Dust Pollution from Agriculture

Dust Pollution from Agriculture B Sharratt, USDA Agricultural Research Service, Pullman, WA, USA B Auvermann, Texas A&M AgriLife Research and Extension Center, Amarillo, TX, USA r 2014 Elsevier Inc. All rights reserved.

Glossary Dust Fine particulate matter, usually with an aerodynamic diameter of ≤10 µm. Emission factor Amount of particulate matter emitted per unit of a specific activity.

Dust as a Nuisance, Pollutant, and Natural Resource Dust is often visualized as particles that are carried great distances by the wind or that reflect light and seemly shimmer when suspended in the atmosphere. Dust also casts a dull appearance or haze on otherwise bright and clean surfaces. These particles are considered by some to be a nuisance because they can mask the true appearance of a surface and require work to restore the original appearance of the surface or they can irritate our eyes or pulmonary airway. To others, dust is a valuable natural resource because it is important in the formation of raindrops and soils. The poet Robert Frost may have envisioned dust as a valued resource when he composed the following verse to the poem A Peck of Gold in 1928: “All the dust the wind blew high Appeared like gold in the sunset sky, But I was one of the children told Some of the dust was really gold.”

Although this poem was written before the North American Dust Bowl of the 1930s and societal interest in natural resource conservation, farmers and land managers have long recognized dust as being the most precious of materials (gold) which comprise soils and sustain life. Early explorers were acutely aware of the adverse effects of dust on humans. For example, Meriwether Lewis of the Lewis and Clark Expedition (Moulton, 1991) noted “… soar eyes seem to be a universal complaint among those people; I have no doubt but the fine sand of these plains and river contribute much to this disorder” while traveling along the Columbia River in the United States Pacific Northwest in 1806. Governor-in-Chief George Simpson (1826) of the Hudson Bay Company noted “This district of country is subject to very high winds which, sweeping over the sands, raise such a cloud of dust as renders it dangerous, or even impossible, to leave the house …” while traveling near Walla Walla, Washington in 1826. Little did these explorers realize that this windblown dust was the parent material from which soils formed on the Palouse, one of the most productive wheat-producing regions in the world located on the eastern edge of the Columbia Plateau along the border of modern day Idaho and Washington. Since that time, human activities undertaken

Encyclopedia of Agriculture and Food Systems, Volume 2

PM2.5 Particulate matter having an aerodynamic diameter of ≤2.5 µm. PM10 Particulate matter having an aerodynamic diameter of ≤10 µm. TSP Total suspended particulate matter.

to support a growing population have expanded sources from which dust is emitted into the atmosphere or exacerbated conditions that cause dust to be emitted into the atmosphere. As a result of these activities and a greater awareness of public health, nations began to adopt laws in the mid-twentieth century to protect the health and welfare of its citizens. For example, the Clean Air Act of 1971 required the United States Environmental Protection Agency (USEPA) to establish National Ambient Air Quality Standards for Particulate Matter. Air Quality Standards were established for suspended particles having a nominal diameter of ≤45 µm, but more recent legislation has set standards for regulating much smaller particles suspended in the atmosphere. In this article, dust is defined more specifically as particles with an aerodynamic diameter ≤10 µm. This definition conforms to criteria used to describe particulate matter as a pollutant. Particulate matter having an aerodynamic diameter ≤2.5 µm (PM2.5) and ≤10 µm (PM10) are both regulated as pollutants. Many nations have created laws and established air-quality standards for regulating dust concentrations in the atmosphere. These air-quality standards were developed to protect citizens from the adverse effects of being exposed to dust. This article will, in part, review air-quality standards established by many nations throughout the world and describe techniques that are employed to measure dust concentrations in the atmosphere. Sources that contribute to the dust load in the atmosphere can be classified as either point or nonpoint sources. Point sources emit dust into the atmosphere from a specific source or location, whereas nonpoint sources emit dust into the atmosphere from diffuse or widespread areas. Perhaps, the biggest nonpoint source of atmospheric dust is the Saharan Desert. Warren et al. (2007) suggested that the Bodélé Depression, located along the southern edge of the Saharan Desert, is the dustiest place on Earth. Dust storms in the Bodélé Depression occur approximately 100 days per year. Other major nonpoint sources of dust include wildfires, wood or debris burning, construction and mining sites, unpaved roads, and motor vehicles. Major point sources of atmospheric dust include foundries, paper mills, refineries, and power plants. Agricultural activities also contribute to the dust load in the atmosphere. This is, perhaps, best evidenced by longterm records which indicate a rise in atmospheric dust

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concentrations after the introduction of European farming practices in the Pacific Northwest United States (Busacca et al., 1998) and southeastern Australia (McGowan et al., 2010). This article focuses on agricultural sources of dust and, where possible, strategies to control dust emissions from these sources. Although the goal of developing strategies is to reduce emissions to achieve compliance with air-quality standards, these strategies must also be sustainable to ensure a viable agricultural industry.

Environmental Regulations Many nations around the world have adopted air-quality standards to protect the health and welfare of its citizens against the adverse effects of air pollution. The World Health Organization, which has representation from 194 nations, has adopted a constitution that set guidelines on air pollutants including atmospheric dust. The guidelines established by the Organization recommend the respective daily PM2.5 and PM10 concentrations not exceed 25 and 50 µg m−3 and the respective annual PM2.5 and PM10 concentrations not exceed 10 and 20 µg m−3 (World Health Organization, 2005). There is no clear and unequivocal evidence that associates adverse health effects of people to exposure to specific concentrations of particulate matter in the atmosphere. This lack of evidence is, in part, due to the variability among people in their response to exposure to particulate matter. As a result, nations have adopted guidelines or air-quality standards on the basis of availability of resources and risk assessment. Air-quality standards adopted by individual nations may, therefore, be more relaxed or more stringent than World Health Organization guidelines. The European Union, for example, has adopted a daily PM10 Air Quality Standard of 50 µg m−3 that should not be exceeded more than 35 days per year (European Commission, 2011). The European Union has not set a daily air-quality standard for PM2.5, but has adopted an annual PM2.5 and PM10 Air Quality Standard of, respectively, 25 and 40 µg m−3. Similarly, Australia and New Zealand have adopted a daily PM10 Standard of 50 µg m−3, that is, respectively, not to be exceeded more than 5 and 1 day per year. The United States has adopted a daily PM2.5 Air Quality Standard of 35 µg m−3 that should not exceed the 98th percentile averaged over 3 years and a daily PM10 Air Quality Standard of 150 µg m−3 that should not be exceeded more than 1 day per year averaged over 3 years. Although annual concentrations of PM10 are not regulated, the United States has adopted an annual PM2.5 Air Quality Standard of 15 µg m−3. Chile, Costa Rica, and Mexico have adopted a daily PM10 Air Quality Standard similar to the United States (not to exceed 150 µg m−3). New air-quality standards for particulate matter were established by China in 2012. Before this time, no air quality standard had been established for PM2.5. The new air-quality standards, which are to be implemented by residential, industrial, and rural areas across China by 2016, include a respective daily PM2.5 and PM10 concentration not to exceed 75 and 150 µg m−3 and a respective annual PM2.5 and PM10 concentration not to exceed 35 and 70 µg m−3. Many communities across the world fail or have failed to comply with air-quality standards for particulate matter.

Emission of particulate matter from point and nonpoint sources can contribute to the dust load and exceedance of PM2.5 and PM10 Air Quality Standards. To achieve compliance, the relative contribution of sources to overall emissions is important in devising an abatement program. For this reason, emission factors have been established to identify the relative contribution of sources to the overall dust load. Emission factors are defined as the amount of particulate matter emitted per unit of specific activity and are used to document emission inventories in Australia (http://www. npi.gov.au/), Canada (http://www.ec.gc.ca/inrp-npri/), Europe (http://www.eea.europa.eu/publications/emep-eea-emissioninventory-guidebook-2009), and the United States (http://www. epa.gov/ttn/chief/).

