Long-term observations of the background aerosol at Cabauw, The Netherlands

Long-term measurements of PM2.5 mass concentrations and aerosol particle size distributions from 2008 to 2015, as well as hygroscopicity measurements conducted over one year (2008-2009) at Cabauw, The Netherlands, are compiled here in order to provide a comprehensive dataset for understanding the trends and annual variabilities of the atmospheric aerosol in the region. PM2.5 concentrations have a mean value of 14.4 mu g m(-3) with standard deviation 2.1 mu g m(-3), and exhibit an overall decreasing trend of -0.74 mu g m(-3) year(-1). The highest values are observed in winter and spring and are associated with a shallower boundary layer and lower precipitation, respectively, compared to the rest of the seasons. Number concentrations of particles smaller than 500 nm have a mean of 9.2 x 10(3) particles cm(-3) and standard deviation 4.9x10(3) particles cm(-3), exhibiting an increasing trend between 2008 and 2011 and a decreasing trend from 2013 to 2015. The particle number concentrations exhibit highest values in spring and summer (despite the increased precipitation) due to the high occurrence of nucleation-mode particles, which most likely are formed elsewhere and are transported to the observation station. Particle hygroscopicity measurements show that, independently of the air mass origin, the particles are mostly externally mixed with the more hydrophobic mode having a mean hygroscopic parameter kappa of 0.1 while for the more hydrophilic mode kappa is 0.35. The hygroscopicity of the smaller particles investigated in this work (i.e., particles having diameters of 35 nm) appears to increase during the course of the nucleation events, reflecting a change in the chemical composition of the particles. (C) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Everyday life and environmental change

This paper explores how daily changes in the physical environment intersect and connect with people’s everyday lives, routines and practices in the Maldives. Day-to-day life is often regarded as mundane and ordinary, and therefore not particularly worthy of study. As this paper argues, however, the everyday is central to understanding how environmental change occurs and how people respond to it. Much recent work has challenged the ontological separation of the human and non-human, yet approaches to examining environment-everyday connections have, to date, been largely one-directional, focusing on either how the environment impacts on human practices or is impacted by them. Using the notion of the everyday, this paper explores how ‘impacting on’ and ‘impacted by’ are entangled, ongoing cyclical processes that unfold daily. It draws on a series of innovative methodologies conducted with island-based communities to examine three keys changes in the physical environment that are taking place in the context of the recent and rapid development of tourism on inhabited islands: sand excavation and erosion, the appearance and removal of rubbish and debris, and the expansion of the built environment. The paper reveals the significance of these day-to-day changes and the ways in which they are accommodated by, and incorporated into, the spatial and temporal dimensions of people’s daily practices. It concludes by suggesting that an appreciation of the everyday can contribute to new understandings of human/non-human entanglements

Temperature and volatile organic compound concentrations as controlling factors for chemical composition of alpha-pinene-derived secondary organic aerosol

This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentrations on the chemical composition of particles formed in the dark ozonolysis of alpha-pinene. All experiments were conducted in a 5m(3) Teflon chamber at an initial ozone concentration of 100 ppb and initial alpha-pinene concentrations of 10 and 50 ppb, respectively; at constant temperatures of 20, 0, or -15 degrees C; and at changing temperatures (ramps) from -15 to 20 and from 20 to -15 degrees C. The chemical composition of the particles was probed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). A four-factor solution of a positive matrix factorization (PMF) analysis of the combined HR-ToF-AMS data is presented. The PMF analysis and the elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial alpha-pinene concentration (10 ppb) and at the highest temperature (20 degrees C). A higher initial alpha-pinene concentration (50 ppb) and/or lower temperature (0 or -15 degrees C) results in a lower oxidation level of the molecules contained in the particles. With respect to the carbon oxidation state, particles formed at 0 degrees C are more comparable to particles formed at 15 degrees C than to those formed at 20 degrees C. A remarkable observation is that changes in temperature during particle formation result in only minor changes in the elemental composition of the particles. Thus, the temperature at which aerosol particle formation is induced seems to be a critical parameter for the particle elemental composition. Comparison of the HR-ToF-AMS-derived estimates of the content of organic acids in the particles based on m/z 44 in the mass spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. Higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), while the organic acid functionalities account for an increasing fraction of the measured particle mass.Peer reviewe

