Scientific paper

Annual and interannual variation in boreal forest aerosol particle number and volume concentration and their connection to particle formation

Dal Maso, M.; Hyvarinen, A.; Komppula, M.; Tunved, P.; Kerminen, V.M.; Lihavainen, H.; Viisanen, Y.; Hansson, H.-C.; Kulmala, M.
2008 | Tellus B Chem Phys Meteorol | 60 (4) (495-508)
air pollution , atmospheric aerosols , cloud , events , growth , northern finland , radiation , size distribution data , smear-ii , station

We investigated size-resolved submicrometre aerosol particle number and volume concentration time series as well as aerosol dynamic parameters derived front Differential Mobility Particle Sizer (DMPS) measurements at five background stations in the Nordic boreal forest area. The stations in question were Aspvreten, Hyytiala and Uto in Southern Finland and Sweden, and Varrio and Pallas in the Finnish Lapland. The objective Of Our investigation was to identify and quantity annual and interannual variation observable in the time series. We found that the total number and mass concentrations were touch lower at the Lapland stations than at the southern stations and that the total particle number was strongly correlated to particle formation event frequency. The annual total number concentration followed the annual distribution of particle formation events at the Southern stations but much less clearly at the Lapland stations. The volume concentration was highest during summer, in line with higher condensation growth rates: this is in line with the assumption that a large part of the particle volume is produced by oxidized plant emissions. The decrease of sulphate emissions in Europe was not visible in our data set. Aerosol dynamic parameters such as condensation sink, condensation sink diameter and the power law exponent linking coagulation losses and condensation sink are presented to characterize the submicron Nordic background aerosol.

Scientific paper

SPECIAL ISSUE with results from the Nordic Biosphere-Aerosol-Cloud-Climate Interaction project, BACCI – Foreword

Hansson, H.-C.
2008 | Tellus B Chem Phys Meteorol | 60 (3) (299-299)
Scientific paper

Overview of the biosphere-aerosol-cloud-climate interactions (BACCI) studies

Kulmala, M.; Kerminen, V.M.; Laaksonen, A.; Riipinen, I.; Sipila, M.; Ruuskanen, T.M.; Sogacheva, L.; Hari, P.; Back, J.; Lehtinen, K.E.J.; Viisanen, Y.; Bilde, M.; Svenningsson, B.; Lazaridis, M.; Torseth, K.; Tunved, P.; Nilsson, E. D.; Pryor, S.; Sorensen, L.L.; Horrak, U.; Winkler, P.M.; Swietlicki, E.; Riekkola, M.L.; Krejci, R.; Hoyle, C.; Hov, O.; Myhre, G.; Hansson, H.-C.
2008 | Tellus B Chem Phys Meteorol | 60 (3) (300-317)
atmospheric sulfuric-acid , boreal forest , condensation nuclei , critical supersaturations , evaporation rates , global aerosol , nucleation mode particles , saturation vapor-pressures , size distribution

Here we present research methods and results obtained by the Nordic Centre of Excellence Biosphere-Aerosol-Cloud-Climate Interactions (BACCI) between 1 January 2003 and 31 December 2007. The centre formed an integrated attempt to understand multiple, but interlinked, biosphere-atmosphere interactions applying inter and multidisciplinary approaches in a coherent manner. The main objective was to study the life cycle of aerosol particles and their importance on climate change. The foundation in BACCI was a thorough understanding of physical, meteorological, chemical and ecophysiological processes, providing a unique possibility to study biosphere-aerosol-cloud-climate interactions. Continuous measurements of atmospheric concentrations and fluxes of aerosol particles and precursors and, CO2/aerosol trace gas interactions in different field stations (e.g. SMEAR) were supported by models of particle thermodynamics, transport and dynamics, atmospheric chemistry, boundary layer meteorology and forest growth. The main progress was related to atmospheric new particle formation, existence of clusters, composition of nucleation mode aerosol particles, chemical precursors of fresh aerosol particles, the contribution of biogenic aerosol particles on the global aerosol load, transport, transformation and deposition of aerosol particles, thermodynamics related to aerosol particles and cloud droplets, and the microphysics and chemistry of cloud droplet formation.

Scientific paper

Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments – a review

Swietlicki, E.; Hansson, H.-C.; Hameri, K.; Svenningsson, B.; Massling, A.; McFiggans, G.; McMurry, P.H.; Petaja, T.; Tunved, P.; Gysel, M.; Topping, D.; Weingartner, E.; Baltensperger, U.; Rissler, J.; Wiedensohler, A.; Kulmala, M.
2008 | Tellus B Chem Phys Meteorol | 60 (3) (432-469)
amazon rain-forest , ammonium-sulfate , differential mobility analyzer , growth measurements , nucleation mode , organic compounds , sea salt , size distribution , soluble volume fraction , water activities

The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the size-resolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.

