Research Project Synopsis

The project aims to evaluate the contribution of different sources to the atmospheric oxidative potential (OP) and their seasonal variability throughout a year in a heavily inhabited and polluted environment such as Athens and will provide an unprecedented dataset of ROS activity measurements both locally and regionally. A variety of state-of-the-art instrumentation and well established measurement techniques will be applied in continuous measurements and intensive field campaigns. The findings of PARADOX-H will unravel the OP-PM exposure link for the 5 million inhabitants residing in the Greater Athens Area throughout a year. It will provide important insight on the toxicity of various PM sources that can be linked to diverse health effects. Finally, PARADOX-H will quantitatively elucidate both the local and the regional influence of distinct aerosol sources in the area, inferring, thus, which sources systemically cause health problems to such a majority of the Greek population residing in Athens.


Project Scope

The scope of the project is to answer the following scientific questions:

  1. What are ROS levels and the OP of the atmosphere in the urban environment of Athens?
  2. What is the spatial and temporal variability of ROS and of the main aerosol constituents in this polluted urban environment?
  3. Which aerosol factor has the highest toxicity and which source contributes most to ROS levels seasonally?

Research Objectives

The project is organized around 3 main objectives:

  • Characterization of Particulate Matter Sources. Through targeted chemical analyses that will provide long term timeseries of different aerosol constituents, trend analysis and spatial variability of the various sources will be obtained. Sources of pollution have been identified using a widely applied mathematical technique named Positive Matrix Factorization (PMF) analysis. The technique, which relies on mass conservation, solves a system of mass balance equations, arbitrarily set by the user, using chemical composition time series as input. It will provide the first ever experimental characterization of the major natural/anthropogenic PM sources in the capital of Greece-Athens in an annual basis and will distinguish between local and regional ones.
  • Estimation of Oxidative Potential. Novel facilities, and state-of-the-art measurement techniques & instrumentation will be used to quantify the amount and stability of ROS near sources and urban background locations. This information is critically important for understanding the sources and atmospheric transformation of the climate- and health-relevant parameters of different types of aerosol. The OP of these sources will be characterized and the mechanisms and chemical species controlling their variability will be addressed. For comparison reasons, the ROS levels representative of background conditions will also be determined.
  • Impact on Health. The final aim of this objective is to identify the aerosol sources having the most important health impact. For this, a cost benefit analysis will be performed to propose alternatives, especially for local sources, to mitigate their adverse health effect. Until now, emission control policies take into account only the contribution of high PM levels. Our approach aims at a ROS/OP exposure minimization, where even though a mitigation strategy may not lead to limitation of PM levels, but will surely work towards minimizing the exposed population’s health effects.


For the determination of ROS at all the selected sites, sampling will be performed either by high- or low-volume samplers on quartz fiber filter substrates (4.7 cm and 15 cm diameter PallFlex) for 24-h, and during intensive measurement campaigns, on a 12-h basis. After sampling, filters will be stored in a freezer (-18 oC) until their analysis.

From the developed methods, the DTT assay has been characterized as being able to mimic the electron-transfer mechanism of ROS production in mitochondria, through the transfer of electrons from DTT to oxygen by redox-active species. The reaction rate, expressed by the consumption of DTT over time, is directly proportional to the concentration of the redox-active species in PM extracts. The semi-automated system developed for this kind of measurements (Fang et al., 2015) uses programmable syringe pumps with selector valves, where aerosol extracts oxidize DTT in a single vial. A small volume is withdrawn at several time intervals in order to determine the DTT concentration that remains in the solution, and calculate the consumption rate of DTT.

For the determination of the chemical composition, high-resolution measurements during the intensive measurement campaigns in Athens will be performed using an Aerosol Chemical Speciation Monitor (ACSM) which provides the concentrations of the main atmospheric constituents, namely sulfate, organics, ammonium, nitrate and chloride. ACSM has been already used successfully in a long-term study in Athens (Stavroulas et al., 2018).

Finally, for the determination of the different aerosol sources, over the last few years, several studies have successfully exploited the PMF algorithm, for apportioning the obtained organic mass spectra in terms of source/process-related constituents (Zhang et al., 2011).




Communication/ Outreach

The results of the research have already been communicated to the scientific community via four (4) participations in International Conferences:

1) *A. Bougiatioti, I. Stavroulas, D. Paraskevopoulou, , G. Grivas, E. Liakakou, E. Gerasopoulos, and N. Mihalopoulos: "Fat Thursday" (Tsiknopempti) as an important source of Organic Aerosol in the urban environment of Athens", European Aerosol Conference 2019, Gothenburg-Sweden, 25-30 August 2019, Abstract P3_153.

2) *D. Paraskevopoulou, A. Bougiatioti, I. Stavroulas, M. Tsagaraki, A. Nenes, and N. Mihalopoulos: "Wintertime oxidative potential and optical properties of brown carbon in atmospheric aerosol", European Aerosol Conference 2019, Gothenburg-Sweden, 25-30 August 2019, Abstract O1_F1_A04.

3) *D. Paraskevopoulou, G. Grivas, A. Bougiatioti, I. Stavroulas, M. Tsagkaraki, E. Liakakou, A. Nenens, and N. Mihalopoulos: "PM-indeced oxidative potential: Two years measurements and source apportionment, on a seasonal basis, in Athens, Greece", European Geosciences Union General Assembly 2020, Virtual Conference, 19-30 April 2021, Abstract EGU21-15961.

4) *D. Paraskevopoulou, A. Bougiatioti, P. Zarmpas, A. Nenes, and N. Mihalopoulos: "Oxidative potential of particulate matter in Eastern Mediterranean: Impact of COVID-19 lockdown", European Aerosol Conference 2021, Virtual Conference, August 30- September 3, 2021.

Furthermore, the major findings have been submitted in the form of publications in peer-reviewed journals:

1) D. Paraskevopoulou, A. Bougiatioti, P. Zarmpas, M. Tsagkaraki, A. Nenes and N. Mihalopoulos: Impact of COVID-19 lockdown on Oxidative potential of particulate matter: Case of Athens (Greece), Toxics, 10, 280,, 2022.

2) I. Stavroulas, A. Bougiatioti, G. Grivas, D. Paraskevopoulou, D.G. Kaskaoutis, E. Liakakou, K. Petrinoli, P. Kalkavouras, K. Kourtidis, E. Gerasopoulos, and N. Mihalopoulos: Cooking as an important source of organic aerosol in the urban environment: The case of Greece, submitted to Environmental Pollution.

Contact Information

Dr. Aikaterini Bougiatioti
Senior Researcher
Atmospheric Physics and Chemistry Group, Institute for Environmental Research and Sustainable Development
National Observatory of Athens
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