Techniques to Measure Dust in the Atmosphere Dust in the atmosphere can be characterized by mass, number of particles, or size of particles using active and passive sensors. Active sensors rely on artificial aspiration to draw particles into the sensor whereas passive sensors use natural ventilation to guide particles into the sensor. Active sensors are seldom isokinetic and, thus, tend to underestimate or overestimate the mass or concentration of particles in the atmosphere. Passive sensors are dependent on wind to draw particles into the sensor and, therefore, are impractical for characterizing particles under stagnant atmospheric conditions. Although several active and passive sensors are highlighted in this section, other sensors have been developed or are commercially available to characterize atmospheric dust. Active sensors characterize particles in the atmosphere using optical detectors, β-attenuation analyzers, and filters. The DataRAM, DustTrak, E-sampler, and Grimm Environmental Dust Monitor characterize particles using optical detectors. These detectors measure the scattering or absorption of light passing through a column of air with the amount of scattering or absorption being proportional to concentration of dust in the column of air. These sensors can be programmed to measure near real-time mass or particle characteristics, including PM10. Beta-attenuation analyzers measure the intensity of β-rays passing through dust, which is generally collected on a filter. A reduction in intensity is due to absorption of β-rays by dust on an otherwise clean filter. The Tapered Element Oscillating Microbalance (TEOM) is a common instrument used to measure near real-time PM2.5 or PM10 concentration. The TEOM (Figure 1) aspirates the sedimentladen air, captures the particles on a filter affixed to the end of an oscillating element, and periodically measures the oscillating frequency of that element to ascertain either PM2.5 or PM10 concentration. Both the β-attenuation analyzer and TEOM are approved devices for measuring PM10 concentration in many nations including China, the United Kingdom, and the United States. Sensors that rely on filters to extract particles from an airstream are typically classified by the volume of air moving through the sensor. Both the low-volume and high-volume sampler aspirate air at a known rate through a preweighed hydrophobic filter. The change in weight of the filter over time provides a time-integrated measure of dust in suspension. The high volume sampler (Figure 1) is the most

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Figure 1 A Tapered Element Oscillating Microbalance (TEOM) and three High Volume samplers for measuring PM10 concentration on the leeward side of an erodible field. The inlet to the TEOM (foreground) is located above the silver enclosure (door to the enclosure is open) whereas the inlets to the High Volume samplers (behind and to the left of the TEOM) are protected by a windshield and positioned at 1, 3, and 5 m above the soil surface. Figure 3 A profile of Big Spring Number Eight sensors used to trap windblown sediment. The fins (rectangular objects to the left) maintain alignment of the sensors into the wind. The airstream enters through the rectangular opening on the windward face and exits through the wedge-shaped screen on the top of the sensor.

Figure 2 A profile of Modified Wilson and Cooke sensors used to trap windblown sediment. The mast to the right of the sensors maintains their alignment into the wind. Photo courtesy of Dr. R. Scott Van Pelt, Big Spring, TX, USA.

common instrument employed by regulatory agencies throughout the world for measuring PM10 concentration. Passive sensors include the Modified Wilson and Cooke (MWAC) (Wilson and Cooke, 1980), Big Spring Number Eight (BSNE) (Fryrear, 1986), and Wedge Dust Flux Gauge (WDFG) (Hall et al., 1994). These sensors manually collect airborne sediment during high wind events and are typically inspected and cleaned after each event. Another passive sensor, the Suspended Sediment Trap (SUSTRA), weighs the collected sediment for automated real-time characterization of particles (Janssen and Tetzlaff, 1991). The most widely used passive sensors include the MWAC (Figure 2) and the BSNE (Figure 3). Passive sensors vary in sampling efficiencies (percentage of sediment trapped inside the sensor to that entering the sensor) due to differences in design characteristics of the sensors. For example, the sampling efficiency of the MWAC,

BSNE, WDFG, and SUSTRA sensors, respectively, vary from 90%, 40%, 22%, to 15% when trapping particles ≤63 µm in diameter at a wind speed of 5 m s−1 (Goossens and Offer, 2000). Particle size and wind speed can dramatically affect the sampling efficiency with efficiencies typically being higher when trapping larger particles or trapping particles at lower wind speeds (Goossens et al., 2000; Sharratt and Feng, 2009). Sharratt and Feng (2009) observed the BSNE sensor trapped PM10 with greater efficiency at lower wind speeds with an efficiency of approximately 15% and 30% when exposed to respective wind speeds of 8 and 3 m s−1.

Sources of Agricultural Dust Dust can be generated by a multitude of activities within the agricultural industry. These activities might include traveling on unpaved roads, using an internal combustion engine, stockpiling manure, transporting feed or fiber from the field to market, feeding livestock, cleaning pens or machines, aerial spraying, and welding. This article focuses attention on two main sources of agricultural dust that pollute the atmosphere, namely, agricultural facilities and lands. Dust emitted from agricultural facilities occurs primarily from enclosures that confine livestock and store or process raw materials into feed, fiber, food, and fuel. These facilities are regulated as point sources because activities that generate dust are confined to enclosures or buildings often occupied by workers. Dust emitted from agricultural lands result primarily from natural events (e.g., high wind event) and farming operations (e.g., harvesting crops).

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Agricultural Facilities Agricultural facilities, or primarily those enclosures that confine livestock and store or process raw materials into feed, fiber, food, and fuel, can contribute to the dust load in the atmosphere. These facilities generate dust from grinding, shearing, and pulverizing raw products; dander, hair, or feather shedding from animals; or vegetative particles from crop processing, storage, and transfer. Dust emitted from these facilities can be controlled through management practices that involve filtration, design, and husbandry. The primary risks associated with dust generated by agricultural facilities include explosions, respiratory impairment of humans or animals, nuisance (including associated odors) to neighbors, and reduced visibility (together with its associated traffic hazards). Explosions require confined spaces, threshold concentrations of entrained, flammable dusts, and an ignition source. Therefore, explosions are of concern in grain elevators, feed mills, and similar structures and facilities. Respiratory impairment of livestock and poultry in confined facilities may result in economically significant reductions in productivity or increases in maintenance costs. Exposure to dust in these facilities has more wide-ranging effects on humans, from reduced occupational productivity to impaired health. Agricultural dust as a nuisance can cause interferences in the use or enjoyment of property by neighbors whereas reduced visibilities caused by dust can be a safety hazard and detract from the enjoyment of particularly scenic areas. Our focus will be on livestock facilities and grain storage and processing facilities that are major sources of agricultural dust.