Fragmentation inside proton-transfer-reaction-based mass spectrometers limits the detection of ROOR and ROOH peroxides

Proton transfer reaction (PTR) is a commonly applied ionization technique for mass spectrometers, in which hydronium ions (H3O+) transfer a proton to analytes with higher proton affinities than the water molecule. This method has most commonly been used to quantify volatile hydrocarbons, but later-generation PTR instruments have been designed for better throughput of less volatile species, allowing detection of more functionalized molecules as well. For example, the recently developed Vocus PTR time-of-flight mass spectrometer (PTR-TOF) has been shown to agree well with an iodide-adduct-based chemical ionization mass spectrometer (CIMS) for products with 3-5 O atoms from oxidation of monoterpenes (C10H16). However, while several different types of CIMS instruments (including those using iodide) detect abundant signals also at "dimeric" species, believed to be primarily ROOR peroxides, no such signals have been observed in the Vocus PTR even though these compounds fulfil the condition of having higher proton affinity than water. More traditional PTR instruments have been limited to volatile molecules as the inlets have not been designed for transmission of easily condensable species. Some newer instruments, like the Vocus PTR, have overcome this limitation but are still not able to detect the full range of functionalized products, suggesting that other limitations need to be considered. One such limitation, well-documented in PTR literature, is the tendency of protonation to lead to fragmentation of some analytes. In this work, we evaluate the potential for PTR to detect dimers and the most oxygenated compounds as these have been shown to be crucial for forming atmospheric aerosol particles. We studied the detection of dimers using a Vocus PTR-TOF in laboratory experiments, as well as through quantum chemical calculations. Only noisy signals of potential dimers were observed during experiments on the ozonolysis of the monoterpene alpha-pinene, while a few small signals of dimeric compounds were detected during the ozonolysis of cyclohexene. During the latter experiments, we also tested varying the pressures and electric fields in the ionization region of the Vocus PTR-TOF, finding that only small improvements were possible in the relative dimer contributions. Calculations for model ROOR and ROOH systems showed that most of these peroxides should fragment partially following protonation. With the inclusion of additional energy from the ion-molecule collisions driven by the electric fields in the ionization source, computational results suggest substantial or nearly complete fragmentation of dimers. Our study thus suggests that while the improved versions of PTR-based mass spectrometers are very powerful tools for measuring hydrocarbons and their moderately oxidized products, other types of CIMS are likely more suitable for the detection of ROOR and ROOH species.Peer reviewe

Types, obstacles and sources of empowerment in co-design: the role of shared material objects and processes

Co-design is intrinsically linked to the notion of empowerment, however little research has focussed specifically on understanding the types, obstacles and sources of empowerment in co-design. This paper combines theoretical investigations with observations derived from co-designed research by academic and non-academic partners to explore these issues, in particular, the role of shared material objects and processes in supporting empowerment during co-design. The paper uses the notions of ‘power over,’ ‘power to’, ‘power with’ and ‘power within’ to tease out different aspects of empowerment, and draws on empirical observations to determine different obstacles and sources associated with each. The study therefore makes a theoretical contribution to the understanding of co-design as an empowerment process and should be useful for design researchers undertaking co-design projects with non-experts

Patterns of suspended particulate matter across the continental margin in the Canadian Beaufort Sea during summer

