Veli-Matti Kerminen

University of Helsinki, Helsinki, Southern Finland Province, Finland

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Publications (119)363.99 Total impact

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    ABSTRACT: Nitrous acid (HONO) plays a key role in atmospheric chemistry via influencing the budget of hydroxyl radical (OH). In this study, a two-month measurement period of HONO and related quantities were analyzed during a biomass burning season in 2012 at a suburban site in the western Yangtze River delta, eastern China. An overall high HONO concentration with the mean value of 1.1 ppbv was observed. During biomass burning (BB) periods, both HONO concentration and HONO / NO2 ratio were enhanced significantly compared with non-biomass burning periods. A correlation analysis showed that the HONO concentration was not associated potassium (a tracer of BB) in BB plumes, but showed a high correlation with the NO2 concentration, suggesting a principle role of secondary production rather than direct emissions in elevated HONO concentrations. A further analysis based on comparing the surface area at similar PM levels and HONO / NO2 ratios at similar surface area levels suggested larger specific surface areas and higher NO2 conversion efficiencies of BB aerosols. A mixed plume of BB and anthropogenic fossil fuel (FF) emissions was observed on 10 June with even higher HONO concentrations and HONO / NO2 ratios. The strong HONO production potential (high HONO / NO2 to PM2.5 ratio) was accompanied with a high sulfate concentration in this plume, suggesting a promotion of mixed aerosols to HONO formation. In summary, our study suggests an important role of BB in atmospheric oxidation capacity by affecting the HONO budget. This can be especially important in eastern China, where agricultural burning plumes are inevitably mixed with urban pollutions.
    02/2014; 14(6).
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    ABSTRACT: Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth's radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours, but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies. We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere-aerosol-climate feedback mechanisms, and the air quality and climate effects of biogenic emissions generally.
    Nature 02/2014; 506(7489):476-9. · 38.60 Impact Factor
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    ABSTRACT: We used a monoterpene volume mixing ratio dataset measured from 12 June 2006 to 24 September 2007 and from 1 June 2008 to 3 March 2009 at the SMEAR II station to quantify the magnitude of anthropogenic monoterpene emissions aside from biogenic origins, to examine the anthropogenic sources, and to look at other associated pollutants. We discuss the relations between increased monoterpene mixing ratios and particle concentrations. We also characterize chemical properties of aerosol particles during two monoterpene pollution episodes in case studies. Out of 580 days analyzed, anthropogenic monoterpene pollution episodes were found on 341 (58.8%) days. The average monoterpene mixing ratio increased from 0.19 to 0.26 ppbv due to the presence of anthropogenic monoterpenes, which is equal to an increase of 36.8%. The observed anthropogenic monoterpenes were mostly from the Korkeakoski sawmill. Other gas pollutants might occasionally be emitted during the episodes, but did not show clear association with anthropogenic monoterpenes. Aerosol particle concentrations substantially increased during episodes, and monoterpene mixing ratios showed strong connections with Aitken mode particles both in number and volume concentrations. Particles associated with monoterpene episodes reached a CCN (cloud concentration nucleus) size. The chemical characterizations of aerosol particles in case studies show that the increase in aerosol particle mass was mainly from secondary organic aerosol.
    Boreal Environment Research 08/2013; 16:288-303. · 1.75 Impact Factor
  • Veli-Matti Kerminen, Kimmo Teinilä, Risto Hillamo
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    ABSTRACT: The chemistry of sea-salt particles was investigated in summer Antarctica at a site about 150 km from the open ocean. Aerosol samples were collected using a low-pressure impactor which divides particles into 12 size fractions over the aerodynamic particle diameter range 0.045–15 μm. Measured sea-salt particle concentrations were clearly lower than concentrations typically observed at coastal Antarctica. The mass size distribution of sea salt was tri-modal with a submicron mode centering at 0.5–1 μm and two supermicron modes centering slightly below 2 μm and somewhere between 2 and 10 μm, respectively. On average more than 70% of sea salt was found in the supermicron size range, the lower supermicron mode being usually the dominant. Sea-salt particles displayed a large chloride loss with respect to the bulk sea water. The average loss percentage was more than 90% for submicron particles and decreased to about 50% for particles larger than 3 μm in diameter. The primary ions causing the chloride loss were sulfate, nitrate, and methanesulfonate (MSA). The aerosol MSA to non-sea-salt sulfate weight ratio seemed to have been increased by the presence of sea-salt particles. Particulate nitrate was associated strongly with sea salt, the most likely formation pathway being the interaction of nitric acid or some other gaseous nitrogen compounds with these particles in the Antarctic atmosphere.
