Micro-flood (MF) technology for sustainable manufacturing operations that are coolant less and occupationally friendly

This paper presents a new technology for minimizing the use of metalworking fluids (MWFs) during the machining process that is atomization-less and occupational friendly. Micro-flood (MF) technology utilizes direct contact between the cutting tool and the MWF without the interaction of a gas medium. Experiments were conducted in high volume mass production environment turning HSLA (high strength low alloy) SAE 070Y steel. Machining performance and total air mass particulates were investigated in dry machining, Near dry machining (NDM) via atomized spray mist and MF technology. Open-atmosphere air monitoring indicated that total mass particulates behaved in an almost linear fashion with respect to gas atomization pressure, whereas the MWF flow rate demonstrated logarithmic trends in NDM applications using an atomized spray. Nozzle orientations directed upward into the air also produced higher mg/m³ concentrations (such as flank) than chip and rake face orientations that were directed down. Greater separation existed at higher gas atomization pressures, MWF flow rates and by changing the MWF type. At extreme limits, nozzle orientation affected mg/m³ concentration as much as 4–5 mg/m³ for water-miscible MWFs and 15–22 mg/m³ for non-water-miscible MWFs. Tool-life performance varied greatly among MWF type and flow rate, and in all cases MF technology performed better than NDM using an atomized spray mist. Direct and consistent MWF penetration to cutting zone using MF technology lowered tool-wear on the average of 12–75% compared to NDM at the same MWF flow rate. Compared to dry machining, NDM improved tool-wear on the average by 20–243%. In one case, tool-wear performance was improved by 616% at 0.15 mm using MF technology compared to dry machining at a nominal 0.925 mm tool-wear. Overall, a large mass reduction of particulates can be achieved employing MF technology that would have been unrealistic for an open-atmosphere machining environment employing an atomized spray mist. On the average, MF technology can maintain a total air mass particulate of less than 0.4 mg/m³ in the occupational work zone using MWF flow rates up to 1260 ml/h, regardless of the MWF classification. Atomized spray mist applications are capable meeting the 5 mg/m³ OSHA limit if MWF flow rates are less than 160 ml/h, air pressures are less than 0.137 MPa (20 psi) using water-miscible MWFs and air pressures are less than 0.0344 MPa (5 psi) using non-water-miscible MWFs.     

Evaluation of the effectiveness of low frequency workpiece vibration in deep-hole micro-EDM drilling of tungsten carbide

The application of micro-electrical discharge machining (micro-EDM) in deep-hole drilling is still limited due to the difficulty in flushing of debris and unstable machining. Present study introduces a simplistic analytical model to evaluate the effectiveness of low frequency workpiece vibration during the micro-EDM drilling of deep micro-holes. In addition, experimental investigation has been conducted to validate the model by studying the effects of workpiece vibration on machining performance, surface quality and dimensional accuracy of the micro-holes. The effect of vibration frequency and amplitude for three different settings of aspect ratios has been studied experimentally. Moreover, the vibration experiments have been conducted at different levels of gap voltages and capacitances in order to understand the effect of electrical parameters and effectiveness of low-frequency workpiece-vibration at different levels of discharge energies. It has been shown analytically that the effectiveness of low frequency workpiece vibration during micro-EDM drilling can be evaluated by a parameter ‘K_v’ (ratio of maximum acceleration of the vibrating plate in gravitational direction to gravitational acceleration ‘g’), which can be determined from the vibration frequency, amplitude and phase angle of the vibrating workpiece. The theoretical model reveals that for K_v > 1, the position of debris particles will be above the workpiece; thus can be flushed away from machined zone effectively. The experimental reasons for improved micro-EDM drilling performance at the setting of K_v > 1 are found to be the increased effective discharge ratio, reduced short-circuits and improved dielectric flushing. The experimental results also reveal that the low frequency vibration is more effective at the low discharge energy level, thus making it more suitable for micro-EDM. Considering the effect on both the machining characteristics and micro-hole accuracy parameters, vibration frequency of 750 Hz and amplitude of 1.5 μm was found to provide improved performance for the developed vibration device.     

