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Author: Kulmala, M. × End date: 2011 ×

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    MALTE - Model to predict new aerosol formation in the lower troposphere
    (München : European Geopyhsical Union, 2006) Boy, M.; Hellmuth, O.; Korhonen, H.; Nilsson, E.D.; ReVelle, D.; Turnipseed, A.; Arnold, F.; Kulmala, M.
    The manuscript presents a detailed description of the meteorological and chemical code of Malte – a model to predict new aerosol formation in the lower troposphere. The aerosol dynamics are achieved by the new developed UHMA (University of Helsinki Multicomponent Aerosol Model) code with kinetic limited nucleation as responsible mechanism to form new clusters. First results indicate that the model is able to predict the on- and offset of new particle formation as well as the total aerosol number concentrations that were in good agreement with the observations. Further, comparison of predicted and measured H2SO4 concentrations showed a satisfactory agreement. The simulation results indicated that at a certain transitional particle diameter (2–7 nm), organic molecules can begin to contribute significantly to the growth rate compared to sulphuric acid. At even larger particle sizes, organic molecules can dominate the growth rate on days with significant monoterpene concentrations. The intraday vertical evolution of newly formed clusters and particles in two different size ranges resulted in two maxima at the ground. These particles grow around noon to the detectable size range and agree well with measured vertical profiles.
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    The contribution of sulphuric acid to atmospheric particle formation and growth: A comparison between boundary layers in Northern and Central Europe
    (München : European Geopyhsical Union, 2005) Fiedler, V.; Dal Maso, M.; Boy, M.; Aufmhoff, H.; Hoffmann, J.; Schuck, T.; Birmili, W.; Hanke, M.; Uecker, J.; Arnold, F.; Kulmala, M.
    Atmospheric gaseous sulphuric acid was measured and its influence on particle formation and growth was investigated building on aerosol data. The measurements were part of the EU-project QUEST and took place at two different measurement sites in Northern and Central Europe (Hyytiälä, Finland, March-April 2003 and Heidelberg, Germany, March-April 2004). From a comprehensive data set including sulphuric acid, particle number size distributions and meteorological data, particle growth rates, particle formation rates and source rates of condensable vapors were inferred. Growth rates were determined in two different ways, from particle size distributions as well as from a so-called timeshift analysis. Moreover, correlations between sulphuric acid and particle number concentration between 3 and 6 nm were examined and the influence of air masses of different origin was investigated. Measured maximum concentrations of sulphuric acid were in the range from 1x106 to 16x106cm-3. The gaseous sulphuric acid lifetime with respect to condensation on aerosol particles ranged from 2 to 33min in Hyytiälä and from 0.5 to 8 min in Heidelberg. Most calculated values (growth rates, formation rates, vapor source rates) were considerably higher in Central Europe (Heidelberg), due to the more polluted air and higher preexistent aerosol concentrations. Close correlations between H2SO4 and nucleation mode particles (size range: 3-6 nm) were found on most days at both sites. The percentage contribution of sulphuric acid to particle growth was below 10% at both places and to initial growth below 20%. An air mass analysis indicated that at Heidelberg new particles were formed predominantly in air advected from southwesterly directions.
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    Number size distributions and seasonality of submicron particles in Europe 2008–2009
    (München : European Geopyhsical Union, 2011) Asmi, A.; Wiedensohler, A.; Laj, P.; Fjaeraa, A.-M.; Sellegri, K.; Birmili, W.; Weingartner, E.; Baltensperger, U.; Zdimal, V.; Zikova, N.; Putaud, J.-P.; Marinoni, A.; Tunved, P.; Hansson, H.-C.; Fiebig, M.; Kivekäs, N.; Lihavainen, H.; Asmi, E.; Ulevicius, V.; Aalto, P.P.; Swietlicki, E.; Kristensson, A.; Mihalopoulos, N.; Kalivitis, N.; Kalapov, I.; Kiss, G.; de Leeuw, G.; Henzing, B.; Harrison, R.M.; Beddows, D.; O'Dowd, C.; Jennings, S.G.; Flentje, H.; Weinhold, K.; Meinhardt, F.; Ries, L.; Kulmala, M.
