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

BAERLIN2014 - stationary measurements and source apportionment at an urban background station in Berlin, Germany

The Berlin Air quality and Ecosystem Research: Local and long-range Impact of anthropogenic and Natural hydrocarbons (BAERLIN2014) campaign was conducted during the 3 summer months (June–August) of 2014. During this measurement campaign, both stationary and mobile measurements were undertaken to address complementary aims. This paper provides an overview of the stationary measurements and results that were focused on characterization of gaseous and particulate pollution, including source attribution, in the Berlin–Potsdam area, and quantification of the role of natural sources in determining levels of ozone and related gaseous pollutants. Results show that biogenic contributions to ozone and particulate matter are substantial. One indicator for ozone formation, the OH reactivity, showed a 31% (0.82±0.44s−1) and 75% (3.7±0.90s−1) contribution from biogenic non-methane volatile organic compounds (NMVOCs) for urban background (2.6±0.68s−1) and urban park (4.9±1.0s−1) location, respectively, emphasizing the importance of such locations as sources of biogenic NMVOCs in urban areas. A comparison to NMVOC measurements made in Berlin approximately 20 years earlier generally show lower levels today for anthropogenic NMVOCs. A substantial contribution of secondary organic and inorganic aerosol to PM10 concentrations was quantified. In addition to secondary aerosols, source apportionment analysis of the organic carbon fraction identified the contribution of biogenic (plant-based) particulate matter, as well as primary contributions from vehicles, with a larger contribution from diesel compared to gasoline vehicles, as well as a relatively small contribution from wood burning, linked to measured levoglucosan