The effects of highway environmental conditions on photocatalytic pavement\u27s ability to reduce nitrogen oxides

Nitrogen oxides (NOx) emitted from vehicle exhaust are associated with negative health impacts and are a precursor to ozone. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can degrade pollutants such as NOx through heterogeneous photocatalysis. Although this technology has the potential to support environmentally friendly road infrastructure, a number of design and operational parameters may affect its effectiveness and thus need to be evaluated. The goal of this study was to measure the NOx reduction efficiencies from photocatalytic pavements under various environmental conditions common to highways. To achieve this goal, the objectives were to: (a) evaluate the influence of photocatalytic layer design and operating parameters on the efficiency of photocatalytic concrete pavement; (b) measure the impact of mixed pollutants on NOx reduction efficiency; and (c) measure the impact of roadway contaminants on NOx reduction. To achieve the first objective, the effects of relative humidity level, pollutants’ flow rate, and photocatalytic layer design parameters, including titanium dioxide (TiO2) percent content and aggregate sizes, were investigated. The environmental efficiency of the samples to remove NOx from the atmosphere was measured using a newly developed laboratory setup. The photocatalytic layer designs without fines achieved the highest photodegradation rates. In addition, the increase from 3% to 5% TiO2 resulted in minimal improvement to the NOx removal efficiency. To achieve the second objective, NOx reduction efficiencies were measured for various NO2/NOx ratios at various flow rates and humidity levels. Increasing the flow rate and NO2/NOx ratio negatively affects the effectiveness of the photocatalytic process. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface. To achieve the third objective, three common roadway contaminants were tested - dirt, de-icing salt, and motor oil - at two contrasting coverage levels. The contaminants had a strong, negative impact on the photocatalytic NOx removal efficiency. The impact of contaminants’ coverage was largely dependent on the soilure type, with oil having the largest negative impact. An increase in the flow rate and air relative humidity also resulted in lower NOx efficiencies

Quantification of the environmental impact of titanium dioxide photocatalytic pavements for air pollution remediation

Photocatalytic concrete pavements are a promising technology for mobile source air pollution remediation, however before widespread application of this technology is realized many unanswered questions remain regarding its overall environmental impact. In response to these questions, the goal of this study was to increase the understanding of the environmental impact of photocatalytic concrete pavement highways. To achieve this goal, the objectives of this study were to (A) construct a model that evaluates the nitrogen oxides (NOx) reduction from photocatalytic pavements, (B) quantify the nitrates released from the photocatalytic degradation of NOx, and (C) identify and characterize pathways for TiO2 nanoparticle exposure. To achieve objective A, a field study was conducted to evaluate the NOx reduction. Results showed evidence of minimal photocatalytic reductions with large variability due to many unknown and known parameters. As a result, this study also investigated the use of laboratory results to better understand the significance of the NOx reduction through the creation of a theoretical mass balance Lavoisier box model. Laboratory results indicated that the nitrogen monoxide (NO) oxidation rate is reaction rate mass transfer controlled following the Langmuir- Hinshelwood (L-H) model. A parametric study was completed to evaluate the L-H constants under different environmental conditions and statistical model was created to describe the NO oxidation rate. Incorporating the resulting NO oxidation rate into a Lavoisier box model the mass transfer mechanisms were compared and objective A was achieved. Objectives B and C of the project deal with evaluating potential unintended consequences resulting from implementation of photocatalytic concretes. To complete objective B, nitrates and TiO2 nanoparticles released to water were quantified. Lastly, TiO2 nanoparticles released to the air during construction activities were quantified and characterized to achieve objective C

Lessons learned in developing an environmental product declaration program for the asphalt industry in North America

