Demonstration of Photocatalytic

Remediation Processes on Air Quality

PhotoPaqs Layman Report

Supported by LIFE Environmental Funding

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Report IndexPage 3 Contact Details & Project

Information

Page 4 Introduction

Page 5 What is photocatalysis?

Page 6 State of the art

Page 7 PhotoPAQs structure & Goals

Page 8 Preparatory actions

Page 9 Demonstration in a tunnel

Page 11 Demonstration outdoor

Page 13 Numerical modelling

Page 14 Conclusions & Outlooks

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Administration:Commission reference: LIFE 08 ENV/F/000487Total Budget: 4 018 190 Total contribution: 1 984 573 Year of finance: 2010 Duration: 01-JAN-2010 to 30-JUN-2014

Beneficiaries:Institut de recherches sur la catalyse et l'environnement de Lyon

Dr. Christian GEORGE (CNRS / University Lyon1, France)

Institut de combustion, arothermique, ractivit et

environnement

Dr. Abdelwahid MELLOUKI (CNRS, France)

Leibniz Institute for Tropospheric Research

Pr. Hartmut HERRMANN (TROPOS, Germany)

Bergische University Wuppertal

Dr. Jrg KLEFFMANN (BUW, Germany)

CTG Italcementi Group

Giuseppe MANGANELLI (CTG, Italy)

Laboratory of Heat Transfer and Environmental Engineering

Prof. Nicolas MOUSSIOPOULOS (LHTEE, Greece)

Belgian road research centre

Dr. Anne BEELDENS (BRRC, Belgium)

Laboratoire inter-universitaire des systmes atmosphriques

Pr. Jran-Franois DOUSSIN (CNRS/Paris UPEC, France).

Project coordinator:Christian GEORGEIRCELYON - Tel: (33) (0)4 37 42 36 81 mail: Christian.George@ircelyon.univ-lyon1.fr

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Introduction Clean air is essential to peoples health and that of theenvironment. Since the industrial revolution, however, thequality of the air that people breathe has deterioratedconsiderably - mainly as a result of human activities. Risingindustrial and energy production, the burning of fossil fuelsand the dramatic rise in traffic all contribute to air pollutionin our towns and cities which, in turn, can lead to serioushealth problems. For example, air pollution is increasinglybeing cited as the main cause of lung diseases such asasthma - twice as many people suffer from asthma todaycompared to 20 years ago.

The need to deliver cleaner air has been recognised forseveral decades with action having been taken at nationaland EU level and also through active participation ininternational conventions. EU action has focused onestablishing minimum quality standards for ambient air andtackling the problems of acid rain and ground level ozone.Polluting emissions from large combustion plant and mobilesources have been reduced; fuel quality improved andenvironmental protection requirements integrated into thetransport and energy sectors.

Despite significant improvements, serious air pollutionproblems still persist. Following its communication on theClean Air For Europe programme (CAFE), the Commission hasexamined whether current legislation is sufficient to achievethe 6th EAP objectives by 2020. This analysis looked at futureemissions and impacts on health and the environment andhas used the best available scientific and health information.This analysis showed that significant negative impacts willpersist even with an effective implementation of currentlegislation.

Among the new technical solutions designed for largedissemination over the public space, new photocatalyticbuilding and coating materials are being widely proposed tostakeholders as well as public consumers.

In this project it was suggested to demonstrate theusefulness of photocatalytic materials for air pollutionreduction in the urban environment.

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What isphotocatalysis?

In the very recent years, photo-catalytic self-cleaning and de-polluting materials have been suggested as a remediationtechnology mainly for NOx and aromatic VOCs in the pollutedurban environment. The associated technologies have beenlaunched on the European market with the aim to have apositive impact on urban air quality. These commercialproducts are based on the photo-catalytic properties of a thinlayer of TiO2 deposited at the surface of the material (such asglass, pavement, ) or embedded in paints or concrete. Theuse of TiO2 photocatalysts as an emerging air pollution controltechnology has been reported in many European areas.However, it seems that both the effectiveness and the realimpact on air quality of these relatively new technologies upto now have been demonstrated only in a very limited mannerbefore going into the European market.