Effect of air-exposed biocathode on the performance of a Thauera-dominated membraneless single-chamber microbial fuel cell (SCMFC)

To investigate the effect of air-exposed biocathode(AEB) on the performance of singlechamber microbial fuel cell(SCMFC), wastewater quality, bioelectrochemical characteristics and the electrode biofilms were researched. It was demonstrated that exposing the biocathode to air was beneficial to nitrogen removal and current generation. In Test 1 of 95%AEB, removal rates of ammonia, total nitrogen(TN) and chemical oxygen demand(COD)reached 99.34% ± 0.11%, 99.34% ± 0.10% and 90.79% ± 0.12%, respectively. The nitrogen removal loading rates were 36.38 g N/m~3/day. Meanwhile, current density and power density obtained at 0.7 A/m3 and 104 m W/m~3 respectively. Further experiments on opencircuit(Test 2) and carbon source(Test 3) indicated that this high performance could be attributed to simultaneous biological nitrification/denitrification and aerobic denitrification, as well as bioelectrochemical denitrification. Results of community analysis demonstrated that both microbial community structures on the surface of the cathode and in the liquid of the chamber were different. The percentage of Thauera, identified as denitrifying bacteria, maintained at a high level of over 50% in water, but decreased gradually in the AEB. Moreover, the genus Nitrosomonas, Alishewanella, Arcobacter and Rheinheimera were significantly enriched in the AEB, which might contribute to both enhancement of nitrogen removal and electricity generation.     

Finite element modeling of microstructural changes in turning of AA7075-T651 Alloy

The surface characteristics of a machined product strongly influence its functional performance. During machining, the grain size of the surface is frequently modified, thus the properties of the machined surface are different to that of the original bulk material. These changes must be taken into account when modeling the surface integrity effects resulting from machining. In the present work, grain size changes induced during turning of AA7075-T651 (160 HV) alloy are modeled using the Finite Element (FE) method and a user subroutine is implemented in the FE code to describe the microstructural change and to simulate the dynamic recrystallization, with the consequent formation of new grains. In particular, a procedure utilizing the Zener–Hollomon and Hall–Petch equations is implemented in the user subroutine to predict the evolution of the material grain size and the surface hardness when varying the cutting speeds (180–720 m/min) and tool nose radii (0.4–1.2 mm). All simulations were performed for dry cutting conditions using uncoated carbide tools. The effectiveness of the proposed FE model was demonstrated through its capability to predict grain size evolution and hardness modification from the bulk material to machined surface. The model is validated by comparing the predicted results with those experimentally observed.     

Reduction of hexavalent chromium by polypyrrole-modified steel mesh electrode

Adherent polypyrrole (ppy) films were electropolymerized from a para-toluenesulfonic sodium (PTS) solution on stainless steel mesh (SSM). Reduced ppy-modified SSM electrode can transfer Cr(VI) to Cr(III) effectively. Lower pH (<2) or higher temperature (>35 °C) is beneficial for the removal of Cr(VI). Electro-reduction achieved 90% removal efficiency after 21 min by cyclic voltammetry. The removal efficiency is 96–56% for one–six contact cycles between ppy and Cr(VI). SEM shows that ppy films on SSM have regular morphology with small nucleus of less than 1 μm in diameter.     

Innovative micro hole machining with minimum burr formation by the use of newly developed micro compound tool

The study focuses on the efforts for minimization of burr formation and improvement of hole surface roughness in micro through-hole machining. It deals with the development of micro compound tool which is consisting of a micro flat drill as the drilling part and a micro diamond-electroplated-grinding part for hole finishing. The finishing diameters of each drilling and grinding parts of the fabricated micro compound tool are 90 μm and 100 μm, respectively. The study focuses mainly on the effect of drill point angle and ultrasonic vibration applied during micro hole machining to the hole entrance and exit burrs formation. The used workpiece is made of stainless steel (SUS304) with a thickness of 100 μm. From the experiment, it was found that the tool having drill point angle of 118° resulted in a smaller burr formation although hole machining was conducted for 600 holes. Furthermore, the application of ultrasonic vibration during hole machining could improve the performance of the developed micro compound tool and decreased the burr size, especially the exit burr.     

Design and evaluation of an atomization-based cutting fluid spray system in turning of titanium alloy

Tool life has been a vital issue in machining titanium alloys. Recently, an atomization-based cutting fluid (ACF) application has been found to be an effective approach for cooling and lubrication in micromachining operations. In this study, an ACF spray system is developed for macro-scale turning of Ti–6Al–4V. The spray system is designed to minimize interaction between the fluid droplets, and the gas nozzle to control the divergence of the fluid droplets. Experiments are conducted to study the effect of five specific ACF spray parameters including fluid flow rate, spray distance, impingement angle, and type and pressure level of the droplet carrier gas on cutting forces, tool life, and chip characteristics. It has been observed that the combination of lower pressure (150 psi) air-mixed CO₂ with a higher flow rate (20 ml/min) and a larger spray distance (35 mm) produces a significantly longer tool life and broken chips. The results also reveal that the ACF spray system can extend tool life up to 40–50% over flood cooling.     

