Agrochemical spray drift; assessment and mitigation--a review

During application of agrochemicals spray droplets can drift beyond the intended target to non-target receptors, including water, plants and animals. Factors affecting this spray drift include mode of application, droplet size, which can be modified by the nozzle types, formulation adjuvants, wind direction, wind speed, air stability, relative humidity, temperature and height of released spray relative to the crop canopy. The rate of fall of spray droplets depends upon the size of the droplets but is modified by entrainment in a mobile air mass and is also influenced by the rate of evaporation of the liquid constituting the aerosol. The longer the aerosol remains in the air before falling to the ground (or alternatively striking an object above ground) the greater the opportunity for it to be carried away from its intended target. In general, all size classes of droplets are capable of movement off target, but the smallest are likely to move the farthest before depositing on the ground or a non-target receptor. It is not possible to avoid spray drift completely but it can be minimized by using best-management practices. These include using appropriate nozzle types, shields, spray pressure, volumes per area sprayed, tractor speed and only spraying when climatic conditions are suitable. Field layout can also influence spray drift, whilst crop-free and spray-free buffer zones and windbreak crops can also have a mitigating effect. Various models are available to estimate the environmental exposure from spray drift at the time of application.     

Acid deposition in rain over hills

A numerical model of the feeder-seeder mechanism of orographic rain (Carruthers and Choularton, 1983) is used to describe the development of acid rain due to collection by initially ‘clean’ raindrops, falling from mid-level clouds, of cloud drops formed in low-level polluted air. The process is most efficient over hills where considerable low-level enhancement by the feeder-seeder mechanism occurs. We describe the distribution of this enhancement over hills of various sizes, the associated acidity and the deposition rate of H⁺ ions. The largest acid deposition rates may be very localized and more than an order of magnitude greater than other modes of deposition such as the turbulent diffusion of cloud droplets to ground.     

A validated 2-D diffusion–advection model for prediction of drift from ground boom sprayers

Correct field drift prediction is a key element in environmental risk assessment of spraying applications. A reduced order drift prediction model based on the diffusion–advection equation is presented. It allows fast assessment of the drift potential of specific ground boom applications under specific environmental wind conditions that obey the logarithmic wind profile. The model was calibrated based on simulations with a validated Computational Fluid Dynamics (CFD) model. Validation of both models against 38 carefully conducted field experiments is successfully performed for distances up to 20 m from the field edge, for spraying on flat pasture land. The reduced order model succeeded in correct drift predictions for different nozzle types, wind velocities, boom heights and spray pressures. It used 4 parameters representing the physical aspects of the drift cloud; the height of the cloud at the field edge, the mass flux crossing the field edge, the settling velocity of the droplets and the turbulence. For the parameter set and range considered, it is demonstrated for the first time that the effect of the droplet diameter distribution of the different nozzle types on the amount of deposition spray drift can be evaluated by a single parameter, i.e., the volume fraction of droplets with a diameter smaller than 191 μm. The reduced order model can be solved more than 4 orders of magnitude faster than the comprehensive CFD model.     

Comparison of methods for measurement of cooling tower drift

An international comparison of methods for measurement of cooling tower drift has been performed at the Massachusetts Institute of Technology. Participants from Belgium, the United States and the Federal Republic of Germany participated in measurements of a spectrum of test environments, which span the range of cases which would typically be encountered in operating cooling towers. The environments differed according to droplet mass flux, droplet size distribution and gas speed. A wind tunnel was built to provide the various test environments, and a special optical drift measurement system was built to permit simultaneous monitoring of the environment sampled in the tests. Cases tested included both mechanical and natural draft cooling tower environments.Among the types of instruments tested are the pulsed laser light scattering system (PILLS), sensitive paper and other sensitive surface droplet impaction systems, isokinetic drift mass flux measurement systems and photographic systems. The results indicate that the instruments tested vary widely in their capabilities, with droplet sizing instruments being more effective in low load, small droplet size spectrum situations, and isokinetic mass and chemical assay techniques being most accurate in high load, large droplet distribution cases. Instruments relying upon thermodynamic state measurements in most cases agreed mutually within an order of magnitude. Their major source of error is believed to arise in the measurement of the gas stream relative humidity. This quantity is necessary for inferring the drift mass flux from the measurement provided by such instruments, which is the mixture saturation deficit or excess. For these tests the relative humidity was typically ⩽ 98%.     

