Publications (8)0 Total impact
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Article: Meteorological and trace gas factors affecting the number concentration of atmospheric Aitken ( D <sub>p</sub>=50 nm) particles in the continental boundary layer: parameterization using a multivariate mixed effects model
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ABSTRACT: Measurements of aerosol size-distribution and different gas and meteorological parameters, made in three polluted sites in Central- and Southern Europe: Po Valley, Italy, Melpitz and Hohenpeissenberg in Germany, were analysed for this study to examine which of the meteorological and trace gas variables affect the number concentration of Aitken (Dp=50 nm) particles. The aim of our study was to predict the number concentration of 50 nm particles by a combination of in-situ meteorological and gas phase parameters. The statistical model needs to describe, amongst others, the factors affecting the growth of newly formed aerosol particles (below 10 nm) to 50 nm size, but also sources of direct particle emissions in that size range. As the analysis method we used multivariate nonlinear mixed effects model. Hourly averages of gas and meteorological parameters measured at the stations were used as predictor variables; the best predictive model was attained with a combination of relative humidity, new particle formation event probability, temperature, condensation sink and concentrations of SO2, NO2 and ozone. The seasonal variation was also taken into account in the mixed model structure. Model simulations with the Global Model of Aerosol Processes (GLOMAP) indicate that the parameterization can be used as a part of a larger atmospheric model to predict the concentration of climatically active particles. As an additional benefit, the introduced model framework is, in theory, applicable for any kind of measured aerosol parameter.Geoscientific Model Development Discussions. 01/2010; -
Article: On the roles of sulphuric acid and low-volatility organic vapours in the initial steps of atmospheric new particle formation
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ABSTRACT: 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.Atmospheric Chemistry and Physics. 01/2010; -
Article: EUCAARI ion spectrometer measurements at 12 European sites – analysis of new-particle formation events
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ABSTRACT: 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 respective 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.Atmospheric Chemistry and Physics Discussions. 01/2010; -
Article: Changes in the production rate of secondary aerosol particles in Central Europe in view of decreasing SO<sub>2</sub> emissions between 1996 and 2006
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ABSTRACT: In anthropogenically influenced atmospheres, sulphur dioxide (SO<sub>2</sub>) is the main precursor of gaseous sulphuric acid (H<sub>2</sub>SO<sub>4</sub>), which in turn is a main precursor for atmospheric particle nucleation. As a result of socio-economic changes, East Germany has seen a dramatic decrease in anthropogenic SO<sub>2</sub> emissions between 1989 and present, as documented by routine air quality measurements in many locations. We have attempted to evaluate the influence of changing SO<sub>2</sub> concentrations on the frequency and intensity of new particle formation (NPF) using two different data sets (1996–1997; 2003–2006) of experimental particle number size distributions (diameter range 3–750 nm) from the atmospheric research station Melpitz near Leipzig, Germany. Between the two periods SO<sub>2</sub> concentrations decreased by 65% on average, while the frequency of NPF events dropped by 45%. Meanwhile, the average formation rate of 3 nm particles decreased by 68% on average. The trends were statistically significant and therefore suggest a connection between the availability of anthropogenic SO<sub>2</sub> and freshly formed new particles. In contrast to the decrease in new particle formation, we found an increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H<sub>2</sub>SO<sub>4</sub>, the SO<sub>2</sub> concentration, and the global radiation intensity, we were able to define the characteristic range of atmospheric conditions under which particle formation events take place at the Melpitz site. While the decrease in the concentrations and formation rates of the new particles was rather evident, no similar decrease was found with respect to the generation of cloud condensation nuclei (CCN; particle diameter >100 nm) as a result of atmospheric nucleation events. On the contrary, the production of CCN following nucleation events appears to have increased by tens of percents. Our aerosol dynamics model simulations suggest that such an increase can be caused by the increased particle growth rate.Atmospheric Chemistry and Physics. 01/2010; -
Article: Changes in the production rate of secondary aerosol particles in central Europe in view of decreasing SO<sub>2</sub> emissions between 1996 and 2006
