Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    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.
  • Publication
    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.
  • Publication
    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.
  • Publication
    Overview of the international project on biogenic aerosol formation in the boreal forest (BIOFOR)
    ( 2001)
    Kulmala, M.
    ;
    Hameri, K.
    ;
    Aalto, P.P.
    ;
    Makela, J.M.
    ;
    Pirjola, L.
    ;
    Nilsson, E.D.
    ;
    Buzorius, G.
    ;
    Rannik, U.
    ;
    Dalmaso, M.
    ;
    Seidl, W.
    ;
    Hoffman, T.
    ;
    Janson, R.
    ;
    Hansson, H.C.
    ;
    Viisanen, Y.
    ;
    Laaksonen, A.
    ;
    Odowd, C.D.
    Aerosol formation and subsequent particle growth in ambient air have been frequently observed at a boreal forest site (SMEAR II station) in Southern Finland. The EU funded project BIOFOR (Biogenic aerosol formation in the boreal forest) has focused on: (a) determination of formation mechanisms of aerosol particles in the boreal forest site; (b) verification of emissions of secondary organic aerosols from the boreal forest site; and (c) quantification of the amount of condensable vapours produced in photochemical reactions of biogenic volatile organic compounds (BVOC) leading to aerosol formation. The approach of the project was to combine the continuous measurements with a number of intensive field studies. These field Studies were organised in three periods, two of which were during the most intense particle production season and one during a non-event season. Although the exact formation route for 3 nm particles remains unclear, the results can be summarised as follows: Nucleation was always connected to Arctic or Polar air advecting over the site, giving conditions for a stable nocturnal boundary layer followed by a rapid formation and growth of a turbulent convective mixed layer closely followed by formation of new particles. The nucleation seems to occur in the mixed layer or entrainment zone. However two more prerequisites seem to be necessary, A certain threshold of high enough sulphuric acid and ammonia concentrations is probably needed as the number of newly formed particles was correlated with the product of the sulphuric acid production and the ammonia concentrations. No such correlation was found with the oxidation products of terpenes. The condensation sink, i.e., effective particle area, is probably of importance as no nucleation was observed at high values of the condensation sink. From measurement of the hygroscopic properties of the nucleation particles it was found that inorganic compounds and hygroscopic organic compounds contributed both to the particle growth during daytime while at night time organic compounds dominated. Emissions rates for several gaseous compounds was determined. Using four independent ways to estimate the amount of the condensable vapour needed for observed growth of aerosol particles we get an estimate of 2-10 x 10(7) vapour molecules cm(-3). The estimations for source rate give 7.5-11 x 10(4) cm(-3) s(-1). These results lead to the following conclusions: The most probable formation mechanism is ternary nucleation (water-sulphuric acid-ammonia). After nucleation, growth into observable sizes (greater than or equal to3 nm) is required before new particles appear. The major part of this growth is probably due to condensation of organic vapours. However, there is lack of direct proof of this phenomenon because the composition of 1-5 nm size particles is extremely difficult to determine using the present state-of-art instrumentation.
  • Publication
    In-flight measurement of aircraft CO and nonmethane hydrocarbon emission indices
    ( 2001)
    Slemr, F.
    ;
    Giehl, H.
    ;
    Habram, M.
    ;
    Slemr, J.
    ;
    Schlager, H.
    ;
    Schulte, P.
    ;
    Haschberger, P.
    ;
    Lindermeir, E.
    ;
    Dopelheuer, A.
    ;
    Plohr, M.
    Emission indices were derived from in-flight measurements of CO, nonmethane hydrocarbons (NMHCs), H2O, and nonvolatile condensation nuclei in the exhaust plumes of the Deutsches Zentrum fur Luft- und Raumfahrt VFW 614 (ATTAS) and NASA DC-8 experimental aircraft. CO emission indices, EIs(CO), of the ATTAS Rolls Royce M 45H Mk501 engines were determined concurrently by two independent techniques: monitoring of exhaust emissions using a customized Fourier transform infrared spectrometer (FTIR) and by simultaneous continuous fast CO and CO, measurements. The EIs(CO) determined by FTIR were systematically 28% lower than those derived from the CO/CO2 concentration ratios. The EIs(CO) of the newer and larger CFM 56-2C1 engines, used on DC-g, were substantially smaller than those of the ATTAS engines. The emission behavior of CFM 56-2C1 engines is very similar to CFM 56-3 engines frequently used on Boeing 737 aircraft. Tn-flight derived EIs(CO) of the ATTAS engines were strongly dependent on the fuel flow rate and agreed well with those calculated from ground-based measurements. Emission indices for individual NMHCs were determined fi om the concentration ratios of NMHC/CO in the plume of ATTAS and DC-g and from the EIs(CO) determined by FTIR or derived from the concentration ratios of CO/CO2. The EIs(NMHC) are highest for alkenes and alkynes generated by a cracking of larger fuel molecules and for benzene from unburnt fuel, and they depend strongly on the power setting of the engines. As with EIs(CO), the EIs(NMHC) of the CFM 56-2C1 engine tend to be smaller than those of the Rolls Royce M 45H Mk501.
  • Publication
    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.
  • Publication
    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.
  • Publication
    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.
  • Publication
    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.