Thomas Holst - Academia.edu (original) (raw)

Papers by Thomas Holst

Enth. ausserdem 5 Sonderabdr. aus verschiedenen Zeitschr. - Beitr. teilw. dt., teilw. engl. Freib... more Enth. ausserdem 5 Sonderabdr. aus verschiedenen Zeitschr. - Beitr. teilw. dt., teilw. engl. Freiburg (Breisgau), Universiẗat, Diss., 2004.

Journal of Geophysical Research Atmospheres

Aerosol particles can modify cloud properties by acting as cloud condensation nuclei (CCN). Predi... more Aerosol particles can modify cloud properties by acting as cloud condensation nuclei (CCN). Predicting CCN properties is still a challenge and not properly incorporated in current climate models. Atmospheric particle number size distributions, hygroscopic growth factors, and polydisperse CCN number concentrations were measured at the remote subarctic Stordalen mire, 200 km north of the Arctic Circle in northern Sweden. The CCN number concentration was highly variable, largely driven by variations in the total number of sufficiently large particles, though the variability of chemical composition was increasingly important for decreasing supersaturation. The hygroscopicity of particles measured by a hygroscopicity tandem differential mobility analyzer (HTDMA) was in agreement with large critical diameters observed for CCN activation ($\kappa$ ≈ 0.07–0.21 for D = 50–200 nm). Size distribution and time‐ and size‐resolved HTDMA data were used to predict CCN number concentrations. Agreeme...

Aerosol particles in a given environment are largely influenced by surrounding regions which can ... more Aerosol particles in a given environment are largely influenced by surrounding regions which can act as either direct sources or via the production of species which become incorporated into pre-existing particles. Presented here are the major characteristics, including chemical composition, of ambient aerosols measured by an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) and other instruments 200 km above the Arctic Circle. Abisko Scientific Research Station, operated by the Royal Swedish Academy of Sciences, is subject to airmasses with several different origins. By comparison of wind trajectories, the influence of the sea, boreal forest, and industrial regions surrounding Abisko are evident in the measured spectra. These aerosol particles are of further interest due to the climate changes occurring in the polar region. Also important to this study is the simultaneous occurrence of an International Polar Year, an intensive research period focusing on the environments of both pol...

Atmospheric Chemistry and Physics

Emissions of biogenic volatile organic compounds (BVOC) from the boreal forest biome contribute a... more Emissions of biogenic volatile organic compounds (BVOC) from the boreal forest biome contribute a large precursor source for formation and growth of secondary organic aerosol, with unknown but potentially substantial effects on atmosphere and climate. However, variation in the BVOC source distribution across the boreal forests and over the course of a growing season is poorly quantified, based on a very limited number of short-term studies in northern Europe and northern America. In eastern Siberia, Larix gmelinni forests dominate an area of ca. 28 X 106ha, one quarter of the entire Eurasian boreal forest. So far, no observations of leaf or ecosystem BVOC fluxes have been reported although it has been argued that larch is a substantial emitter of monoterpenes and sesquiterpenes. We will present first results from a number of measurement campaigns performed at the Spasskaya Pad flux station (ca. 40km to the northeast of Yakutsk, 62o15'18.4''N, 129o37'07.9''E) ...

Biogeosciences Discussions, 2008

High latitude wetlands play an important role for the surface-atmosphere exchange of carbon dioxi... more High latitude wetlands play an important role for the surface-atmosphere exchange of carbon dioxide (CO 2 ) and methane (CH 4 ), but fluxes of biogenic volatile organic compounds (BVOC) in these ecosystems have to date not been extensively studied. This is despite BVOC representing a measurable proportion of the total gaseous C fluxes 5 at northern locations and in the face of the high temperature sensitivity of these systems that requires a much improved process understanding to interpret and project possible changes in response to climate warming. We measured emission of isoprene and photosynthetic gas exchange over two growing seasons (2005)(2006) in a subarctic wetland in northern Sweden with the objective to identify the physiological and 10 20 observations were used to model emissions over the growing season, accounting for effects of temperature history, links to leaf assimilation rate and the light and temperature dependencies of the cold-adapted sedges.

