Browsing by Subject "MCM V3 PART"

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  • Rannik, Ullar; Zhou, Luxi; Zhou, Putian; Gierens, Rosa; Mammarella, Ivan; Sogachev, Andrey; Boy, Michael (2016)
    A 1-D atmospheric boundary layer (ABL) model coupled with a detailed atmospheric chemistry and aerosol dynamical model, the model SOSAA, was used to predict the ABL and detailed aerosol population (characterized by the number size distribution) time evolution. The model was applied over a period of 10 days in May 2013 to a pine forest site in southern Finland. The period was characterized by frequent new particle formation events and simultaneous intensive aerosol transformation. The aim of the study was to analyze and quantify the role of aerosol and ABL dynamics in the vertical transport of aerosols. It was of particular interest to what extent the fluxes above the canopy deviate from the particle dry deposition on the canopy foliage due to the above-mentioned processes. The model simulations revealed that the particle concentration change due to aerosol dynamics frequently exceeded the effect of particle deposition by even an order of magnitude or more. The impact was, however, strongly dependent on particle size and time. In spite of the fact that the timescale of turbulent transfer inside the canopy is much smaller than the timescales of aerosol dynamics and dry deposition, leading us to assume well-mixed properties of air, the fluxes at the canopy top frequently deviated from deposition inside the forest. This was due to transformation of aerosol concentration throughout the ABL and resulting complicated pattern of vertical transport. Therefore we argue that the comparison of timescales of aerosol dynamics and deposition defined for the processes below the flux measurement level do not unambiguously describe the importance of aerosol dynamics for vertical transport above the canopy. We conclude that under dynamical conditions reported in the current study the micrometeorological particle flux measurements can significantly deviate from the dry deposition into the canopy. The deviation can be systematic for certain size ranges so that the time-averaged particle fluxes can be also biased with respect to deposition sink.
  • Eriksson, A. C.; Wittbom, C.; Roldin, P.; Sporre, M.; Str M, E.; Nilsson, P.; Martinsson, J.; Rissler, J.; Nordin, E. Z.; Svenningsson, B.; Pagels, J.; Swietlicki, E. (2017)
    Fresh and aged diesel soot particles have different impacts on climate and human health. While fresh diesel soot particles are highly aspherical and non-hygroscopic, aged particles are spherical and hygroscopic. Aging and its effect on water uptake also controls the dispersion of diesel soot in the atmosphere. Understanding the timescales on which diesel soot ages in the atmosphere is thus important, yet knowledge thereof is lacking. We show that under cold, dark and humid conditions the atmospheric transformation from fresh to aged soot occurs on a timescale of less than five hours. Under dry conditions in the laboratory, diesel soot transformation is much less efficient. While photochemistry drives soot aging, our data show it is not always a limiting factor. Field observations together with aerosol process model simulations show that the rapid ambient diesel soot aging in urban plumes is caused by coupled ammonium nitrate formation and water uptake.
  • Qi, Ximeng; Ding, Aijun; Roldin, Pontus; Xu, Zhengning; Zhou, Putian; Sarnela, Nina; Nie, Wei; Huang, Xin; Rusanen, Anton; Ehn, Mikael; Rissanen, Matti P.; Petäjä, Tuukka; Kulmala, Markku; Boy, Michael (2018)
    Highly oxygenated multifunctional compounds (HOMs) play a key role in new particle formation (NPF), but their quantitative roles in different environments of the globe have not been well studied yet. Frequent NPF events were observed at two "flagship" stations under different environmental conditions, i.e. a remote boreal forest site (SMEAR II) in Finland and a suburban site (SORPES) in polluted eastern China. The averaged formation rate of 6 nm particles and the growth rate of 6-30 nm particles were 0.3 cm(-3) s(-1) and 4.5 nm h(-1) at SMEAR II compared to 2.3 cm(-3) s(-1) and 8.7 nm h(-1) at SORPES, respectively. To explore the differences of NPF at the two stations, the HOM concentrations and NPF events at two sites were simulated with the MALTE-BOX model, and their roles in NPF and particle growth in the two distinctly different environments are discussed. The model provides an acceptable agreement between the simulated and measured concentrations of sulfuric acid and HOMs at SMEAR II. The sulfuric acid and HOM organonitrate concentrations are significantly higher but other HOM monomers and dimers from monoterpene oxidation are lower at SORPES compared to SMEAR II. The model simulates the NPF events at SMEAR II with a good agreement but underestimates the growth of new particles at SORPES, indicating a dominant role of anthropogenic processes in the polluted environment. HOMs from monoter-pene oxidation dominate the growth of ultrafine particles at SMEAR II while sulfuric acid and HOMs from aromatics oxidation play a more important role in particle growth. This study highlights the distinct roles of sulfuric acid and HOMs in NPF and particle growth in different environmental conditions and suggests the need for molecular-scale measurements in improving the understanding of NPF mechanisms in polluted areas like eastern China.
  • Peräkylä, Otso; Vogt, Matthias; Tikkanen, Olli-Pekka; Laurila, Terhi; Kajos, Maija K.; Rantala, Pekka A.; Patokoski, Johanna; Aalto, Juho; Yli-Juuti, Taina; Ehn, Mikael; Sipila, Mikko; Paasonen, Pauli; Rissanen, Matti; Nieminen, Tuomo; Taipale, Risto; Keronen, Petri; Lappalainen, Hanna K.; Ruuskanen, Taina M.; Rinne, Janne; Kerminen, Veli-Matti; Kulmala, Markku; Back, Jaana; Petaja, Tuukka (2014)