Heterogeneous photocatalysis has been reported for gas and liquid phase remediation. Classically, the overall process can be decomposed into five independent steps:

1. transfer of the reactants in gas or liquid phase to thesurface;

2. adsorption of at least one of the reactants;

3. reaction in the adsorbed phase;

4. desorption of the product(s);

5. removal of the products from the interface region.

While these steps are common to all heterogeneous processes(such as the uptake of a gas by a liquid droplet orheterogeneous catalysis), step 3 is where the photocatalyticnature of certain metal oxides plays a role. In fact, when asemiconductor catalyst (SC), such as a metal oxide (TiO2, ZnO,ZrO2, CeO2,), or sulfide (CdS, ZnS,), is illuminated withphotons carrying energy equal or in excess of its band gap,absorption of light promotes one electron into the conductionband, creating an electron-hole pair similar to photoinducedelectron transfer. The oxide may transfer its electron to anyadsorbed electron acceptor (thereby promoting its reduction),while the hole (or the electron vacancy) may accept anelectron from an adsorbed donor (promoting its oxidation).

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O2

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State of the art The work conducted so far has shown that the photocatalytic

technology could reduce the concentrations of NOx and BTEX(benzene, toluene, ethylbenzene and xylenes) in air, althoughthe absolute reduction potentials are still highly uncertain.However, the formation of other harmful species inferredfrom lab studies, such as HONO (known as a OH sources,facilitating ozone pollution, carcinogenic) and other oxidizedhydrocarbons (aldehydes, PAN-type compounds, ) as aresult of the interaction between NOx/VOCs/particles andsurfaces containing TiO2 has not been assessed inatmospherically relevant conditions. The production of theselater species may represent an important source of newpollutants in the urban environment and may have a strongimpact on the oxidation capacity, radical concentrations andconsequently on the building up of ozone pollution("summer smog"). Accordingly, there is an urgent need for abetter characterisation of such surfaces at atmosphericrelevant conditions.

Assessing and demonstrating the effectiveness of thesedepolluting techniques have a real EU added value both interms of policy making (and implementing the EU air qualitystrategy) and economics (by providing a demonstration ofthe actual performance of a new technique).

This project aimed therefore at evaluating the feasibilityof using TiO2 based products to alleviate the air pollutionproblem under real atmospheric conditions. Thisdemonstration project is conducted independently i.e., itaims at testing existing technologies to asses if they work ornot. Such a complete assessment and demonstration has notbeen performed so far (previous actions were always limitedto some aspects (or pollutants) of the air quality issue.

The overall outcome of this project is an assessment ofthe potential of photocatalytic building materials andcoatings for air pollution abatement.

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PhotoPaqsstructure & goals

Our goals

Developing the testing methodology for photocatalyticremoval/production of NOx, HONO, radicals, large type ofVOCs and particles, with all tests being performed underatmospherically relevant conditions.

Testing the photocatalytic activities of the commerciallyavailable TiO2 based products in order to examine thepollutant removal effectiveness, (assessing if thesedepolluting surfaces are sinks or sources of pollutants).

Designing better environmental indicators and methodsto assess the impact of this new technology in Europeancities.

Providing recommendation to the European authoritieson the practical application for air treatment, (includinga numerical "demonstration tool" for the depollutingaction).

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Preparatoryactions

The performed laboratory measurements were important forboth, the preparation, duration and strategic direction of thefield measurement campaigns as well as to provide input datafor the model calculations in the PhotoPAQ project.

The results of the laboratory reactors and chamberexperiments indicated oxidation of several pollutants whileothers showed low or even no reactivity. Mechanistic andkinetic description of the reactions allowed estimation ofpotential atmospheric impact.

Different tools were used i.e., flow reactors and largescale simulation chambers.

The different samples were tested for their reactivity andproduct formation in the reaction of gas phase nitrogen species(NOx, NOy, e.g. nitrous acid, HONO), formaldehyde (HCHO) andselected volatile organic compounds (VOCs). In addition,possible re-noxification by photocatalytic reaction of adsorbednitrate (NO3

-) was also studied. These experiments wereperformed as a function of several environmental parameters,such as relative humidity for which generally decreasing activitywas observed with increasing humidity.