Tellus B, 2008

A B S T R A C T An analysis of particle formation (PF) events over a subarctic mire in northern S... more A B S T R A C T An analysis of particle formation (PF) events over a subarctic mire in northern Sweden was performed, based on numbersize distributions of atmospheric aerosol particles (10-500 nm in diameter) and ions (0.4-40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005-September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis includes calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm h −1 ) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions, repeated particle formation events were observed within 1 d, with differences in onset time of a few hours. These high growth rates were only observed when the condensation sink was higher than 0.001 s −1 .

Plant, Cell and Environment, 2003

At eight different dates during the 2000 growing season, d d d d 13 C and d d d d 18 O were deter... more At eight different dates during the 2000 growing season, d d d d 13 C and d d d d 18 O were determined in the phloem of adult beech trees growing in natural beech stands in south-west Germany differing in stand density and local climate. In addition, stand transpiration, precipitation, photosynthetic active radiation, relative air humidity, water pressure deficit of the air, air and soil temperature, soil water potential, and sugar concentration of the phloem sap were determined directly and evaporation and canopy stomatal conductance were modelled. All parameters were related to d d d d 13 C. The study aimed to identify the time integral within which the d d d d 13 C of organic compounds transported in the phloem is an indicative measure of these environmental influences. d d d d 13 C of soluble carbon transported in the phloem was well correlated with mean stomatal conductance in a two-day integral prior to phloem sampling but did not depend on either light intensity or soil water availability. A strong positive relationship between d d d d 13 C and d d d d 18 O pointed to observed variation in d d d d 13 C of phloem sap being a result of variation in stomatal conductance. Bulk leaf d d d d 13 C was a poor indicator of changes in environmental conditions during the growing season. From these results we conclude that the analysis of d d d d 13 C in soluble carbon transported in the phloem is a reliable indicator of short-term changes in C i / C a . In contrast, the d d d d 13 C of structural carbon in beech foliage represents an integration of a range of factors that mask shortterm influences responsible for C i / C a .