Livestock facilities The worldwide production of animal protein and its coproducts involve a nearly infinite spectrum of management systems. At one extreme, animals are free to roam across expansive and largely nonconfined areas. For example, cattle, sheep, and goats may be free to move within a rangeland or pasture, whereas swine and poultry may be free to roam an entire building and adjacent outdoor areas unconstrained by individual cages or pens. In these nonconfined facilities, animal excreta may be reincorporated into the landscape by natural processes or may be collected and stored for fuel or fertilizer. Dust generated from these nonconfined or open-lot facilities may originate from both animal activity as well as natural processes (erosion of the native landscape). At the other extreme, animals live in confined or concentrated facilities. Animals in these facilities are stocked more densely in space and, in the case of poultry or veal calves, raised in cages or small hutches. Confined beef operations may be either sheltered (under roof) or nonsheltered (open lot without roof) feedyards. Feedyards may have paved or earthen surfaces and be stocked at densities such that no vegetation can be maintained on the surface. Dairy operations may use open-lot facilities similar to beef feedyards, full confinement facilities like poultry buildings, or some intermediate form such as a free-stall barn with both sheltered and nonsheltered areas accessible to the herd. Swine are generally confined within roofed facilities, with animals being segregated according to developmental stage. In confined facilities, animal

excrement is periodically collected to avoid accumulation on the pen surface, which would otherwise impose stress on the animals or the broader environment. Dust from confined facilities can typically be distinguished from dust originating from the broader landscape. In the case of open-lot facilities, dust emissions are strongly modulated by weather, especially precipitation and wind speed. In contrast, dust emissions from under-roof facilities tend to be modulated more indirectly by air temperature and humidity as those variables affect mechanical ventilation rates. Some roofed facilities may be passively or naturally ventilated (instead of mechanically ventilated), in which case, dust emissions are relatively unaffected by precipitation but result primarily from the natural ventilation provided by the wind. Our focus of discussion will be on dust emitted from confined livestock facilities. Beef feedyards Beef cattle are increasingly fed in confinement worldwide to capture economies of scale, increase the rate at which retail beef can be brought to market, and access markets for highergrade beef cuts as compared with animals grazing pasture or rangeland. The United States is the leading producer of cattle for slaughter, but Australia, Canada, Argentina, Brazil, and Mexico also have significant cattle-feeding industries. Developing countries in Asia, Africa, and South America are witnessing rapid growth in the beef sector as long-term disposable income rises. Although it is possible to feed cattle in confinement in temperate and high rainfall areas, feeding systems in those areas tend to be under roof to reduce the amount of rainfall-driven wastewater that must be managed, controlled, and disposed. As a result, open-lot cattle feeding facilities tend to be more prominent in semiarid to arid climates such as the Great Plains and Southwest regions of the United States, the Prairie Provinces in Canada, and areas of Australia west of the Great Dividing Range in Queensland, New South Wales, and Victoria. The primary prerequisite for the development of a growing cattle sector is the availability of feed grains either from local farming or imported by rail, ship, or truck. Feed grains are the primary component in fed-cattle diets. In some regions, depending on grain markets and the scale of food-processing or biofuel-processing industries nearby, the concentrate (or energy and protein fraction) in fed-cattle diets may be provided by byproducts such as processed root vegetables (e.g., potatoes and beets) or spent grains (e.g., distillers grains and sweet bran). Dust emitted from cattle feedyards is derived primarily from manure excreted by the animals, therefore the type of feed provided to confined-beef cattle is thought to influence emission rates, airborne concentrations, and particle-size characteristics of dust. Although the cattle are in confinement, excreted manure is deposited on the pen surface and the feed apron (which may be earthen or paved). As the manure dries and is subjected to the animals' hoof action, it becomes part of the pen surface either as a well-compacted manure–soil matrix or as a noncompacted layer of material dominated by manure solids. Under dry conditions, any mechanical disturbance of the noncompacted manure layer – whether by wind scouring, animal hoof action, or operation of heavy machinery, will

Dust Pollution from Agriculture

generate dust particles and entrain them in the air. This dust, known as fugitive dust or dust emitted from a diffuse or nonpoint source, consists primarily of dried manure particles but will also include soil and waste feed particles, animal dander, exhaust from light vehicles and heavy machinery, dust from unpaved roads, and hair. Fugitive dust emitted from a feedyard surface tends to be dominated by relatively coarse particles. The median aerodynamic diameter of fugitive dust from feedyards is in the range of 15–25 µm. Sweeten et al. (1988) reported that the ratio of PM10 to total suspended particulate (TSP) in fugitive feedyard dust, as measured by high volume samplers, is in the range of 0.19–0.40. Less is known about the relative abundance of fine particles (PM2.5) in feedyard dust, but recent measurements suggest that the PM2.5/TSP ratio is on the order of 0.05. Rainfall events reduce coarse-particle emissions to a greater extent than fine-particle emissions such that both the PM10/TSP and PM2.5/TSP ratios increase temporarily following precipitation but return to original levels within days thereafter. Fugitive dust emissions from cattle feedyards are usually expressed as emission fluxes (mass per unit of pen area per unit time) or emission factors (mass per animal unit per unit time). These quantities are difficult to measure directly and are usually estimated by measuring dust concentrations both upwind and downwind of the source area. The measured dust concentrations are then input to a dispersion model to infer the emission flux that would have been required to generate the difference in measured concentrations. This indirect approach yields estimates of emission fluxes and emission factors that vary over an order of magnitude as shown in Table 1. The high uncertainty in values in Table 1 may be expected given the differences in climate, feedyard management practices, feed composition, aerosol monitor performance, and dispersion-modeling algorithms across all studies. Concentrations of fugitive dust in the air downwind of beef feedyards vary diurnally and seasonally depending on emission flux, topography, atmospheric stability, particle-size distribution, and the distance downwind from the source. Because these emissions occur at ground level, increasing atmospheric stability – associated with nighttime, dense daytime cloud cover, or atmospheric inversions – tends to favor higher ground-level concentrations. Even a short-term inversion may Table 1

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have a dramatic influence on ground-level PM concentrations, especially when the inversion coincides with periods of increased animal activity and depleted surface moisture. Under those conditions, which are quite commonly observed near sunset in semiarid and arid climates, short-term (5 min to 1 h) concentrations of fugitive dust may increase 10–15 times higher than the 24-hour average concentration (Figure 4). Although the absolute values of those evening peak concentrations vary up to 2 orders of magnitude from day to day, the diurnal pattern (especially in the summer) is remarkably consistent. To the extent that wind scouring is responsible for emissions from pen surfaces, wind speed, pen-surface moisture content, and stocking density will all be important factors in determining emission fluxes and predicting downwind concentrations. The mechanisms involved in these emissions will be closely analogous to those at play in wind erosion. To date, however, wind-driven emissions of dust from cattle feedyards remain a relatively unexplored research domain. Dairy cattle Half of the world's dairy production occurs in the European Union, India, and the United States. Dairy operations employ either low-density pasture systems or high-density feeding systems, or a hybrid of the two, depending principally on climate. Fugitive dust from dairy production is associated primarily with high-density systems in which the animals are housed on nonvegetated or minimally vegetated open lots or in free-stall barns with outdoor exercise areas. Superficially, open lots and exercise areas on dairies resemble cattle feedyards, in that pen surfaces begin as exposed mineral soil and evolve into soil–manure mixtures that are partially compacted in place by animal activity. These surfaces are susceptible to dust emissions as noncompacted manure dries and is aerosolized by hoof action, wind scouring, or machinery operations. Dust emission processes from confinement dairies, therefore, are fundamentally similar to those of beef feedyards. Factors that control emissions, however, can differ between beef and dairy operations. First, beef animals tend to be younger, smaller, and more active than lactating cows. This leads to differences in behavior and associated hoof action and moisture-excretion rates. Second, dairy pens are temporarily emptied once or twice daily as lactating cows are moved to the

Published emission factors and/or fluxes of fugitive particulate matter from open-lot beef cattle feedyards

Citation

Peters and Blackwood (1977) Parnell et al. (1999) Flocchini et al. (2001) Wanjura et al. (2004) Lange et al. (2007) McGinn et al. (2010) Bonifacio et al. (2012)

Study location

California (USA) Texas (USA) California (USA) Texas (USA) Texas (USA) Australia Kansas (USA)

Emission fluxa (kg ha−1 d−1)

Emission factorb (g per head d−1)

PM2.5

PM10

Total suspended particulate (TSP)