Modulation-assisted high speed machining of compacted graphite iron (CGI)

The application of controlled, low-frequency modulation (～100 Hz) superimposed onto the cutting process in the feed-direction – modulation-assisted machining (MAM) – is shown to be quite effective in reducing the wear of cubic boron nitride (CBN) tools when machining compacted graphite iron (CGI) at high machining speeds (>500 m/min). The tool life is at least 20 times greater than in conventional machining. This significant reduction in wear is a consequence of the multiple effects realized by MAM, including periodic disruption of the tool–workpiece contact, formation of discrete chips, enhanced fluid action and lower cutting temperatures. The propensity for thermochemical wear of CBN, the principal wear mode at high speeds in CGI machining, is thus reduced. The tool wear in MAM is also found to be smaller at the higher cutting speeds (730 m/min) tested. The feed-direction MAM appears feasible for implementation in industrial machining applications involving high speeds.     

Investigation on mechanism of phosphate removal on carbonized sludge adsorbent

For the removal of phosphate (PO₄^3 -) from water, an adsorbent was prepared via carbonization of sewage sludge from a wastewater treatment plant: carbonized sludge adsorbent (CSA). The mechanism of phosphate removal was determined after studying the structure and chemical properties of the CSA and its influence on phosphate removal. The results demonstrate that phosphate adsorption by the CSA can be fitted with the pseudo second-order kinetics and Langmuir isotherm models, indicating that the adsorption is single molecular layer adsorption dominated by chemical reaction. The active sites binding phosphate on the surface are composed of mineral particles containing Si/Ca/Al/Fe. The mineral containing Ca, calcite, is the main factor responsible for phosphate removal. The phosphate removal mechanism is a complex process including crystallization via the interaction between Ca^2 + and PO₄^3 -; formation of precipitates of Ca^2 +, Al^3 +, and PO₄^3 -; and adsorption of PO₄^3 - on some recalcitrant oxides composed of Si/Al/Fe.     

Growth,yield and system performance simulation of a sugarcane–eucalyptus interface in a sub-tropical region of Brazil

The sugarcane (Sacharum officinarum) monocropping has had a great socio-economic and environmental impact in Brazil, and agroforestry (AFs) has been considered as an alternative to its sustainable production. However, there is a lack of field experiments results under such conditions. Therefore, yield measurement across transect in the tree–crop interface in on-farm conditions, as well as the use of simulation models, may allow the evaluation of biophysical interactions between trees and crops and system productivity. In this work, plant growth and yield in a sugarcane–eucalyptus (Eucalyptus grandis) on-farm interface were evaluated. The experimental site had a Chromic Ferralsol soil and it is located in a sub-tropical region of Brazil. Availability of solar radiation for the crop along the transect was estimated and its effect on sugarcane dry matter production was evaluated. Using such relations, two sugarcane–eucalyptus AFs cycles were simulated to estimate system productivity. The field results showed that the trees presented a higher growth in the AFs, while the crop growth and yield were inversely proportional to their distance from the trees. The eucalyptus wood volume increased from 0.15 to 0.29 m³ per tree from monocropping to AFs. The sugarcane dry matter decreased from 35.1 to 8.70 t ha⁻¹ from the furthest to the closest position from tree along the transect. Simulations suggested that light was the main cause of the crop yield reduction, but the importance of competition for water and nutrients increased inversely according to tree distance. However, both simulated AFs provided land equivalent ratio (LER) similar to one (1). Field measurements and simulations indicate that agroforestry systems are a sound alternative for sugarcane cultivation in the studied region. Combination of on-farm studies and simulation models provided conditions to understand tree–crop interactions and to extrapolate field results so that the performance of a new system could be estimated.     

