ALBERT

Description: 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 the June 2nd and August 29th in the metropolitan area of Berlin-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 an 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 temperature and particulates 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 pointwise volatile organic compounds (VOCs) identification. The quantification displayed notable horizontal heterogeneity of the short lived gases and particle number concentrations. E.g. concentrations of the traffic related chemical species CO and NO varied by more than ±20 % and ±60 % on the scale of one hundred meters, respectively. 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 would focus predominantly on reducing fossil-fuel emissions from traffic as well as on increasing vegetated areas.

Description: 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.

Description: 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 ± 0.44 s−1) and 75 % (3.7 ± 0.90 s−1) contribution from biogenic non-methane volatile organic compounds (NMVOCs) for urban background (2.6 ± 0.68 s−1) and urban park (4.9 ± 1.0 s−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.

Description: Tropospheric ozone and particulate matter affect human health and cause vegetation stress, dysfunction and damages. In this study we investigate the effect of increasing urban vegetation i.e. tree species on atmospheric chemistry, a potential urban management strategy to counteract high levels of local pollutants such as ozone, OH and PM10 caused by e.g. traffic. We use an extended version of an atmospheric chemistry box model including detailed gas-phase chemistry, mixing layer height variation and secondary organic aerosol calculations based on observations for Berlin, Germany. It is shown to accurately simulate the observed ozone volume mixing ratios during the intensive measurement period in July 2014 (BAERLIN2014) if basic parameters such as nitrogen oxides, meteorological conditions, PM10 concentrations as well as volatile organic compounds (VOCs) are considered as 1 h resolved datasets. Based on this setup the effects of changing present day vegetation mixture by 24 different relevant tree species and of urban greening is tested to elucidate benefits and drawbacks in order to support future urban planning. While the present day vegetation causes boundary layer ozone to decline slightly at 35 °C, individual tree types alter the ozone production rate and concentration as well as the secondary organic aerosol mass in different ways. Our results suggest that trees intensively emitting isoprene such as black locust, European oak and poplar result in higher ozone and total PM10 concentrations than at present, while tree species emitting primarily monoterpenes such as beech, magnolia and wayfaring trees yield less of both. This is in line with the similar behaviour of OH concentration and new particle formation rates. Thus, for future urban planning including urban greening, consideration of the beneficial and harmful aspects of tree species need to ensure that citizens benefit from and are not being negatively affected by climate adaptation strategies.

Description: The mixing layer height (MLH) is a measure for the vertical turbulent exchange within the boundary layer, which is one of the controlling factors for the dilution of pollutants emitted near the ground. Based on continuous MLH measurements with a Vaisala CL51 ceilometer and measurements from an air quality network, the relationship between MLH and near-surface pollutant concentrations has been investigated. In this context the uncertainty of the MLH retrievals and the representativeness of ground-based in situ measurements are crucial. We have investigated this topic by using data from the BAERLIN2014 campaign in Berlin, Germany, conducted from June to August 2014. To derive the MLH, three versions of the proprietary software BL-VIEW and a novel approach COBOLT were compared. It was found that the overall agreement is reasonable if mean diurnal cycles are considered. The main advantage of COBOLT is the continuous detection of the MLH with a temporal resolution of 10 min and a lower number of cases when the residual layer is misinterpreted as mixing layer. We have calculated correlations between MLH as derived from the different retrievals and concentrations of pollutants (PM10, O3 and NOx) for different locations in the metropolitan area of Berlin. It was found that the correlations with PM10 are quite different for different sites without showing a clear pattern, whereas the correlation with NOx seems to depend on the vicinity of emission sources in main roads. In the case of ozone as a secondary pollutant, a clear correlation was found. We conclude that the effects of the heterogeneity of the emission sources, chemical processing and mixing during transport exceed the differences due to different MLH retrievals. Moreover, it seems to be unrealistic to find correlations between MLH and near-surface pollutant concentrations representative for a city like Berlin (flat terrain), in particular when traffic emissions are dominant. Nevertheless it is worthwhile to use advanced MLH retrievals for ceilometer data, for example as input to dispersion models and for the validation of chemical transport models.

Description: Ceilometers have been used for several meteorological applications, often in the framework of air qualitystudies. Whereas the particle backscatter coefficient can be retrieved in a quantitative way only recently (withthe improvements of the hardware, Wiegner et al., 2014), mixing layer heights (MLH) have been derived formore than two decades. Several approaches are documented in the literature, however, automated proceduresare still prone to errors because of difficulties in the recognition and attribution of discontinuities (“steps”) inthe backscatter profiles. For example, it is often not clear whether a detected change in the vertical distributionof aerosol backscatter indicates the residual layer, the stable boundary layer, or an elevated layer. Thus, anassessment of the reliability and accuracy of MLH-retrievals is relevant for air quality studies: on the one handMLHs are often inversely correlated with ground-based in-situ measurements of particulate matter and gaseouspollutant concentrations, and on the other hand, MLH-retrievals can be used to validate chemistry transport models.To understand the benefit of MLH in the context of air quality, we have compared several retrievals of theMLH from ceilometer measurements during a field-campaign in summer 2014 (Bonn et al., 2016) for backgroundand polluted sites in Berlin. Correlations between the concentrations of several pollutants and MLH are analyzed,and how they are influenced by the uncertainty of the derived MLH.