PM2.5

PM10

TSP

6 0.6–0.8 1.5–6 1.5 0.3–0.5 3–5 2–3

29 3–4 8–31 8 2–3 13–25 11–16

114 11–15 33–122 31 7–10 51–98 44–64

14 1.4–1.8 4–15 4 0.8–1.2 6–12 5–6

70 7–9 20–75 19 4–6 31–60 27–30

280 28–36 80–300 76 16–24 124–240 108–120

Emission fluxes in this table are computed from the published emission factors on the basis of a nominal animal spacing of 14 m2 per head. PM2.5 and PM10 are assumed to be 5% and 25% of TSP, respectively. b When primary data sources for these columns were provided on an animal unit basis, we have converted them to a per-head basis by assuming a nominal mean live weight of 454 kg per head. a

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Day 1

Day 2

3:00

6:00

12 Day 3

Day 4

10

C/C24 ratio

8

6

4

2

0:00

21:00

18:00

15:00

12:00

9:00

0:00

0

Time of day (local standard time) Figure 4 Typical daily variation of summertime mass concentrations (5-min averages) of fugitive PM10 downwind of a cattle feedyard in the south-central United States, normalized to the 24-h average PM10 concentration.

milking facility. Pens may then be groomed in the absence of livestock. In contrast, feedyard pens are emptied only when the cattle are being reimplanted or shipped to slaughter. Machinery operations for pen-surface maintenance on a beef feedyard must occur either when the animals are in the pen or after the cattle are shipped and the pen is empty. Third, harrowing the pen surface several times a week is commonplace in open-lot dairies. The primary reason for harrowing the pen surface in dairies is to maintain animal comfort, health, and milk production by giving the cows a softer surface on which to rest. Harrowing is not a common practice in beef feedyards except where needed to distribute bedding materials evenly across the surface. Fourth, the spatial density at which pens are stocked with animals differs widely between beef feedyards and open-lot dairies. Depending on climate, breed, topography, surface hydrology, and other factors, the average pen area allocated to a single dairy animal may be 1.5–3 times that allocated to a single beef animal. This difference in space allocation affects: the pen surface's susceptibility to wind scouring; flux of excreted and evaporated moisture; the nature and intensity of social interactions between animals; and the distribution, compaction, and rate of accumulation of manure solids. These characteristics influence dust emissions. In addition to the differences associated with pen surfaces, patterns of truck traffic differ markedly on dairies as compared with feedyards. Depending on the size of the milk-storage tank at a dairy and the size and productivity of the dairy's milking herd, milk tankers may drive in and out 5 to 10 times per day at relatively consistent intervals. This results in periodic emissions of road dust. By contrast, comparable heavy traffic on beef feedyards involves fewer trucks and more episodic ingress and egress. Dust concentrations downwind of open-lot dairies follow similar daily patterns to those of beef feedyards (Figure 5). As with feedyards, a pronounced evening peak in ground-level PM10 concentrations appears to be associated with temporary,

regional inversions that begin shortly before sundown and persist for 4–6 hours. Notably, the ratio of the peak concentration to the 24-hour average concentration appears to be consistently lower downwind of an open-lot dairy than downwind of a cattle feedyard. This observation presumably reflects the combined effect of the major differences, outlined above, between the two types of livestock systems. As with beef feedyards, estimates of PM2.5 and PM10 emission rates and fluxes from dairy operations vary widely (Table 2). Published research on fugitive dust emissions from open-lot dairies is much scarcer than that from beef feedyards; therefore, the uncertainties in emission estimates in Table 2 are at least as great as for beef feedyards. Sheep and goats Small ruminants, predominantly sheep and goats, were among the first livestock to be domesticated for food and fiber. The primary agricultural products of these animals are milk and milk products, meat, wool, mohair, and cashmere. Sheep and goats, because they are ruminants and highly adaptable, are also raised to control invasive plants. Domesticated sheep are primarily raised in China, Australia, India, Iran, Sudan, New Zealand, and the United Kingdom. The United States is responsible for less than 1% of the world's sheep production, with the top five sheepproducing states (Texas, California, Wyoming, Colorado, and South Dakota) being semiarid and coinciding partly with North America's cattle-feeding regions. World goat production is centered in Asia and Africa with more than half the production coming from China and India. India, Bangladesh, and the Sudan dominate world production of goat milk. Goat meat production is centered in China and India, with all other nations together contributing approximately 51%. Mohair production is now centered in South Africa, with Turkey, Australia, and New Zealand having important mohair industries.

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12 Day 1

Day 2

10

C/C24 ratio

8

6

4

2

0:00

21:00

18:00

15:00

12:00

9:00

6:00

3:00

0:00

0

Time of day (local standard time) Figure 5 Typical daily variation of summertime mass concentrations (5-min averages) of fugitive PM10 downwind of a large, open-lot dairy in the southwestern United States, normalized to the 24-h average PM10 concentration.

Table 2

Published or adopted emission factors and/or fluxes of fugitive particulate matter from various dairy-housing systems

Citation

USDA (2000) Goodrich et al. (2002, 2003) NAEI (2010) Countess Environmental (2006)c

Configuration/study location

Open-lot Free-stall, Texas Full confinement, UK Synthesis of data

Emission fluxa (kg ha–1 d–1)

Emission factorb (g per head d–1)

PM2.5

PM10

TSP

PM2.5

PM10

TSP

0.2 0.1–0.4 0.02 0.1

1.1 0.6–1.9 0.1 0.8

4.3 2.2–7 0.4 1.7

0.8 0.4–1.4 0.1 0.3

4 2–7 0.4 3

16 8–27 1.6 6.5

Emission fluxes in this table were computed from published emission factors on the basis of a nominal animal spacing of 37.2 m2 per head. PM2.5 and PM10 are assumed to be 5% and 25% of TSP, respectively, except where noted. b When primary data sources for these columns were provided on an animal unit basis, we have converted to a per-head basis on the assumption of standard Holstein cows having a nominal live weight of 636 kg per head. c PM2.5 and PM10 emission factors were determined on the basis of the California Air Resources Board guidance that assumes PM10 and PM2.5 are 48% and 5.3% of TSP, respectively. a

Most of the sheep and goats raised around the world are pastured, with sheep preferring grasslands and goats being raised in more woody or brushy rangelands. Animals raised for milk may be confined near the milking parlor during the winter months. Sheep and goats raised for meat or fiber typically live on pasture or range, but meat animals may be finished on grain-based diets to achieve desirable meat qualities. Nonvegetated sheep and goat feedlots are common in the United States and Australia and have many similarities to cattle feedyards and, to a lesser extent, open-lot dairies. As with the beef and open-lot dairy operations, dust emissions and downwind concentrations from sheep and goat feedlots are driven by regional climate, short-term weather phenomena, feeding and pen-surface management, and patterns of animal activity. However, researchers have not examined emission rates of fugitive dust from sheep and goat feedlots. Fully confined (i.e., in buildings or under roof) sheep and goat production does have a substantial presence in Europe, and limited research there has provided some estimates of

emission rates and concentrations of dust associated with total-confinement facilities. Aarnink et al. (2012) reported annual emissions of TSP at 69 g per head, PM10 at 22 g per head, and PM2.5 at 1 g per head from goat houses in the Netherlands. Dust emissions were largely attributed to the straw used for bedding inside the houses and, to a lesser extent, dry fecal material resuspended in air by animal activity. Papanastasiou et al. (2011) reported that PM10 and PM2.5 concentrations inside sheep houses in Greece varied inversely with ventilation rate, but they measured neither outdoor concentrations nor emission rates through the ventilation system. Swine and poultry Swine, poultry meat, and eggs are produced at respective annual rates of 110, 87, and 68 million metric tons worldwide, as compared with beef (62 million tons), mutton/lamb (14 million tons), and milk (671 million tons) (UNFAO, 2009). As nonruminants, pigs and poultry cannot be raised on grass or