    Atmospheric Environment 07/2013; · 3.11 Impact Factor
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    ABSTRACT: Atmospheric fine particle black carbon (BC) was measured close to downtown of Helsinki, during November 1996–June 1997. The average BC concentrations were 1.5 μg m−3 for working days, 1.2 μg m−3 for Saturdays, and about 1 μg m−3 for Sundays and public holidays. The overall average BC concentration was equal to 1.38 μg m−3 and its average contribution to fine particle mass equal to 19%. On working days BC concentrations showed a clear diurnal variation with the highest hourly average values occurring during the morning (2.7 μg m−3) and evening (1.9 μg m−3) rush hours. Contribution of the long-range transport to the BC was estimated to be on average about 0.4 μg m−3, which is believed to represent the average regional background over southern Finland. However, this transport was very different from different geographical regions: from the densely populated areas of East- and Central-Europe it was about 0.8 μg m−3, while in northerly and northwesterly air masses it was only about 0.15 μg m−3. Local traffic was by far the most important local BC source contributing about 63, 54 and 44% on working days, Saturdays and Sundays, respectively. Other local sources were largely masked by the traffic and their contribution was estimated roughly to be of the order of 10%. The rest of BC was attributed to long-range transport.
    Atmospheric Environment 07/2013; 34(9):1497–1506. · 3.11 Impact Factor
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    ABSTRACT: Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. Apart from black carbon aerosol, aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases. In the future, tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect. Natural aerosols, too, might affect future warming. Here we analyse long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapours in continental mid- and high-latitude environments. We use measurements of particle number size distribution together with boundary layer heights derived from reanalysis data to show that the boundary layer burden of cloud condensation nuclei increases exponentially with temperature. Our results confirm a negative feedback mechanism between the continental biosphere, aerosols and climate: aerosol cooling effects are strengthened by rising biogenic organic vapour emissions in response to warming, which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei. This natural growth mechanism produces roughly 50% of particles at the size of cloud condensation nuclei across Europe. We conclude that biosphere-atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls, both on climate and air quality.
    Nature Geoscience 06/2013; 6(6):438-442. · 11.67 Impact Factor
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    ABSTRACT: Measured aerosol size distributions from three measurement stations and modeled air mass trajectory data were combined to study aerosol dynamics in the boreal forest zone in Northern Scandinavia. Three approaches were used: investigation of new particle formation events, analysis of air masses arriving from ocean to continent, and study of changes in the aerosol size distributions when air masses travel from one measurement site to another. The statistical analysis of air masses travelling either from the Atlantic Ocean to measurement sites or from one site to another showed that on average the condensational growth was present during the summer season, and it was not restricted only to the days when evident new particle formation was observed. The rate of this average apparent growth of particle diameter was 3-7 times smaller than the growth rate of nucleation mode particles during the new particle formation events.
    05/2013;
  • Li Liao, Veli-Matti Kerminen, Markku Kulmala, Miikka Dal Maso
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    ABSTRACT: Long-term atmospheric dataset including aerosol field measurement and back trajectories was used to investigate the impact of temperature to the production of secondary organic aerosols from biogenic monoterpene emissions among boreal forest area. Temperature was equally divided into five bins ranging from 0 to 20 °C in this study, and all parameters were classified into the corresponding temperature bins. Own results suggest that increase in temperature causing an increase in MT emission will not necessarily result in the increase of secondary organic aerosol production. Therefore, to predict the aerosol production potential in the future with rising temperature, a simple extrapolation cannot be applied between the total aerosol production and temperature. In addition, the climatic feedback due to the increase in aerosol production to buffer the warming over boreal forest area may be less significant as previously expected.
    05/2013;
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    ABSTRACT: Ambient aerosol CCN and hygroscopic properties were measured with a size-segregated CCNc in a boreal environment of Southern Finland at the SMEAR II station since February 2009. The overall median critical diameter Dc for CCN activation is reported at 75 nm, exhibiting a clear maximum in February and a minimum in July. The overall median aerosol hygroscopicity parameter κ is reported at 0.22, indicating that ambient aerosol in Hyytiälä is less hygroscopic than the global continental and European continental averages. It is, however, more hygroscopic than ambient aerosol in an Amazon rainforest, the European high alpine site or the mountainous forest. The low hygroscopicity in the boreal forest is attributed to a large organic fraction present in the aerosol mass comparative to other locations within Europe. Aerosol mass spectrometer (AMS) data were used to demonstrate a positive correlation between κ and sulphate and ammonia, and a negative correlation between κ and the organic mass fraction. No distinguishable effect of atmospheric new particle formation (NPF) on Dc and κ was observed. Ambient aerosol was found to be internally mixed in the summer, and externally mixed during the rest of the year.