The objective of this paper is to report the technical and organizational challenges involved in the development of the North American Environmental Product Declaration program for asphalt mixtures. Developing a Life Cycle Assessment (LCA) for asphalt mixtures presents the challenge of coordinating consistent assumptions across industries and stakeholders, and requiring a harmonized decision-making process that accounts for the impacts of materials across the supply and value chain. While, the methods of LCA are rational and well defined, the decisions defining the various assumptions are often arrived at through a negotiation process shaped by stakeholder relationships and priorities. There is much discussion in the literature regarding the technical challenges of conducting an LCA involving choice of system boundary, functional unit, and allocation procedures used for co-products and recycled products. However, the formulation process of these technical questions within the context of stakeholder biases and heuristics are seldom explicitly discussed, even though they play an important role in how the technical challenges are resolved. Hence, the paper explores how differences in stakeholder priorities and perspectives, in the pavement construction industry, directly shape the Product Category Rules (PCR) defining the program by drawing attention to specific LCA related technical questions and highlights how the solutions were negotiated. The primary challenge identified is how to ensure technical rigor of the underlying LCA, while recognizing the interests of the stakeholders and ensuring the delivery of a program that is effective. The paper discusses how technical issues regarding system boundary choice, data use and allocation presented challenges for the PCR Development Working Group accounting for different stakeholder interests. Within this context the paper will highlight the developed PCR and present relevant results from the underlying LCA

Challenges to using environmental product declarations in communicating life-cycle assessment results case of the asphalt industry

© 2017, SAGE Publications Ltd. All rights reserved. The objective of this paper is to discuss the challenges encountered in creating an environmental product declaration (EPD) program for asphalt mixtures that ensures the consistent, transparent, and reliable communication of life-cycle assessment (LCA) results between stakeholders in the paving industry. The formal process outlined in ISO 14025 for developing an EPD program has partially ameliorated the challenges that have deterred the adoption of LCA by requiring stake-holder participation and industrywide agreement on assumptions that define an LCA. This requirement has led to a new set of challenges, both technical and organizational, in addressing issues of data quality, validation, consistency, and transparency during the product category rules (PCR) development process. The paper provides an overview of the EPD program development process and establishes the role played by stakeholders in the decision-making process given their affiliations and relationship to the asphalt materials industry. Some of the LCA results that supported the decision-making process in developing the PCR are discussed. In addition, the paper highlights how the analysis supporting an EPD can also be used to improve plant operational efficiencies, while providing insights into the asphalt mixture design process, accounting for performance and environmental impacts

Effect of vehicle classification and activity on field evaluation of photocatalytic concrete pavements’ ability to remove nitrogen oxides-a case study

There has been an increasing interest in photocatalytic pavements, which can decompose pollutants to nonhazardous waste products with little energyrequirements and selectivity.The objective of this study is to evaluate the effects of vehicle activity and classification on nitrogen oxide (NOx) pollution emitted and correlating these factors to the NOx reduction from photocatalytic pavements. To achieve this objective, a field study was conducted with 22.3 m2of photocatalytic spray coated area and 22.3 m2 of uncoated control area. Evidence of photocatalytic reduction of NOx was evaluated by directly measuring NOx reductions from the ambient air.A traffic study was conducted for the photocatalytic control areas to characterize the variability in traffic classification and activity between the two areas and its effects on interpreting NOx reduction.Results showed that the amount of NOx emitted in the area predicted to be from traffic sources is no more than 5 grams per hour.Due to the low values of pollution emitted in the both the photocatalytic area and the control area, minor differences in traffic activity between these two areas resulted in significant differences in the amount of pollution emitted between the photocatalytic and the control areas.This may complicate the interpretation of the NOx reduction results. Furthermore,there was no significant linear correlation of vehicle class and speed and NOx reduction

Characterization of nanoparticles released during construction of photocatalytic pavements using engineered nanoparticles

With the increasing use of titanium dioxide (TiO2) nanoparticles in self-cleaning materials such as photocatalytic concrete pavements, the release of nanoparticles into the environment is inevitable. Nanoparticle concentration, particle size, surface area, elemental composition, and surface morphology are pertinent to determine the associated risks. In this study, the potential of exposure to synthetic nanoparticles released during construction activities for application of photocatalytic pavements was measured during laboratory-simulated construction activities of photocatalytic mortar overlays and in an actual field application of photocatalytic spray coat. A scanning mobility particle sizer system measured the size distribution of nanoparticles released during laboratory and field activities. Since incidental nanoparticles are released during construction activities, nanoparticle emissions were compared to those from similar activities without nano-TiO2. Nanoparticle counts and size distribution suggest that synthetic nanoparticles are released during application of photocatalytic pavements. In order to identify the nanoparticle source, nanoparticles were also collected for offline characterization using transmission electron microscopy. However, positive identification of synthetic nanoparticles was not possible due to difficulties in obtaining high-resolution images. As a result, further research is recommended to identify nanoparticle composition and sources. © Springer Science+Business Media B.V. 2012

