precursors. Total secondary aerosol mass exceeded primary PM emissions and was dominated by inorganic aerosol (ammonium and nitrate) for all driving cycles. Further chamber experiments in high temperature conditions verified that more ammonium nitrate nucleates to form new particles, forming a secondary peak in particle size distribution instead of condensing to black carbon particles. The results of this study revealed that the absorption of radiation by black carbon particles can lead to changes in secondary ammonium nitrate formation. Our work indicates the potential formation of new ammonium nitrate particles during low temperature conditions favored by the tailpipe ammonia and nitrogen oxide emissions from gasoline vehicles

Freeform Modelling Using Sweep Differential Equation with Haptic Interface

This paper presents the development of a virtual sculpting system and addresses the issues of interactive freeform solid modelling with haptic interface. A virtual reality (VR) approach is taken to make the developed system more intuitive and interactive. The virtual sculpting method is based on the metaphor of carving a primitive or imported solid model into a 3D freeform object. The geometric modelling is based on the sweep differential equation method to compute the boundary of the tool swept volume. The ray-casting method is used to perform Boolean operations to simulate the sculpting process. A new method of surface reconstruction from dexel data is presented. The PHANToM™ manipulator is used to provide the position and orientation data of the sculpting tool and also to provide haptic sensation to the user hand during the sculpting. An accuracy analysis is performed to determine the limitations on the sculpted geometric details

Surface Reconstruction for Interactive Modeling of Freeform Solids by Virtual Sculpting

This paper presents a new method for surface reconstruction from dexel data for virtual sculpting. This is part of our research efforts to develop a dexel model based sculpting system with the capability of interactive solid modeling with haptics interface. Dexel data are converted to a series of planar contours in parallel slices (i.e. cross sections). Then triangular meshes are created by connecting the contour points in adjacent slices. Examples are given to demonstrate the ability of the described method to convert from dexel data to triangular meshes for the viewing of a sculpted model in different directions

A Novel Contour Generation Algorithm for Surface Reconstruction from Dexel Data

This paper presents a method of reconstructing a triangular surface patch from dexel data generated by ray casting to represent solid models for applications, such as virtual sculpting and numerically controlled (NC) machining simulation. A novel contour generation algorithm is developed to convert dexel data into a series of planar contours on parallel slices. The algorithm categorizes the dexels on two adjacent rays into different groups by using a “grouping” criterion. The dexel points in the same group are connected using a set of rules to form subboundaries. After checking the connections among all the dexel points on one slice, a connection table is created and used to obtain the points of connection in a counterclockwise sequence for every contour. Finally, the contours on all the parallel slices are tiled to obtain triangular facets of the boundary surface of the 3D object. Computational costs and memory requirements are analyzed, and the computational complexity analysis is verified by numerical experiments. Example applications are given to demonstrate the described method

Accuracy and Computational Complexity Analysis of Design Models Created by Virtual Sculpting

We have developed an experimental virtual sculpting system with haptic interface, which allows the user to create a freeform model interactively. The virtual sculpting method is based on the metaphor of carving a solid block into a 3D freeform object. The PHANToMTM manipulator is used to provide the position and orientation data of the sculpting tool and to generate haptic sensation to the user\u27s hand during the sculpting process. The goal is to provide a high-fidelity simulation system with real-time performance and adequate accuracy of the generated model. In order to understand the limitations on the geometric details that can be generated, we perform an accuracy analysis in different aspects. The computational complexity due to various parameters of the virtual sculpting system is also analyzed. Numerical data are presented to verify the analytical results

Surface Reconstruction from Dexel Data for Virtual Sculpting

This paper presents a new method for surface reconstruction from dexel data for virtual sculpting. We are in the midst of developing a dexel model based sculpting system having the capability of interactive solid modeling with haptics interface. The geometric modeling of our sculpting system is based on the Sweep Differential Equation method to compute the boundary of the tool swept volume. Ray casting is used to perform Boolean operations between the tool swept volume and the virtual stock in dexel models to simulate the sculpting process. The dexel data are converted to a series of planar contours in parallel slices (i.e. cross sections). The overlapping ratio between two contour areas is used as the criterion for deciding on the corresponding contours in two adjacent slices. The tiling problem is tackled by using the rule of the shortest distance between points on two corresponding contours. The branching problem is solved by adding one line segment between two contours to form one composite contour. Examples are given to demonstrate the ability of the developed code to convert from dexel data to triangular meshes for the viewing of a sculpted model in different directions

PAK1-Dependent Regulation of Microtubule Organization and Spindle Migration Is Essential for the Metaphase I–Metaphase II Transition in Porcine Oocytes

P21-activated kinase 1 (PAK1) is a critical downstream target that mediates the effect of small Rho GTPase on the regulation of cytoskeletal kinetics, cell proliferation, and cell migration. PAK1 has been identified as a crucial regulator of spindle assembly during the first meiotic division; however, its roles during the metaphase I (MI) to metaphase II (MII) transition in oocytes remain unclear. In the present study, the potential function of PAK1 in regulating microtubule organization and spindle positioning during the MI–MII transition was addressed in porcine oocytes. The results showed that activated PAK1 was co-localized with α-tubulin, and its expression was increased from the MI to MII stage (p p p p < 0.001). Nevertheless, these adverse effects of IPA-3 on oocytes were reversed when the disulfide bond between PAK1 and IPA-3 was reduced by dithiothreitol (DTT). Co-immunoprecipitation revealed that PAK1 could recruit activated Aurora A and transform acidic coiled-coil 3 (TACC3) to regulate spindle assembly and interact with LIM kinase 1 (LIMK1) to facilitate actin filament-mediated spindle migration. Together, PAK1 is essential for microtubule organization and spindle migration during the MI–MII transition in porcine oocytes, which is associated with the activity of p-Aurora A, p-TACC3 and p-LIMK1