Rural areas have long been idealized as the place to go for good,
clean air. However, the "fresh" air of the countryside may not be
so fresh after all. Since farmers began tilling the soil to grow
crops and raise animals, agricultural production practices have
generated a variety of substances that enter the atmosphere and
have the potential of creating health and environmental problems.
The relationship between agriculture and air quality first entered
the public psyche in the 1930s with the severe dust storms of the
Dust Bowl. Although huge dust storms are long gone, and air emissions
in most rural areas are not high enough to cause concern, the air
in some farming communities can now be as impaired by pollutants
such as ozone and particulates as air in urban areas.
Air quality policies have traditionally focused on urban areas
and industrial emissions. Extending these laws to cover agriculture
would require an understanding of how farmers respond to different
policy incentives. Farmers have many choices in deciding on what
to produce and the production practices to use. Their production
decisions are based on market prices, the characteristics of the
farm's resources, the technologies that are available, and the farmer's
particular level of management skill. But incentives to consider
wider impacts of their production choices on environmental quality
are often lacking. Environmental policy can influence a farmer's
decisions by changing the costs of inputs to encourage or discourage
input use, or by mandating that particular management practices
be used or abandoned. Currently, a lack of knowledge about air emissions
from agriculture could hinder the development of cost-effective
policies.
Policy formation is also compounded by the fact that possible
efforts to reduce agricultural air emissions could diminish the
effectiveness of ongoing efforts to address water quality concerns.
At a minimum, regulations and incentives designed to address a problem
in one medium (air or water) may not be as cost effective at meeting
resource quality goals as those that are coordinated across multiple
media.
Putting the Brakes on Agricultural Emissions
Agricultural production releases a wide variety of material into
the air—for example, windblown soil, nitrogen gases from fields
and livestock, fine particulates from diesel engines and controlled
burning of fields, and pesticides. Pesticides can move in air currents
in two ways: aerial drift (when applied with crop dusters), and
volatilization (a process by which solids or liquids are converted
into gases). Other potential pollutants associated with agricultural
production include hydrogen sulfide, ammonia, odors, and other volatile
organic compounds from animal manure; methane from dairy cows and
cattle; and nitrogen oxides from fertilized fields and internal
combustion engines. These pollutants can affect people's health,
reduce visibility, contribute to global warming, or simply be a
nuisance.
Air quality is protected primarily through the Clean Air Act and
the Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA). The Clean Air Act sets limits on how much of a pollutant
can be in the air anywhere in the United States. When the air quality
standard for any of six air pollutants is exceeded, States must
inform the U.S. Environmental Protection Agency (EPA) how they plan
to respond. Any farm in a nonattainment region (regions where air
quality standards are exceeded) found to be a "major source" of
regulated emissions could be required to apply for and comply with
an operating permit. CERCLA requires facilities to report to EPA
when more than a "reportable quantity" (100 pounds in a 24-hour
period) of a hazardous substance is released.
Regulation of air emissions under the Clean Air Act and CERCLA
has focused on such sources as factories and cars but not on emissions
from agriculture. Part of the reason is a lack of information about
the sources and effects of agricultural air emissions that would
be necessary to develop regulations. Pollution from agriculture
generally has characteristics that make it difficult to control
through conventional policy tools that are applied to industrial
sources. Agricultural emissions tend to be generated diffusely over
a broad land area, rather than from a single pipe or smokestack,
so it has not been cost effective to accurately monitor emissions
from individual agricultural sources using current technology. For
example, ammonia emissions from an animal operation can come from
a barn, manure storage structure, and field. The difficulty and
cost of monitoring agricultural pollution sources is one reason
that agriculture is largely exempt from environmental regulations
that were primarily designed to address urban and industrial air
pollution problems.
However, new State regulations may seek to reduce air emissions
from agriculture, particularly from animal feeding operations. Under
the Federal Clean Air Act (and its amendments), States are responsible
for achieving the air quality standards established by EPA. Recent
lawsuits, court decisions, and consent agreements have induced States
to start regulating emissions. California is the first State where
air quality regulations are significantly affecting agriculture.