494

Dust Pollution from Agriculture

other forages. Therefore, pork, poultry meat, and eggs are produced predominantly in a wide range of confinement systems. Swine and poultry facilities may be fully or quasi-confined, roofed or open-lot, actively or passively ventilated, and on earthen or paved surfaces. Quasi-confined facilities allow animals to move liberally around a relatively large and partialoutdoor environment, but are fed in specified locations. Examples of quasi-confined facilities include free-range areas for poultry and hoop barns for swine. By contrast, fully confined facilities are essentially designed to optimize the animals' stocking density and to control their environment for economic productivity. Although there is some trend toward quasi-confined facilities for the sake of animal-welfare considerations, the majority of swine, poultry meat, and eggs is produced under roof with controlled or semicontrolled indoor environments. As a result, most of the dust emitted from swine or poultry houses originates as an indoor air pollutant that poses health and productivity risks to both the animals and the workers. Where natural wind currents are insufficient to maintain acceptable indoor air quality, forced ventilation, and attentive dust-management practices in swine (Pedersen et al., 2000) and poultry houses are essential. Among all of the world's major livestock-production systems, swine and poultry houses have been the most extensively studied with respect to dust concentrations, characteristics, and emissions. Swine China accounts for nearly one-half, whereas the European Union accounts for 20% and the United States and Brazil together account for 10% of the world's swine production (USDA, 2012). Swine production generally involves the use of confined facilities with houses having paved or earthen floors, natural or artificial lighting, and passive or forced ventilation. Moreover, different growth stages of the animals may be raised in different housing types to ensure that animals in the growth stages most vulnerable to health impairment or productivity loss (sows, baby pigs, and breeding boars) are subjected to the least environmental stress. As a result, the sources, mechanisms, and characteristics of dust produced in swine houses may be meaningfully stratified by animal growth stage. For example, one recent study found that dust from a growingfinishing house, in which slaughter pigs were fed on a concrete, partially slatted floor, was composed primarily of feed, feces, and skin particles. In contrast, dust was largely composed of straw fragments when finishing houses used straw for bedding material (Aarnink et al., 2004). Reflecting the diversity in swine-production systems, Haeussermann et al. (2008) developed a mathematical model to predict PM10 emissions from swine facilities that accounted for variations in stocking rate, animal liveweight, animal growth stage, and characteristics of the housing system. The rate at which dust is emitted from swine houses is governed by the indoor dust concentration and the ventilation rate, both of which vary strongly with time. Estimating emissions from houses with forced-air ventilation systems involves continuously measuring the flow rate of air through the exhaust fans and synchronized monitoring of indoor dust concentrations at the fan intake (Hinz and Linke, 1998a). Emissions from passively ventilated houses are more difficult to measure and are characterized by greater uncertainty, as

airflow patterns (directions and flow rates) are highly variable. In a study at a swine finishing house, Hinz and Linke (1998b) found total dust concentrations as high as 5000 mg m−3 during the daytime when animal activity was high and as high as 2000 mg m−3 during the nighttime hours. Emission rates of inhalable dust (nominally PM10) from swine houses in northern Europe ranged from 121 to 1364 mg h−1 per 500 kg of animal liveweight in the house, suggesting that dust-emission rates scale approximately with each facility's animal capacity (Takai et al., 1998). Poultry Eggs, broiler chickens, turkeys, and other poultry products are important sources of animal protein throughout the world. The United States leads global production of broiler meat (20%), with China, Brazil, and the European Union together producing another 40%. The United States also produces more than half of the world's turkey meat, followed by the European Union, Brazil, and Canada (Pedersen et al., 2000). Of the approximately one trillion eggs produced globally per year, China produces approximately half and the United States another 10%. India, Japan, European Union, Mexico, and Russia round out the top seven egg-producing regions. Broiler and turkey houses are typically designed to raise the birds on bedding materials (e.g., sawdust, wood shavings, and crop residues) that optimize meat quality and growth rates while absorbing excreta. Dust from poultry raised for meat is composed of feather fragments, crystals from dried urine, feed and feces particles, bedding fragments, and microorganisms (Aarnink et al., 2004). Layer houses, by contrast, seldom have bedding; excreta are collected and removed frequently or even continuously. Animals in layer houses are raised in cages, or stacks of cages, that facilitate egg removal. As a result, dust from broiler and turkey houses differs from that of layer houses, both in composition and emission rates (Seedorf et al., 1998; Takai et al., 1998). As with swine facilities, dust emissions from broiler houses tend to scale with the total liveweight housed in a single building (Hinz and Linke, 1998b). In northern Europe, researchers (Takai et al., 1998) found that inhalable dust (nominally PM10) concentrations in caged-layer and broiler houses ranged from 750 to 1640 and 3830 to 10 360 mg m−3, respectively, with emission rates ranging from 398 to 872 and 1856 to 6218 mg h−1, respectively, per 500 kg of animal liveweight in the houses.

Processing and storage facilities Dust generated in facilities that process or store raw materials for manufacturing feed, food, fiber, or fuel is of particular concern to the occupational safety and welfare of workers within these facilities. Explosions and fires at grain-storage facilities are not uncommon and can result in death of occupants; such an explosion killed six workers at a facility in Atchison, Kansas in 2011. The health of occupants can also be impaired by inhaling dust within or near these facilities. Dust generated at grain-processing facilities can be even more hazardous than storage facilities because processing involves grinding grain into fine particles. Agricultural processing and storage facilities that are major sources of dust include cotton gins, grain elevators, and feed mills.

Dust Pollution from Agriculture

Cotton gins Cotton is a natural fiber derived from the fruit, or boll, of the woody plant. Cotton requires a long growing season with abundant sunshine; thus, it is grown throughout the desert, temperate, and tropical climates of the world. Most of the cotton produced worldwide comes from Asia (i.e., China, India, Pakistan), Brazil, Australia, Turkey, and the United States. In the United States, major cotton-growing states include California, Georgia, Mississippi, and Texas. Together, China and India are responsible for more than half of the world's cotton production. The mature cotton boll consists of three main parts, namely the seed, lint, and burr. The seed is high in protein and oil and is embedded within and attached to the lint; the lint consists of fibers used to manufacture fabrics. Modern cotton harvesting is highly automated and is accomplished with either a cotton picker or cotton stripper. Cotton pickers are designed to mimic the selective action of manual harvesting and may pass through a field more than once. Cotton strippers move more quickly through the field and strip nearly all of the bolls from the plant leaving behind the main stalk and larger stems. The raw products obtained from these two harvesters differ primarily in terms of the relative amounts of mature versus immature lint and the amount of nonlint material in the harvested bulk. Cotton ginning is essentially a two-stage mechanical process of removing gin trash (stems, burrs, soil, and other debris) from cotton bolls and separating the cotton fibers from the seed. The modern cotton gin originated in the late eighteenth century but has become a highly sophisticated, multistage, high-throughput operation that yields compressed lint bales weighing 200–225 kg. Cotton gins now consist of many specialized, mechanical processes (Figure 6). The conveyors in a cotton gin are pneumatic, using air flow at high speed to move the materials from point to point. Along the way, debris, lint, and seeds must be removed from the various air streams with the conveying air ultimately exhausted to the outside. Dust emissions from cotton gins originate from the exhaust of conveying systems within the gin enclosure. The dust consists of soil particles, insect fragments, and fragments of lint, leaves, stems, and other plant parts. Each of the specialized, mechanical processes within a gin produces a characteristic type of dust. Moreover, the manner in which the cotton is harvest (i.e., picker vs. stripper) strongly influences the load on each stage of the ginning process. Stripper-harvested cotton may generate 6–7 times as much trash during the ginning process as picker-harvested cotton (USEPA, 1995). As with most agricultural dusts, cotton gin dust is composed of both organic (plant-derived) and mineral (soil derived) particles. Most of the dust generated by cotton ginning, therefore, is relatively coarse with aerodynamic diameters exceeding 10 mm. The ratio of PM10 to TSP varies slightly between processes, but is typically between 0.25 and 0.5. In addition to the parent materials, dust associated with cottongin exhaust may also contain traces of chemical residues, including pesticides and harvest aids (defoliants). As implied by Figure 6, estimates of the total dust emissions from cotton gins are assembled from individual process emissions. As shown in Table 3, emissions are typically calculated from an emission factor for each process (mass of

