Publications by authors named "Pasi Aalto"

14 Publications

  • Page 1 of 1

Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition.

Sci Data 2017 03 14;4:170003. Epub 2017 Mar 14.

Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen 5232, Switzerland.

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.
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http://dx.doi.org/10.1038/sdata.2017.3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5349251PMC
March 2017

Direct observations of atmospheric aerosol nucleation.

Science 2013 Feb;339(6122):943-6

Department of Physics, University of Helsinki, Finland.

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.
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http://dx.doi.org/10.1126/science.1227385DOI Listing
February 2013

Measurement of the nucleation of atmospheric aerosol particles.

Nat Protoc 2012 Sep 16;7(9):1651-67. Epub 2012 Aug 16.

Department of Physics, University of Helsinki, Helsinki, Finland.

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.
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http://dx.doi.org/10.1038/nprot.2012.091DOI Listing
September 2012

Chemical composition of fine particles in fresh smoke plumes from boreal wild-land fires in Europe.

Sci Total Environ 2010 May 1;408(12):2527-42. Epub 2010 Apr 1.

Finnish Meteorological Institute, P.O. Box 503, FI-00101 Helsinki, Finland.

A series of smoke plumes was detected in Helsinki, Finland, during a one-month-lasting period in August 2006. The smoke plumes originated from wildfires close to Finland, and they were short-term and had a high particulate matter (PM) concentration. Physical and chemical properties of fine particles in those smokes were characterised by a wide range of real-time measurements that enabled the examination of individual plume events. Concurrently PM(1) filter samples were collected and analysed off-line. Satellite observations employing MODIS sensor on board of NASA EOS Terra satellite with the dispersion model SILAM and the Fire Assimilation System were used for evaluation of the emission fluxes from wildfires. The model predicted well the timing of the plumes but the predicted PM concentrations differed from the observed. The measurements showed that the major growth in PM concentration was caused by submicrometer particles consisting mainly of particulate organic matter (POM). POM had not totally oxidised during the transport based on the low WSOC-to-OC ratio. The fresh plumes were compared to another major smoke episode that was observed in Helsinki during April-May 2006. The duration and the source areas of the two episode periods differed. The episode in April-May was a period of nearly constantly upraised level of long-range transported PM and it was composed of aged particles when arriving in Helsinki. The two episodes had differences also in the chemical composition of PM. The mass concentrations of biomass burning tracers (levoglucosan, potassium, and oxalate) increased during both the episodes but different concentration levels of elemental carbon and potassium indicated that the episodes differed in the form of burning as well as in the burning material. In spring dry crop residue and hay from the previous season were burnt whereas in August smokes from smouldering and incomplete burning of fresh vegetation were detected.
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http://dx.doi.org/10.1016/j.scitotenv.2010.03.010DOI Listing
May 2010

Ambient air pollution and daily mortality among survivors of myocardial infarction.

Epidemiology 2009 Jan;20(1):110-8

Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.

Background: Certain subgroups in the general population, such as persons with existing cardiovascular or respiratory disease, may be more likely to experience adverse health effects from air pollution.

Methods: In this European multicenter study, 25,006 myocardial infarction (MI) survivors in 5 cities were recruited from 1992 to 2002 via registers, and daily mortality was followed for 6 to 12 years in relation to ambient particulate and gaseous air pollution exposure. Daily air pollution levels were obtained from central monitor sites, and particle number concentrations were measured in 2001 and estimated retrospectively based on measured pollutants and meteorology. City-specific effect estimates from time-series analyses with Poisson regression were pooled over all 5 cities.

Results: Particle number concentrations and PM10 averaged over 2 days (lag 0-1) were associated with increased total nontrauma mortality for patients of age 35 to 74 (5.6% [95% confidence interval, 2.8%-8.5%] per 10,000/cm and 5.1% [1.6%-9.3%] per 10 microg/m, respectively). For longer averaging times (5 and 15 days), carbon monoxide and nitrogen dioxide were also associated with mortality. There were no clear associations with ozone or sulfur dioxide.