On the relationship between PM2.5 concentrations and regional-scale primary PM emissions for the United Kingdom: an issue of subsidiarity

A site-specific particulate matter PM source apportionment model has been used to estimate the contributions from local primary PM emissions, regional primary PM emissions and the regional background to PM_2.5 concentrations at 102 monitoring site locations and to the centres of 1 km × 1 km grid squares across the United Kingdom. The local primary PM contributions have then been compared with Europe-wide urban PM_2.5 increments estimated at 50 km × 50 km in European-scale integrated assessment models. It is concluded that Europe-wide PM increments used in policy analyses grossly underestimate urban PM concentrations obtained from the site-specific PM source apportionment model for the United Kingdom. Europe-wide urban PM_2.5 increments estimated at 5 km × 5 km scale are significantly improved, particularly for London, but underestimate those for smaller towns and cities by factors of 2–3. These underestimations have important air quality policy ramifications. Although environmental policies may well be best formulated at the European scale, the underpinning air quality modelling may be best carried out at the local scale.     

Effect of Silicon Powder Mixed EDM on Machining Rate of AISI D2 Die Steel

In this paper, the effect of silicon powder mixing into the dielectric fluid of EDM on machining characteristics of AISI D2 (a variant of high carbon high chrome) die steel has been studied. Six process parameters, namely peak current, pulse-on time, pulse-off time, concentration of powder, gain, and nozzle flushing have been considered. The process performance is measured in terms of machining rate (MR). The research outcome will identify the important parameters and their effect on MR of AISI D2 in the presence of suspended silicon powder in a kerosene dielectric of EDM. The study indicated that all the selected parameters except nozzle flushing have a significant effect on the mean and variation in MR (S/N ratio). Optimization to maximize MR has also been undertaken using the Taguchi method. The ANOVA analysis indicates that the percentage contribution of peak current and powder concentration toward MR is maximum among all the parameters. The confirmation runs showed that the setting of peak current at a high level (16 A), pulse-on time at a medium level (100 μs), pulse-off time at a low level (15 μs), powder concentration at a high level (4 g/l), and gain at a low level (0.83 mm/s) produced optimum MR from AISI D2 surfaces when machined by silicon powder mixed EDM.     

Agroforestry associating coffee and Inga densiflora results in complementarity for water uptake and decreases deep drainage in Costa Rica

The shade impact by Inga densiflora on water use and drainage in a coffee agroforestry system (AFS) was compared to coffee monoculture (MC) in Costa Rica. Rainfall interception, transpiration, runoff and soil water content were monitored during 3 years. Runoff was lower in AFS than MC (5.4 and 8.4% of total rainfall, respectively) and a higher water infiltration was observed under AFS. Still, the higher combined rainfall interception + transpiration of coffee and shade trees in AFS resulted in a lower drainage than in MC. No coffee water stress was recorded either in AFS or MC as relative extractable soil water remained above 20% during the dry seasons. Time course of soil water content showed enhanced access to soil water between 100 and 200 cm depth in AFS. This suggests complementarity for soil water between coffee and shade trees. The model HYDRUS 1D predicted that drainage at 200 cm depth accounted for a large fraction of annual rainfall (68% for MC and 62% for AFS). Climatic scenario simulations showed (1) a potential competition for water between coffee and shade trees when the dry season was extended by 4–6 weeks compared to actual, and (2) a severe reduction in annual drainage, but without competition for water when rainfall was reduced down to 40% of the actual.     

Effects of irrigation,fertilization and crop straw management on nitrous oxide and nitric oxide emissions from a wheat–maize rotation field in northern China

One-year winter wheat–summer maize rotation is the most popular double cropping system in north-central China, and this highly productive system is an important source of nitrous oxide (N₂O) and nitric oxide (NO) emissions due to the high fertilizer N and irrigation water inputs. To sustain the high crop production and mitigate the detrimental impacts of N₂O and NO emissions, improved management practices are extensively applied. The aim of this study is therefore to evaluate the effects of an improved management practice of irrigation, fertilization and crop straw on grain yield and N₂O and NO emissions for a wheat–maize rotation field in northern China. Using automated and manual chamber measuring systems, we monitored N₂O and NO fluxes for the conventional (CT, 2007–2008), improved (IT, 2007–2008), straw-amended (WS, 2008–2009), straw-not-amended (NS, 2008–2009), and no N-fertilizer treatments (WS–NN, 2008–2009), respectively, for one rotation-year. The grain yields were determined for CT and IT for three rotation-years (2005–2008) and for WS, NS and WS–NN for one rotation-year (2008–2009). The improved management of irrigation and fertilization reduced the annual N fertilization rate and irrigation amount by 17% and 30%, respectively; increased the maize yield by 7–14%; and significantly decreased the N₂O and NO emissions by 7% (p < 0.05) and 29% (p < 0.01), respectively. The incorporation of wheat straw increased the cumulative N₂O and NO emissions in the following maize season by 58% (p < 0.01) and 13%, respectively, whereas the effects of maize straw application were not remarkable. The N₂O and NO emission factors of applied N were 2.32 ± 2.32% and 0.42 ± 1.69% for wheat straw and 0.67 ± 0.23% and 0.54 ± 0.15% for chemical N-fertilizers, respectively. Compared to conventional management practices using high application rates of irrigation water and chemical N-fertilizer as well as the field burning of crop straw, the improved management strategy presented here has obvious environmentally positive effects on grain yield and mitigation of N₂O and NO emissions.     