    Two years of harmonized aerosol number size distribution data from 24 European field monitoring sites have been analysed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distribution of aerosols in the particle sizes most important for climate applications are presented. We also analyse the annual, weekly and diurnal cycles of the aerosol number concentrations, provide log-normal fitting parameters for median number size distributions, and give guidance notes for data users. Emphasis is placed on the usability of results within the aerosol modelling community. We also show that the aerosol number concentrations of Aitken and accumulation mode particles (with 100 nm dry diameter as a cut-off between modes) are related, although there is significant variation in the ratios of the modal number concentrations. Different aerosol and station types are distinguished from this data and this methodology has potential for further categorization of stations aerosol number size distribution types. The European submicron aerosol was divided into characteristic types: Central European aerosol, characterized by single mode median size distributions, unimodal number concentration histograms and low variability in CCN-sized aerosol number concentrations; Nordic aerosol with low number concentrations, although showing pronounced seasonal variation of especially Aitken mode particles; Mountain sites (altitude over 1000 m a.s.l.) with a strong seasonal cycle in aerosol number concentrations, high variability, and very low median number concentrations. Southern and Western European regions had fewer stations, which decreases the regional coverage of these results. Aerosol number concentrations over the Britain and Ireland had very high variance and there are indications of mixed air masses from several source regions; the Mediterranean aerosol exhibit high seasonality, and a strong accumulation mode in the summer. The greatest concentrations were observed at the Ispra station in Northern Italy with high accumulation mode number concentrations in the winter. The aerosol number concentrations at the Arctic station Zeppelin in Ny-\AA lesund in Svalbard have also a strong seasonal cycle, with greater concentrations of accumulation mode particles in winter, and dominating summer Aitken mode indicating more recently formed particles. Observed particles did not show any statistically significant regional work-week or weekday related variation in number concentrations studied. Analysis products are made for open-access to the research community, available in a freely accessible internet site. The results give to the modelling community a reliable, easy-to-use and freely available comparison dataset of aerosol size distributions.
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    EUCAARI ion spectrometer measurements at 12 European sites – analysis of new particle formation events
    (München : European Geopyhsical Union, 2010) Manninen, H.E.; Nieminen, T.; Asmi, E.; Gagné, S.; Häkkinen, S.; Lehtipalo, K.; Aalto, P.; Vana, M.; Mirme, A.; Mirme, S.; Hõrrak, U.; Plass-Dülmer, C.; Stange, G.; Kiss, G.; Hoffer, A.; Törő, N.; Moerman, M.; Henzing, B.; de Leeuw, G.; Brinkenberg, M.; Kouvarakis, G.N.; Bougiatioti, A.; Mihalopoulos, N.; O'Dowd, C.; Ceburnis, D.; Arneth, A.; Svenningsson, B.; Swietlicki, E.; Tarozzi, L.; Decesari, S.; Facchini, M.C.; Birmili, W.; Sonntag, A.; Wiedensohler, A.; Boulon, J.; Sellegri, K.; Laj, P.; Gysel, M.; Bukowiecki, N.; Weingartner, E.; Wehrle, G.; Laaksonen, A.; Hamed, A.; Joutsensaari, J.; Petäjä, T.; Kerminen, V.-M.; Kulmala, M.
    We present comprehensive results on continuous atmospheric cluster and particle measurements in the size range ~1–42 nm within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) project. We focused on characterizing the spatial and temporal variation of new particle formation events and relevant particle formation parameters across Europe. Different types of air ion and cluster mobility spectrometers were deployed at 12 field sites across Europe from March 2008 to May 2009. The measurements were conducted in a wide variety of environments, including coastal and continental locations as well as sites at different altitudes (both in the boundary layer and the free troposphere). New particle formation events were detected at all of the 12 field sites during the year-long measurement period. From the data, nucleation and growth rates of newly formed particles were determined for each environment. In a case of parallel ion and neutral cluster measurements, we could also estimate the relative contribution of ion-induced and neutral nucleation to the total particle formation. The formation rates of charged particles at 2 nm accounted for 1–30% of the corresponding total particle formation rates. As a significant new result, we found out that the total particle formation rate varied much more between the different sites than the formation rate of charged particles. This work presents, so far, the most comprehensive effort to experimentally characterize nucleation and growth of atmospheric molecular clusters and nanoparticles at ground-based observation sites on a continental scale.