Meteorologische Zeitschrift, 2008

ABSTRACT The short-term limit value for PM10 having become effective in January 2005 was exceeded... more ABSTRACT The short-term limit value for PM10 having become effective in January 2005 was exceeded in many regions within the EU in 2005 and 2006. Therefore, strategies, particularly with respect to traffic control, are discussed, which could cause reduced PM10 concentrations leading to a more effective compliance with the short-term PM10 limit value. These strategies are often justified on PM10 differences between a roadside and an adjacent urban background station. As PM10 is a complex mixture of species originating from different sources, the working hypothesis has been posted that the meteorological exchange conditions strongly affect the PM10 concentration. Therefore, the role of the meteorological exchange conditions with respect to different PM10 patterns, like cycles and PM10 episodes, was investigated on the basis of mean daily PM10 values from air pollution monitoring stations in Baden-Württemberg (SW Germany) in the period January 2001 to February 2006. To characterise the meteorological exchange conditions in a spatial resolution, different meteorological variables were used. Partly, they are directly measured at the air pollution monitoring stations or, as for the height of the mixing-layer (MLH) and the stagnation index (SI), they were derived from results of the local model (LM) of the German Weather Service. For periods without precipitation, the results show a statistically significant relationship between PM10 and MLH as well as SI. PM10 increased with decreasing MLH and increasing SI. During periods with precipitation, these relationships were very weak and had no statistical significance. The analysis of the influence of precipitation performed on a daily basis revealed a distinct reduction of PM10 on the first day with precipitation after a period without precipitation. On following days without precipitation, PM10 increased again. Characteristic of the PM10 episodes analysed were remarkably reduced meteorological exchange conditions described by MLH, near-surface wind speed and precipitation. As a case study, two extreme PM10 episodes in January/February 2006 were investigated in detail. As expected, the station-specific variability of the mean daily PM10 values correlated well with daily values of MLH and SI reflecting the pattern of the regional meteorological exchange conditions. Altogether, all results of this investigation point out the main significance of the meteorological exchange conditions on the PM10 level, which is particularly dominant during PM10 episodes. German Der seit dem 1. Januar 2005 gültige Kurzzeit-Grenzwert von PM10 wurde in den Jahren 2005 und 2006 in vielen Regionen innerhalb der EU überschritten. Deshalb werden Maßnahmen, vor allem im Verkehrsbereich, diskutiert, die zu einer Reduzierung der PM10 Konzentration führen könnten, so dass sich der Kurzzeit-Grenzwert von PM10 besser einhalten lässt. Sie beruhen häufig auf PM10 Unterschieden zwischen einer Straßenstation und einer nahen städtischen Hintergrundstation. Da PM10 eine summarische Größe darstellt, die aus verschiedenen natürlichen und anthropogenen Quellen stammt und daher verschiedene Bestandteile aufweist, wurde die Arbeitshypothese aufgestellt, dass die meteorologischen Austauschbedingungen einen dominanten Einfluss auf die PM10 Konzentration haben. Zur Prüfung dieser Hypothese wurde anhand von PM10 Tagesmittelwerten für Luftmessstationen in Baden-Württemberg (SW Deutschland) im Zeitraum Januar 2001 bis Februar 2006 untersucht, welche Rolle die meteorologischen Austauschbedingungen hinsichtlich verschiedener PM10 Muster, wie Zyklen und PM10 Episoden, einnehmen. Zur Charakterisierung der räumlich differenzierten meteorologischen Austauschbedingungen wurden unterschiedliche meteorologische Variable verwendet. Sie werden teilweise direkt an den Luftmessstationen gemessen oder wurden, wie die Höhe der Mischungsschicht (MLH) und der Stagnationsindex (SI), aus Ergebnissen des Lokalmodells (LM) des Deutschen Wetterdienstes abgeleitet. Die Ergebnisse zeigen für niederschlagsfreie Perioden statistisch signifikante Zusammenhänge zwischen PM10 sowie MLH und SI. Mit abnehmendem MLH, was eine Zunahme von SI zur Folge hat, steigt PM10 an. Dieser statistische Zusammenhang ist in Niederschlagsperioden nicht mehr gegeben. Die spezielle Analyse des Einflusses von Niederschlag auf Tagesbasis ergab eine deutliche PM10 Reduzierung für den Tag mit Niederschlag nach einem niederschlagsfreien Zeitraum. An darauf folgenden Tagen ohne Niederschlag nahm der PM10 Tagesmittelwert wieder zu. Die im Untersuchungszeitraum analysierten PM10 Episoden zeichneten sich durch erheblich eingeschränkte meteorologische Austauschbedingungen aus. Sie wurden über MLH, die bodennahe Windgeschwindigkeit und den Niederschlag beschrieben. Als Fallstudie wurden die extremen PM10 Episoden im Januar/Februar 2006 näher analysiert. Die erwartete stationsspezifische Variabilität der PM10 Tagesmittelwerte sowie der Tageswerte von MLH und SI ließ sich…

Meteorologische Zeitschrift, 2005

Within the framework of an interdisciplinary project on the impact of climate and forest manageme... more Within the framework of an interdisciplinary project on the impact of climate and forest management on beech dominated deciduous forests, forest meteorological measurements are carried out within and above different beech stands (Fagus sylvatica L.

Journal of Geophysical Research, 2009

Subarctic aerosol was sampled during July 2007 at the Abisko Research Station Stordalen field sit... more Subarctic aerosol was sampled during July 2007 at the Abisko Research Station Stordalen field site operated by the Royal Swedish Academy of Sciences. Located in northern Sweden at 68° latitude and 385 m above sea level (m asl), this site is classified as a semicontinuous permafrost mire. Number density, size distribution, cloud condensation nucleus properties, and chemical composition of the