Nanosecond pulsed laser micromachining of PMMA-based microfluidic channels

This paper reports an investigation into the effects of nanosecond laser processing parameters on the geometry of microchannels fabricated from polymethylmethacrylate (PMMA). The Nd:YAG solid-state pulsed laser has a wavelength of 1064 nm and a measured maximum power of 4.15 W. The laser processing parameters are varied in a scanning speed range of 400–800 pulses/mm, a pulse frequency range of 5–11 Hz, a Q-switch delay time range of 170–180 μs. Main effects plots and microchannel images are utilized to identify the effects of the process parameters for improving material removal rate and surface quality simultaneously for laser micromachining of microchannels in PMMA polymer. It is observed that channel width and depth decreased linearly with increasing Q-switch delay time (hence average power) and increased non-linearly with higher scanning rates and not much affected by the increase in pulse frequency.     

Headwater streams: neglected ecosystems in the EU Water Framework Directive. Implications for nitrogen pollution control

The European Union Water Framework Directive (WFD) aims to achieve the “good status” of waters by 2015, through monitoring and control of human impacts on “bodies of surface water” (BSWs), discrete elements for quality diagnosis and management. Headwater streams, however, are frequently neglected as they are not usually recognised as BSW. This poses limitations for the management of river catchments, because anthropogenic impacts on headwaters can constrain the quality of downstream rivers. To illustrate this problem, we compared nitrate levels and land use pressures in a small agricultural catchment with those recorded in the catchment in which it is embedded (Ega), and in the Ebro River Basin (NE Spain) comprising both. Agriculture greatly influenced water nitrate concentration, regardless of the size of the catchments: R² = 0.91 for headwater catchments (0.1–7.3 km²), and R² = 0.82 for Ebro tributary catchments (223–3113 km²). Moreover, nitrate concentration in the outlet of a non-BSW small river catchment was similar to that of the greater downstream BSW rivers. These results are of interest since, despite representing 76% of the length of the Ega catchment hydrographical network, only 3.1% of the length of the headwater streams has been identified as BSWs. Human activities affecting headwater streams should therefore be considered if the 2015 objective of the WFD is to be achieved.     

Using supercritical carbon dioxide as solvent to replace water in polyethylene terephthalate (PET) fabric dyeing procedures

Dyeing fabrics in supercritical carbon dioxide (SCD) instead of water can save energy, reduce water use and prevent pollution. The special pilot plant was designed to test dyeing procedures in supercritical carbon dioxide and the analyses of the results indicate major benefits as compared to water based procedures. The dyeing of polyethylene terephthalate (PET) fabric in supercritical carbon dioxide using special pilot plant was investigated. Disperse dye, C.I. (color index) Disperse Blue 79, was used in this study. After dyeing, rinsing in supercritical carbon dioxide, which removes the excess dyes, was also discussed. At the same dyeing conditions, K/S (color yield) of dyed fabric significantly increased with increasing the dye concentration from 1% o.w.f. (on weight of fabric) to 5% o.w.f. Dyeing temperature and pressure had a strong influence on the color yield. When the temperature rose above 110 °C, the increase in color yield was obvious. At 20 MPa, 120–130 °C, dyeing reached equilibrium after 60 min. The excess dye of the dyed PET fabric was small. The suitable condition in supercritical carbon dioxide for removal of excess dye from the dyed fabric was 70 °C, 20 MPa. The PET fabric dyed in supercritical carbon dioxide had good fastness and physical properties.     