Rates and mechanisms of cloud water deposition to a subalpine balsam fir forest

A resistance model for deposition of cloud droplets to a balsam fir forest canopy is described. The model accounts for impaction and sedimentation of cloud droplets, as well as evaporation and condensation of cloud water on canopy surfaces. It considers multiple height strata in the canopy, seven canopy component types in each stratum, and three size classes of cloud droplets. The model was tested against field data and was found to predict cloud water deposition rates in good agreement with measured values. Analysis of the model shows that in the windy, subalpine zone of New England for which the model was developed, advected cloud water can be deposited at rates on the order of tenths of a millimeter per hour, with deposition velocities ranging from 1 to 80 cm s⁻¹. Most of the cloud water deposition takes place in the top 3 m of the canopy. Inertial impaction is the dominant deposition mechanism, but sedimentation can be important at low wind speeds and in the interior of the canopy. Increases in wind speed cause increased deposition via impaction and decreased deposition via sedimentation.     

Foliar and ground deposits of fenitrothion following aerial application over a plantation forest

Abstract

Spray deposits were measured on spruce foliage at tree canopy level and on glass plates at ground level, after aerial application of an emulsion formulation of fenitrothion at the rate of 0.21 kg AI in 1.46 L per ha over a 16 ha plot in a plantation forest. Fenitrothion deposits were quantified by gas‐liquid chromatography. A wide variation was observed in deposits on foliage and at the forest floor. Deposits were relatively higher on foliar samples collected from the upwind side of a tree canopy than those on the downwind side. Similarly, the glass plate placed under a tree on the upwind side received relatively higher deposit than the one on the downwind side. However, the glass plates placed in the adjacent forest openings collected markedly higher deposits. Results clearly indicate filtration of the spray droplets by canopy foliage. Assessment of the average deposit of fenitrothion at ground level (mean deposit from all sampling locations) indicated that ca. 19.4% of the applied material reached the forest floor. Within a sampling station, correlation was poor between foliar depsits and those on glass plates under the same trees or in nearby clearings. Analysis of fenitrothion deposits on foliage collected at 1 and 2 h after application indicated that the droplets took, more than 1 h for deposition on the tree canopy. On the other hand, deposition on the glass plates at ground level appeared to be practically complete within 1 h post‐treatment. This was attributed to the higher sedimentation velocities of the larger droplets which tend to travel faster to the floor level than the smaller droplets which float for a longer period near the tree canopy.     

Comparison of calculated evaporation rates of water droplets with those of pesticide droplets measured in a wind tunnel by Dennison and Wedding (1984)

Abstract

Calculations, based on Fuchs’ (1959) formula, of evaporation rates of water droplets freely falling through air are compared with those of water‐based pesticide droplets measured by Dennison and Wedding (1984) in a wind tunnel. Results indicate that calculations of evaporation rates of water droplets, are not significantly different from measurements of that of water‐based pesticide droplets under conditions of 20 °C and 20% relative humidity, but different under other measurement conditions.     

The Atmospheric Effects of Thermal Discharges into a Large Lake

Concern for the biological and ecological effects of heated water has resulted in legal actions that will prevent power companies from dumping the waste heat from the majority of their new generating units into rivers and lakes. Many nuclear- and fossil-fueled plants now under construction, and even some now online, are being required to change from once-through cooling systems to other methods, such as wet cooling towers, cooling ponds, and spray canals, despite higher costs and lower thermal efficiencies. Yet, these alternate cooling procedures are not without their own environmental problems.

The primary weather change due to once-through cooling on a large water body is a small local increase in fogginess at the plant outfall. But the relative probability of significant local meteorological effects is much higher with alternate cooling procedures, since these reduce the area of heat and moisture transfer. It is therefore concluded that, from a meteorological point of view, the least undesirable way to dispose of waste heat is by using once-through cooling on large water bodies.     

