Final Report Summary - PARTHENO2N (Pollution of air in the extended region of Athens: Space-based Nitrogen Dioxide (NO2) observations and their comparison with remote and ground–based measurements and modeling simulations.) Athens, the capital of Greece, is a heavily polluted city in the Eastern Mediterranean Basin gathering almost half of the total population of the country. As a result, this densely populated area suffers from high levels of air pollutants emanating mainly from anthropogenic sources. One of the most important tropospheric trace gases, linked to air pollution is the nitrogen dioxide, NO2. NO2 reduces air quality and cause significant changes in Earth’s atmosphere, on both short and long timescales. Public exposure to NO2 at urban environments is of great health concern, as it is known to cause human respiratory problems; therefore, it is subject to several EU directives on pollution levels.In order to access the significance of the above changes and their impact, a deep and thorough understanding of all relevant, physical and chemical processes, that control the atmosphere, is required. One of the most important steps towards filling the gap of knowledge on nitrogen oxides relevant processes has been made recently, via space-based observations of the NO2 vertical column densities. The advantage of satellite measurements is their efficiency to pinpoint the emission sources, or in other words the hotspots where high concentrations of NO2 occur. During PARTHENO2N-project, a suite of various observations have been used to obtain the complete image of the temporal and spatial variability of NO2 over Greece using the city of Athens as a case study. Data from four individual ultraviolet and visible spectrometers (GOME/ERS2, SCIAMACHY/ENVISAT, GOME2/METOP-A, OMI/AURA) have been analyzed, providing more than fifteen years of NO2 vertical columns over Greece. Complementary in surface situ observations of pollutants (NO, CO, SO2, O3) from sixteen monitoring stations have been collected and statistically analyzed for the period 1984-2012. Additional information on the NO2 levels emanated from two remote sensing ground based instruments a) a state-of-the art two dimensions Multi-axis Differential Optical Absorption Spectrometer (developed in the frame of PARTHENO2N) used to provide information on the horizontal and vertical distribution of the tropospheric nitrogen dioxide columns and b) a Brewer-MKIV spectrometer focusing on the stratospheric NO2 columns. The above observations have been used to guide the development and evaluation of chemical models with respect to their capability of simulating the NO2 column densities.The results revealed that over Greece, the tropospheric NO2 columns depict an accelerated reduction since 2008 onward. Noteworthy, the vertical NO2 columns (VCDs) dropped more than 30% in Athens during the period 2007-2012. Concurrent in situ observations of NO2 and SO2 confirmed the reduction observed via the satellite observations. Comparison with economic metrics including the gross domestic product (GDP), the industrial production index (IPI) and the oil consumption per day revealed that the rapid decline in pollutant levels is directly linked to the economic recession. In other words, the financial crisis resulted to the observed decrease of pollution. Overall, the financial crisis in terms of reduced nitrogen oxides (NOx) and sulfur oxides (SOx) emissions can be seen as a large scale abatement strategy/mitigation effort and gives us the opportunity to access its impact on air quality.