Ozone and particulate levels in the San Joaquin Valley of California,
which has some of the most polluted air in the country, with nonattainment
areas for both Federal ozone and particulate matter standards, have
led to new requirements for agricultural producers. Farmers must
develop management plans showing how they will reduce dust, the
burning of crop residue (e.g., rice straw, orchard trimmings) is
restricted, and large dairies must manage their manure to reduce
ammonia emissions.
However, farmers do not bear the cost alone. USDA helps farmers
in California's nonattainment areas with a cost- share program funded
through the Environmental Quality Incentives Program to help finance
farming practices that reduce airborne dust and ozone precursors.
USDA also funds research to understand the processes of air pollution
emissions from agricultural operations, to develop and test control
measures, and to provide decision aids that can be used to reduce
agricultural air pollution emissions.
Protect Air Quality, Compromise Water Quality?
An important issue in addressing pollution from agriculture is
that emissions to the atmosphere do not necessarily occur in isolation,
but can be linked by biological and chemical processes to emissions
to water. Nitrogen emissions from animal feeding operations are
the best example. Nitrogen excreted from an animal can follow any
of a number of pathways between collection and disposal, and enter
water or the atmosphere in the form of any of a number of compounds.
These interactions have important consequences for policies to protect
environmental quality. Reducing nitrogen movement along one pathway
by changing its form will increase nitrogen movement along a different
path. For example, reducing ammonia losses from a field by injecting
animal waste directly into the soil increases the amount of nitrogen
that can be made available for crop production, but, because more
nitrogen is now available in the soil profile, the risk that nitrates
will enter water resources is increased. The fact that these processes
are linked requires that efficient management of manure consider
how different environmental media (that is, land, water, and air)
are affected. (See "Nitrogen Follows Many Pathways
in a Livestock Operation.")
The nitrogen cycle is
a complex one, without a beginning, middle, or end.
The principle of mass-balance ensures that the amount
of nitrogen in a closed system is constant. Thus, any
action to divert it from one pathway must necessarily
transfer it into another. In this stylized figure:
1
animals in the "house" release nitrogen
in three ways: they produce manure (which then enters
a storage system); they store nitrogen internally, which
is bound in animal products distributed to markets;
and they produce gases (directly and indirectly in manure
production), which are released as air emissions;
3
manure nitrogen applied to fields
may be stored in the soil, leached into groundwater,
run off into surface water, volatilized into air emissions,
and be bound in crops; or
2
manure is stored in lagoons, tanks, pits, or other structures
before being transported to fields for use as fertilizer;
4
nitrogen bound in crops may be
used for feed for the animals, and the cycle begins
again.
Nitrogen also enters and exits the system through
intermediate pathways, for example, some of the nitrogen
released into the air will settle back on the fields
(deposition) and some new nitrogen will be added in
the form of commercial fertilizer.
Potential cross-media links in the emission process suggest possible
advantages to a multimedia perspective in developing regulations.
A multimedia perspective is neither new nor unique to agriculture.
Many industries generate multiple pollutants that affect several
environmental media. Yet, environmental regulations, by and large,
take a single-medium perspective. The Clean Water Act addresses
surface water quality (not ground water). The Clean Air Act addresses
air quality. The Resource Conservation and Recovery Act (RCRA) addresses
hazardous waste disposed on land.
Over the past decade, EPA has experimented with coordinated implementation
of the Clean Air Act, Clean Water Act, and RCRA to reduce implementation
costs and to help regulated industries organize pollution control
activities more efficiently. The pulp and paper industry was the
first to benefit from this multimedia approach. EPA developed integrated
air and water rules that set emission levels based on the performance
of a combination of source reduction technologies and management
practices, air pollution control devices, and upgrades on existing
wastewater treatment systems.
