Bo L. B. Wiman

Aerosol depletion and deposition in forests—A model analysis

A system of partial differential equations is developed to describe an aerosol entering from an open field into a downwind forest, where deposition and turbulent transfer affect particle concentration. The model considers the interplay between forest structure, open field and forest aerodynamics and aerosol characteristics. The modelling problem is broken down into a set of simpler submodels which can be refined or simplified individually. Model results suggest, basically, significant horizontal (vertical) depletion of super-μm particles downwind from the forest edge (downwards from the canopy top). Distinct edge effects in deposition rates are common. In certain cases vertical exchange processes predominate, leading to enrichment of the aerosol. Sub-μm particles (unless extremely small) are subject to almost negligible depletion and edge effects. Deposition of super-μm particle oriented aerosols are governed by a complex interaction between particle size, forest structure and aerodynamics whereas deposition of sub-μm particles is simply controlled by particle concentration and forest structure. Under certain conditions (dense homogenous forests) aerosol particle concentration across the open field to forest roughness transition increases again after initial depletion.

Aerosol characteristics in a mature coniferous forest—Methodology, composition, sources and spatial concentration variations

A forest site in southern Sweden representative of a wider range of coniferous forest Londscapes has been characterized with respect to aerosol composition (NO−3, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn. Br and Pb). In one series aerosol sampling was carried out simultaneously along a horizontal transect with four stations, one located in open field, one at the forest edge and two within the forest. In another series simultaneous sampling was performed along a vertical transect with four sampling points, one located below but near the canopy top and the others further downwards through the canopy (height c. 25 m). Sampling strategy and analytical methods are presented in detail. Statistical analyses of concentration data suggest that K, Ca, Ti, Mn and Fe in the coarse particle fractions originated from soil, whereas other components (S, V, Cu and Pb) were of mainly anthropogenic origin. Depletion of coarse fraction concentrations within the forest was detected for several elements, whereas spatial variations of fine fraction concentrations showed weak or no systematic trends. This result is interpreted as a net effect of counteracting mechanisms in the forest: losses due to deposition and inputs due to turbulence and gravitationally settling particles.

Implications of environmental complexity for science and policy

Theoretical as well as empirical reevaluations of nature are occurring in response to failures to predict environmental changes, recent developments in systems theory, and new research into environmental attitudes. At present, holistic concepts in ecological theory are marked by dissension, and environmental policy is beset with turmoil — both situations are due in part to differing perceptions of the role of complexity in natural systems. This article identifies and analyses links between changing scientific perspectives on nature and emerging perceptions of environmental policies. It is argued that because society faces basic uncertainty in predicting environmental futures, it is time to formulate a fundamentally new risk philosophy, complementary interdisciplinary management approaches, and a more modern attitude towards efficient and renewable resource systems.

Aerosol concentration profiles within a mature coniferous forest—Model versus field results

Aerosol mass concentration profiles along a horizontal and a vertical transect in a forest are modelled from field site information on aerosol particle size distributions, forest structure and aerodynamics. Model outputs are compared with concentration profiles obtained from field measurements at the site. The comparisons suggest that model properties are qualitatively valid. Though field data are insufficient for a systematic quantitative test of model behaviour, the investigation does not indicate any quantitatively fundamental model deficiencies.

Metaphors, analogies, and models in communicating climate-change uncertainties and economics to policy: a note on a pre-UNCED U.S. case

Metaphors, analogies, and models in communicating climate-change uncertainty and economics to policy: a note on a pre-UNCED U.S. case

Diurnal Variations of Aerosol Concentrations Inside and Above a Young Spruce Stand: Modelling and Measurements

Aerosol characteristics and aerodynamic conditions above and inside forests are strongly dynamic, especially for landscapes subject to frequent frontal activity and episodic anthropogenic aerosol inflows. Using empirical data of 1-hr time- resolution a non-stationary partial differential equation model (based on K-theory and classical filtration theory for concentration and deposition variations in a forest) is shown reasonably capable of handling such temporal complexity, which is also shown to be reflected in a temporally complex deposition pattern.

Aerosols at air/water/land interfaces: modelling and measurements

Anthropogenic as well as natural aerosol-borne, ecologically active substances are transported and deposited in complex landscapes, such as characterized by forest/open-field, lake/forest, and sea/shore transitions (cf., Wiman et al., 1990). Aerosol mass exchange between the troposphere and natural waters has two important aspects: mass-flow towards (deposition) and from (bubble-bursting) the surface. However, despite substantial progress over the recent two decades uncertainties pertaining to the physico-chemical mechanisms and quantities defining source and, in particular, sink strengths, remain large (e.g., Wiman 1998). Much of the uncertainty is due to the limitations to current theory, to the methodological difficulties involved in field experiments, and to basic problems with generalising laboratory (such as wind-wave tunnel) results. The need for theoretical developments resides mainly in adequate handling of the strongly variable and coupled aerodynamics and hydrodynamics at natural water surfaces, and the resulting effects upon particle size distributions (and thus fluid dynamics behaviour) of aerosols. The methodological/empirical problems originate mainly in the fact that the system is one of multiple phases (ambient gases, hygroscopic as well as non-hygroscopic particles, air film interfacing with water film, in turn interacting with bulk water), wherein rapid processes must be studied, often under harsh experimental conditions implying a compromise between robustness and precision of measuring equipment.

Energy policy in the greenhouse: From warming fate to warming limit: Vol. 1. Florentin Krause, Wilfrid Bach and Jon Koomey. Earthscan Publications Ltd, London, 1990. xii 198 pp., [UK pound]17.50

Climate stability - a limited resource (Invited review of Krause F., Bach W. and Koomey J., Energy Policy in the Greenhouse: From Warming Fate to Warming Limit; Vol. 1, Earthscan Publications Ltd., London, 1990)

Designing Resource Systems for Sustainability: Safe-Fail versus Fail-Safe Strategies

The complexity of natural systems opens up new risk perspectives for resource utilization, but also new opportunities. Efficient use of renewable resources, and of carbon-sequestering techno-ecology, can be combined into aggregates. These aggregates could be designed to contribute to safe-failing environmental futures. Tactical and strategical ecological engineering, however, invokes crucial questions of an intangible character. These include accounting for attitudes towards nature so as to render possible local-specific, culturally acceptable and ‘bottom-up’ tailor-made designs of multiple-use and flexible resource systems. Indicators of progress with respect to sustainable development will have to be formulated for use on the local, regional and global scale. Such indicators would benefit from adopting non-conventional perceptions, aimed at tracking resource-use efficiency, and at recognizing the stabilizing as well as destabilizing qualities of the complexity provided by ecological systems.