Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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Airborne measurements of nucleation mode particles I: Coastal nucleation and growth rates

2007 , O'Dowd, C.D. , Yoon, Y.J. , Junkerman, W. , Aalto, P. , Kulmala, M. , Lihavainen, H. , Viisanen, Y.

A light aircraft was equipped with a bank of Condensation Particle Counters (CPCs) (50% cut from 3-5.4-9.6 nm) and a nano-Scanning Mobility Particle Sizer (nSMPS) and deployed along the west coast of Ireland, in the vicinity of Mace Head. The objective of the exercise was to provide high resolution micro-physical measurements of the coastal nucleation mode in order to map the spatial extent of new particle production regions and to evaluate the evolution, and associated growth rates of the coastal nucleationmode aerosol plume. Results indicate that coastal new particle production is occurring over most areas along the landsea interface with peak concentrations at the coastal plume-head in excess of 106 cm-3. Pseudo-Lagrangian studies of the coastal plume evolution illustrated significant growth of new particles to sizes in excess of 8 nm approximately 10 km downwind of the source region. Close to the plume head (<1km) growth rates can be as high as 123-171 nm h-1, de creasing gradually to 53-72 nm h-1 at 3km. Further along the plume, at distances up to 10km, the growth rates are calculated to be 17-32 nm h-1. Growth rates of this magnitude suggest that after a couple of hours, coastal nucleation mode particles can reach significant sizes where they can contribution to the regional aerosol loading.

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Suspen intercomparison of ultraviolet spectroradiometers

2001 , Bais, A.F. , Gardiner, B.G. , Slaper, H. , Blumthaler, M. , Bernhard, G. , Mckenzie, R. , Webb, A.R. , Seckmeyer, G. , Kjeldstad, B. , Koskela, T. , Kirsch, P.J. , Grobner, J. , Kerr, J.B. , Kazadzis, S. , Leszczynski, K. , Wardle, D. , Josefsson, W. , Brogniez, C. , Gillotay, D. , Reinen, H. , Weihs, P. , Svenoe, T. , Eriksen, P. , Kuik, F. , Redondas, A.

Results from an intercomparison campaign of ultraviolet spectroradiometers that was organized at Nea Michaniona, Greece July, 1-13 1997, are presented. Nineteen instrument systems from 15 different countries took part and provided spectra of global solar UV irradiance for two consecutive days from sunrise to sunset every half hour. No data exchange was allowed between participants in order to achieve absolutely independent results among the instruments. The data analysis procedure included the determination of wavelength shifts and the application of suitable corrections to the measured spectra, their standardization to common spectral resolution of 1 nm full width at half maximum and the application of cosine corrections. Reference spectra were calculated for each observational time, derived for a set of instruments which were objectively selected and used as comparison norms for the assessment of the relative agreement among the various instruments. With regard to the absolute irradiance measurements, the range of the deviations from the reference for all spectra was within +/- 20%. About half of the instruments agreed to within +/-5%, while only three fell outside the +/- 10% agreement limit. As for the accuracy of the wavelength registration of the recorded spectra, for most of the spectroradiometers (14) the calculated wavelength shifts were smaller than 0.2 nm. The overall outcome of the campaign was very encouraging, as it was proven that the agreement among the majority of the instruments was good and comparable to the commonly accepted uncertainties of spectral UV measurements. In addition, many of the instruments provided consistent results relative to at least the previous two intercomparison campaigns, held in 1995 in Ispra, Italy and in 1993 in Garmisch-Partenkirchen, Germany. As a result of this series of intercomparison campaigns, several of the currently operating spectroradiometers operating may be regarded as a core group Of instruments, which with the employment of proper operational procedures are capable of providing quality spectral solar UV measurements.

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Detailed analysis of the isotopic composition of CO and characterization of the air masses arriving at mount Sonnblick (Austrian-Alps)

2001 , Gros, V. , Braunlich, M. , Rockmann, T. , Jockel, P. , Bergamaschi, P. , Brenninkmeijer, C.A.M. , Rom, W. , Kutschera, W. , Kaiser, A. , Scheel, H.E. , Mandl, M. , Plicht, J. van der , Possnert, G.