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    A statistical proxy for sulphuric acid concentration
    (München : European Geopyhsical Union, 2011) Mikkonen, S.; Romakkaniemi, S.; Smith, J.N.; Korhonen, H.; Petäjä, T.; Plass-Duelmer, C.; Boy, M.; McMurry, P.H.; Lehtinen, K.E.J.; Joutsensaari, J.; Hamed, A.; Mauldin III, R.L.; Birmili, W.; Spindler, G.; Arnold, F.; Kulmala, M.; Laaksonen, A.
    Gaseous sulphuric acid is a key precursor for new particle formation in the atmosphere. Previous experimental studies have confirmed a strong correlation between the number concentrations of freshly formed particles and the ambient concentrations of sulphuric acid. This study evaluates a body of experimental gas phase sulphuric acid concentrations, as measured by Chemical Ionization Mass Spectrometry (CIMS) during six intensive measurement campaigns and one long-term observational period. The campaign datasets were measured in Hyytiälä, Finland, in 2003 and 2007, in San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007. The long term data were obtained in Hohenpeissenberg, Germany, during 1998 to 2000. The measured time series were used to construct proximity measures ("proxies") for sulphuric acid concentration by using statistical analysis methods. The objective of this study is to find a proxy for sulfuric acid that is valid in as many different atmospheric environments as possible. Our most accurate and universal formulation of the sulphuric acid concentration proxy uses global solar radiation, SO2 concentration, condensation sink and relative humidity as predictor variables, yielding a correlation measure (R) of 0.87 between observed concentration and the proxy predictions. Interestingly, the role of the condensation sink in the proxy was only minor, since similarly accurate proxies could be constructed with global solar radiation and SO2 concentration alone. This could be attributed to SO2 being an indicator for anthropogenic pollution, including particulate and gaseous emissions which represent sinks for the OH radical that, in turn, is needed for the formation of sulphuric acid.
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    Primary versus secondary contributions to particle number concentrations in the European boundary layer
    (München : European Geopyhsical Union, 2011) Reddington, C.L.; Carslaw, K.S.; Spracklen, D.V.; Frontoso, M.G.; Collins, L.; Merikanto, J.; Minikin, A.; Hamburger, T.; Coe, H.; Kulmala, M.; Aalto, P.; Flentje, H.; Plass-Dülmer, C.; Birmili, W.; Wiedensohler, A.; Wehner, B.; Tuch, T.; Sonntag, A.; O'Dowd, C.D.; Jennings, S.G.; Dupuy, R.; Baltensperger, U.; Weingartner, E.; Hansson, H.-C.; Tunved, P.; Laj, P.; Sellegri, K.; Boulon, J.; Putaud, J.-P.; Gruening, C.; Swietlicki, E.; Roldin, P.; Henzing, J.S.; Moerman, M.; Mihalopoulos, N.; Kouvarakis, G.; Ždímal, V.; Zíková, N.; Marinoni, A.; Bonasoni, P.; Duchi, R.
    It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N50) and >100 nm (N100) were well captured by the model (R2≥0.8) and the normalised mean bias (NMB) was also small (−18% for N50 and −1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R2≥0.8, NMB = −52% and −29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the "effective emission size" and composition of primary particles appropriate for different resolution models.
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    Intercomparison of air ion spectrometers: An evaluation of results in varying conditions
    (München : European Geopyhsical Union, 2011) Gagné, S.; Lehtipalo, K.; Manninen, H.E.; Nieminen, T.; Schobesberger, S.; Franchin, A.; Yli-Juuti, T.; Boulon, J.; Sonntag, A.; Mirme, S.; Mirme, A.; Hõrrak, U.; Petäjä, T.; Asmi, E.; Kulmala, M.
