Interstitial cell migration: integrin-dependent and alternative adhesion mechanisms

Adhesion and migration are integrated cell functions that build, maintain and remodel the multicellular organism. In migrating cells, integrins are the main transmembrane receptors that provide dynamic interactions between extracellular ligands and actin cytoskeleton and signalling machineries. In parallel to integrins, other adhesion systems mediate adhesion and cytoskeletal coupling to the extracellular matrix (ECM). These include multifunctional cell surface receptors (syndecans and CD44) and discoidin domain receptors, which together coordinate ligand binding with direct or indirect cytoskeletal coupling and intracellular signalling. We review the way that the different adhesion systems for ECM components impact cell migration in two- and three-dimensional migration models. We further discuss the hierarchy of these concurrent adhesion systems, their specific tasks in cell migration and their contribution to migration in three-dimensional multi-ligand tissue environments

Analysis of nucleation events in the European boundary layer using the regional aerosol–climate model REMO-HAM with a solar radiation-driven OH-proxy

This work describes improvements in the regional aerosol–climate model REMO-HAM in order to simulate more realistically the process of atmospheric new particle formation (NPF). A new scheme was implemented to simulate OH radical concentrations using a proxy approach based on observations and also accounting for the effects of clouds upon OH concentrations. Second, the nucleation rate calculation was modified to directly simulate the formation rates of 3 nm particles, which removes some unnecessary steps in the formation rate calculations used earlier in the model. Using the updated model version, NPF over Europe was simulated for the periods 2003–2004 and 2008–2009. The statistics of the simulated particle formation events were subsequently compared to observations from 13 ground-based measurement sites. The new model shows improved agreement with the observed NPF rates compared to former versions and can simulate the event statistics realistically for most parts of Europe

Black carbon concentration and deposition estimations in Finland by the regional aerosol–climate model REMO-HAM

The prediction skill of the regional aerosol–climate model REMO-HAM was assessed against the black carbon (BC) concentration measurements from five locations in Finland, with focus on Hyytiälä station for the year 2005. We examined to what extent the model is able to reproduce the measurements using several statistical tools: median comparison, overlap coefficient (OVL; the common area under two probability distributions curves) and Z score (a measure of standard deviation, shape and spread of the distributions). The results of the statistics showed that the model is biased low. The local and regional emissions of BC have a significant contribution, and the model tendency to flatten the observed BC is most likely dominated by the lack of domestic burning of biofuel in the emission inventories. A further examination of the precipitation data from both measurements and model showed that there is no correlation between REMO's excessive precipitation and BC underestimation. This suggests that the excessive wet removal is not the main cause of the low black carbon concentration output. In addition, a comparison of wind directions in relation with high black carbon concentrations shows that REMO-HAM is able to predict the BC source directions relatively well. Cumulative black carbon deposition fluxes over Finland were estimated, including the deposition on snow

Physical properties and processes of secondary organic aerosol and its constituents

Atmospheric aerosol particles are involved in several important processes including the formation of clouds and precipitation. A considerable fraction of the ambient aerosol mass consists of organic compounds of both primary and secondary origin. These organic compounds are often semi-volatile and susceptible to oxidation which makes the organic aerosol a dynamic system, both chemically and physically. Once an aerosol is formed or released into the atmosphere, several processes will begin to alter its chemical and physical properties. The focus of the work presented in this thesis has been to use experimental methods to characterise single aerosol components and more complex experimental systems, involving the formation and processing of secondary organic aerosol (SOA). The volatility of aerosol particles, e.g. the evaporation rate of the particles upon heating, can provide information of several important properties. From an aerosol consisting only of one pure compound it is possible to derive physical quantities like saturation vapour pressure and enthalpy of evaporation. In more complex systems like a secondary organic aerosol the volatility can give information about changes in composition, state of oxidation and degree of internal or external mixing. With the use of a volatility tandem differential mobility analyser (VTDMA), the saturation vapour pressures and enthalpies of evaporation have been determined for pure compounds that are known constituents of ambient aerosol samples i.e. nine carboxylic acids. Two of them were cyclic, pinic and pinonic acid and seven of them were straight chain dicarboxylic acids with number of carbons ranging from C4 to C10. These properties were in addition evaluated for the aminium nitrates of mono-, di-, and trimethylamine, ethyl- and monoethanolamine. The calculated saturation vapour pressures for the carboxylic acids were in the range of 10-6 to 10-3 Pa and the determined enthalpies of evaporation ranged from 83 to 161 kJ mol-1. The corresponding values for the aminium nitrates were for the calculated saturation vapour pressures approximately 10-4 Pa and for the enthalpies of evaporation 54 to 72 kJ mol-1. The VTDMA system has also been utilised to characterise SOA formed in the AIDA and SAPHIRE smog chambers from the ozonolysis of α-pinene and limonene and the change in the SOA thermal properties during OH radical induced ageing. Further, the effect of elevated ozone concentration and radical chemistry on SOA formed from limonene ozonolysis in the G-FROST laminar flow reactor was investigated. In addition, to compare with vapour pressures of aminium nitrates SOA generated from photooxodation of alkyl amines have been characterised in the EUPHORE smog chamber. The calculated vapour pressures of all the investigated pure compounds in this work characterise them to be in the semi-volatile organic compound (SVOC) category; hence they will be present both in the gaseous and condensed phase in the atmosphere. This implied that all these compounds will be susceptible for gas phase OH radical oxidation that was demonstrated to be an important process for the complex mixtures investigated in the smog chamber facilities. The OH chemistry was also influencing the volatility of aerosol produced in G-FROST by ozonlysis. Regarding photooxodation of amines the aerosols produced under high NOx conditions initially mimicked the pure salts but was efficiently transformed by oxidation into an aerosol with similar volatility properties as observed in the terpene oxidation experiments