Journal of Geophysical Research, 2010

1] Aerosol particles can modify cloud properties by acting as cloud condensation nuclei (CCN). Pr... more 1] Aerosol particles can modify cloud properties by acting as cloud condensation nuclei (CCN). Predicting CCN properties is still a challenge and not properly incorporated in current climate models. Atmospheric particle number size distributions, hygroscopic growth factors, and polydisperse CCN number concentrations were measured at the remote subarctic Stordalen mire, 200 km north of the Arctic Circle in northern Sweden. The CCN number concentration was highly variable, largely driven by variations in the total number of sufficiently large particles, though the variability of chemical composition was increasingly important for decreasing supersaturation. The hygroscopicity of particles measured by a hygroscopicity tandem differential mobility analyzer (HTDMA) was in agreement with large critical diameters observed for CCN activation (k % 0.07 -0.21 for D = 50 -200 nm). Size distribution and time-and size-resolved HTDMA data were used to predict CCN number concentrations. Agreement of predictions with measured CCN within ±11% was achieved using parameterized Köhler theory and assuming a surface tension of pure water. The sensitivity of CCN predictions to various simplifying assumptions was further explored: We found that (1) ignoring particle mixing state did not affect CCN predictions, (2) averaging the HTDMA data in time with retaining the size dependence did not introduce a substantial bias, while individual predictions became more uncertain, and (3) predictions involving the hygroscopicity parameter recommended in literature for continental sites (k % 0.3 ± 0.1) resulted in a significant prediction bias. Future modeling studies should therefore at least aim at using averaged, size-resolved, site-specific hygroscopicity or chemical composition data for predictions of CCN number concentrations.

International Journal of Environment and Pollution, 2009

The influence of atmospheric exchange conditions on near-surface PM 10 concentrations is analysed... more The influence of atmospheric exchange conditions on near-surface PM 10 concentrations is analysed for four cities in the South-West of Germany in the period from 2001 to 2005. For each city, the PM 10 data originates from roadside stations and Urban Background (UB) stations, that is, two types of official urban air quality monitoring stations characterised by different emission situations. The atmospheric exchange conditions are represented by solar radiation, air temperature, wind speed, mixing-layer height, precipitation and backward-trajectories. The results of the statistical analysis indicate that

International Journal of Biometeorology, 2005

Measurements of the net radiation balance of two forested sites on the opposite slopes of a valle... more Measurements of the net radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming radiation was adjusted according to the slope's angle to convert horizontally measured radiation data into surfaceparallel radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal radiation fluxes were available, the calculation of surfaceparallel radiation fluxes from the horizontally recorded net radiation components were compared with measured values. The net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the net radiation balance. In June, when the elevation of the sun is highest, incoming solar radiation K# received on the NE-slope was 9% lower than K# received on the SW-slope. During the winter months, the differences were much greater and incoming solar radiation to the NE-slope was 50% of that to the SWslope. Due to the differing solar irradiance, net radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the net radiation balance between the slopes are important for the vegetation.

International Journal of Biometeorology, 2004

For some beech (Fagus sylvatica L.) stands with different stand densities the plant area index (P... more For some beech (Fagus sylvatica L.) stands with different stand densities the plant area index (PAI) was measured by means of a Licor LAI-2000 plant canopy analyser. The stands are located on the slopes of a valley in south-west Germany and had been treated by different types of silvicultural management (heavy shelterwood felling, light shelterwood felling, control plot). The analyser was used (a) to investigate the light conditions on plots of the same thinning regime, (b) to quantify the differences between the different treatments and (c) to obtain absolute values of PAI for interdisciplinary research. PAI was measured at three different phenological stages (leafless, leaf-unfolding and fully leafed season in 2000) and was found to be about 5.2 for the fully developed canopy on the control plots, 3.2 on the light fellings and about 2.0 for the heavy fellings. In the leafless period PAI was between 1.1 (control) and 0.4 (heavy felling). Measurements made in summer 2000 and summer 2002 were compared, and showed an increase of PAI, especially on the thinned plots. Measurements of photosynthetically active radiation (PAR) above and below the canopy in combination with measured PAI were used to apply Beer's Law of radiation extinction to calculate the extinction coefficient k for different sky conditions and for the different growing seasons on the control plots. The extinction coefficient k for the beech stands was found to be between 0.99 and 1.39 in the leafless period, 0.62 to 0.91 during leaf unfolding and between 0.68 and 0.83 in the fully leafed period. Using PAR measurements and the k values obtained, the annual cycle of PAI was modelled inverting Beer's Law.