Conclusion: Exposure to traffic-related air pollution was associated with daily mortality in MI survivors. Point estimates suggest a stronger effect of air pollution in MI survivors than among the general population.
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http://dx.doi.org/10.1097/EDE.0b013e3181878b50DOI Listing
January 2009

Air pollution and inflammation (interleukin-6, C-reactive protein, fibrinogen) in myocardial infarction survivors.

Environ Health Perspect 2007 Jul;115(7):1072-80

GSF National Research Centre for Environment and Health, Institute of Epidemiology, Neuherberg, Germany.

Background: Numerous studies have found that ambient air pollution has been associated with cardiovascular disease exacerbation.

Objectives: Given previous findings, we hypothesized that particulate air pollution might induce systemic inflammation in myocardial infarction (MI) survivors, contributing to an increased vulnerability to elevated concentrations of ambient particles.

Methods: A prospective longitudinal study of 1,003 MI survivors was performed in six European cities between May 2003 and July 2004. We compared repeated measurements of interleukin 6 (IL-6), fibrinogen, and C-reactive protein (CRP) with concurrent levels of air pollution. We collected hourly data on particle number concentrations (PNC), mass concentrations of particulate matter (PM) < 10 microm (PM(10)) and < 2.5 microm (PM(2.5)), gaseous pollutants, and meteorologic data at central monitoring sites in each city. City-specific confounder models were built for each blood marker separately, adjusting for meteorology and time-varying and time-invariant covariates. Data were analyzed with mixed-effects models.

Results: Pooled results show an increase in IL-6 when concentrations of PNC were elevated 12-17 hr before blood withdrawal [percent change of geometric mean, 2.7; 95% confidence interval (CI), 1.0-4.6]. Five day cumulative exposure to PM(10) was associated with increased fibrinogen concentrations (percent change of arithmetic mean, 0.6; 95% CI, 0.1-1.1). Results remained stable for smokers, diabetics, and patients with heart failure. No consistent associations were found for CRP.

Conclusions: Results indicate an immediate response to PNC on the IL-6 level, possibly leading to the production of acute-phase proteins, as seen in increased fibrinogen levels. This might provide a link between air pollution and adverse cardiac events.
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http://dx.doi.org/10.1289/ehp.10021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913563PMC
July 2007

Associations of fine and ultrafine particulate air pollution with stroke mortality in an area of low air pollution levels.

Stroke 2007 Mar 15;38(3):918-22. Epub 2007 Feb 15.

Environmental Epidemiology Unit , Kuopio, Finland.

Background And Purpose: Daily variation in outdoor concentrations of inhalable particles (PM(10) <10 microm in diameter) has been associated with fatal and nonfatal stroke. Toxicological and epidemiological studies suggest that smaller, combustion-related particles are especially harmful. We therefore evaluated the effects of several particle measures including, for the first time to our knowledge, ultrafine particles (<0.1 microm) on stroke.

Methods: Levels of particulate and gaseous air pollution were measured in 1998 to 2004 at central outdoor monitoring sites in Helsinki. Associations between daily levels of air pollutants and deaths caused by stroke among persons aged 65 years or older were evaluated in warm and cold seasons using Poisson regression.

Results: There was a total of 1304 and 1961 deaths from stroke in warm and cold seasons, respectively. During the warm season, there were positive associations of stroke mortality with current- and previous-day levels of fine particles (<2.5 microm, PM(2.5)) (6.9%; 95% CI, 0.8% to 13.8%; and 7.4%; 95% CI, 1.3% to 13.8% for an interquartile increase in PM(2.5)) and previous-day levels of ultrafine particles (8.5%; 95% CI, -1.2% to 19.1%) and carbon monoxide (8.3; 95% CI, 0.6 to 16.6). Associations for fine particles were mostly independent of other pollutants. There were no associations in the cold season.

Conclusions: Our results suggest that especially PM(2.5), but also ultrafine particles and carbon monoxide, are associated with increased risk of fatal stroke, but only during the warm season. The effect of season might be attributable to seasonal differences in exposure or air pollution mixture.
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http://dx.doi.org/10.1161/01.STR.0000257999.49706.3bDOI Listing
March 2007

Ambient air pollution is associated with increased risk of hospital cardiac readmissions of myocardial infarction survivors in five European cities.