495

particles per bale of cotton produced) multiplied by the gin's throughput (bales per unit of time). Modern, high-capacity gins can process 1500 bales per day. Concentrations of dust at ground level downwind of cotton gins depend on the efficiency of the control systems (cyclones and screens); the elevation of the exhaust points; the flow velocities, orientation, and temperatures of the exhaust streams; and atmospheric conditions. Every cotton gin is unique, but ground-level concentrations of PM10 and TSP have been measured over the past several decades. Recently, Hughs et al. (2008) measured respective daily PM2.5 and PM10 concentrations of 0.02–0.92 and 5–40 mg m−3 downwind of a gin in the southwestern United States. Grain elevators and feed mills Grain-storage and grain-processing facilities are found across a wide range of sizes, configurations, and capacities throughout the world. For example, individual farmers may have on-site bunkers and silos for grain storage. Local farmers' cooperatives typically have one or more storage elevators, sometimes known as country elevators, to facilitate grain marketing for their members. Animal-feeding operations may also use bunkers and silos to store and mills to process grains and other components into animal feed. Flour mills, bread factories, breweries, and other grain-processing industries may maintain on-site storage of grains to ensure adequate production capacity. Regional transfer facilities in larger towns and cities will aggregate grain from surrounding country elevators into numerous, large elevators for long-distance transport by rail or tractor-trailer. Terminals and processing facilities along major waterways or harbors will have sizeable elevators and mills to store and process a wide range of grains for import/export markets. At all scales, however, the dust associated with loading, unloading, transferring, storing, and processing grain has significant implications for human safety, human health, and environmental air quality. Grain dust, which is rich in organic carbon, is highly flammable and can detonate or deflagrate, with catastrophic results in fatalities, injuries, and loss of property. The risk of grain-dust explosions is present when the suspended dust concentration exceeds the minimum explosive concentration (MEC), dusty air is confined within an enclosed space, adequate oxygen is available to support combustion, and an ignition source (e.g., static electricity, electrical shorts or loose connections, unsealed motors, pilot lights, failing bearings between metal parts, and cigarettes) is present (Jones, 2011). Particles of grain dust are intrinsically flammable, but their explosive risk increases as particle size decreases. The MEC of grain dusts may be as low as 45–50 g m−3, with optimum explosive concentrations between 100 and 150 g m−3 (Gillis, 1985). Occupational health is at risk when grain-storage or grainprocessing workers do not wear adequate respiratory protection. Grain dusts may include soil particles, fragments of plant tissues and grains, insect fragments, mold spores, fungi, bacteria, viruses, and other biological aerosols. Even when biological aerosols are noninfectious, they may contain nonviable or dead organisms whose cellular components (e.g., endotoxins, lipopolysaccharides, and peptidoglycans) may be toxic to humans, with either chronic or acute health effects

496

Dust Pollution from Agriculture

Cotton cleaning system

Unloading system

Emissions (3-02-004-01)

No. 1 dryer and cleaner

Emissions (3-02-004-20)

Stick machine

No. 2 dryer and cleaner (No. 3 dryer and cleaner optional)

Emissions (3-02-004-21) (3-02-004-22)

Overflow system

Distributor

Emissions (3-02-004-25) - Optional process - Trash

Extractor/ feeder Lint cotton system

Cotton seed storage

Gin stands

No. 1 lint cleaner*

- Exhaust stream - Product stream - Low pressure side components

*

Emissions (3-02-004-07)

No. 2 lint cleaner* Mote fan

Mote cleaner

Emissions (3-02-004-35) Mote trash fan

Emissions (3-02-004-36)

Baled motes

Battery condenser and baling system*

Emissions (3-02-004-08) Master trash fan

Bale storage

Emissions (3-02-004-03) Solid waste

Cyclone robber system

Emissions (3-02-004-30)

Figure 6 Schematic of a modern cotton gin showing the numerous discrete processes that generate dust emissions (USEPA, 1995). Numbers in parentheses are Source Classification Codes used by the USEPA to categorize operations that emit particulate matter.

(Schwartz et al., 1995). Environmental air quality may also be a concern for neighboring residences and communities, especially for susceptible persons including the young, elderly, asthmatics, or those with weak or compromised immune function. In general, grain dust from elevators and feed mills is a class of air pollutants subject to governmental regulatory standards.

Emission rates from elevators and mills are generally computed using emission factors or process-weight tables and, similar to cotton gins, each discrete process within an elevator or mill will have its own emission factor (Figure 7). For example, the emission factor for grain cleaning in elevators or grain crushing in feed mills is at least twice that of receiving grain at either facility (Table 4). In addition, each

Dust Pollution from Agriculture

Table 3

497

Emission factors for modern cotton gins with high-efficiency cyclone controls on the exhaust streams (USEPA, 1995)

Source

TSP (kg bale−1)

PM10 (kg bale−1)

PM10/TSP ratio

Unloading fan #1 Dryer/cleaner #2 Dryer/cleaner #3 Dryer/cleaner Overflow fan

0.132 0.164 0.109 0.043 0.032

0.055 0.005 0.042 0.015 0.012

0.41 0.03 0.39 0.35 0.37

Lint cleaners: • with high-efficiency cyclones • with screen drums or cages Cyclone robber Mote fan Mote trash fan

0.264 0.500 0.082 0.127 0.035

0.109 – 0.024 0.059 0.010

0.41 – 0.29 0.46 0.27

Battery condenser: • with high-efficiency cyclones • with screen drums or cages Master trash fan Grand total

0.018 0.077 0.245 1.828

0.006 – 0.034 0.370

0.36 – 0.14 0.30

type of grain has its own intrinsic dustiness, which may vary with moisture content, harvest method, or other management factors (USEPA, 2003). In principle, then, there could be a unique emission factor for each permutation of grain type, grain condition, harvest method, and elevator or mill process.

Agricultural Lands Agricultural lands, primarily in the arid and semiarid regions of the world, contribute to the dust load in the atmosphere. The lack of precipitation in these regions impairs crop production and generally results in dry and poorly structured soils, both of which affect dust emissions from agricultural lands. Dust is emitted into the atmosphere from agricultural lands as a result of natural events and farming operations. Although natural events cannot be controlled or regulated, management practices or farming operations imposed on these lands can dramatically influence dust emissions.