European Journal of Forest Research, 2006

We assessed seasonal changes of total soluble nonprotein nitrogen compounds (TSNN) in adult Europ... more We assessed seasonal changes of total soluble nonprotein nitrogen compounds (TSNN) in adult European beech trees (Fagus sylvatica, L.) growing under different local climate during the growing season immediately following a thinning treatment and 3 years later. In both years, samples of leaves, xylem sap and phloem exudates from beech trees growing in thinned and unthinned (control) stands on a dry, warm SW exposed and a cooler, moist NE exposed site were collected in May, July and September. In May of both years, asparagine (Asn) and glutamine (Gln) were most abundant in leaves and xylem, respectively, whereas arginine (Arg) dominated in the phloem. In July, TSNN concentrations decreased in all tissues and sites, but differences in water availability between aspects were reflected in TSNN concentrations. In September, differences in the increase of Arg concentration in the phloem were related to differences in the onset of senescence between treatments. Thinning treatment increased amino compound concentrations of beech tissues in July on both aspects, particularly at the NE thinned site. It is supposed that, the N balance of adult beech is favoured by both, the thinning treatments as well as the cool-moist climate prevailing at the NE aspect.

European Journal of Forest Research, 2004

Within the framework of an interdisciplinary project on the effects of climate and forest managem... more Within the framework of an interdisciplinary project on the effects of climate and forest management on beech-dominated deciduous forests (Swabian Jura, south-western Germany), forest meteorological investigations are carried out to analyse the influences of exposure and canopy density on the microclimate within various beech stands (Fagus sylvatica L.). This second paper of the series ''Microclimate within beech stands'' focuses on the thermal conditions that exist mainly in the near-surface layer at different test plots. They were analysed by air temperature, T a , (at 1.5 m a.g.l) and soil temperature, T s , at six depths measured continuously in the period 1999-2003. The main results can be summarized as follows. The thermal situation within the beech stands described by T a depended primarily on the turbulent air-mass exchange conditions which were based on the slope-specific energy balance of the forest floor and advective heat fluxes. (2) The thermal situation within the soil described by T s at 3 and 20 cm depth was governed by the molecular heat transport. Therefore, the heating and cooling rates of T s were always lower than for T a . Higher T a and T s values for the test plots on the SW slope showed that the thermal conditions within the beech stands depended primarily on the exposure. (3) Based on slope-specific differences of daily extremes of T a and T s at 3 cm depth between the silviculturally treated and control plots, the influence of the more pronounced height growth of the understorey vegetation under the near-surface thermal conditions could be clearly verified for the NE slope.

European Journal of Forest Research, 2007

The effect of forest management (thinning) on in situ carbon dioxide (CO 2 ), methane (CH 4 ) and... more The effect of forest management (thinning) on in situ carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) trace gas exchange between soil and atmosphere was studied in three consecutive years at three beech forest sites, which differ in aspect [southwest (SW), northeast (NE), northwest (NW)]. At all sites adjacent thinning plots (''T'') and untreated control plots (''C'') were established. Measurements at the SW and NE sites covered the years 4-6 after thinning while at the NW site measurements covered the year before and the first 2 years after thinning. Mean N 2 O fluxes were <3 lg N 2 O-N m À2 h À1 at all plots except for the newly thinned NWT plot. CH 4 uptake was rather low, too. Very low CH 4 oxidation rates during dry periods are explained by physiological drought stress for CH 4 oxidizers. Heterotrophic litter decomposition constitutes the largest part of total soil respiration. On the whole, no significant positive or negative effects of the silvicultural treatment on the magnitude of CO 2 -, CH 4 -and N 2 O-trace gas exchange could be observed at the SW site 4-6 years after thinning. Also at the NE site, no effects of thinning on CO 2 and N 2 O fluxes could be demonstrated. However, at this site a significant moisture-induced lower CH 4 uptake could be shown. At the NW site forest management led to a dramatic increase in N 2 O emissions in the first two summers after thinning and to distinct effects on CO 2 emissions and CH 4 uptake in the first year after the felling. The unambiguous effects of thinning at the NW site are mainly related to higher C input by dead residues leading to enhanced mineralization activity, to a shift in the competition for nutrients favoring microorganisms as compared to trees and to changes in the soil water availability at the thinned plot. Considering the data obtained from the NE and SW site we expect that with the development of an understorey vegetation at the NW site the observed effects on the magnitude of trace gas exchange due to thinning will continue to decline in the following years. Our results implicate that it is indispensable to take account of the effects of forest management in order to accurately calculate trace gas emission inventories for the investigated forest ecosystem in case thinning took place immediately before.