Circulation 2005 Nov;112(20):3073-9

Institute of Epidemiology, GSF-National Research Center for Environment and Health, Neuherberg, Germany.

Background: Ambient air pollution has been associated with increases in acute morbidity and mortality. The objective of this study was to evaluate the short-term effects of urban air pollution on cardiac hospital readmissions in survivors of myocardial infarction, a potentially susceptible subpopulation.

Methods And Results: In this European multicenter cohort study, 22,006 survivors of a first myocardial infarction were recruited in Augsburg, Germany; Barcelona, Spain; Helsinki, Finland; Rome, Italy; and Stockholm, Sweden, from 1992 to 2000. Hospital readmissions were recorded in 1992 to 2001. Ambient nitrogen dioxide, carbon monoxide, ozone, and mass of particles <10 microm (PM10) were measured. Particle number concentrations were estimated as a proxy for ultrafine particles. Short-term effects of air pollution on hospital readmissions for myocardial infarction, angina pectoris, and cardiac causes (myocardial infarction, angina pectoris, dysrhythmia, or heart failure) were studied in city-specific Poisson regression analyses with subsequent pooling. During follow-up, 6655 cardiac readmissions were observed. Cardiac readmissions increased in association with same-day concentrations of PM10 (rate ratio [RR] 1.021, 95% CI 1.004 to 1.039) per 10 microg/m3) and estimated particle number concentrations (RR 1.026 [95% CI 1.005 to 1.048] per 10,000 particles/cm3). Effects of similar strength were observed for carbon monoxide (RR 1.014 [95% CI 1.001 to 1.026] per 200 microg/m3 [0.172 ppm]), nitrogen dioxide (RR 1.032 [95% CI 1.013 to 1.051] per 8 microg/m3 [4.16 ppb]), and ozone (RR 1.026 [95% CI 1.001 to 1.051] per 15 microg/m3 [7.5 ppb]). Pooled effect estimates for angina pectoris and myocardial infarction readmissions were comparable.

Conclusions: The results suggest that ambient air pollution is associated with increased risk of hospital cardiac readmissions of myocardial infarction survivors in 5 European cities.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.105.548743DOI Listing
November 2005

Aerosol particle number concentration measurements in five European cities using TSI-3022 condensation particle counter over a three-year period during health effects of air pollution on susceptible subpopulations.

J Air Waste Manag Assoc 2005 Aug;55(8):1064-76

Department of Physical Sciences, University of Helsinki, Helsinki, Finland.

In this study, long-term aerosol particle total number concentration measurements in five metropolitan areas across Europe are presented. The measurements have been carried out in Augsburg, Barcelona, Helsinki, Rome, and Stockholm using the same instrument, a condensation particle counter (TSI model 3022). The results show that in all of the studied cities, the winter concentrations are higher than the summer concentrations. In Helsinki and in Stockholm, winter concentrations are higher by a factor of two and in Augsburg almost by a factor of three compared with summer months. The winter maximum of the monthly average concentrations in these cities is between 10,000 cm(-3) and 20,000 cm(-3), whereas the summer min is approximately 5000-6000 cm(-3). In Rome and in Barcelona, the winters are more polluted compared with summers by as much as a factor of 4-10. The winter maximum in both Rome and Barcelona is close to 100,000 cm(-3), whereas the summer minimum is > 10,000 cm(-3). During the weekdays the maximum of the hourly average concentrations in all of the cities is detected during the morning hours between 7 and 10 a.m. The evening maxima were present in Barcelona, Rome, and Augsburg, but these were not as pronounced as the morning ones. The daily maxima in Helsinki and Stockholm are close or even lower than the daily minima in the more polluted cities. The concentrations between these two groups of cities are different with a factor of about five during the whole day. The study pointed out the influence of the selection of the measurement site and the configuration of the sampling line on the observed concentrations.
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http://dx.doi.org/10.1080/10473289.2005.10464702DOI Listing
August 2005

Particle size characterization and the indoor-to-outdoor relationship of atmospheric aerosols in Helsinki.

