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Recent developments in the remote sensing allow acquiring vertical column information of NO2 as well as other air pollutants in the atmosphere with the use of electromagnetic radiation. The availability of these state-of-the-art retrievals as tropospheric NO2 columns with comparable spatial resolutions to regional air quality models and global coverage within days including remote areas where other means of measurements are not available are long-needed additions to the sparse ground-based observations. Using satellite observations to improve our scientific understanding of atmospheric processes by integrated analysis of satellite, and ground-based observations with regional air quality models is the starting point of IMNOXE.
The overall objective of IMNOXE is to improve the NOx emission inventories by integrating observations from satellite retrievals, and available ground observations with regional air quality modeling. One of the important endpoints of this research is informing the decision-makers in their design of environmental policy in understanding and reducing NOx emissions via multidisciplinary research which combines environmental sciences, modeling, remote sensing and environmental policy. The novelty of IMNOXE that distinguishes it from similar research in Europe is its focus area; Turkey, where the emission inventories have less detail and higher uncertainties. Specifically looking at emissions in Turkey has not yet been done in the literature and will be very helpful to improve European Monitoring and Evaluation Programme (EMEP) NOx emissions inventory for the region as well.
The specific objectives IMNOXE are:
i. Assessment of NO2 satellite retrievals over Turkey and comparison with the NOx emissions;
ii. Investigation of the potential of NO2 satellite retrievals on better defining the NOx emissions;
iii. Comparison of satellite NO2 retrievals with available ground observations of NO2;
iv. Comparison of satellite NO2 retrievals with simulated tropospheric NO2 concentrations using a regional air quality model;
v. Comparison of tropospheric gas concentrations simulated by a regional air quality model, with ground-based measurements of tropospheric species to evaluate the model and identify reasons for discrepancies;
vi. Assessment of the uncertainties in comparing satellite NO2 retrievals with NOx emissions estimates and model results;
vii. Identification of biases in emission inventories by data assimilation of satellite NO2 retrievals, and ground-based NO2 and O3 observations;
viii. Improvement of our understanding of NOx emissions, and the interaction between regional and global air pollution by an integrated analysis of satellite NO2 retrievals with the regional air quality model.
In the first period of IMNOXE, the detailed comparison of the OMI and SCIAMACHY NO2 retrievals have been performed. The satellite retrievals were also compared with EMEP and TNO NOx emission inventories. In order to understand the NOx emissions and contributions from different sectors, emission parameters were selected (population, traffic intensity, large-scale power plants) and their relationship with NOx emissions and NO2 retrievals were investigated. The results suggested significant discrepancies in the emission inventories, especially for large-scale power plants and emphasized the importance of spatial resolution for the NOx emission inventories. Population was the highest correlated emission parameter and can be taken as an emission indicator. In addition, the available ground NO2 observations of three cities in Turkey were obtained and compared with corresponding satellite retrievals. Weekend/weekday ratios for OMI (overpass time 13:00-14:00) were greater than one and SCIAMACHY (overpass time 10:00-11:00) were less than one and the weekend weekday ratios for the ground observations for the same hours were similar with corresponding satellite retrievals. This result indicates the daily profile of the NOx emissions and accordingly NO2 concentrations change during the day and combining different satellite retrievals can provide information on daily variability of the NO2.
The second period of IMNOXE, the air quality modeling (using CMAQ) is performed using EMEP emission inventories. Comparing simulated NO2 concentrations with satellite and ground observations expected to give better comparisons because the effects of meteorology and atmospheric chemistry will be included to connect NOx emissions with NO2 concentrations. Finally, after detailed evaluation of the modeling results, sensitivity runs and inverse modeling are being performed using the NO2 retrievals to improve NOx emissions in Turkey. With IMNOXE, we have contributions to the usage of satellite NO2 retrievals, to the scientific literature through a better evaluation of NOx sources, and their distributions in different source categories in Turkey, to the EMEP emission inventory for Turkey where information is currently not as accurate as the other regions. IMNOXE is dedicated to make significant contributions to the European Research Area (ERA) with a better understanding of the further use of satellite NO2 retrievals in air quality modeling, and improvements in the NOx emission inventories.
Therefore, it may provide groups that develop emission estimates guidance on areas for improvement and help decision-groups in order to give better-informed decisions in NOx emission lowering strategies in Europe. In addition, this research will help further understand the strengths and the weaknesses of the satellite NO2 retrievals and offers suggestions to improve the quality of the retrievals for further use in the tropospheric air pollution research.

Project website:

Contact Details:
Fellow: Assist. Prof. Dr. Burcak Kaynak
Environmental Engineering Department, School of Civil Engineering, Istanbul Technical University,
34469, Maslak/Istanbul, Turkiye. Telephone: +90 212 2856784

Scientist in charge: Prof. Dr. Ismail Toroz
Environmental Engineering Department, School of Civil Engineering, Istanbul Technical University,
34469, Maslak/Istanbul, Turkiye. Telephone: +90 212 2856548