    We evaluated 11 air ion spectrometers from Airel Ltd. after they had spent one year in field measurements as a part of the EUCAARI project: 5 Air Ion Spectrometers (AIS), 5 Neutral cluster and Air Ion Spectrometers (NAIS) and one Airborne NAIS (ANAIS). This is the first time that an ANAIS is evaluated and compared so extensively. The ion spectrometers' mobility and concentration accuracy was evaluated. Their measurements of ambient air were compared between themselves and to reference instruments: a Differential Mobility Particle Sizer (DMPS), a Balanced Scanning Mobility Analyzer (BSMA), and an Ion-DMPS. We report on the simultaneous measurement of a new particle formation (NPF) event by all 11 instruments and the 3 reference instruments. To our knowledge, it is the first time that the size distribution of ions and particles is measured by so many ion spectrometers during a NPF event. The new particle formation rates (~0.2 cm−3 s−1 for ions and ~2 cm−3 s−1 for particles) and growth rates (~25 nm h−1 in the 3–7 nm size range) were calculated for all the instruments. The NAISs and the ANAIS gave higher concentrations and formation rates than the AISs. For example, the AISs agreed with the BSMA within 11 % and 28 % for negative and positive ion concentration respectively, whereas the NAISs agreed within 23 % and 29 %. Finally, based on the results presented here, we give guidelines for data evaluation, when data from different individual ion spectrometers are compared.
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    On the roles of sulphuric acid and low-volatility organic vapours in the initial steps of atmospheric new particle formation
    (München : European Geopyhsical Union, 2010) Paasonen, P.; Nieminen, T.; Asmi, E.; Manninen, H.E.; Petäjä, T.; Plass-Dülmer, C.; Flentje, H.; Birmili, W.; Wiedensohler, A.; Hõrrak, U.; Metzger, A.; Hamed, A.; Laaksonen, A.; Facchini, M.C.; Kerminen, V.-M.; Kulmala, M.
    Sulphuric acid and organic vapours have been identified as the key components in the ubiquitous secondary new particle formation in the atmosphere. In order to assess their relative contribution and spatial variability, we analysed altogether 36 new particle formation events observed at four European measurement sites during EUCAARI campaigns in 2007–2009. We tested models of several different nucleation mechanisms coupling the formation rate of neutral particles (J) with the concentration of sulphuric acid ([H2SO4]) or low-volatility organic vapours ([org]) condensing on sub-4 nm particles, or with a combination of both concentrations. Furthermore, we determined the related nucleation coefficients connecting the neutral nucleation rate J with the vapour concentrations in each mechanism. The main goal of the study was to identify the mechanism of new particle formation and subsequent growth that minimizes the difference between the modelled and measured nucleation rates. At three out of four measurement sites – Hyytiälä (Finland), Melpitz (Germany) and San Pietro Capofiume (Italy) – the nucleation rate was closely connected to squared sulphuric acid concentration, whereas in Hohenpeissenberg (Germany) the low-volatility organic vapours were observed to be dominant. However, the nucleation rate at the sulphuric acid dominant sites could not be described with sulphuric acid concentration and a single value of the nucleation coefficient, as K in J=K [H2SO4]2, but the median coefficients for different sites varied over an order of magnitude. This inter-site variation was substantially smaller when the heteromolecular homogenous nucleation between H2SO4 and organic vapours was assumed to take place in addition to homogenous nucleation of H2SO4 alone, i.e., J=KSA1[H2SO4]2+KSA2[H2SO4][org]. By adding in this equation a term describing homomolecular organic vapour nucleation, Ks3[org]2, equally good results were achieved. In general, our results suggest that organic vapours do play a role, not only in the condensational growth of the particles, but also in the nucleation process, with a site-specific degree.
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    Atmospheric data over a solar cycle: No connection between galactic cosmic rays and new particle formation
    (München : European Geopyhsical Union, 2010) Kulmala, M.; Riipinen, I.; Nieminen, T.; Hulkkonen, M.; Sogacheva, L.; Manninen, H.E.; Paasonen, P.; Petäjä, T.; Dal Maso, M.; Aalto, P.P.; Viljanen, A.; Usoskin, I.; Vainio, R.; Mirme, S.; Mirme, A.; Minikin, A.; Petzold, A.; Hõrrak, U.; Plaß-Dülmer, C.; Birmili, W.; Kerminen, V.-M.
