Ambient air ion size distributions have been measured continuously at the Finnish boreal forest site in Hyytiälä since spring 2003. In general, these measurements show a maximum of air ions below 1.0 nm in diameter. But this physical characterization does not provide any information about the ion's chemical composition, which is one key question regarding the explanation of nucleation events observed. In this study we propose a link of the observed maximum of negative air ions between 0.56 and 0.75 nm to the socalled stabilised Criegee biradical, formed in the reaction of biogenic sesquiterpenes with ozone and predominantly destroyed by its reaction with ambient water vapour. Calculations of the electron and proton affinities of 120 kJ mol^-1 (1.24eV) and of 960 kJ mol^-1 support this link. Other possible candidates such as sulphuric acid derived clusters are unable to explain the observations made. By using this approach, we are able to calculate the ambient concentration of sesquiterpenes at the air ion instrument inlet with a high time resolution on the daily and seasonal scale. The estimated concentration is found to reveal the same seasonal pattern as emission measurements conducted at shoot level. As expected for biogenic VOCs, the concentration is obtained highest during summer (maximum values of about 100pptv) and smallest during winter (minimum less than 1 pptv). Because of the sesquiterpenes high reactivity and its low ambient concentrations, this approach can be a first step in understanding their emission and their impact on atmospheric chemistry in more detail. The findings presented are highly relevant for emission budgets too, since boreal forests are extended over large areas of the globe.

B. Bonn;A. Hirsikko;H. Hakola;T. Kurtén;L. Laakso;M. Boy;M. Dal Maso;J. M. Mäkelä;Markku Kulmala

Atmospheric Chemistry and Physics

2007

Miikka Dal Maso;Hanna Vehkamäki;Kari E.J. Lehtinen;Markku Kulmala

Journal of Aerosol Science

2004-7

REMO-HAM is a new regional aerosol-climate model. It is based on the REMO regional climate model and includes most of the major aerosol processes. The structure for aerosol is similar to the global aerosol-climate model ECHAM5-HAM, for example the aerosol module HAM is coupled with a two-moment stratiform cloud scheme. On the other hand, REMO-HAM does not include an online coupled aerosol-radiation nor a secondary organic aerosol module. In this work, we evaluate the model and compare the results against ECHAM5-HAM and measurements. Four different measurement sites were chosen for the comparison of total number concentrations, size distributions and gas phase sulfur dioxide concentrations: Hyytiälä in Finland, Melpitz in Germany, Mace Head in Ireland and Jungfraujoch in Switzerland. REMO-HAM is run with two different resolutions: 50 × 50 km₂ and 10 × 10 km₂. Based on our simulations, REMO-HAM is in reasonable agreement with the measured values. The differences in the total number concentrations between REMO-HAM and ECHAM5-HAM can be mainly explained by the difference in the nucleation mode. Since we did not use activation nor kinetic nucleation for the boundary layer, the total number concentrations are somewhat underestimated. From the meteorological point of view, REMO-HAM represents the precipitation fields and 2 m temperature profile very well compared to measurement. Overall, we show that REMO-HAM is a functional aerosol-climate model, which will be used in further studies.

J. P. Pietik̈ainen;D. O'Donnell;C. Teichmann;U. Karstens;S. Pfeifer;J. Kazil;R. Podzun;S. Fiedler;H. Kokkola;W. Birmili;C. O'Dowd;U. Baltensperger;E. Weingartner;R. Gehrig;G. Spindler;Markku Kulmala;J. Feichter;D. Jacob;A. Laaksonen

Geoscientific Model Development

2012

A molecular approach to heterogeneous nucleation has been developed. The expressions for the equilibrium cluster distribution, the reversible work of the cluster formation, and the nucleation rate have been derived. Two separate statements for the work of formation were formulated. If the equilibrium cluster distribution is normalized on the monomer concentration near the substrate surface, the reversible work of formation is expressed by Δ GhetI = (Fnhet - Fnhom) - (F1het - F1hom) +Δ Ghom where Fnhet and Fnhom are the Helmholtz free energies of a cluster interacting with a substrate and a cluster not interacting with the substrate, respectively. If the equilibrium cluster distribution is normalized on the monomer concentration far from the substrate surface, the work of cluster formation is given by Δ GhetII = (Fnhet - Fnhom) +Δ Ghom. The former expression corresponds to the approach of the classical heterogeneous nucleation theory. The cluster partition function appears to be dependent on the location of a virtual plane, which separates the volume, where the interaction of the clusters with the substrate is effective from the one where interaction is negligible. Our Monte Carlo simulations have shown that the dependence is rather weak and thus the location of the plane is not very important. According to the simulations the variation of the plane position in the range from 20 to 50 Å does not lead to a considerable change of the heterogeneous nucleation rate.