The particulate beam attenuation coefficient at 660&thinsp;nm, cp(660), was measured in conjunction with properties of suspended particle assemblages in August 2009 within the Canadian Beaufort Sea continental margin, a region heavily influenced by freshwater and sediment discharge from the Mackenzie River, but also by sea ice melt. The mass concentration of suspended particulate matter (SPM) ranged from 0.04 to 140&thinsp;g&thinsp;m−3, its composition varied from mineral to organic dominated, and the median particle diameter determined over the range 0.7–120&thinsp;µm varied from 0.78 to 9.45&thinsp;µm, with the fraction of particles &lt;1&thinsp;µm in surface waters reflecting the degree influenced by river water. Despite this range in particle characteristics, a strong relationship between SPM and cp(660) was found and used to determine SPM distributions across the shelf based on measurements of cp(660) taken during summer seasons of 2004, 2008, and 2009. SPM spatial patterns on the stratified shelf reflected the vertically sheared two-layer estuarine circulation and SPM sources (i.e., fluvial inputs, bottom resuspension, and biological productivity). Along-shelf winds generated lateral Ekman flows, isopycnal movements, and upwelling or downwelling at the shelf break. Cross-shelf transects measured during three summers illustrate how sea ice meltwater affects river plume extent, while the presence of meltwater on the shelf was associated with enhanced near-bottom SPM during return flow of upwelled Pacific-origin water. SPM decreased sharply past the shelf break with further transport of particulate matter occurring near the bottom and in interleaving nepheloid layers. These findings expand our knowledge of particle distributions in the Beaufort Sea controlled by river discharge, sea ice, and wind, each of which is sensitive to weather and climate variations.</p

Lo-Fi Matchmaking: A Study of Social Pairing for Backpackers

There is a new world emerging around mobile social networks and the technologies used to facilitate and mediate them. It is technically feasible for mobile social software such as pairing or matchmaking systems to introduce people to others and assist information exchange. However, little is known about the social structure of many mobile communities or why they would want pairing systems. When these systems are built, it is not clear what the social response by those communities will be or what the systems will be like to use in practice. While engaged in other work determining requirements for a mobile travel assistant we saw a potentially useful application for a pairing system to facilitate the exchange of travel information between backpackers. To explore this area, we designed two studies involving usage of a low-fidelity role prototype of a social pairing system for backpackers. Graphs of the resulting social pairings showed backpackers who were hubs in the network of travel information. It also demonstrated the effect of travel direction on information utility. Backpackers rated the utility of different pairing types, and provided feedback on the social implications of being paired based on travel histories. Practical usage of the social network pairing activity and the implications of broader societal usage are discussed

Sediment-laden sea ice in southern Hudson Bay: Entrainment, transport, and biogeochemical implications

During a research expedition in Hudson Bay in June 2018, vast areas of thick (>10 m), deformed sediment-laden sea ice were encountered unexpectedly in southern Hudson Bay and presented difficult navigation conditions for the Canadian Coast Guard Ship Amundsen. An aerial survey of one of these floes revealed a maximum ridge height of 4.6 m and an average freeboard of 2.2 m, which corresponds to an estimated total thickness of 18 m, far greater than expected within a seasonal ice cover. Samples of the upper portion of the ice floe revealed that it was isothermal and fresh in areas with sediment present on the surface. Fine-grained sediment and larger rocks were visible on the ice surface, while a pronounced sediment band was observed in an ice core. Initial speculation was that this ice had formed in the highly dynamic Nelson River estuary from freshwater, but δ^{18}O isotopic analysis revealed a marine origin. In southern Hudson Bay, significant tidal forcing promotes both sediment resuspension and new ice formation within a flaw lead, which we speculate promotes the formation of this sediment-laden sea ice. Historic satellite imagery shows that sediment-laden sea ice is typical of southern Hudson Bay, varying in areal extent from 47 to 118 km2 during June. Based on an average sediment particle concentration of 0.1 mg mL^{–1} in sea ice, an areal extent of 51,924 km2 in June 2018, and an estimated regional end-of-winter ice thickness of 1.5 m, we conservatively estimated that a total sediment load of 7.8 × 106 t, or 150 t km^{–2}, was entrained within sea ice in southern Hudson Bay during winter 2018. As sediments can alter carbon concentrations and light transmission within sea ice, these first observations of this ice type in Hudson Bay imply biogeochemical impacts for the marine system

Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N)

Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation. However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show that the region is characterized by a relatively large change of the seasonal freshwater content, corresponding to ~2 m of freshwater, and that solar heating during the short open water period results in surface layer temperatures above 1 °C. Observations of temperature and salinity supported that the outlet glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat of sea ice adjacent to the terminus and the duration of open water