Meteorological and air quality measurements in a city region with complex terrain: influence of meteorological phenomena on urban climate

On 8 and 9 July 2018 extensive observations were conducted under fair-weather conditions in the German city of Stuttgart and its surroundings. This intensive observation period, part of the four weeks Urban Climate Under Change (UC)2 campaign, intended to provide a comprehensive data set to understand the complex interactions of thermally induced wind systems, vertical turbulent mixing and air pollutant concentration distribution in the atmospheric boundary layer of the city. Stuttgart has a very special and complex topography with a city center located in a basin surrounded by hills with heights of 250 to 300 m influencing the wind and flow system, reducing the wind speed, causing inhibited dispersion of air pollutants. Cold air flows from the surrounding plains can penetrate into the urban areas and influence the urban climate including the air quality. For investigating these effects with a focus on urban climate, combinations of different measurement platforms and techniques were used, such as in situ stationary and mobile measurements with cars, vertical profiling by means of tethered balloons, radiosondes, a drone, and aircraft observations, remote sensing devices and satellite-based instruments. Numerous atmospheric processes in an urban area regarding boundary layer evolution, inversion, local wind systems, urban heat island, etc. were observed. Some important findings are: Temperature observations provide local information about the warmest areas in the city and about the city and its surroundings. The urban heat island effect was evident from the results of stationary and mobile air temperature measurements as higher air temperature was measured in Stuttgart basin compared to its surroundings. Considerable spatio-temporal differences concerning the wind (speed and direction), turbulence and the convective boundary depth are evident. Lower wind speeds were observed during the nighttime and the main wind direction in the Stuttgart valley was measured to be southwest, which carried cold air from the hillsides into the city and pollutants to the windward side of the city into the Neckar valley. The low wind speed favored the accumulation of pollutants in a shallow nocturnal boundary layer close to the surface. During the day, the overall pollutant concentration was reduced by vertical convective mixing. The vertical profile measurements have shown that the applied techniques provided a good overview to understand the vertical characteristics of meteorological parameters and pollutants as well as the stability of the atmosphere and extent of the urban boundary layer. It also showed that the extent of atmospheric mixing determines the dispersion, dilution and mixing of emitted pollutants. Finally, the additional comprehensive air-chemical observations (surface and satellite based) allow understanding the diurnal cycle of air pollutants in the atmospheric boundary layer of the city of Stuttgart. Satellite-based observations from Sentinel‑5P/TROPOMI have shown their potential for mapping urban pollution islands and urban pollution plumes even in cities with a complex terrain like Stuttgart. These observations assisted to obtain a comprehensive data set intended for the validation of a novel urban climate model, PALM‑4U

Quantification of lightning-produced NOx over the Pyrenees and the Ebro Valley by using different TROPOMI-NO2 and cloud research products

. Lightning, one of the major sources of nitrogen oxides (NOx ) in the atmosphere, contributes to the tropospheric concentration of ozone and to the oxidizing capacity of the atmosphere. Lightning produces between 2 and 8 Tg N yr−1 globally and on average about 250 ± 150 mol NOx per flash. In this work, we estimate the moles of NOx produced per flash (LNOx production efficiency) in the Pyrenees (Spain, France and Andorra) and in the Ebro Valley (Spain) by using nitrogen dioxide (NO2) and cloud properties from the TROPOspheric Monitoring Instrument (TROPOMI) as well as lightning data from the Earth Networks Global Lightning Network (ENGLN) and from the EUropean Co-operation for LIghtning Detection (EUCLID)

Analysis of the Algerian severe weather event in November 2001 and its impact on ozone and nitrogen dioxide distributions