Evgeni Zapadinsky;Antti Lauri;Markku Kulmala

Journal of Chemical Physics

2005-3-15

Heikki Lihavainen;Yrjö Viisanen;Markku Kulmala

Journal of Chemical Physics

2008

This study presents an evaluation and modeling exercise of the size fractionated aerosol particle number concentrations measured nearby a major road in Helsinki during 23 August-19 September 2003 and 14 January-11 February 2004. The available information also included electronic traffic counts, on-site meteorological measurements, and urban background particle number size distribution measurement. The ultrafine particle (UFP, diameter<100 nm) number concentrations at the roadside site were approximately an order of magnitude higher than those at the urban background site during daytime and downwind conditions. Both the modal structure analysis of the particle number size distributions and the statistical correlation between the traffic density and the UFP number concentrations indicate that the UFP were evidently from traffic related emissions. The modeling exercise included the evolution of the particle number size distribution nearby the road during downwind conditions. The model simulation results revealed that the evaluation of the emission factors of aerosol particles might not be valid for the same site during different time.

T. Hussein;J. Kukkonen;H. Korhonen;M. Pohjola;L. Krjola;D. Wraith;J. Härkönen;K. Teinilä;I. K. Koponen;A. Karppinen;R. Hillamo;Markku Kulmala

Atmospheric Chemistry and Physics

2007

Aerosol optical properties (AOPs) describe the ability of aerosols to scatter and absorb radiation at different wavelengths. Since aerosol particles interact with the sun's radiation, they impact the climate. Our study focuses on the long-term trends and seasonal variations of different AOPs measured at a rural boreal forest site in northern Europe. To explain the observed variations in the AOPs, we also analyzed changes in the aerosol size distribution. AOPs of particles smaller than 10&thinsp;<span classCombining double low line"inline-formula">μ</span>m (PM<span classCombining double low line"inline-formula">10</span>) and 1&thinsp;<span classCombining double low line"inline-formula">μ</span>m (PM<span classCombining double low line"inline-formula">1</span>) have been measured at SMEAR II, in southern Finland, since 2006 and 2010, respectively. For PM<span classCombining double low line"inline-formula">10</span> particles, the median values of the scattering and absorption coefficients, single-scattering albedo, and backscatter fraction at <span classCombining double low line"inline-formula">λCombining double low line550</span>&thinsp;nm were 9.8 Mm<span classCombining double low line"inline-formula">-1</span>, 1.3&thinsp;Mm<span classCombining double low line"inline-formula">-1</span>, 0.88, and 0.14. The median values of scattering and absorption Ångström exponents at the wavelength ranges 450-700 and 370-950&thinsp;nm were 1.88 and 0.99, respectively. We found statistically significant trends for the PM<span classCombining double low line"inline-formula">10</span> scattering and absorption coefficients, single-scattering albedo, and backscatter fraction, and the slopes of these trends were <span classCombining double low line"inline-formula">-0.32</span>&thinsp;Mm<span classCombining double low line"inline-formula">-1</span>, <span classCombining double low line"inline-formula">-0.086</span>&thinsp;Mm<span classCombining double low line"inline-formula">-1</span>, <span classCombining double low line"inline-formula"><math xmlnsCombining double low line"http://www.w3.org/1998/Math/MathML" idCombining double low line"M14" displayCombining double low line"inline" overflowCombining double low line"scroll" dspmathCombining double low line"mathml"><mrow><mn mathvariantCombining double low line"normal">2.2</mn><mo>×</mo><msup><mn mathvariantCombining double low line"normal">10</mn><mrow><mo>-</mo><mn mathvariantCombining double low line"normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svgCombining double low line"http://www.w3.org/2000/svg" widthCombining double low line"51pt" heightCombining double low line"14pt" classCombining double low line"svg-formula" dspmathCombining double low line"mathimg" md5hashCombining double low line"2bc215b5413edc794fada3c2c45684de"><svg:image xmlns:xlinkCombining double low line"http://www.w3.org/1999/xlink" xlink:hrefCombining double low line"acp-19-11363-2019-ie00001.svg" widthCombining double low line"51pt" heightCombining double low line"14pt" srcCombining double low line"acp-19-11363-2019-ie00001.png"/></svg:svg></span></span>, and <span classCombining double low line"inline-formula"><math xmlnsCombining double low line"http://www.w3.org/1998/Math/MathML" idCombining double low line"M15" displayCombining double low line"inline" overflowCombining double low line"scroll" dspmathCombining double low line"mathml"><mrow><mn mathvariantCombining double low line"normal">1.3</mn><mo>×</mo><msup><mn mathvariantCombining double low line"normal">10</mn><mrow><mo>-</mo><mn mathvariantCombining double low line"normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svgCombining double low line"http://www.w3.org/2000/svg" widthCombining double low line"51pt" heightCombining double low line"14pt" classCombining double low line"svg-formula" dspmathCombining double low line"mathimg" md5hashCombining double low line"04a27347f61a1f99a51c2eac11d4e503"><svg:image xmlns:xlinkCombining double low line"http://www.w3.org/1999/xlink" xlink:hrefCombining double low line"acp-19-11363-2019-ie00002.svg" widthCombining double low line"51pt" heightCombining double low line"14pt" srcCombining double low line"acp-19-11363-2019-ie00002.png"/></svg:svg></span></span> per year. The tendency for the extensive AOPs to decrease correlated well with the decrease in aerosol number and volume concentrations. The tendency for the backscattering fraction and single-scattering albedo to increase indicates that the aerosol size distribution consists of fewer larger particles and that aerosols absorb less light than at the beginning of the measurements. The trends of the single-scattering albedo and backscattering fraction influenced the aerosol radiative forcing efficiency, indicating that the aerosol particles are scattering the radiation more effectively back into space.