Scientific paper

Factors affecting non-tailpipe aerosol particle emissions from paved roads: On-road measurements in Stockholm, Sweden

Hussein, T.; Johansson, C.; Karlsson, H.; Hansson, H.-C.
2008 | Atmos. Environ. | 42 (4) (688-702)
finland , impact , model , number concentrations , particle size distribution , particulate matter , pm10 , re-suspension , resuspended dust , road dust , road wears road traffic , tire wear , traker , unpaved roads , urban

A large fraction of urban PM10 concentrations is due to non-exhaust traffic emissions. In this paper, a mobile measurement system has been used to quantify the relative importance of road particle emission and suspension of accumulated dust versus direct pavement wear, tire type (studded, friction, and summer), pavement type, and vehicle speed. Measurements were performed during May-September on selected roads with different pavements and traffic conditions in the Stockholm region. The highest particle mass concentrations were always observed behind the studded tire and the lowest were behind the summer tire; studded-to-summer ratios were 4.4-17.3 and studded-to-friction ratios were 2.0-6.4. This indicates that studded tires lead to higher emissions than friction and summer tires regardless to the asphalt type. By comparing with measurements in a road simulator, it could be estimated that the pavement wear due to the friction tires was 0.018-0.068 of the suspension of accumulated road dust. Likewise for studded tires road-wear was estimated to be 1.2-4.8 the suspension of accumulated dust. This indicates that wear due to friction tires is very small compared to the suspension of accumulated dust and that suspension due to studded tires may sometimes be as large as the wear of the road. But this will vary depending on, e.g. the amount of dust accumulated on the roads. An important dependence on vehicle speed was also observed. During May, the particle mass concentrations behind the studded tire at vehicle speed 100 km h(-1) were about 10 times higher than that at 20 km h(-1). The speed dependence was not so pronounced in September, which could be due to less accumulated dust on the roads. The particle number size distribution of the emissions due to road wear by studded tire was characterized by a clear increase in number concentrations of the coarse fraction of aerosol particles, with a geometric mean diameter between 3 and 5 mu m. The size distribution of the emissions due to the summer tire was very similar with smaller concentrations. An important limitation with the measurements presented is that they were made by using a van, which is bigger than regular cars and has bigger tires. Thus, road wear and dust suspension due to cars are expected to be different. (C) 2007 Elsevier Ltd. All rights reserved.

Scientific paper

Factors affecting non-tailpipe aerosol particle emissions from paved roads: on road measurements in Stockholm, Sweden.

Hussein, T.; Johansson, C.; Karlsson, H.; Hansson, H.-C.
2008 | Atmos. Environ. | 42 (688-702)
Scientific paper

Elemental and organic carbon in PM10: a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP

Yttri, K.E.; Aas, W.; Bjerke, A.; Cape, J.N.; Cavalli, F.; Ceburnis, D.; Dye, C.; Emblico, L.; Facchini, M.C.; Forster, C.; Hanssen, J.E.; Hansson, H.-C.; Jennings, S.G.; Maenhaut, W.; Putaud, J.P.; Torseth, K.
2007 | Atmos. Chem. Phys. | 7 (22) (5711-5725)
adsorption , atmospheric aerosols , levoglucosan , los-angeles , mass , norway , particles , particulate matter , sampling artifacts , urban

In the present study, ambient aerosol (PM10) concentrations of elemental carbon (EC), organic carbon (OC), and total carbon (TC) are reported for 12 European rural background sites and two urban background sites following a one-year (1 July 2002 & ndash;1 July 2003) sampling campaign within the European Monitoring and Evaluation Programme, EMEP (http://www.emep.int/). The purpose of the campaign was to assess the feasibility of performing EC and OC monitoring on a regular basis and to obtain an overview of the spatial and seasonal variability on a regional scale in Europe. Analyses were performed using the thermal-optical transmission (TOT) instrument from Sunset Lab Inc., operating according to a NIOSH derived temperature program. The annual mean mass concentration of EC ranged from 0.17 +/- 0.19 mu G m(-3) (mean +/- SD) at Birkenes (Norway) to 1.83 +/- 1.32 mu g m(-3) at Ispra (Italy). The corresponding range for OC was 1.20 +/- 1.29 mu g m(-3) at Mace Head (Ireland) to 7.79 +/- 6.80 mu g m-3 at Ispra. On average, annual concentrations of EC, OC, and TC were three times higher for rural background sites in Central, Eastern and Southern Europe compared to those situated in the Northern and Western parts of Europe. Wintertime concentrations of EC and OC were higher than those recorded during summer for the majority of the sites. Moderate to high Pearson correlation coefficients (r(p)) (0.50-0.94) were observed for EC versus OC for the sites investigated. The lowest correlation coefficients were noted for the three Scandinavian sites: Aspvreten (SE), Birkenes (NO), and Virolahti (FI), and the Slovakian site Stara Lesna, and are suggested to reflect biogenic sources, wild and prescribed fires. This suggestion is supported by the fact that higher concentrations of OC are observed for summer compared to winter for these sites. For the rural background sites, total carbonaceous material accounted for 30 +/- 9% of PM10, of which 27 +/- 9% could be attributed to organic matter (OM) and 3.4 +/- 1.0% to elemental matter (EM). OM was found to be more abundant than SO42- for sites reporting both parameters.