Sensitivity of urban ozone formation to chlorine emission estimates

Recent evidence has demonstrated that chlorine radical chemistry can enhance tropospheric volatile organic compound oxidation and has the potential to enhance ozone formation in urban areas. In order to investigate the regional impacts of chlorine chemistry in southeastern Texas, preliminary estimates of atmospheric releases of atomic chlorine precursors from industrial point sources, cooling towers, water and wastewater treatment, swimming pools, tap water, reactions of chlorides in sea salt aerosols, and reactions of chlorinated organics were developed. To assess the potential implications of these estimated emissions on urban ozone formation, a series of photochemical modeling studies was conducted to examine the spatial and temporal sensitivity of ozone and a unique marker species for chlorine chemistry, 1-Chloro-3-methyl-3-butene-2-one (CMBO), to molecular chlorine emissions estimates. Based on current estimates of molecular chlorine emissions in southeastern Texas, chlorine chemistry has the potential to enhance ozone mixing ratios by up to 11–16 ppbv. Impacts varied temporally, with emissions from cooling towers primarily responsible for a morning enhancement in ozone mixing ratios and emissions from residential swimming pools for an afternoon enhancement. Maximum enhancement in CMBO mixing ratios ranged from 59 to 69 pptv.     

Investigation on downwind short-range transport of pesticides after application in agricultural crops

For the assessment of potential risks from total exposure to both spray drift and volatilised pesticides, field experiments in barley were carried out with insecticide application in May and June 2000. Pesticide concentrations in the air at the edge of the treated plot and at various distances in downwind direction were determined. The concentrations at 10 m distance were 0.29 and 0.58 microg/m(3) (lindane), 0.07 and 0.12 microg/m(3) (parathion) or <0.02 and 0.04 microg/m(3) (pirimicarb) after 1 d. To quantify the exposure of aquatic ecosystems, water containers simulating surface waters were placed in downwind direction of the plot at distances of 10 and 50 m. Lindane as the most volatile and most persistent of the investigated active substances showed the highest entries in surface water with 35 and 153 microg/m(2) after 1 d at a distance of 10 m, attributable to a larger extent to deposition of volatilised compound than to spray drift when drift reducing nozzles were used. Similar results were obtained for parathion, but at a lower level. Mainly due to its photolytic instability in water, pirimicarb decayed in surface water, where a maximum deposition was measured 2 h after application.     

Enhancement of the deposition of ultrafine secondary organic aerosols by the negative air ion and the effect of relative humidity

Deposition is an important process for the removal of aerosol particles. Negative air ion (NAI) generators can charge the ultrafine airborne particles and enhance their deposition rate. However, many NAI generators may also emit ozone and increase the concentration of particles in the presence of biogenic volatile organic compounds owing to the secondary organic aerosol (SOA) production. To validate the effectiveness of NAI generator, the authors investigated the enhancement effect of an NAI generator on the deposition of the ultrafine SOAs generated from the ozonolysis of d-limonene in a test chamber under controlled ventilation rate and relative humidity (RH). The experimental results demonstrated that compared with other effects, including the gravity, particle eddy diffusion, and the Brownian diffusion, the effect of NAIs is the most dominate one on the deposition of SOA particles onto the wall surface in the near-wall region (<1 cm away from the wall). According to these experiments, the tested NAI generator could efficiently enhance the deposition rate by an enhancement factor ranging from 8.17 ± 0.38 to 25.3 ± 1.1, with a low ozone production rate. This NAI generator had better performance on the deposition of the SOAs with smaller particle sizes and it performed even better under higher RH. The enhancement effect of the NAI generator was related to its high NAI production and electric field strength.

Implications: This study investigated a novel technique of negative air ion (NAI) generator that can enhance the precipitation of nano-scale secondary organic aerosol (SOA). The tested NAI generator can significantly improve the deposition rate of SOA with an enhancement factor of about 8.17 ± 0.38 to 25.3 ± 1.1. The enhancement factor rose when relative humidity increased.     

Fog as a Fresh-Water Resource: Overview and Perspectives

The collection of fog water is a simple and sustainable technology to obtain fresh water for afforestation, gardening, and as a drinking water source for human and animal consumption. In regions where fresh water is sparse and fog frequently occurs, it is feasible to set up a passive mesh system for fog water collection. The mesh is directly exposed to the atmosphere, and the foggy air is pushed through the mesh by the wind. Fog droplets are deposited on the mesh, combine to form larger droplets, and run down passing into a storage tank. Fog water collection rates vary dramatically from site to site but yearly averages from 3 to 10 l m⁻² of mesh per day are typical of operational projects. The scope of this article is to review fog collection projects worldwide, to analyze factors of success, and to evaluate the prospects of this technology.     