Air sampling for analysis of CO and its isotopic composition (C-13, O-18, and C-14) has been performed at the alpine station Sonnblick(47 degreesN, 13 degreesE, 3106 m above sea level) since September 1996. A high degree of variability is observed, which is due to the wide variation in the origin of air masses sampled. On the basis of the CO and isotope results, a classification of the different samples is performed. Other data such as Be-7, O-3, relative humidity, and back trajectories are used to give additional information about the air mass origin. Background values, representative of the NH midlatitudes free troposphere, are observed about 50% of the time and are used to define seasonal cycles. CO and its isotopes show a minimum in summer and a maximum in winter with extreme values of 90 and 160 ppb for CO, -30 and -25 parts per thousand for delta C-13, 0 and 8 parts per thousand for delta O-18, and 8 and 20 molecules cm(-3) STP for (CO)-C-14. CO and stable isotope data are compared with results from a three-dimensional model (TM2). Generally good agreement supports the CO, delta (CO)-C-13, and deltaC(18)O source/sink distributions inferred by the model. According to model calculations, fossil fuel combustion contributes 35% in summer and 50% in winter of total CO for such a midlatitude location. Other categories of sampled air are "subtropical," "polluted," and "stratospheric" and are observed 24%, 18%, and 4% of the time. Corresponding signatures of CO and its isotopic variations are presented, and some specific events are discussed.

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Emission fluxes and atmospheric degradation of monoterpenes above a boreal forest. Field measurements and modelling

2001 , Spanke, J. , Rannik, U. , Forkel, R. , Nigge, W. , Hoffmann, T.

The contribution of monoterpenes to aerosol formation processes within and above forests is not well understood. This is also true for the particle formation events observed during the BIOFOR campaigns in Hyytiala, Finland. Therefore, the diurnal variation of the concentrations of several biogenic volatile organic compounds (BVOCs) and selected oxidation products in the gas and particle phase were measured on selected days during the campaigns in Hyytiala, Finland. alpha -pinene and Delta (3)-carene were found to represent the most important monoterpenes above the boreal forest. A clear vertical gradient of their concentrations was observed together with a change of the relative monoterpene composition with height. Based on concentration profile measurements of monoterpenes, their fluxes above the forest canopy were calculated using the gradient approach. Most of the time, the BVOC fluxes show a clear diurnal variation with a maximum around noon. The highest fluxes were observed for alpha -pinene with values up to 20 ng m(-2) s(-1) in summer time and almost 100 ng m(-2) s(-1) during the spring campaign. Furthermore, the main oxidation products from a-pinene, pinonaldehyde, and from beta -pinene, nopinone, were detected in the atmosphere above the forest. In addition to these more volatile oxidation products, pinic and pinonic acid were identified in the particle phase in a concentration range between 1 and 4 ng m(-3). Beside these direct measurement of known oxidation products, the chemical sink term in the flux calculations was used to estimate the amount of product formation of the major terpenes (alpha -pinene, beta -pinene, Delta (3)-carene). A production rate of very low volatile oxidation products (e.g., multifunctional carboxylic) from . OH- and O-3-reaction of monoterpenes of about 1.3 (.) 10(4) molecules cm(-3) s(-1) was estimated for daylight conditions during summer time. Additionally, model calculations with the one-dimensional multilayer model CACHE were carried out to investigate the diurnal course of BVOC fluxes and chemical degradation of terpenes.

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Highlights of the tropospheric lidar studies at IFU within the TOR project

2002 , Carnuth, W. , Kempfer, U. , Trickl, T.