    05/2013;
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    ABSTRACT: Atmospheric new particle formation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2 nm size range. We have recently shown that at a lower-troposphere site (Hyytiälä, Southern Finland) with abundant biogenic emissions and moderate anthropogenic influence, based on comprehensive observations of atmospheric clusters in the size range of 1-2 nm mobility diameter, there are significant differences between neutral and charged cluster properties. The differences are with respect to cluster size and chemical composition, and whether the observations were made in background conditions or during periods of active aerosol formation. According to our results, sub-2 nm clusters were always present and cluster concentrations were dominated by neutral ones in all sizes and almost all the time, indicating that cluster formation and their subsequent growth i.e. atmospheric aerosol formation were dominated by neutral pathways.
    05/2013;
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    ABSTRACT: A comprehensive suite of chemical ionization mass spectrometers (CIMS) were deployed for chamber studies of monoterpene oxidation. The CIMS instruments were able to detect several different groups of compounds ranging from volatile to practically non-volatile. The compound groups showed very different behavior and correlations with aerosol number and mass. Results suggest that major gas phase contributors are not considered in current models.
    05/2013;
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    ABSTRACT: Sulfur emissions from the Kola Peninsula smelter industry have been decreasing over the past two decades. We investigated the effect of this to new particle formation at SMEAR I station in Eastern Lapland, Finland, using long-term measurements of trace gases and aerosol size distributions. We show that the number of events per year has decreased and can be linked with the decreasing sulfur emissions from Kola.
    05/2013;
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    ABSTRACT: The use of the first nucleation theorem on atmospheric particle formation events is studied under simulated conditions trying to represent the varying conditions of a typical field campaign. The aerosol dynamics model UHMA is used to produce synthesized DMPS data, which are analyzed using typical techniques to obtain particle formation rates, and with back calculation, nucleation rates. The results show that under conditions that cause time and/or size dependent growth rates, standard techniques can result in serious errors when estimating nucleation rates. In addition, the validity of obtaining information about nucleation mechanisms by plotting data at different conditions into a single log J vs. log [H2SO4] plot to deduce mechanisms based on slope values, seems questionable.
    05/2013;
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    ABSTRACT: The role of ion-ion recombination in new particle formation is still unclear. In this work, we present a new method to estimate the size distribution of recombination products from atmospheric measurements. By applying our method to size distributions of charged and neutral clusters measured in Hyytiälä, Finland, we show that only a minor fraction of all sub-2nm neutral clusters originate from ion-ion recombination in boreal forest conditions.
    05/2013;
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    ABSTRACT: Boreal forests are a substantial source of greenhouse gases, biogenic volatile organic compounds (BVOCs) and natural aerosols, the critical atmospheric components related to climate change processes. A large fraction of boreal forests of the world is situated in Siberian region. Representative measurements of carbon dioxide (CO2) and methane (CH4) concentrations, BVOC emissions and aerosols production from Siberian are of special importance when estimating global budgets of climate change relevant factors. The scope of a new concept of the Pan Eurasian Experiment (PEEX) is to set up a process for planning of a large-scale, long-term, coordinated observations and modeling experiment in the Pan Eurasian region, especially to cover ground base, airborne and satellite observations together with global and regional models to find out different forcing and feedback mechanisms in the changing climate. University of Helsinki together with Finnish Meteorological institute are organizing the Pan-Eurasian Experiment and to gather all the European and Russian key players in the field of climate and Earth system science to plan the future research activities in the Pan-Eurasian region. In the European scale PEEX is part of the JPI Climate Fast Track Activity 1.3. "Changing cryosphere in the climate system - from observations to climate modeling". PEEX research topics are closely related the NordForsk's Top Research Initiative CRAICC - Cryosphere - atmosphere interaction in the changing Arctic climate. PEEX is also a central part of the ongoing the Finnish Cultural Foundation - Earth System modeling Working Group activity (2012-2013). PEEX scientific aims and future actions to develop Pan Eurasian research infrastructure can be linked to several EC and ESA funded activities aiming to develop next generation research infrastructures and data products: EU-FP7-ACTRIS-I3-project (Aerosols, Clouds, and Trace gases Research InfraStructure Network-project 2011-2015); ICOS a research infrastructure to decipher the greenhouse gas balance of Europe and adjacent regions; EU-FP-7 e-infra ENVRI "Common Operations of Environmental Research Infrastructures" project. New Siberian research infrastructure and data products should be developed in line with the ACTRIS, ICOS and ENVRI approaches. Furthermore, The Pan-Eurasian Experiment will be supported iLEAPS (Integrated Land Ecosystem - Atmosphere Processes Study) bringing the PEEX under umbrella of the International Geosphere-Biosphere Programme (IGBP). The permafrost regions and boreal forests of the Pan Eurasian area can be identified as a hot spot of climate change research in a global scale. PEEX experiment can be considered as a crucial part of the strategic aims of several international and national roadmaps for climate change research and the development of next-generation research infrastructures. In this work we present the overall Science Plan for the Pan-Eurasian Experiment and report on the progress made in two PEEX science workshops organized in Helsinki in October 2012 and in Moscow in February 2013.