Scientific paper

Modelling the cloud condensation nucleus activity of organic acids on the basis of surface tension and osmolality measurements

Varga, Z; Kiss, G; Hansson, H.-C.
2007 | Atmos. Chem. Phys. | 7 (17) (4601-4611)
aerosol-particles , ccn activation , component , droplets , inorganic solute , substances , water

In this study vapour pressure osmometry was used to determine water activity in the solutions of organic acids. The surface tension of the solutions was also monitored in parallel and then Kohler curves were calculated for nine organic acids (oxalic, malonic, succinic, glutaric, adipic, maleic, malic, citric and cis-pinonic). Surface tension depression is negligible for most of the organic acids in dilute (= 1 w/w%) solutions. Therefore, these compounds affect equilibrium vapour pressure only in the beginning phase of droplet formation when the droplet solution is more concentrated but not necessarily at the critical size. An exception is cis-pinonic acid which remarkably depress surface tension also in dilute (0.1 w/w%) solution and hence at the critical point. The surface tension of organic acid solutions is influenced by the solubility of the compound, the length of the carbon chain and also by the polar functional groups present in the molecule. Similarly to surface tension solubility plays an important role also in water activity: compounds with higher solubility (e.g. malonic, maleic and glutaric acid) reduce water activity significantly in the early phase of droplet formation while less soluble acids (e.g. succinic and adipic acid) are saturated in small droplets and the solution starts diluting only in bigger droplets. As a consequence, compounds with lower solubility have a minor effect on water activity in the early phase of droplet formation. To deduce the total effect Kohler curves were calculated and critical supersaturations (S-c) were determined for the organic acids using measured surface tension and water activity. It was found that critical supersaturation grew with growing carbon number. Oxalic acid had the lowest critical supersaturation in the size range studied and it was comparable to the activation of ammonium sulphate. The S-c values obtained in this study were compared to data from CCNC experiments. In most cases good agreement was found. For modelling purposes S-c vs. d(dry) plots are given and the dependence of water activity and surface tension on concentration are also formulated.

Scientific paper

The role of ambient temperature for particle number concentrations in a street canyon

Olivares, G; Johansson, C.; Ström, J; Hansson, HC
2007 | Atmos. Environ. | 41 (10) (2145-2155)
Scientific paper

Aerosol size distribution measurements at four Nordic field stations: identification, analysis and trajectory analysis of new particle formation bursts

Dal Maso, M.; Sogacheva, L.; Aalto, P.P.; Riipinen, I.; Komppula, M.; Tunved, P.; Korhonen, L.; Suur-Uski, V.; Hirsikko, A.; Kurten, T.; Kerminen, V.M.; Lihavainen, H.; Viisanen, Y.; Hansson, H.-C.; Kulmala, M.
2007 | Tellus B Chem Phys Meteorol | 59 (3) (350-361)
atmospheric particles , boreal forest , growth , hyytiala , nucleation events , smear-ii , southern finland

We analyzed aerosol size distributions from the Finnish measuring stations at Hyytiala, Varrio and Pallas and the Swedish station at Aspvreten over a period of several years. We identified occurrences of new particle formation bursts and obtained characteristics for the bursts from the size distribution data. In addition, we analyzed the directions from which air masses leading to new particle formation arrived. We found that new particle formation occurs over the whole area covered by the measurement stations. The Northern Atlantic is dominating as a source for air leading to new particle formation at all of the analyzed stations. The formation occurrence had a similar annual variation at all the stations, with peaks in springtime and autumn and minima in winter and summer. The ratio of event days to non-event days had a North-South dependence, with northern stations having lower event ratios. Particle growth rates ranged from 0.5 to 15 nm/h, with the mean growth rate being slightly higher at the southern stations. Southern stations also had a stronger particle source, on average 0.5 cm(-3) s(-1), compared to the northern stations (0.1 cm(-3) s(-1)). Based on our analysis, it is evident that new particle formation occurs often in whole Nordic boreal forest area when air is transported from the North Atlantic, and that the same process or processes are very probably responsible for the formation over the whole area.

Scientific paper

High Natural Aerosol Loading over Boreal Forests

Tunved, P.; Hansson, H.-C.; Kerminen, V.M.; Ström, J.; Dal Maso, M.; Lihavainen, H.; Visanen, Y.; Aalto, P.; Komppula, M.; Kulmala, M.
2006 | Science | 312 (261-263)

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