Open Access

Abstract. Urban air quality and human health are among the key aspects of future urban planning. In order to address pollutants such as ozone and particulate matter, efforts need to be made to quantify and reduce their concentrations. One important aspect in understanding urban air quality is the influence of urban vegetation which may act as both emitter and sink for trace gases and aerosol particles. In this context, the "Berlin Air quality and Ecosystem Research: Local and long-range Impact of anthropogenic and Natural hydrocarbons 2014" (BAERLIN2014) campaign was conducted between 2 June and 29 August in the metropolitan area of Berlin and Brandenburg, Germany. The predominant goals of the campaign were (1) the characterization of urban gaseous and particulate pollution and its attribution to anthropogenic and natural sources in the region of interest, especially considering the connection between biogenic volatile organic compounds and particulates and ozone; (2) the quantification of the impact of urban vegetation on organic trace gas levels and the presence of oxidants such as ozone; and (3) to explain the local heterogeneity of pollutants by defining the distribution of sources and sinks relevant for the interpretation of model simulations. In order to do so, the campaign included stationary measurements at urban background station and mobile observations carried out from bicycle, van and airborne platforms. This paper provides an overview of the mobile measurements (Mobile BAERLIN2014) and general conclusions drawn from the analysis. Bicycle measurements showed micro-scale variations of temperature and particulate matter, displaying a substantial reduction of mean temperatures and particulate levels in the proximity of vegetated areas compared to typical urban residential area (background) measurements. Van measurements extended the area covered by bicycle observations and included continuous measurements of O3, NOx, CO, CO2 and point-wise measurement of volatile organic compounds (VOCs) at representative sites for traffic- and vegetation-affected sites. The quantification displayed notable horizontal heterogeneity of the short-lived gases and particle number concentrations. For example, baseline concentrations of the traffic-related chemical species CO and NO varied on average by up to ±22.2 and ±63.5 %, respectively, on the scale of 100 m around any measurement location. Airborne observations revealed the dominant source of elevated urban particulate number and mass concentrations being local, i.e., not being caused by long-range transport. Surface-based observations related these two parameters predominantly to traffic sources. Vegetated areas lowered the pollutant concentrations substantially with ozone being reduced most by coniferous forests, which is most likely caused by their reactive biogenic VOC emissions. With respect to the overall potential to reduce air pollutant levels, forests were found to result in the largest decrease, followed by parks and facilities for sports and leisure. Surface temperature was generally 0.6–2.1 °C lower in vegetated regions, which in turn will have an impact on tropospheric chemical processes. Based on our findings, effective future mitigation activities to provide a more sustainable and healthier urban environment should focus predominantly on reducing fossil-fuel emissions from traffic as well as on increasing vegetated areas.

A significant Sahara dust event took place at the beginning of April 2014 over large areas of Germany and Europe. The German Weather Service (DWD) detected and monitored the expansion and propagation of this dust cloud with a ceilometer network of more than 50 ceilometers. Moreover, these ceilometers were also able to track the altitude of the dust cloud at the positions of the ceilometers. Additionally, aircraft measurements over Germany and France were performed with two aircraft by the Duesseldorf University of Applied Sciences. These aircraft were equipped with optical particle counters (OPC) and were able to measure the particle size distribution within the Sahara dust cloud and as a result of this to calculate the particle mass concentration of the dust. The ceilometer measurements and the aircraft measurements complemented each other: whereas the ceilometers gave continuous information about the Sahara dust cloud at the ceilometer positions, the aircraft measurements delivered interpolating results between the ceilometer positions. Moreover, at several ceilometer positions intercomparison flights were performed by spiraling with the aircraft up or down around the ceilometer laser beam. This gave the unique possibility for comparing the remote sensing results of the ceilometers with the in-situ measurements of the aircraft. This study shows that a significant high amount of Saharan dust particles was transported over Germany during a several days long episode. Furthermore, the intercomparison study between the German ceilometer network and aircraft measurements results shows a good agreement. A combination of these techniques could help to detect the vertical and horizontal distribution of the dust cloud and additionally the particle mass concentration.