Landscape patchiness creates aerodynamic transitions zones that affect the exchange of nutrients and pollutants between the atmosphere and vegetation. Using an artificially generated NaCl aerosol, with its mass-versus-particle-size distribution characterised by an aerodynamic mean particle diameter of 1.6 µm and a geometrical standard deviation of 1.9, we investigate the forest-edge effect on aerosol deposition within a model oak (Quercus robur L.) canopy in a wind tunnel with a smooth up-wind surface, and provide quantitative estimates of deposition rates within the emulated beach-to-forest transition. The deposition rate is maximal around the forest edge with an enhancement factor in relation to the beach deposition of 2.4 for Cl^- and 2.0 for Na⁺. Results are in reasonable agreement with those obtained from deposition models, field studies, and other wind-tunnel based investigations. We find a tendency towards an edge effect also at the downwind forest end, which is in support of model predictions. Estimates of deposition velocities at the edge are 0.06 cms^-1 and 0.05 cms^-1 for Cl^- and Na⁺, respectively. Because of the edge effect the model forest’s deposition velocity is enhanced, being 1.4 times higher around the edge in comparison with the entire forest. This suggests that field measurements of deposition in the interior of a forest “island” in an otherwise open landscape would underestimate the deposition to the entire forest. Our results can help improve estimates of aerosol-borne inputs of nutrients or pollutants to forests that would experience shifts in meteorological regimes due to changes in climate and forestry practices, in particular with respect to deciduous species in coastal environments where forest-edge effects might be substantial.

Based on a novel combination of approaches and instruments, this article presents campaign-based results from atmospheric boundary layer (ABL) height and aerosol optical depth (AOD) measurements carried out at two different experimental sites in Sofia, as well as from three-point measurements of aerosol number concentrations. Several instruments (lidar (developed by the IE), ceilometer, aerosol particle counter, sun photometer and meteorological sensors) were used in this study. Based on joint interpretation of the instruments' data we assess the influence of the atmospheric aerosol in the planetary boundary layer and the significant influence of aerosol layers and high clouds on AOD values. Measurements of AOD in the city basin gave values in the range 0.22-0.41 for cloud-free skies, and up to around 0.8 under partly cloudy conditions. The information obtained during the two campaigns indicates that aerosol particle concentrations were lower in park areas than along heavy-traffic thoroughfares in the city, but higher than in the mountain area. In conclusion, our study demonstrates the potential of employing a broad array of instruments for the study of boundary layer and aerosol over large, valley-situated and heavily urbanized city areas.

Within the framework of aerosol deposition to vegetation we present a specially designed leaf wash-off method used in a wind-tunnel based study, where leaves of Quercus robur L. were exposed to NaCl aerosols. We summarise the principles and illustrate the method for two types of substances, the chloride ion and the sodium ion, and for two levels of aerosol exposure prior to leaf washing. On the average, in the low-exposure experiments (S1), the 1st (2nd) wash-off step provided 90% (96%) of the amount of Cl− on the leaves. In the high-exposure experiments (S2) the corresponding values were 96% and 99%. For sodium, the general dynamics resembles that of chloride, but the amounts washed off were, in both series, on the average below what would be expected if the equivalent ratio in the tunnel aerosol were to be preserved. Na+ showed adsorption and/or absorption at the leaf surfaces. The difference between the mean values of the amounts of chloride and of sodium washed off in S1 was not statistically significant, the mean Na+ to Cl− difference as a fraction of Cl− being minus 18%±27%; corresponding values for S2 were minus 16%±9%, however (p<0.05). In the latter case, 101±57 μequiv Na+ per m2 of leaf area were missing for the equivalent relationship 1:1 with Cl− to be met. Although uncertainties are thus large, this indicates the magnitude of the Na+-retention. The method is suitable not only for chloride, an inexpensive and easy-to-handle tracer, but also for sodium under exposure at high aerosol concentrations. Our findings will help design further studies of aerosol/forest interactions.

The paper presents the results from planetary boundary layer (PBL) height and aerosol optical depth (AOD) measurements carried out in two different experimental sites in Sofia as well as from three-point measurements of aerosol number concentration.

The main aim of the present investigation is to determine optical and microphysical characteristics of the atmospheric aerosol in three points of the valley and their variation during the PBL formation over urban area, park zone and mountain site. Four instruments (lidar, ceilometer, aerosol particle counter and sun photometer) were used in this study.

The experimental AOD data obtained at lambda = 500nm gave values in the range from 0.22 to 0.41 in case of cloud-free skies and up to around 0.8 under partly cloudy conditions. Aerosol particle counter data on aerosol-particle concentration variations in the size range 0.3-1 mu m provided supportive information on the evolution of the valley-mountain aerosol in time and height during the mixing layer development. Joint interpretation of sun photometer, aerosol lidar and ceilometer CHM 15k data allow the influence of the main part of the atmospheric aerosol in the planetary boundary layer to be accounted as well as the significant influence of aerosol layers and high clouds on AOD values.

This paper examines Earth System Science as a novel approach to global environmental change research. Drawing upon Michel Foucault's governmentality concept, the paper opens up the Earth System metaphor to political analysis and asks what it does to our understanding of nature and society as a governable domain. We trace the scientific practices that have produced the Earth System as a thinkable analytical category back to the International Geophysical Year in 1957. We also identify 'the Anthropocene' as a central and yet ambiguous system of thought for Earth System Science that harbours different strategies for sustainability in terms of (1) the persons over whom government is to be exercised; (2) the distribution of tasks and actions between authorities; and (3) contrasting ideals or principles for how government should be directed.

Advancing the understanding of the aerosol-capture efficiencies of forest components such as leaves and needles, and of the mechanisms that underpin these efficiencies, is essential to the many related issues of forest turnover of nutrients and pollutants. For idealized collectors (such as artificial plates or cylinders) aerosol-mechanics offers a means for calculating capture efficiencies. For living collectors, in particular deciduous leaves, experimental investigations become necessary to assist in formulating the sub-models of capture efficiency that are fundamental to the modelling of fluxes of aerosol-borne substances to forests. We here present wind-tunnel based methods and results for leaves of Quercus robur L. exposed to an aerosol whose mass versus aerodynamic particle size distribution is characterised by a geometric mean aerodynamic particle diameter around 1.2 mu m and a geometric standard deviation around 1.8. With respect to that distribution, and founded on a specially designed leaf wash-off method, we obtained average oak-leaf capture efficiencies ranging from 0.006% of the approaching aerosol mass flux at wind-speed 2 ms(-1) to 0.012% of the flux at wind-speeds 10 ms(-1), respectively. These values can be translated into deposition velocities (V (d) ) for a leaf ensemble with a given leaf area index (LAI). With LAI in the range 2-5 (commonly found in the field) and for wind-speeds 2, 5 and 10 ms(-1), resulting V (d) -values would be 0.02-0.05, 0.05-0.13, and 0.2-0.6 cm/s, respectively. To the extent comparisons are possible, our capture efficiency values are at the low end of the range of values reported by other researchers. The strong wind-speed sensitivity of V (d) has implications for the deposition of aerosol-borne substances to forests for which wind regimes may shift as a result of climatic and land-use changes.