Implementation Actions

B4. Characterization of the decontaminating effect of the photocatalytic materials in urban scenarios

This Action has been developed by the Atmospheric Pollution Characterization Unit and COPs and the Emissions Unit of CIEMAT's Department of the Environment in collaboration with the FOTOAIR group of CIEMAT’s Energy Department, Alcobendas Town Hall and INECO.

In the first phase of Action B4, the NOx sink effect of the chosen material for its real-scale carriageway implementation has been characterized (November 2014 - November 2015). To this end, in a town near Madrid (Alcobendas), Paseo de la Chopera was chosen as the study scenario, a two-way rectilinear street with moderate traffic.

The selected photocatalytic material was implemented in an area of approximately 1000 m2, which occupied 60 linear metres of both lanes per direction of traffic, in addition to the median, so that three consecutive areas were arranged along the chosen street: conventional carriageway-conventional photocatalytic carriageway. The objective of the measurements was to verify if horizontal gradients of NOx are formed by the sink effect induced by the photocatalytic carriageway.

Before applying the photocatalytic material the environmental and atmospheric characteristics were studied on the surface and height of the chosen street and its behaviour as a linear source of atmospheric pollutants. After the application of the photocatalytic material (September 2015) the decontaminating capacity of NOx of the material was evaluated. For this the following activities were carried out:

  1. Implementation of the selected photocatalytic material in an area of approximately 1000 m2 (60m along the street for the two lanes per direction and median).
  2. Continuous measurement of the concentrations of gaseous pollutants on the surface and height, as well as of the meteorological variables in height for two months after the application of the photocatalytic material.
  3. Carrying out of intensive field investigations of complementary measures:
    1. Particulate matter in the air and deposited on the road.
    2. Volatile Organic Compounds (VOCs).
    3. Road Traffic.
    4. UV-A radiation and horizontal and vertical street temperatures.
    5. Extraction of roadway samples to evaluate the decay of the photocatalytic activity and loss of surface titanium due to the wear of the coating as a result of road traffic.
    6. Realization of controlled washes on different areas of the treated area and collection of leachate.

The results obtained allow us to conclude that:

  1. In spite of: a) having used the material with the best performance in terms of photocatalytic activity and durability, b) having performed NO concentration measurements at a low altitude with respect to the treated surface, c) having evaluated the associated data to the optimum meteorological conditions for which the maximum horizontal gradient of the concentrations due to the sink effect on NO should be observed, the application of the photocatalytic material over a significant section of the carriageway has not detected any improvement effect on the concentrations of NO which can be directly attributable to the presence of said material.
  2. Deposited TiO 2 was observed associated with the presence of the photocatalytic coating on the road, with a loss in titanium content due to wear caused by road traffic and, consequently, photoactive activity under ISO 22197-1:2007 (Action B1).
  3. The leachates collected in the treated area indicate that no significant amount of nitrate has been deposited on the photocatalytic asphalt.


In the second phase of Action B4 (November 2015 - June 2016), the characterization of the NOx sink effect induced by the material chosen for its implementation on a full-scale pavement was carried out. The chosen scenario was a double "street canyon" built to scale in an urban area of Alcobendas near a public thoroughfare, with moderate levels of pollution but that were not affected by direct traffic.

In collaboration with Alcobendas Town Hall, and to evaluate the NOx decontamination capacity, the following activities were carried out:

  1. Design of the "street canyon" and choice of its location and orientation making it more suitable for the study according to the determinant meteorological parameters (radiation and wind direction).
  2. Construction and implementation of the "street canyon" consisting of two linear, parallel and contiguous streets, 20m long and 4m wide, delimited by 5m-high walls and paved with tiles of the type previously selected in the previous actions of the project. One street was used as a "reference street" and the other as the "photoactive street".
  3. Installation of the experimental system in the double "street canyon".
  4. Characterization of the dynamic and chemical behaviour of the air masses in the "street canyon" before implementing the photocatalytic material.
  5. Installation of a mobile unit for the continuous measurement of the environmental concentrations of gaseous pollutants and various meteorological parameters outside the "street canyon".
  6. Application of the selected photocatalytic material for use on pavements in one of the streets of the "street canyon" and continuous recording of NO and NO2 concentration in both streets, as well as the meteorological parameters in the street treated.
  7. Carrying out intensive field investigations of measures of concentration of VOCs in both streets.
  8. Monitoring of the photocatalytic activity of the material used exposed to the elements (Action B1).

The results obtained after the analysis of the measurements have not shown any reduction of the ambient NO concentration attributable to the decontaminating effect of the photocatalytic material implemented.


In the third phase of Action B4 (July - December 2016), the characterization of the NOx sink effect of the chosen material for its real-scale façade implementation was carried out using the exterior wall of the double east-facing “street canyon”. The activities carried out on the façade were as follows:

  1. Characterization of the dynamics of the air mass close to the surface.
  2. Coating with bricks facing the chosen wall and application of the selected photocatalytic material.
  3. Installation of the experimental system designed to characterize the sink effect generated by the photocatalytic façade and continuous recording of the concentration of NO, NO2 and meteorological parameters, to characterize possible concentration gradients of NOx in the parallel or perpendicular dimension to the façade.
  4. Installation of a mobile unit for the continuous measurement of environmental concentrations of gaseous pollutants and the recording of various meteorological parameters outside the "street canyon".
  5. Carrying out of intensive field investigations of VOC concentration measures.
  6. Exposure to the weather of sample bricks treated with photocatalytic paint to evaluate the possible deterioration of the depurative capacity of NOx by means of tests with ISO 22197-1:2007 (Action B1).

The results obtained after the analysis of the measurements show that during a short period of time and under specific environmental and meteorological conditions a short episode of significant reduction of the NO concentration unequivocally attributed to the presence of the photocatalytic coating could be seen.

Phase 1 photos

Field investigation of measurement using a Mobile Air Quality Laboratory Application of the first product of the selected photocatalytic product in an area of 4 m2 on the Paseo de la Chopera carriageway in Alcobendas Implementation of the photocatalytic material over 1000 m2 on the carriageway of the Paseo de la Chopera Intensive field investigations: Particulate material (TiO 2) in ambient and deposited air, VOCs, road traffic, leachate, removal of samples.

Fotos fase 2

Area chosen for the implementation of selected photocatalytic material for pavements on a "street canyon" configuration in Alcobendas. Construction of the "street canyon" in Alcobendas. Street canyon pavements with paving slabs treated with photocatalytic material (left) and untreated (right). Mobile unit located outside the "street canyon" for continuous measurement of NO, NO2 , O3 and meteorological parameters. Street Canyon façade with weather sensors. East façade of the Street Canyon with applied photocatalytic material.