A summary of the ozone soundings with the tropospheric ozone lidar at IFU in the years 1991 and 1993 is given. The results cover vertical distributions obtained under a variety of meteorological conditions in different seasons such as during high pressure, before and after frontal passages and during stratospheric air intrusions. The lidar time series, carried out between typically 0.25 and 10 km and at intervals of about 1 h, are an excellent tool for transport studies. Quite frequently contributions of different processes may be observed even simultaneously which may yield insight on the troposphere as a whole. Although the time series were limited to single days during that phase information on a number of relevant transport processes could be extracted. In particular, the uplifting in the Alpine thermal wind system was investigated. The air in the valley is vented to heights in part even beyond 4 km a.s.l. during fair-weather summer days. The high efficiency of the underlying mechanism suggests a major contribution of the orographically induced transport in the Alps to the pollution export from the Central European boundary layer. A spectacular case of trans-Alpine ozone transport was examined which resulted in an ozone increase by about 40% after sunset. This case may, again, reflect the role of the Alps in the redistribution of air pollution in a larger area. In addition, episodes of long-range ozone and aerosol transport have been studied. In this paper, we present the example of intense Fohn with advection of dust-loaded air from the Sahara desert and beyond containing just 35 ppb of O-3. A rather complex layering may be observed after cold-front passages associated with subsequent anticyclonic advection. The analysis of a two-day vertical-sounding series reveals that the air in different height ranges originated in the troposphere or stratosphere above rather different source regions, even in the lowermost 4 km above the United States. More recent studies have confirmed the reproducibility of the general layer pattern under such conditions. The in part considerable difference in ozone concentration makes the definition of a free-tropospheric background ozone level a difficult task.

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Transport of boreal forest-fire emissions from Canada to Europe

2001 , Forster, C. , Wandinger, U. , Wotawa, G. , James, P. , Mattis, I. , Althausen, D. , Simmonds, P. , Odoherty, S. , Jennings, S.G. , Kleefeld, C. , Schneider, J. , Trickl, T. , Kreipl, S. , Jager, H. , Stohl, A.

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Vertical variation of frequency distributions of wind speed in and above the surface layer observed by sodar

2001 , Emeis, S.

10 min-averaged wind speed data have been measured with a mini-sodar for 13 months subsequently at different sites in level terrain and on hill tops in Germany in the last three years. The data presented here is from a height range between 25 and 140 m above ground, the vertical resolution is 5 to 10 m. From the data monthly mean diurnal courses of wind speed and of directional shear have been computed as well as monthly mean vertical profiles of the scale factor and the shape parameter of the Weibull wind speed frequency distribution. These profiles extend beyond the top of the surface layer into the Ekman layer. Therefore the profiles have to be described by Ekman layer laws instead of by surface layer laws if they have to be extrapolated upward. Typical features of the profiles characterizing level terrain and hill top sites have been analyzed. Most prominent feature is the maximum of the shape parameter at the top of the surface layer. Implications for the siting of wind turbines are discussed

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An ultralight aircraft as platform for research in the lower troposphere - system performance and first results from radiation transfer studies in stratiform aerosol layers and broken cloud conditions

2001 , Junkermann, W.

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Differences in early contrail evolution of two-engine versus four engine aircraft

2001 , Sussmann, R. , Gierens, K.M.

Jet- and vortex-regime evolution of contrails behind cruising aircraft is investigated by focusing on the role of aircraft type. Cross-section measurements by ground-based lidar and observational analysis are combined with numerical simulations of fluid dynamics and microphysics in the wake of two-engine aircraft. Depending on ambient himidity levels, contrail evolution behind short/medium-range twin-turbofan airliners is classified into two scenarios, which is in contrast to the three scenario observed for wide-body four-turbofan aircraft. In case of ice-subsaturated ambient air, a short visible contrail is formed behind two-engine aircraft that disappears before the ice is fully entrained into the wingtip vortices (in most cases > 4 s behind aircraft). The early evaporation of the ice is mainly due to the fast initial jet expansion, mixing the exhaust with the ambient air. Contrails behind wide-body four-engine aircraft always survive at least until vortex breakdown (i. e., typically 2 min behind aircraft). This is simply due to the larger ice mass in the contrail because of the higher fuel flow rate. Generally, in case of ice-supersaturation, a diffuse secondary wake evolves above the primary vortex wake. For two-engine aircraft, always the whole contrail persists, while for four-engine aircraft the ice inside the primary wake disappears in most cases after vortex breakdown, when the relative humidity is only slightly above ice saturation. In the more rare cases of higher ice-supersaturation the ice in the primary wake survives vortex breakdown and becomes part of the persistent contrail.

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Hygroscopic and ccn properties of aerosol-particles in boreal forests

2001 , Hameri, K. , Vakeva, M. , Aalto, P.P. , Kulmala, M. , Swietlicki, E. , Zhou, J. , Seidl, W. , Becker, E. , Odowd, C.D.

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