Terra Preta Australis: Reassessing the carbon storage capacity of temperate soils

Soils developed on the sites of Australian Aboriginal oven mounds along the Murray River in SE Australia, classified as Cumulic Anthroposols under the Australian Soil Classification, are shown to have traits similar to the Terra Preta de Indio of the Amazon basin. Seven such sites were characterised and compared with adjacent soils. The Cumulic Anthroposols contained significantly (p < 0.05) more soil carbon (C), compared to adjacent non-Anthroposols. Solid-state ¹³C NMR spectroscopy showed that the C in the Cumulic Anthroposols was predominantly aromatic, especially at depth, confirming the presence of charcoal. Radiocarbon analysis carried out on charcoal collected from two of these sites showed that it was deposited 650 ± 30 years BP at one site and 1609 ± 34 years BP at the other site, demonstrating its recalcitrance in soil. The charcoal originated from plant material, as shown by SEM, and had high levels of Ca agglomeration on its surfaces. The Cumulic Anthroposols were shown to have altered nutrient status, with total N, P, K and Ca being significantly greater than in the adjacent soils throughout the profile. This was also reflected in the higher mean CEC of 31.2 cmol (+) kg^?1 and higher pH by 1.3 units, compared to the adjacent soils. Based on the similarity of these Cumulic Anthroposols with the Terra Preta de Indio of the Amazon, we suggest that these Cumulic Anthroposols can be classified as Terra Preta Australis. The existence of these soils demonstrates that Australian soils, in temperate climates, are capable of storing C in much higher quantities than has been previously recognised, and that this capability is founded on the unique stability and properties of charred organic matter. Furthermore, the addition of charcoal appears to have improved the physical and chemical properties of these soils. Together, this provides important support for the concept of soil amendment with “biochar”, the charred residue produced by pyrolysis of biomass, as a means for sequestering C and enhancing agricultural productivity.     

Effects of Asian dust events on atmospheric bacterial communities at different distances downwind of the source region

Aeolian dust particles arising from arid and semiarid zones are known to carry microbes by air currents. The effect of wind-borne bacteria on atmospheric bacterial population at various downwind distances from the dust source regions must be clarified, but has not yet been reported. This study monitored the bacterial abundance and community composition in outdoor aerosol samples in Beijing, China, which is close to the Asian dust source regions, and compared them with the results obtained in a distant region(Osaka, Japan).The Asian dust collected in Beijing contained(4 ± 3) × 10~4 bacterial cells/m~3, approximately~4 times higher than in Osaka. On 15 April 2015, Beijing experienced severe Asian dust events with a 1000-fold increase in bacterial abundance, relative to non-Asian dust days. Dominant bacterial phyla and classes in Asian dust collected in Beijing were Actinobacteria, Bacilli and Acidobacteria, and the bacterial community composition varied more widely than in Osaka.The bacterial community compositions differed between the Beijing and Osaka dusts, even for the same Asian dust events. These results indicated that aerosol bacterial communities nearer the dust source are more affected by eolian dust than their distant counterparts.     

The influence of long term trends in pollutant emissions on deposition of sulphur and nitrogen and exceedance of critical loads in the United Kingdom

In the United Kingdom, as with other European countries, land-based emissions of NO_x and SO₂ have fallen significantly over the last few decades. SO₂ emissions fell from a peak of 3185 Gg S in 1970 to 344 Gg S in 2005 and are forecast by business-as-usual emissions scenarios to fall to 172 Gg by 2020. NO_x emissions were at a maximum of 951 Gg N in 1970 and fell to 378 by 2005 with a further decrease to 243 Gg N forecast by 2020. These large changes in emissions have not been matched by emissions changes for NH₃ which decreased from 315 Gg N in 1990 to 259 in 2005 and are forecast to fall to 222 by 2020. The Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME) has been applied to model the spatial distribution of sulphur and nitrogen deposition over the United Kingdom during a 15-year time period (1990–2005) and compared with measured deposition of sulphate, nitrate and ammonium from the national monitoring network. Wet deposition of nitrogen and sulphur was found to decrease more slowly than the emissions reductions rate. This is attributed to a number of factors including increases in emissions from international shipping and changing rates of atmospheric oxidation. The modelled time series was extended to a 50-year period from 1970 to 2020. The modelled deposition of SO_x, NO_y and NH_x to the UK was found to fall by 87%, 52% and 25% during this period. The percentage area of sensitive habitats in the United Kingdom for which critical loads are exceeded is estimated to fall from 85% in 1970 to 37% in 2020 for acidic deposition and from 73% to 49% for nutrient nitrogen deposition. The significant reduction in land emissions of SO₂ and NO_x focuses further attention in controlling emissions from international shipping. Future policies to control emissions of ammonia from agriculture will be required to effect further significant reductions in nitrogen deposition.