Boris Bonn

Boreal forests, aerosols and the impacts on clouds and climate

Previous studies have concluded that boreal forests warm the climate because the cooling from storage of carbon in vegetation and soils is cancelled out by the warming due to the absorption of the Suns heat by the dark forest canopy. However, these studies ignored the impacts of forests on atmospheric aerosol. We use a global atmospheric model to show that, through emission of organic vapours and the resulting condensational growth of newly formed particles, boreal forests double regional cloud condensation nuclei concentrations (from approx. 100 to approx. 200 cm−3). Using a simple radiative model, we estimate that the resulting change in cloud albedo causes a radiative forcing of between −1.8 and −6.7 W m−2 of forest. This forcing may be sufficiently large to result in boreal forests having an overall cooling impact on climate. We propose that the combination of climate forcings related to boreal forests may result in an important global homeostasis. In cold climatic conditions, the snow–vegetation albedo effect dominates and boreal forests warm the climate, whereas in warmer climates they may emit sufficiently large amounts of organic vapour modifying cloud albedo and acting to cool climate.

Effect of VOC Emissions from Vegetation on Air Quality in Berlin during a Heatwave

The potential of emissions from urban vegetation combined with anthropogenic emissions to produce ozone and particulate matter has long been recognized. This potential increases with rising temperatures and may lead to severe problems with air quality in densely populated areas during heat waves. Here, we investigate how heat waves affect emissions of volatile organic compounds from urban/suburban vegetation and corresponding ground-level ozone and particulate matter. We use the Weather Research and Forecasting Model with atmospheric chemistry (WRF-Chem) with emissions of volatile organic compounds (VOCs) from vegetation simulated with MEGAN to quantify some of these feedbacks in Berlin, Germany, during the heat wave in 2006. The highest ozone concentration observed during that period was ∼200 μg/m3 (∼101 ppbV). The model simulations indicate that the contribution of biogenic VOC emissions to ozone formation is lower in June (9-11%) and August (6-9%) than in July (17-20%). On particular days within the analyzed heat wave period, this contribution increases up to 60%. The actual contribution is expected to be even higher as the model underestimates isoprene concentrations over urban forests and parks by 0.6-1.4 ppbv. Our study demonstrates that biogenic VOCs can considerably enhance air pollution during heat waves. We emphasize the dual role of vegetation for air quality and human health in cities during warm seasons, which is removal and lessening versus enhancement of air pollution. The results of our study suggest that reduction of anthropogenic sources of NOx, VOCs, and PM, for example, reduction of the motorized vehicle fleet, would have to accompany urban tree planting campaigns to make them really beneficial for urban dwellers.

Mixing layer height measurements determines influence of meteorology on air pollutant concentrations in urban area

Mixing layer height (MLH) is a key parameter to determine the influence of meteorological parameters upon air pollutants such as trace gas species and particulate concentrations near the surface. Meteorology, and MLH as a key parameter, affect the budget of emission source strengths, deposition, and accumulation. However, greater possibilities for the application of MLH data have been identified in recent years. Here, the results of measurements in Berlin in 2014 are shown and discussed. The concentrations of NO, NO2, O3, CO, PM1, PM2.5, PM10 and about 70 volatile organic compounds (anthropogenic and biogenic of origin) as well as particle size distributions and contributions of SOA and soot species to PM were measured at the urban background station of the Berlin air quality network (BLUME) in Nansenstr./Framstr., Berlin-Neukölln. A Vaisala ceilometer CL51, which is a commercial mini-lidar system, was applied at that site to detect the layers of the lower atmosphere in real time. Special software for these ceilometers with MATLAB provided routine retrievals of MLH from vertical profiles of laser backscatter data. Five portable Bruker EM27/SUN FTIR spectrometers were set up around Berlin to detect column averaged abundances of CO2 and CH4 by solar absorption spectrometry. Correlation analyses were used to show the coupling of temporal variations of trace gas compounds and PM with MLH. Significant influences of MLH upon NO, NO2, PM10, PM2.5, PM1 and toluene (marker for traffic emissions) concentrations as well as particle number concentrations in the size modes 70 – 100 nm, 100 – 200 nm and 200 – 500 nm on the basis of averaged diurnal courses were found. Further, MLH was taken as important auxiliary information about the development of the boundary layer during each day of observations, which was required for the proper estimation of CO2 and CH4 source strengths from Berlin on the basis of atmospheric column density measurements.

Secondary Particle Production in Urban Areas

Suspended particles in air and their corresponding mass can originate from three different types of sources. One is primary, expressing the release into the atmosphere as a particle straight away. This includes mineral dust, sea salt, soot, heavy metals, clay and biological material (pollen, bacteria, etc.). Those are usually located at larger diameters above half a micron. The second type originates from atmospheric trace gases (precursors), which react in the gas phase to form products of different volatility and reactivity. Some of them will either form new particles in number or produce new aerosol mass by partitioning between the gas and the aerosol phase. The third source type refers to the cloud phase and is essentially a mixture of both other types. Gases are absorbed in the cloud water, subsequently processed chemically and either stick primary aerosols included in the cloud water as well or form new aggregates. When the cloud starts evaporating as nine of ten clouds do, re-entering the atmosphere either as gases or as particulate matter. The primary particles dissolved in the cloud phase and interacting with the processed chemicals consist mainly of dissolved salts and water-soluble compounds, organic as well as inorganic.

Simulation of the interaction of terpenes and their oxidation products with ice

26th European Crystallographic Meeting, ECM 26, Darmstadt, 2010 Acta Cryst. (2010). A66, Page s75 s75 After equilibration the obtained structures are analyzed by clustering [2, 4]. It allows us to visualize the relationship between the idealized crystal structures and the obtained crystal structures in a classification tree. In dependence of the conditions we observe structural changes in the different polymorphs in accordance with the experimental phase diagram. At high pressure we find the structures VII and VIII stable, at low pressure ice I.