Determination of pendimethalin (PROWL®480 EC) spray drift from ground applications

Abstract

Pendimethalin herbicide (PROWL^®480 EC) spray drift was determined from ground applications representing the highest rate applied to corn in eastern Canada. A novel drift collector pattern was laid out on the ground immediately before herbicide application. Most of the drift collectors were located downwind of the application target area. The maximum labelled rate of 1.68 kg ai/Ha was applied on 2 occasions on separate sites. In both applications, drift collector cards indicated that concentrations of pendimethalin were not detectable outside the target zone (<0.01 μg/cm²) at or beyond the 10 metre drift collector stations. Risk assessment calculations indicated that non‐target organisms would not be at significant risk from off‐site movement of pendimethalin.     

电厂冲灰水回用于冷却循环水系统的试验研究

火电厂冲灰水经絮凝沉降和反渗透处理后用作电厂循环冷却水 ,经多项试验证明 ,此工艺方法技术可行 ,灰水处理回用后不会增加冷却水系统结垢和腐蚀 ,且回用灰水代替部分地下水增加了明显的经济效益。     

Buffer zone widths for honeybees from ground and aerial spraying of insecticides

The relative field hazards of insecticides to honeybees have been estimated by considering intrinsic toxicity levels and field application rates. This approach is extended here to a consideration of buffer zones downwind of sprayed areas by estimating the distance at which bees would encounter an LD(50) dose from spray drift. 'LD(50) distances' are determined for both ground and aerial spraying of ground crops in Britain using published data on spray deposition under various weather conditions. For ground spraying at low wind speeds (< or =3 m s(-1)), this zone of risk is up to 5 m for the great majority of compounds. Aerial spraying in unstable atmospheric conditions appears to produce drift deposits of about the same order of magnitude as from ground spraying at wind speeds of about 4 m s(-1), with maximum LD(50) distances of < or =40 m for chlorpyrifos, fenitrothion and triazophos. For aerial spraying in stable atmospheric conditions these distances would be much greater. Pieris brassicae larvae are contrasted with honeybees in their relative sensitivities to insecticides and consequent LD(50) distances.     

Measurements and modelling of the ozone deposition velocity to concrete tiles,including the effect of diffusion

A range of models were fitted to the experimental time-dependent curves for the deposition velocity of O₃ to concrete floor tile samples. The models included modified Langmuir isotherms assuming adsorption of O₃ on the material surfaces and models assuming direct reaction on and diffusion of O₃ into the material from the air. The best fit was obtained with a simple two-parameter model assuming direct reaction of O₃ with adsorbed surface water and direct diffusion of O₃ into the material from the air. However, models assuming an additional second-order reaction of O₃ with an adsorbed surface species with a given start mass gave improved curve fit in the first 500 min. Applying the best model to experimental data obtained over the whole air humidity range resulted in markedly lower equilibrium deposition velocities than those measured after 48 h. The modelling gave a deposition velocity minimum in the 50–70% relative air humidity range in agreement with observations. The deposition velocity minimum could be explained with a reduced constant for the reaction of O₃ with water or OH⁻ ions on the surface.     

The humidity dependence of ozone deposition onto a variety of building surfaces

Measurements of the dry deposition velocity of O₃ to material samples of calcareous stone, concrete and wood at varying humidity of the air, were performed in a deposition chamber. Equilibrium surface deposition velocities were found for various humidity values by fitting a model to the time-dependent deposition data. A deposition velocity-humidity model was derived giving three separate rate constants for the surface deposition velocities, i.e. on the dry surface, on the first mono-layer of adsorbed water and on additional surface water. The variation in the dry air equilibrium surface deposition velocities among the samples correlated with variations in effective areas, with larger effective areas giving higher measured deposition velocities. A minimum for the equilibrium surface deposition velocity was generally measured at an intermediate humidity close to the humidity found to correspond to one mono-layer of water molecules on the surfaces. At low air humidity the equilibrium surface deposition velocity of O₃ was found to decrease as more adsorbed water prevented direct contact of the O₃ molecules with the surface. This was partly compensated by an increase as more adsorbed water became available for reaction with O₃. At high air humidity the equilibrium surface deposition velocity was found to increase as the mass of water on the surface increased. The deposition velocity on bulk de-ionised water at RH=90% was an order of magnitude lower than on the sample surfaces.     