    04/2013;
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    ABSTRACT: Aerosol emissions from international shipping are known to cause detrimental health effects on people mainly via increased lung cancer and cardiopulmonary diseases. On the other hand, the aerosol particles from the ship emissions modify the properties of clouds and are believed to have a significant cooling effect on the global climate. In recent years, aerosol emissions from shipping have been more strictly regulated in order to improve air quality and thus decrease the mortality due to ship emissions. Decreasing the aerosol emissions from shipping is projected to decrease their cooling effect, which would intensify the global warming even further. In this study, we use a global aerosol-climate model ECHAM5.5-HAM2 to test if continental air quality can be improved while still retaining the cooling effect from shipping. The model explicitly resolves emissions of aerosols and their pre-cursor gases. The model also calculates the interaction between aerosol particles and clouds, and can thus predict the changes in cloud properties due to aerosol emissions. We design and simulate a scenario where ship fuel sulfur content is strictly limited to 0.1% near all coastal regions, but doubled in the open oceans from the current global mean value of 2.7% (geo-ships). This scenario is compared to three other simulations: 1) No shipping emissions at all (no-ships), 2) present-day shipping emissions (std-ships) and 3) a future scenario where sulfur content is limited to 0.1% in the coastal zones and to 0.5% in the open ocean (future-ships). Global mean radiative flux perturbation (RFP) in std-ships compared to no-ships is calculated to be -0.4 W m-2, which is in the range of previous estimates for present-day shipping emissions. In the geo-ships simulation the corresponding global mean RFP is roughly equal, but RFP is spatially distributed more on the open oceans, as expected. In future-ships the decreased aerosol emissions provide weaker cooling effect of only -0.1 W m-2. In order to assess the health effects of different emission scenarios we diagnose PM2.5 concentrations from each simulation. Then, we use PM2.5 concentrations and C-R functions to calculate the changes in mortality related to lung cancer and cardiopulmonary diseases. Our preliminary analysis suggests that mortality in geo-ships would be lower than in std-ships. Strict sulfur content limits also in the open oceans (future-ships) would decrease the mortality even more. Idea of deliberately increasing fuel sulfur content in order to produce a cooling effect can be classified as one form of solar radiation management (SRM). There are several scientific, ethical and political problems associated with SRM technologies and a number of them would be applicable to the idea we present here. For example, there would be a conflict between the existing international treaties and the proposed increase in ship fuel sulfur content. However, our study is increasing the knowledge of air quality and climate trade-offs related to ship emission controls. If the cooling effect of ship traffic is considered too precious to lose, there might be ways to preserve it, while still notably increasing the continental air quality.
    04/2013;
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    ABSTRACT: Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation--more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.
    Science 02/2013; 339(6122):943-6. · 31.20 Impact Factor
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    ABSTRACT: While laboratory and field measurements indicate that atmospheric nucleation most likely initiates with the formation clusters of ~1.0–1.5 nm diameter, most atmospheric observations to date measure only particles larger than 3–10 nm in size. Because of this, several analytical formulations have been developed to estimate the real nucleation rate at the initial cluster size from the “apparent” nucleation rate at the measured larger sizes. All previous analytical formulations have assumed a constant particle growth rate below the instrument detection limit; however, recent atmospheric measurements have shown that the growth rate is often strongly size dependent. This study presents new analytical equations to connect the real and “apparent” nucleation rates in two special cases, i.e. when the cluster growth rate follows a 1) linear, or 2) power-law dependence on the particle size. The accuracy of these equations is tested with an ensemble of numerical model simulations of new particle formation events. Both new formulations are capable of estimating the nucleation rate at 1.5 nm fairly accurately (largest normalised mean bias −1.4% for the power-law and −23% for the linear events). We find, however, that the power law formulation gives a more accurate estimate of the nucleation rate even for a majority of the events with linear growth rate dependence. Further analysis indicates that previous studies of atmospheric nucleation events, which have assumed a constant cluster growth rate, may have clearly underestimated the real nucleation rate.