    Aerosol particles affect the Earth's radiative balance by directly scattering and absorbing solar radiation and, indirectly, through their activation into cloud droplets. Both effects are known with considerable uncertainty only, and translate into even bigger uncertainties in future climate predictions. More than a decade ago, variations in galactic cosmic rays were suggested to closely correlate with variations in atmospheric cloud cover and therefore constitute a driving force behind aerosol-cloud-climate interactions. Later, the enhancement of atmospheric aerosol particle formation by ions generated from cosmic rays was proposed as a physical mechanism explaining this correlation. Here, we report unique observations on atmospheric aerosol formation based on measurements at the SMEAR II station, Finland, over a solar cycle (years 1996–2008) that shed new light on these presumed relationships. Our analysis shows that none of the quantities related to aerosol formation correlates with the cosmic ray-induced ionisation intensity (CRII). We also examined the contribution of ions to new particle formation on the basis of novel ground-based and airborne observations. A consistent result is that ion-induced formation contributes typically significantly less than 10% to the number of new particles, which would explain the missing correlation between CRII and aerosol formation. Our main conclusion is that galactic cosmic rays appear to play a minor role for atmospheric aerosol formation events, and so for the connected aerosol-climate effects as well.
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    Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation
    (München : European Geopyhsical Union, 2010) Spracklen, D.V.; Carslaw, K.S.; Merikanto, J.; Mann, G.W.; Reddington, C.L.; Pickering, S.; Ogren, J.A.; Andrews, E.; Baltensperger, U.; Weingartner, E.; Boy, M.; Kulmala, M.; Laakso, L.; Lihavainen, H.; Kivekäs, N.; Komppula, M.; Mihalopoulos, N.; Kouvarakis, G.; Jennings, S.G.; O'Dowd, C.; Birmili, W.; Wiedensohler, A.; Weller, R.; Gras, J.; Laj, P.; Sellegri, K.; Bonn, B.; Krejci, R.; Laaksonen, A.; Hamed, A.; Minikin, A.; Harrison, R.M.; Talbot, R.; Sun, J.
    We synthesised observations of total particle number (CN) concentration from 36 sites around the world. We found that annual mean CN concentrations are typically 300–2000 cm−3 in the marine boundary layer and free troposphere (FT) and 1000–10 000 cm−3 in the continental boundary layer (BL). Many sites exhibit pronounced seasonality with summer time concentrations a factor of 2–10 greater than wintertime concentrations. We used these CN observations to evaluate primary and secondary sources of particle number in a global aerosol microphysics model. We found that emissions of primary particles can reasonably reproduce the spatial pattern of observed CN concentration (R2=0.46) but fail to explain the observed seasonal cycle (R2=0.1). The modeled CN concentration in the FT was biased low (normalised mean bias, NMB=−88%) unless a secondary source of particles was included, for example from binary homogeneous nucleation of sulfuric acid and water (NMB=−25%). Simulated CN concentrations in the continental BL were also biased low (NMB=−74%) unless the number emission of anthropogenic primary particles was increased or a mechanism that results in particle formation in the BL was included. We ran a number of simulations where we included an empirical BL nucleation mechanism either using the activation-type mechanism (nucleation rate, J, proportional to gas-phase sulfuric acid concentration to the power one) or kinetic-type mechanism (J proportional to sulfuric acid to the power two) with a range of nucleation coefficients. We found that the seasonal CN cycle observed at continental BL sites was better simulated by BL particle formation (R2=0.3) than by increasing the number emission from primary anthropogenic sources (R2=0.18). The nucleation constants that resulted in best overall match between model and observed CN concentrations were consistent with values derived in previous studies from detailed case studies at individual sites. In our model, kinetic and activation-type nucleation parameterizations gave similar agreement with observed monthly mean CN concentrations.