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ABSTRACT: In anthropogenically influenced atmospheres, sulphur dioxide (SO2) is the main precursor of gaseous sulphuric acid (H2SO4), which in turn forms new aerosol particles (diameter 2 emissions between 1989 and present, as documented by routine air quality measurements in many locations. Using two different data sets of experimental particle number size distributions (3–750 nm) from the research station Melpitz (1996–1997 and 2003–2006) we have attempted to evaluate the possible influence of changing SO2 concentrations on the frequency and intensity of new particle formation (NPF). Between the two periods SO2 concentrations decreased on average by 65%, while the frequency of NPF events dropped by 45%. In addition, the average formation rate of 3 nm particles decreased by 68%. The trends were statistically significant, therefore suggesting a connection between the availability of anthropogenic SO2 and the production of new particle number. A contrasting finding was the increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H2SO4, the SO2 concentration, and global radiation intensity, we could define the characteristic range of atmospheric conditions under which particle formation events at the Melpitz site take place or not. While the connection between anthropogenic SO2, H2SO4 and NPF appears very plausible, our analysis yielded no significant evidence whether decreasing SO2 concentrations did affect the production of cloud condensation nuclei (CCN).Atmospheric Chemistry and Physics Discussions. 01/2009; -
Article: Nucleation and growth of new particles in Po Valley, Italy
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ABSTRACT: Aerosol number distribution measurements are reported at San Pietro Capofiume (SPC) station (44°39' N, 11°37' E) for the time period 2002–2005. The station is located in Po Valley, the largest industrial, trading and agricultural area in Italy with a high population density. New particle formation was studied based on observations of the particle size distribution, meteorological and gas phase parameters. The nucleation events were classified according to the event clarity based on the particle number concentrations, and the particle formation and growth rates. Out of a total of 769 operational days from 2002 to 2005 clear events were detected on 36% of the days whilst 33% are clearly non-event days. The event frequency was high during spring and summer months with maximum values in May and July, whereas lower frequency was observed in winter and autumn months. The average particle formation and growth rates were estimated as ~6 cm<sup>−3</sup> s<sup>−1</sup> and ~7 nm h<sup>−1</sup>, respectively. Such high growth and formation rates are typical for polluted areas. Temperature, wind speed, solar radiation, SO<sub>2</sub> and O<sub>3</sub> concentrations were on average higher on nucleation days than on non-event days, whereas relative and absolute humidity and NO<sub>2</sub> concentration were lower; however, seasonal differences were observed. Backtrajectory analysis suggests that during majority of nucleation event days, the air masses originate from northern to eastern directions. We also study previously developed nucleation event correlations with environmental variables and show that they predict Po Valley nucleation events with variable success.Atmospheric Chemistry and Physics. 01/2007; -
Article: Using discriminant analysis as a nucleation event classification method
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ABSTRACT: More than three years of measurements of aerosol size-distribution and different gas and meteorological parameters made in Po Valley, Italy were analysed for this study to examine which of the meteorological and trace gas variables effect on the emergence of nucleation events. As the analysis method, we used discriminant analysis with non-parametric Epanechnikov kernel, included in non-parametric density estimation method. The best classification result in our data was reached with the combination of relative humidity, ozone concentration and a third degree polynomial of radiation. RH appeared to have a preventing effect on the new particle formation whereas the effects of O<sub>3</sub> and radiation were more conductive. The concentration of SO<sub>2</sub> and NO<sub>2</sub> also appeared to have significant effect on the emergence of nucleation events but because of the great amount of missing observations, we had to exclude them from the final analysis.Atmospheric Chemistry and Physics. 01/2006; -
Article: Relation of air mass history to nucleation events in Po Valley, Italy, using back trajectories analysis
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ABSTRACT: In this paper, we study the transport of air mass to San Pietro Capofiume (SPC) in Po Valley, Italy, by means of back trajectory analysis. Our main aim is to investigate whether air masses originate from different regions on nucleation event days and on nonevent days, during three years when nucleation events have been continuously recorded at SPC. The results indicate that nucleation events occur frequently in air masses arriving form Central Europe, whereas event frequency is much lower in air transported from southern directions and from the Atlantic Ocean. We also analyzed the behaviour of meteorological parameters during 96 h transport to SPC, and found that on average, event trajectories undergo stronger subsidence during the last 12 h before the arrival at SPC than nonevent trajectories. This causes a reversal in the temperature and relative humidity (RH) differences between event and nonevent trajectories: between 96 and 12 h back time, temperatures are lower and RH's higher for event than nonevent trajectories and between 12 and 0 h vice versa. Boundary layer mixing is stronger along the event trajectories compared to nonevent trajectories. The absolute humidity (AH) is similar for the event and nonevent trajectories between about 96 h and about 60 h back time, but after that, the event trajectories AH becomes lower due to stronger rain. We also studied transport of SO2 to SPC, and conclude that although sources in Po Valley most probably dominate the measured concentrations, certain Central and Eastern European sources can also have a non-negligible contribution.Atmospheric Chemistry and Physics Discussions. 01/2006;
