Abstract
Abstract. Satellite observations of nitrogen dioxide (NO2) tropospheric columns over south-eastern Europe are analyzed to study the characteristics of the spatial and temporal variability of pollution in the area. The interannual variability of the tropospheric NO2 columns is presented over urban, rural and industrial locations based on measurements from four satellite instruments, GOME/ERS-2, SCIAMACHY/Envisat, OMI/Aura and GOME-2/MetOp spanning a period of over twelve years. The consistency between the different datasets over the area is investigated. Two operational algorithms for the retrieval of tropospheric NO2 are considered, the one developed jointly by the Royal Netherlands Meteorological Institute and Belgian Institute for Space Astronomy and the one developed by the University of Bremen. The tropospheric NO2 columns for the area under study have been simulated for the period 1996–2001 with the Comprehensive Air Quality Model (CAMx) and are compared with GOME measurements. Over urban and industrial locations the mean tropospheric NO2 columns range between 3 and 7.0×1015 molecules/cm2, showing a seasonal variability with a peak to peak amplitude of about 6.0×1015 molecules/cm2, while the background values over rural sites are close to 1.1×1015 molecules/cm2. Differences in the overpass time and spatial resolution of the different satellites, as well as differences in the algorithms, introduce significant differences in the estimated columns however the correlation between the different estimates is higher than 0.8. It is found that the model simulations reveal similar spatial patterns as the GOME observations, a result which is consistent with both algorithms. Although the model simulations show a mean bias of −0.1×1015 molecules/cm2 under clean conditions, the modeled temporal correlation of 0.5 is poor in absence of biogenic and biomass burning emissions.
Highlights
Nitrogen dioxide plays a key role in tropospheric chemistry with important implications for air quality and climate change
We used only the forward scans for Global Ozone Monitoring Experiment (GOME), SCIAMACHY, and GOME-2 and from Ozone Monitoring Instrument (OMI) pixels with CTP (Cross Track Position) 10 to 50 that corresponds to the OMI pixels which are closest to the near-nadir viewing position
Over the polluted sites there is a relative offset between SCIAMACHY and OMI measurements as shown here, as typical examples, for Maritsa and Thessaloniki The estimated average values for Thessaloniki and Maritsa are 3.8±1.7×1015 molecules/cm2 and 3.2±1.0×1015 molecules/cm2 respectively as derived from OMI monthly mean measurements, while the corresponding values estimated from SCIAMACHY are 4.0±2.36×1015 molecules/cm2 and 2.7±0.9×1015 molecules/cm2
Summary
Nitrogen dioxide plays a key role in tropospheric chemistry with important implications for air quality and climate change. Tropospheric NO2 columns retrieved from the Global Ozone Monitoring Experiment (GOME), the Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) and the Ozone Monitoring Instrument (OMI) span more than ten years and have been used for air quality studies and satellite instrument validations (Richter et al, 2000, 2005; van der A et al, 2006, 2008). 9po1r6al and spatial distribution of tropospheric NO2 columns over the area through satellite observations and model simumay help the detection of potential transboundary transport of NO2 inside the Balkan Peninsula. For all these locations overpass files for the tropospheric NO2 columns were generated from level-2 data of GOME, SCIAMACHY, OMI and. 9gsio1sr.9itIhnmSsecatn.d3twheepihnvoetosctihgeamteicthael model we used in our long-term variability analyof tro-
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