All samples, freshly prepared in the laboratory, werestudied for their reactivity against nitrogen monoxide (NO).Reasonably high reactivities were observed for all samplesshowing the ability of the different tested materials todepollute air contaminated with NOx. Furthermore, it wasdemonstrated that the experimental conditions have a highimpact on the degradation rates. It was found out thatespecially the pollutant concentration and the relative humidityare strongly influencing parameters. Atmospherically relevantlow pollutant concentrations (below 50 ppb NO/NO2) andmoderate relative humidities (RH 20-35%) resulted in thehighest degradation rates.

The photocatalytic degradation of some VOCs wasalso studied, demonstrating a clear dependence of thereactivity of toluene, isopentane, 1butane, -pinene andbenzene on the tested materials.

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Demonstrationin a tunnel

The first field site which has been chosen is an urban tunnel:the Leopold II tunnel. It is a bi-directional tunnel located atBrussels city centre, along the Basilica Midi axis, within adensely built urban environment.

The geometry of the overall tunnel is highly complex, as itis about 2.5 km long and consists of two segments separated bya wall.

The tunnel is subject to a heavy traffic with a flowregularly reaching several thousands of vehicles per hourallowing us to have a sufficient level of pollutants. In spite ofthe complexity of the tunnel geometry, it was possible toidentify a section of a length of 160m exhibiting a regular cross-section which enables a precise modelling of the air flow. Itshould be noted that as both tunnel tubes are separated in thechosen section by a wall, the used tunnel section can beconsidered as an one-directional tunnel.

Tunnel segment of 200m

Traffic: up to 65 000 vehicles per day

Two heavily instrumented monitoring stations

have been set up before and after the testsection which was equipped with anadditional UV lighting system. The firststation referred to as site 1 is the first to beencountered by an air mass when the flow ofcars induces sufficient air movements. At thatstation, the measurements are not consideredto be affected by photocatalytic materialeffects in most of the time. The second one referred to as site 2 is generally fed with airwhich has been in contact with thephotocatalytic materials.

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Nitrogen oxides (NOx)

The effect of the photocatalytic cement based coatings on theair remediation of NOx inside the tunnel test sections (70 and160 m) was assessed by different means, using data of theNOx/CO2 ratio from the two measurement sites, up- anddownwind of the test section. Three different approaches wereused to quantify the pollution reduction, i.e. measurementsbefore/after application, upwind/downwind of the test sectionand with UV lamps on/off.

In contrast to first estimations based on laboratorystudies on fresh samples, the field results show no observablereduction of NOx in the tunnel. An upper limit of 2 % wasdetermined for the maximum possible NOx reduction,corresponding to the experimental uncertainties. As a mainreason for the low remediation observed, serious passivationof the surface reactivity under the heavily polluted tunnelconditions was identified in laboratory experiments. Otherreasons could be the high relative humidity, low temperatures,low level of irradiation and the wind speed inside the tunnel. Areduction of 10-15% can be calculated for the entire length ofthe tunnel.

Formaldehyde (HCHO)

Unexpected formation of small amounts HCHO was observed inthe active test section. Higher concentrations were detected atthe downwind site with the UV lamps on. In addition, thedifferences between the two sites were increasing withdecreasing wind speed in the tunnel, which is explained by thevariable dilution of the HCHO source.

Nitrous Acid (HONO)

During the tunnel campaigns no photocatalytic remediation ofHONO could be observed during lamps on/off experiments, inagreement with the laboratory experiments.

Oxygenated volatile organic compounds (OVOCs)

Concerning acetaldehyde, for the data analysis all measuredacetaldehyde mixing ratios were plotted vs. CO2, no significantdifference in the acetaldehyde/CO2 ratio was observed for allperiods. Thus, there was no evidence for a photocatalyticdegradation of acetaldehyde based on the applied material andthe artificial lighting system under the experimental conditionsin this tunnel.

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Demonstrationoutdoor

The choice of the outdoor field campaign site was the subjectof many investigations and discussions. A field site insouthern Europe (Petosino, Italy) was finally chosen. The fieldsite is an industrial site located in Petosino Sorisole fewkilometers north of Bergamo. It is located on the side of amajor road with an average traffic of ca. 8000 light vehicleand ca. 1500 heavy duty vehicles per day.