Cooling Pond Steam Fog

This paper is responsive to needs to describe and predict the environmental effects from power plant cooling ponds. A study was made to determine atmospheric and pond surface conditions required for steam fog to occur from power plant cooling ponds, to define the dimensions of the fog, and to collect data on deposition of ice. Data, collected principally at the 4-Corners Plant over a three-year period, included water surface temperature, ambient meteorological conditions and occurrence and magnitude of steam fog and ice deposition. With strong winds, the fog extended onshore without lifting. With light winds, the fog extended some distance onshore but then lifted to form stratus. With almost calm winds, the steam fog lifted over the pond and drifted downwind as stratus. Steam fog was observed in winds to 28 mph, air-water temperature differences from 21.5° to 68°F and in atmospheric stability categories C, D, E, and F. A fog index number, Ar/(e_s — e_a)°F/mbs, was defined and used for data interpretation, where Ar is temperature of water less temperature of ambient air, e_s is the saturation vapor pressure of the ambient air and e_a is the actual vapor pressure of the ambient air. The probability of occurrence of steam fog as a function of the fog index number varied from 0.04 for an index number less than 10 to 1.00 for an index number greater than 90. From the data, if fog occurred, its extent along the ground was &#x2265;100 feet 88% of the time, &#x2265;500 feet 35% of the time, &#x2265;1000 feet 18% of the time, and &#x2265;5000 feet 12% of the time. If stratus occurred its extent above ground was &#x2265;1 mile 91% of the time, &#x2265;5 miles 55% of the time and &#x2265;10 miles 36% of the time. Measurements showed that steam fog droplet sizes predominate in the 10 micron diameter size. Values of liquid water content up to 0.20 g/m³ were reported. Ice accretion data show build-up rates from 0.23 to 13 mm/hr of rime.     

Uptake of atmospheric mercury by deionized water and aqueous solutions of inorganic salts at acidic,neutral and alkaline pH

Mercury (Hg) is well known as a toxic environmental pollutant that is among the most highly bioconcentrated trace metals in the human food chain. The atmosphere is one of the most important media for the environmental cycling of mercury, since it not only receives mercury emitted from natural sources such as volcanoes and soil and water surfaces but also from anthropogenic sources such as fossil fuel combustion, mining and metal smelting. Although atmospheric mercury exists in different physical and chemical forms, as much as 90% can occur as elemental vapour Hg0, depending on the geographic location and time of year. Atmospheric mercury can be deposited to aquatic ecosystems through both wet (rain or snow) and dry (vapour adsorption and particulate deposition) processes. The purpose of the present study was to measure, under laboratory conditions, the rate of deposition of gaseous, elemental mercury (Hg0) to deionized water and to solutions of inorganic salt species of varying ionic strengths with a pH range of 2-12. In deionized water the highest deposition rates occurred at both low (pH 2) and high (pH 12). The addition of different species of salt of various concentrations for the most part had only slight effects on the absorption and retention of atmospheric Hg0. The low pH solutions of various salt concentrations and the high pH solutions of high salt concentrations tested in this study generally showed a greater tendency to absorb and retain atmospheric Hg0 than those at a pH closer to neutral.     

An application and review of the critical load concept to the soils of northern England

In common with other member states of UN-ECE, maps of critical loads of transboundary air pollutants are to be produced in the UK for different receptor (waters, soils and vegetation) types. These maps will be used as a tool for assessing different deposition scenarios with proposed pollution abatement strategies. This paper presents the methodology, results and a discussion of the principles used in applying critical loads of sulphur as a pilot study for soils in northern England. For the study area, critical load classes for soils vary with geology, drift cover and slope/elevation. The area of soils in which the critical load is exceeded varies significantly according to the type of deposition data utilised.