Scand J Work Environ Health 2004 ;30 Suppl 2:54-62

University of Helsinki, Department of Physical Sciences, Helsinki, Finland.

Objectives: The influence of traffic and meteorological conditions on aerosol characteristics outdoors, the relationship between indoor and outdoor aerosol particles, and the pollutant transport indoors by means of a mechanical ventilation system were studied.

Methods: Indoor and outdoor concentrations of fine-particle numbers were measured during the summer (15 May--30 June 2000) in one office located in the basement of a building in Helsinki, Finland. The total number concentration was measured with a condensation particle counter, and the particle number size distribution (7-600 nm) was measured with a differential mobility particle sizer. The size distribution (0.3-25 microm) of the indoor particle numbers was periodically measured with a laser particle counter.

Results: Meteorological conditions, especially wind direction, had the greatest effect on the total number concentration and the size distribution of aerosol particles outdoors. The outdoor number concentration of ultrafine particles (diameter <100 nm) was strongly dependent on traffic density. The temporal variations in the indoor number concentration of ultrafine and fine particles (7-600 nm) closely followed the corresponding temporal variations outdoors. The building ventilation system was the main means of transporting aerosols indoors. The mean penetration factor was 0.41 (SD 0.11) for the nucleation mode (7-25 nm), 0.74 (SD 0.09) for the Aitken mode (25-100 nm), and 0.87 (SD 0.06) for the accumulation mode (100-600 nm).

Conclusions: The ultrafine particles were bimodal with a nucleation mode (particle diameter <25 nm) and an Aitken mode (25 nm
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February 2005

Characterisation of organic compounds in aerosol particles from a Finnish forest by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry.

Anal Bioanal Chem 2004 Apr 27;378(8):1982-90. Epub 2004 Jan 27.

Laboratory of Analytical Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, 00014, Helsinki, Finland.

During the European Union project Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST), which began in spring 2003, atmospheric aerosol particles were collected in a Finnish Scots pine forest using a high-volume sampler. The organic compounds in the filter samples were then analysed by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS). The sample was first extracted by SFE. During LC the extracts were fractionated into three fractions according to polarity. The final separation was carried out by GC-MS. A fraction volume as high as 840 microL was transferred to the GC, using the partial concurrent eluent evaporation technique. The same instrumentation, with an in-situ SFE derivatisation method, was used to analyse organic acids. Major compounds such as n-alkanes and PAH were analysed quantitatively. Their concentrations were lower than those usually observed in urban areas or in other forest areas in Europe. The wind direction was one of the most important factors affecting changes in the daily concentrations of these compounds. Scots pine needles were analysed with the same system to obtain reference data for identification of biogenic compounds in aerosol particles. Other organic compounds found in this study included hopanes, steranes, n-alkanals, n-alkan-2-ones, oxy-PAH, and alkyl-PAH; some biogenic products, including oxidation products of monoterpenes, were also identified.
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http://dx.doi.org/10.1007/s00216-003-2424-xDOI Listing
April 2004

Particle concentration profile in a vertical displacement flow: a study in an industrial hall.

Appl Occup Environ Hyg 2003 Mar;18(3):183-92

Finnish Institute of Occupational Health, Helsinki, Finland.

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 1 microm 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 microm 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 microm in diameter.
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http://dx.doi.org/10.1080/10473220301351DOI Listing
March 2003

Aerosol formation: atmospheric particles from organic vapours.

Nature 2002 Apr;416(6880):497-8

Division of Atmospheric Sciences, Department of Physical Sciences, PO Box 64, University of Helsinki, 00014 Helsinki, Finland.

Aerosol particles produced over forested areas may affect climate by acting as nuclei for cloud condensation, but their composition (and hence the chemical species that drive their production) remains an open question. Here we show, to our knowledge for the first time, that these newly formed particles (3-5 nm in diameter) are composed primarily of organic species, such as cis-pinonic acid and pinic acid, produced by oxidation of terpenes in organic vapours released from the canopy.
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http://dx.doi.org/10.1038/416497aDOI Listing
April 2002
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