Exposure to nanoparticles during asphalt paving of photocatalytic asphalt pavements

Recent epidemiologic studies suggest that nanoparticles or ultrafine particles are correlated with negative health impacts, including adverse pulmonary and cardiovascular effects. Nanoparticle concentration, particle size, surface area, elemental composition, and surface morphology are all pertinent to comprehend the associated risks. Despite this, there are few studies quantifying and characterizing the nanoparticle exposure necessary for proper risk assessments, especially from the construction industry. As a result, the aim of this study was to quantify and characterize nanoparticle exposure to construction workers during asphalt paving activities for an emerging asphalt pavement: photocatalytic asphalt pavement using TiO2 engineered nanoparticles capable of reducing traffic emissions. Results were compared to nanoparticle exposure of conventional asphalt binder to identify if there is an increase in potential risks. The exposure was measured using the Scanning Mobility Particle Sizer, which provides the size distribution, surface area, mass, and particle concentrations. Particles were also collected for offline characterization using Transmission Electron Microscopy and Scanning Electron Microscopy for further evidence of particle size, morphology, and chemical composition. Positive identification of the source of these nanoparticles was not possible and requires further research, which was out of the scope of this study

Quantification of reduction of nitrogen oxides by nitrate accumulation on titanium dioxide photocatalytic concrete pavement

Field trials of photocatalytic pavements were recently initiated and are being considered by many states (e.g., Virginia, Texas, New York, and Missouri). Results from this study are from the country\u27s first air-purifying asphalt and concrete photocatalytic pavements on December 20, 2010. The test area was a pavement site located on the Louisiana State University campus in Baton Rouge. The objective of this study was validation of photocatalytic degradation of nitrogen oxides (NOx) at the test site by measuring nitrate salts (NO3) deposited on the pavement surface. With quantification of the nitrate levels produced in the field attributable to photocatalytic activity, measurements were correlated to laboratory test results of NOx reduction efficiency. A field sampling procedure of NO3 deposited on the pavement surface is presented. On the basis of the results of the experimental program, the proposed method to quantify photocatalytic efficiency through nitrate measurements was successful. There was definite evidence that photocatalytic degradation of NOx was taking place in the treated section. In addition, the photocatalytic process was active during the first 4 days followed by a slight decrease in degradation of NOx. Full regeneration of photocatalytic activity took place through a self-cleaning process during a rain event. Six months of traffic and in-service operating conditions had negligible effects on the efficiency of the photocatalytic coating. In addition, there was good agreement between nitric oxide removal efficiency measured in the field after one day of nitrate accumulation and in the laboratory at the same relative humidity

Field evaluation of ability of photocatalytic concrete pavements to remove nitrogen oxides

Numerous laboratory studies have demonstrated the ability of nano and ultrafine titanium dioxide (TiO2) photocatalytic pavements to trap and degrade nitrogen oxides in the air when irradiated with ultraviolet light. However, to understand better how photocatalytic pavements will perform under real-world conditions, field studies are necessary. Quantification of the reduction of nitrogen oxides (NOx) in field studies is difficult and challenging because of the many environmental and operating variables. The objective of this paper is to identify evidence of photocatalytic NOx reduction and to determine the environmental and operating factors that affect efficiencies under real-world conditions. A quarter-mile concrete roadway was sprayed with a photocatalytic coating in Baton Rouge, Louisiana. This section was the first field installation of TiO2 photocatalytic pavement in the United States. NOx concentrations were monitored for both the coated and uncoated sections simultaneously for 3 weeks during the spring season to measure photocatalytic degradation directly. Further, nitrates were collected from the coated and uncoated areas for evidence of photocatalytic NOx reduction. Results from both approaches show evidence of photocatalytic NO x reduction. Environmental factors with significant impact on photocatalytic efficiency include relative humidity, solar intensity, and wind speed and direction