In this case, the demonstration strategy relied on thebuilding of two identical areas on the field site delimited bywalls.

Two artificial parallel street-canyons of 55 m long, 5 mwide and 5 m high were hence built equipped with samplinglines. After having checked the comparability of the twocanyons, one has received the application of the photo-catalytic coating while the other not. Two similarmeasurement stations were installed in both canyon andparallel measurements were carried out. The demonstrationof the efficiency of the photocatalytic air cleaning wasperformed by comparing both sets of measurements.

Workshop

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The first ante-operam measurement wascarried out from April 9th through to April16th, data acquisition involved local pollutiondata such as concentrations of NO, NO2, O3,HONO, carbonyls, VOCs, CO2, the sub-micronaerosol size distribution, chemicalcomposition and mass and local weatherparameters (temperature and relativehumidity, wind direction and speed, spectralsolar light flux). The outdoor campaign tookplace post-operam from April 9th to May8th, 2013, involving more than 20 persons.

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Nitrogen oxides

NOx concentration showed average differences between theactive and the reference canyon of

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Numericalsimulations

Leopold II road tunnel campaigns in Brussels

In order to assess the de-pollution efficiency two pollutantswere assumed to be emitted inside the tunnel. One of themwas assumed to be photocatalysed on the treated surfaces viathe introduction of a sink in the transport equation. In thissense, numerical results reflect the upper limit of the expectedreductions in the tunnel. In reality the deposition velocityinside the tunnel was much lower compared to lab scale tests,mainly as a result of the higher humidity, the heavily pollutedtunnel conditions and the weaker than expected irradiance.Results for the expected reductions for the 70 m and 160 msections and the entire tunnel are presented in the Tablebelow.

Outdoor field trial in Petosino, Bergamo

The prevailing daylight meteorological conditions wereidentified and simulated. The de-polluting efficiency inside thestreet canyon was predicted a 15.2%, 4.4%, 5.2% and 7.1% forthe E, S, SW and W wind directions.

Assessment of the measured de-pollution

Experimental findings lay in overall agreement with thenumerical results in the sense that the estimated numerical de-pollution was in fact the upper limit that could be achieved.Similar conclusions were drawn for the case of the outdoorfield campaign in Petosino, Bergamo.

Cost benefit analysis

The efficiency of this technology as an alternative means forthe abatement of air pollution is highly dependent on the totalcosts at a local level and the potential monetary benefits interms of reducing the external costs attributed to the adversehealth effects of air pollution. As a result the efficiency of thistype of technology differs among locations across Europe.

Ventilation scenario

Estimated reduction (%)

70 m 160 m Entire tunnel

Ventilation OFF

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Conclusions&Outlooks

While the laboratory studies clearly demonstrate theeffectiveness of the tested material for the degradation ofNOx and potentially of some VOCs, the field testing revealedthat the deployed conditions are critical for the expectedpollution abatement. Within this project, two very differentenvironments were tested, i.e. a heavily polluted tunnel inBrussels (Belgium) and an outdoor site in Petosino (Italy).Depending on the material tested, it was observed that heavypollution could lead to a rapid passivation of the material. Inaddition, high relative humidity or emission of secondarypollutants (e.g. HCHO) could alter the depollution activities.Based on the experimental and modelling results of thepresent study it appears that reducing the air pollution by afew percent (i.e. 10%) is a realistic target in typical urbanenvironments which is limited - at least in part - by thetransport of the pollutant to the active surfaces. In thiscontext, however, it is important to note that just a fewpercent reduction of the NOx concentration is in range whichcan be expected from any applicable after-emission airquality improvement technology. Such abatements canhowever only be achieved with well formulated materials,exhibiting high depollution efficiencies and low passivationproperties. Simple numerical tools have been developed toassess the required abatement efficiency and experimentalconditions prior to any on site application.Supported by

LIFE Environmental Funding

Prior to any application, werecommend small-sizeexperiments on possibledeactivation of thephotocatalytic activity underreal atmospheric conditions. Itis recommended to confirmhigh photocatalytic activity inreal ambient air by using smallscale flow reactor set-ups fromthe laboratory.