Natural events High winds, volcanic eruptions, and wildfires are natural events that can affect atmospheric PM10 concentrations. Highwind events are of particular relevance to agriculture. Dust emitted into the atmosphere as a result of high winds eroding agricultural lands (Figure 8) constitutes 10% of the atmospheric dust load worldwide (Tegen et al., 2004). Windblown dust has contributed to exceedance of national PM10 airquality standards in China, Europe, and the United States (Liu et al., 2011; Escudero et al., 2007; Sharratt and Lauer, 2006). Long-range transport of PM10 from eroding agricultural land has also contributed to exceedance of PM10 air-quality standards. For example, transport from agricultural lands in the Ukraine have resulted in exceedance of the European Union air quality standard for PM10 (daily concentration not to exceed 50 µg m−3) in Slovakia, the Czech Republic, Poland,

and Germany (Birmili et al., 2008) whereas transport from agricultural lands in Africa has contributed to exceedance of the European Union PM10 air-quality standard in Spain (Escudero et al., 2007). Although intercontinental transport of dust has not contributed to the exceedance of PM10 Standards in the United States, erosion of agricultural lands in China (Wang et al., 2004) has contributed to a rise in PM10 concentrations in the Pacific Northwest of greater than 100 µg m−3 (Husar et al., 2001). In the United States, windblown dust generated from agricultural lands has contributed to exceedance of the PM10 Air Quality Standard in Arizona (Fields et al., 2001), California (Chow and Watson, 2001), and Washington (Sharratt and Lauer, 2006). Very few studies have examined the emission of PM2.5 or PM10 from agricultural lands during high-wind events (Table 5). Sharratt et al. (2007) measured a PM10 concentration of greater than 8500 µg m−3 above an eroding agricultural field during a high-wind event in eastern Washington. More recent field data collected in eastern Washington indicate that PM10 concentration and vertical flux can exceed those in Table 5. For example, PM10 concentration and vertical flux, respectively, exceeded 70 000 µg m−3 and 10 000 µg m−2 s−1 above an eroding agricultural field during a high-wind event on 3 September 2009 (Figure 9). The daily PM10 concentration at a 2 m height during this high-wind event was 1735 µg m−3. Others have measured concentrations and fluxes of fine particles above eroding agricultural fields, but these measurements have been limited to particles either smaller or larger than 10 µm in diameter. For example, Gillette et al. (1972) observed a vertical flux of PM6 (particles with aerodynamic diameters ≤6 µm) of 1 µg m−2 s−1 over an eroding field before sowing wheat in Nebraska. Gillette (1977) observed a vertical flux of PM20 (particles with geometric diameters of o20 µm) of 10 to 5×105 µg m−2 s−1 above eroding sands, loamy sands, sandy loams, and clays in Texas. Gomes et al. (2003) have reported vertical fluxes of PM20 of respectively 66 and 302 µg m−2 s−1 over eroding agricultural fields in Spain and Niger.

498

Dust Pollution from Agriculture

Truck/rail receiving

Barge/ship receiving

Conveyor

Conveyor

Optional Boot Intermediate storage bin (vent)

Tunnel belt

Leg

Receiving leg Annex storage bin (vent)

Grain dryer

Conveyor

Headhouse Distributor

Grain cleaner

Gallery belt

Interstice bin

Garner scale

Tripper

Storage bin (vent)

= Potential PM/PM-10 emission source

Conveyor Truck/rail shipping Barge/ship shipping

= Potential voc emission source

Figure 7 Schematic of emissions sources in a grain elevator (USEPA, 2003). VOC, volatile organic compound.

Table 4

Example emission factors for processes within grain elevators and feed mills in the United States (USEPA, 2003)

Process Feed mill: • Grain receiving • Hammer mill with cyclone • Feed shipping Grain elevator: • Grain cleaning with cyclone • Grain receiving, hopper truck • Grain handling

TSP emission factor (g mg−1)

PM10 emission factor (g mg−1)

PM10/TSP ratio

8.5 33.5 1.65

1.25

0.15

0.4

0.24

37.5 17.5 12.5

9.5 3.9 3.15

0.25 0.22 0.25

Dust Pollution from Agriculture

Two studies have estimated PM10 emissions from agricultural lands during high winds. Saxton et al. (2000) estimated PM10 vertical fluxes as high as 300 000 µg m−2 s−1 from agricultural fields during a design wind storm in some portions of the Columbia Plateau. These estimates, based on an integrated meteorological/chemical transport/PM10 emissions model, were not confirmed in the field. Xuan and Sokolik (2002) estimated an annual PM10 loss across gridded locations in northern China using an empirical model which estimates PM10 loss from surface characteristics and climate. Their analyses suggest that annual PM10 loss can approach 10 kg ha−1 in agricultural regions. Geologic material is generally composed of coarser particle matter and, thus, PM2.5 constitutes a small percentage of PM10 emitted from agricultural lands. For example, PM2.5 comprised from 4% to 7% of PM10 that was observed downwind of eroding agricultural lands in the Columbia Plateau region of the Inland Pacific Northwest (Sharratt and Lauer, 2006). Gillette and Walker (1977) measured the size distribution of particulate matter 1.5 m above eroding agricultural soils in Texas and found that PM2.5 comprised from approximately 1% to 4% of PM10. Best management practices to reduce dust emissions from agricultural soils during high-wind events are similar to those required to control wind erosion. These practices include the use of wind barriers, ridge tillage, tillage operations that enhance surface roughness or cover with crop

Figure 8 Dust rising from an isolated cultivated field during an October 2003 high-wind event near Ralston, WA, USA.

499

residue, mulching with vegetation or manure, cover crops, perennial, or multiyear crops, strip cropping, delayed tillage, and sowing when soil moisture is adequate for timely seed germination and emergence. Fields et al. (2001) estimated the reduction in emissions during a high-wind event in Arizona for various management practices and found that multiyear crops, residue management, and timing of tillage operations were the best strategies for reducing PM10 emission from cropland.

Farming operations Tillage, harvest, seeding, fertilizing, and spraying are routine farming operations that generate dust. Dust generated by agricultural operations is typically characterized by particles with diameters larger than 2.5 µm (Capareda et al., 2004) and, therefore, does not solely contribute to exceedance of the PM2.5 air-quality standard. Dust emitted into the atmosphere as a result of farming operations has contributed to the exceedance of the PM10 air-quality standards in the United States, most notably in California (Chow et al., 1992; Dolislager and Motallebi, 1999). Dust generated by farming operations is the second largest source, with road dust being the largest source, in the San Joaquin Valley of California (Cassel et al., 2003). Air stagnation in the Imperial Valley and San Joaquin Valley during the autumn, winter, and spring trap fine particles in the atmosphere that are emitted during tillage or harvest operations (Chow and Watson, 2001). In northern Europe, high atmospheric dust concentrations in the spring have been linked to tillage activities (Goossens, 2004). Tillage and harvest operations typically generate a higher proportion of coarse particulate matter (particulates with a diameter 2.5–10 µm) as compared with PM2.5 (Matsumura et al., 2003; Kasumba et al., 2011). Particulates emitted during tillage or land preparation operations are affected by the type of implement, speed of implement, surface characteristics (e.g., roughness and residue cover), soil properties (e.g., type and moisture), and atmospheric conditions. Particulates emitted during harvest, however, tend to be unique to each crop. Some crops require only one harvest operation (e.g., direct combine), whereas the harvest of other crops, such as nut trees, require multiple operations. Each operation can contribute to the particulate load in the atmosphere. Particulates can be emitted during the cutting, swathing, raking, or combining operations of field crops or the shaking, sweeping, and pickup operations of tree crops. For example, the harvest of almonds in California involves shaking the tree to allow the

Table 5 PM10 concentration, vertical flux and loss measured within eroding agricultural fields during a high-wind event. PM10 concentration was measured at various heights above an eroding surface Citation

Location

Height (m)

Concentration (mg m−3)

Vertical flux (mg m−2 s−1)

Gillette (1974) Zobeck and VanPelt (2006) Kjelgaard et al. (2004) Sharratt et al. (2007) Stetler and Saxton (1996)

Texas Texas Washington Washington Washington

2 3 5 1.5

2200 6500 8535 1255

10 000 0.48 258 255 260

Loss (kg ha−1)

212

Dust Pollution from Agriculture

Wind speed (m s–1) Vertical PM10 flux (mg m–2 s–1)

15

80

12 60 9 40 6 20 3

PM10 concentration (mg m–3)