Krista Luoma;Aki Virkkula;Pasi Aalto;Tuukka Petäjä;Markku Kulmala

Atmospheric Chemistry and Physics

2019-9-9

Particles formed in the automobile exhaust might form a significant fraction of fine particles in urban air. We have developed a model and produced parametrizations for predicting the particle formation rate at exhaust conditions. We studied the formation in the mixture of water and sulfuric acid vapors and at temperatures between 300 and 400 K. A thermodynamically consistent version of the classical binary homogeneous nucleation model was used. The needed thermodynamical input data (vapor pressures, chemical activities, surface tensions, densities) are carefully investigated and utilized in thermodynamically consistent way. The obtained nucleation rates are parametrized in order to be able to use this nucleation model in aerosol dynamic models, exhaust models, or other process models. The parametrization reduces computational time at least by a factor of 500.

H. Vehkamäki;Markku Kulmala;K. E.J. Lehtinen;M. Noppel

Environmental Science & Technology

2003-8-1

Missing data has been a challenge in air quality measurement. In this study, we develop an input-adaptive proxy, which selects input variables of other air quality variables based on their correlation coefficients with the output variable. The proxy uses ordinary least squares regression model with robust optimization and limits the input variables to a maximum of three to avoid overfitting. The adaptive proxy learns from the data set and generates the best model evaluated by adjusted coefficient of determination (adjR²). In case of missing data in the input variables, the proposed adaptive proxy then uses the second-best model until all the missing data gaps are filled up. We estimated black carbon (BC) concentration by using the input-adaptive proxy in two sites in Helsinki, which respectively represent street canyon and urban background scenario, as a case studyAccumulation mode, traffic counts, nitrogen dioxide and lung deposited surface area are found as input variables in models with the top rank. In contrast to traditional proxy, which gives 20–80% of data, the input-adaptive proxy manages to give full continuous BC estimation. The newly developed adaptive proxy also gives generally accurate BC (street canyon: adjR² = 0.86–0.94; urban backgroundadjR² = 0.74–0.91) depending on different seasons and day of the week. Due to its flexibility and reliability, the adaptive proxy can be further extend to estimate other air quality parameters. It can also act as an air quality virtual sensor in support with on-site measurements in the future.

Pak Lun Fung;Martha A. Zaidan;Salla Sillanpää;Anu Kousa;Jarkko V. Niemi;Hilkka Timonen;Joel Kuula;Erkka Saukko;Krista Luoma;Tuukka Petäjä;Sasu Tarkoma;Markku Kulmala;Tareq Hussein

Sensors

2020-1-1

The effect of displacement flow on the distribution of aerosol concentration was investigated in an industrial hall. According to the displacement ventilation principle, vertical upflow is accomplished by introducing fresh air, cooler than room air, into the occupied zone near floor level. The fresh air is introduced from low-velocity devices and heated by warm processes. This technique allows warm air contaminants to rise to the ceiling, and the rising plume is then exhausted close to the ceiling. This study presents the results of a field study conducted in an industrial environment. The aerosol properties and behavior, especially the vertical gradients, are characterized in a displacement flow field. The results indicate that the fine particles, less than 0.1 μm in diameter, are transported away from the breathing zone by the ventilation process. However, the air quality is significantly influenced by the emission source, and therefore the number concentration of fine and ultrafine (smaller than 0.1 μm in diameter) aerosol particles in the breathing zone was clearly elevated compared to that of the incoming clean air. The vertical gradients displayed clear size dependence; the strongest gradients were found for particles between 0.003 and 0.015 μm in diameter.

Kaarle Hämeri;Anca Gaman;Tareq Hussein;Jouni Räisänen;Raimo Niemelä;Pasi P. Aalto;Markku Kulmala

Applied Occupational and Environmental Hygiene

2003-3-1