    Journal of Aerosol Science 01/2013; · 2.69 Impact Factor
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    ABSTRACT: The formation of new atmospheric aerosol particles and their subsequent growth have been observed frequently at various locations all over the world. The atmospheric nucleation rate (or formation rate) and growth rate (GR) are key parameters to characterize the phenomenon. Recent progress in measurement techniques enables us to measure atmospheric nucleation at the size (mobility diameter) of 1.5 (±0.4) nm. The detection limit has decreased from 3 to 1 nm within the past 10 years. In this protocol, we describe the procedures for identifying new-particle-formation (NPF) events, and for determining the nucleation, formation and growth rates during such events under atmospheric conditions. We describe the present instrumentation, best practices and other tools used to investigate atmospheric nucleation and NPF at a certain mobility diameter (1.5, 2.0 or 3.0 nm). The key instruments comprise devices capable of measuring the number concentration of the formed nanoparticles and their size, such as a suite of modern condensation particle counters (CPCs) and air ion spectrometers, and devices for characterizing the pre-existing particle number concentration distribution, such as a differential mobility particle sizer (DMPS). We also discuss the reliability of the methods used and requirements for proper measurements and data analysis. The time scale for realizing this procedure is 1 year.
    Nature Protocol 08/2012; 7(9):1651-67. · 8.36 Impact Factor
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    ABSTRACT: In this study the characteristics, sources and water-solubility of submicron organic aerosol (OA) were investigated in Helsinki, Finland. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used to determine the submicron non-refractory aerosol components nitrate, sulfate, ammonium, chloride and organics between April 9 and May 8, 2009. The concentrations of the major water-soluble ions and water-soluble organic carbon (WSOC) were measured by a particle-into-liquid sampler (PILS) combined with a total organic carbon (TOC) analyzer and two ion chromatographs (IC) between April 25 and May 28, 2009. Parallel measurements of the submicron particulate matter (PM1), organic carbon (OC), black carbon (BC), meteorological quantities and trace gases were used to complement and validate the AMS and PILS-TOC-IC data. Sources or atmospheric processes affecting the organic aerosol were investigated by applying the Positive Matrix Factorization (PMF) analysis to the high-resolution mass spectra of the HR-ToF-AMS organics. All together seven factors were needed to describe the variation in the obtained dataset. The factors consisted of two different types of low-volatility oxygenated OA (LV-OOA), local and long-range-transported (LRT) biomass burning OA (BBOA), semi-volatile OA (SV-OOA), hydrocarbon-like OA (HOA), and one local source (coffee roastery). These factors were interpretable and could be connected to specific sources or chemical characteristics (biomass burning, traffic, biogenic emissions, oxidized long-range-transported aerosols, marine-processed aerosols and nearby industrial activity) of ambient aerosols. In order to study the organic fraction and PMF factors further, the elemental ratios OM:OC, O:C, H:C and N:C were calculated. The value of the OM:OC ratio varied between 1.4 and 2.1. A high OM:OC ratio (1.5–2.1) was observed for the highly-oxidized and water-soluble fraction, whereas this ratio was clearly lower (1.2–1.4) for local and fresh sources such as traffic. Two different factors representing local and long-range-transported biomass burning were observed. Local biomass burning emissions had a lower OM:OC ratio, indicating that this factor was less aged and had a different source area compared with the LRT BBOA. The water-solubilities of the OA factors were studied by investigating the correlation between these factors and WSOC and by reconstructing the concentration of water-soluble particulate organic matter (WSPOM) from the OA factors. The reconstructed WSPOM had a good correlation with the measured concentration of WSPOM.
    Journal of Aerosol Science 01/2012; · 2.69 Impact Factor

Publication Stats

3k Citations
363.99 Total Impact Points

Institutions

  • 2000–2014
    • University of Helsinki
      • • Department of Physics
      • • Department of Physical Sciences
      Helsinki, Southern Finland Province, Finland
  • 1997–2013
    • Research Institute of the Finnish Economy, Finland, Helsinki
      Helsinki, Southern Finland Province, Finland
  • 1994–2012
    • Finnish Meteorological Institute
      • Air Quality Research
      Helsinki, Southern Finland Province, Finland
  • 2008
    • National Center for Atmospheric Research
      • Division of Atmospheric Chemistry
      Boulder, CO, United States
    • Forschungszentrum Jülich
      Jülich, North Rhine-Westphalia, Germany
  • 1994–1998
    • University of Delaware
      • Department of Mechanical Engineering
      Delaware, United States