500

0

0 0

6

12

18

24

Time (hour) Figure 9 Five-minute averages of wind speed at 2 m (black line), Tapered Element Oscillating Microbalance PM10 concentration at 1 (blue line) and 2 m (light blue line), and vertical PM10 flux (red line) above an eroding agricultural field during a September 2009 high-wind event in eastern Washington.

almonds to fall to the soil surface to air dry, sweeping the almonds on the soil surface into windrows, and picking up the almonds from the soil surface with a machine that separates the almonds from the soil and other debris. Each sequential operation emits one magnitude more PM10 into the atmosphere (Faulkner and Capareda, 2012). PM2.5 and PM10 emission factors for tillage and harvest operations are provided in Table 6. The range in emission factors for any operation is likely due to differences in atmospheric conditions (e.g., relative humidity), moisture content of soil, depth of tillage, implement speed through the field during the operation, and methodology used to measure emissions during the operation. Virtually no information is available on PM10 emission factors for seeding, fertilizing, and spraying operations. However, data of Bogman et al. (2007) would suggest that the PM10 emission factor for the seeding operation is similar to the plowing or disking operations whereas the PM10 emission factors for fertilizing and spraying operations are an order of magnitude less than the cultivating, disking, and plowing operations. Exceedance of PM10 air-quality standards due to farming operations have forced local or national government organizations to adopt alternative practices that emit less particulate matter into the atmosphere. For example, exceedance of the PM10 standard in Maricopa County prompted the development of best management practices to reduce dust emissions from agricultural lands in Arizona (State of Arizona, 2008). Best management practices for field crops include using onepass operations (e.g., apply fertilizer when cultivating or seeding), reduced or no tillage practices, tillage tools that do not invert the soil, and stripper headers rather than traditional headers on combines. Other best management practices include cultivating the soil at lower speeds or when the soil is moist, roughening the soil surface, and minimizing the chopping and spreading of residue from the combine. Best management practices for tree crops include sweeping or pickup of nuts from the soil surface when the surface is moist

and using less invasive operations and modified harvest equipment.

Biomass burning Biomass burning is used throughout the world to control diseases and pests in crops, remove crop residue that otherwise interferes with harvest or seeding operations, and as a fuel source. Biomass burning, however, can contribute to the dust load in the atmosphere. For example, burning wheat and corn residue is a major contributor to high PM2.5 concentrations in Beijing, China (Li et al., 2007; Song et al., 2006), whereas burning sugarcane is the main source of PM2.5 in some Brazilian cities (Lara et al., 2005). Burning biomass generates a higher proportion of PM2.5 as compared with coarser particulate matter. In fact, 93% and 98% of the PM10 liberated from burning respectively wheat straw and corn stover is PM2.5 (Li et al., 2007). In addition, biomass burning can release toxic compounds such as polycyclic aromatic hydrocarbons and phenols. PM2.5 and PM10 emission factors for burning agricultural residues are provided in Table 7. The range in emission factors for any crop is likely due to differences in atmospheric conditions (e.g., relative humidity), configuration of residue, or moisture content of residue during the burn. A greater awareness of biomass burning being a source of atmospheric PM2.5 has prompted government organizations around the world to adopt policies that regulate burning of crop residue. In Washington, for example, agricultural burning has been reduced by half over the past decade and is currently allowed on certain days by those possessing a permit. Violation of this law has resulted in fines that exceed US$20 000. Other methods of handling crop residue are being advocated rather than burning; these include removing residue from the soil surface after harvest, incorporating residue into the soil after harvest, or using no-till seeding technologies and pesticides.

Dust Pollution from Agriculture

501

Table 6 PM2.5 and PM10 emission factors for tillage and harvest operations of agricultural crops

Table 7 PM2.5 and PM10 emission factors applicable to burning biomass of agricultural crops

Operation

Crop

PM2.5

PM10

g m−2 Tillage Chisel Cultivate Disk

Harrow Land smoothing Plow Subsoil Weeding Harvest Almond Shake

0.03c 0.55d 0.01–0.13c 0.01–0.12d

Sweep Pickup Corn Cotton Oat Potato Rice Sugar beet Wheat

0.0002k

PM10

g kg−1 a

0.01c 0.01c, 0.01– 0.11d

PM2.5

b

0.13 , 0.25 0.19c 0.08–0.65d, 0.08–1.38e, 0.09f, 0.13a, 0.14c, 0.21b 0.08c 0.12–2.32e, 0.50–0.65b, 1.34d, 1.40a 0.12–1.05c 0.04–0.72d, 0.51f, 0.52a 0.09a 4.58g 0.015h, 0.042g, 0.05b, 1.65i 0.08b, 0.20h, 0.42g, 1.94i 0.19b, 1.07j, 1.22h, 3.23i, 4.12g 0.19a 0.04h, 0.05k, 0.11e, 0.38a 0.65a 0.19a 0.19a 0.19a 0.65a

Almond Apple Barley Canola Corn Cotton Kentucky bluegrass Oat Olive Rice Sugarcane Walnut Wheat

4.1a, 4.5b 4.0a 7.4a,b 8.5a 5.0c, 6.0b, 11.7d 6.2c, 8.5a 11.6c, 12.1e, 29.6f 10.9a 8.3a 2.4c, 3.2b, 13.0g 2.2i, 2.6j, 4.3c, 5.0a 4.7b 0.8–4.7e, 3.6k, 4.0c, 4.7g, 5.4a,b, 7.6d

4.3a, 4.8b 4.2a 7.7a,b 8.9a 6.2b, 10.7c 8.9a, 15.8c 11.4a 8.9a 3.3c, 3.5b, 3.7h 4.9c, 5.4a 5.0b 5.7a,b, 7.0c

a

Air Sciences Inc. (2005). Jenkins et al. (1996). c McCarty (2011). d Li et al. (2007). e Dhammapala et al. (2006). f Air Sciences Inc. (2004). g Hays et al. (2005). h Kadam et al. (2000). i Yokelson et al. (2008). j de Azeredo Franca et al. (2012). k Air Sciences Inc. (2003). b

a

Countess Environmental (2006). Flocchini et al. (1994). c Hinz and Funk (2007). d Trzepla−Nabaglo et al. (2003). e Cassel et al. (2003). f Holman et al. (2001). g California Air Resources Board (2003). h Ashbaugh et al. (1996). i Ashbaugh et al. (1997). j Faulkner and Capareda (2012). k Wanjura et al. (2008). b

challenge will require the development of more cost-effective practices to control dust emissions from agricultural facilities and lands.

See also: Air: Confined Animal Facilities and Air Quality Issues. Beef Cattle. Dairy Animals. Land Use: Management for Biodiversity and Conservation. Swine Diseases and Disorders. Tree Fruits and Nuts

Future Perspectives The pursuit of clean air will intensify as societies become more urbanized and interest escalates in protecting public health. Air-quality standards are being adopted and revised by many nations around the world. For example, China will fully implement new air-quality standards by 2016. In addition, the USEPA is mandated to review and revise, if appropriate, air-quality standards every 5 years. There is expectation that stricter or tighter PM2.5 and PM10 airquality standards will be adopted as more evidence associates adverse health effects with exposure to dust. Tighter or more restrictive air-quality standards will necessitate that even greater measures be taken or better practices be implemented to control dust emissions. This will be a challenge for the agricultural industry, particularly in regions where weather affects emissions and profit margins are thin. Meeting this

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Relevant Websites http://Pnw-winderosion.wsu.edu Columbia Plateau Wind Erosion Air Quality Project.

http://school.dustwatch.edu.au/site.html Office of Environment and Heritage and Griffith University. http://www.dustwatch.edu.au/ Office of Environment and Heritage and Griffith University. http://www.weru.ksu.edu/ USDA Agricultural Research Service Wind Erosion Research Unit. http://www.wrapair.org/ Western Regional Air Partnership.