An analysis of the severe weather event in November 2001 over the western Mediterranean is presented focusing on satellite-based trace gas measurements from the Global Ozone Monitoring Experiment (GOME) on board the European Remote Sensing Satellite (ERS-2). This study is supplemented by a synoptic analysis and simulations of the three-dimensional stratospheric chemical transport model ROSE. Arctic air masses moved rapidly from Scandinavia to the Iberian peninsula and were mixed with subtropical air over the still warm Mediterranean Sea. This caused severe thunderstorms and extreme rainfall along the coasts of Morocco and Algeria and later on the Balearic Islands. Associated with the meridional transport an intrusion of stratospheric air below 3 km above sea level was observed. The maximum potential vorticity (PV) derived from UK Meteorological Office analysis data was about 9.3 potential vorticity units (pvu) at 330 K at the equatorward position of 35°N. These very high values went along with remarkably enhanced total ozone levels obtained from GOME backscatter measurements of collocated GOME/ERS-2 overpasses. Further investigation of GOME data showed unusually high levels of nitrogen dioxide (NO2) above the western Mediterranean. We present a new method to derive the tropospheric content of nitrogen dioxide (NO2) from a combination of satellite measurements and results of a chemical transport model. We show that about two-third of the total atmospheric content of nitrogen dioxide in the observed plume is found in the troposphere, due to lightning activity, advection and vertical transport in the thunderstorms from the planetary boundary layer (PBL) to atmospheric levels above clouds

Observation of volcanic ash from Puyehue-Cordon Caulle with IASI

On 4 June 2011 an eruption of the Chilean volcano complex Puyehue-Cordon Caulle injected large amounts of volcanic ash into the atmosphere and affected local life as well as hemisphere-wide air traffic. Observations of the Infrared Atmospheric Sounding Interferometer (IASI) flown on board of the MetOp satellite have been exploited to analyze the evolution of the ash plume around the Southern Hemisphere. A novel singular vector-based retrieval methodology, originally developed for observation of desert dust over land and ocean, has been adapted to enable remote sensing of volcanic ash. Since IASI observations in the 8–12 μm window are applied in the retrieval, the method is insensitive to solar illumination and therefore yields twice the observation rate of the ash plume evolution compared to solar backscatter methods from polar orbiting satellites. The retrieval scheme, the emission characteristics and the circumpolar transport of the ash are examined by means of a source-receptor analysis

Analysis of NO2 pollution in megacities by Earth Observation

In this study we investigate the variability and trends of NO2 pollution in 30 megacities by analyzing different Earth Observation data sets. Multi-annual records of tropospheric NO2 from SCIAMACHY (2002-2012) and GOME-2 (2007-2015) are combined with the global urban footprint of each megacity as a proxy for urban growth. The consistent and homogenous data sets enable a global comparison of the findings for the megacities and a classification with respect to their socio-economic development. The possibilities of current and upcoming Earth Observation missions are discussed

Tropospheric NO2: Explorative analyses of spatial variability and impact factors

In order to study spatial patterns of nitrogen dioxide (NO2) and its impact factors, consistent and area-wide information is essential. With TROPOMI aboard Sentinel-5 Precursor (S-5P), daily tropospheric NO2 observations have become available with an unprecedented spatial resolution of 3.5 km × 5.5 km. However, a systematic study of tropospheric NO2 patterns on a national scale and with preserved high spatial resolution is still pending. In addition, the increasing availability of area-wide, high-resolution data for large study areas presents new challenges for analyzing impact factors, such as spatial heterogeneity. Based on the annual mean tropospheric NO2 of Germany (September 2018 to August 2019) resampled to a 1 km × 1 km spatial resolution, the subject of this study was twofold: on the one hand a hot and cold spot analysis was performed, on the other hand, non-meteorological factors influencing tropospheric NO2 were investigated within spatial regimes of different land use / land cover (LU/LC) compositions. A total of 24 national hot spots were identified with the majority located in urban areas. The spatial regime-based impact factor analysis revealed that most correlation coefficients between LU/LC and tropospheric NO2 are highly dependent on the location. Some other factors, however, were found to have a strong impact on tropospheric NO2 independent of the location (impervious surfaces, population and road density). Although this study is based on tropospheric column data, and meteorology has not been considered yet, the analyses demonstrate the contribution of Sentinel-5P/TROPOMI data to a better understanding of the high-dimensional and complex relationship between NO2, the atmosphere and the composition of the land surface and its use