Why might a multimedia approach be important for agriculture? The
increasing size and geographic concentration of animal feeding operations,
driven by the economics of domestic and export markets for animal
products, have resulted in large quantities of manure accumulating
in relatively small areas. In 2003, EPA introduced revised Clean
Water Act regulations to protect surface waters from nutrients from
concentrated animal feeding operations (CAFOs). The regulations
require CAFOs to follow a nutrient management plan to minimize nitrogen
and phosphorus runoff to surface water. Those plans will specify
the application rate for nutrients that must be followed when applying
manure to land (the primary disposal method). The cost to farmers
of complying with the plans can be relatively high because compliance
often will entail moving manure to a larger land base. To meet the
requirements as cheaply as possible, and without any incentives
to protect air quality, farmers could continue to use (or adopt)
uncovered lagoons and apply animal waste to the surface of fields
without incorporating it into the soil. Those practices reduce the
nitrogen content of manure spread on fields by volatilizing nitrogen
to the atmosphere. In so doing, however, nitrogen that otherwise
would be available for runoff to water bodies is transformed into
atmospheric ammonia emissions to the possible detriment of air quality.
According to a 2003 National Academy of Sciences study, animal
feeding operations are the primary source of ammonia emissions in
the U.S., and ammonia emissions are already a cause for concern
in some rural communities. Ammonia emissions are regulated in parts
of California. Current Federal air quality rules (e.g., Clean Air
Act's PM 2.5 standards and CERCLA) might force more States to consider
regulating ammonia emissions from animal operations.
An ERS study estimates that farmers would respond to hypothetical
ammonia emission standards by adopting manure management practices
that reduce nitrogen emissions to the air but increase the nutrient
content of animal waste spread on fields. Depending on how the air
quality regulations were applied, this could have two impacts on
CAFOs and water quality. First, CAFOs might need to further increase
the amount of land on which they spread manure in order to continue
to meet nutrient application standards. This increase could be particularly
costly in a region where animal concentrations are high and cropland
available for spreading manure is relatively scarce. For example,
in the Chesapeake Bay watershed, ERS found that requiring CAFOs
to adopt practices that reduce ammonia emissions would increase
the nitrogen content of manure and thus the CAFOs' cost of applying
manure to land to meet water quality requirements.
An uncoordinated approach between air and water policies could
also reduce water quality. The Clean Water Act‘s manure regulations
apply only to CAFOs. If ammonia reductions are required on farms
other than CAFOs, the water quality benefits of the CAFO regulations
are potentially reduced by increased nutrient applications on these
other farms. In the Chesapeake Bay watershed, for example, ERS research
estimates that the nutrient content of manure produced on farms
not covered by current regulations would more than double if ammonia
restrictions were applied to all animal feeding operations. This
would increase the risk of nitrogen runoff that eventually reaches
the Chesapeake Bay.
USDA has long recognized the impacts of conservation practices
on multiple environmental resources (soil, water, and air). Yet,
when a set of conservation practices is recommended to improve water
quality, full consideration is not always given for accompanying
air quality benefits. In the Conservation Reserve Program, for example,
the Environmental Benefits Index used to rank applications for enrollment
includes wind erosion benefits but not benefits for reduced ammonia,
odor, fine particulates, oxides of nitrogen, or pesticide volatilization.
A fuller accounting of the multimedia benefits in the implementation
of conservation programs could result in a redirection of resources
to producers who could provide a higher level of overall environmental
quality for a given cost.
Better Data for Better Coordination
Information on environmental emissions from production practices
would improve coordination of environmental policies. The National
Academy of Sciences review of air emissions from animal feeding
operations found that, while pressure to regulate air emissions
from animal operations has mounted, the basic scientific information
needed for effective regulation and management of emissions is lacking.
The study was requested jointly by EPA and USDA to assess the state
of knowledge and to recommend steps for bridging the information
gap that is hindering the development of effective regulations and
management measures. Existing data are insufficient to establish
thresholds for emissions from livestock operations that would trigger
compliance with air quality requirements.
This need for better data about air emissions from animal feeding
operations has led to an innovative agreement between EPA and some
sectors of the animal industry to monitor air quality on farms.
The Air Emissions Consent agreement and National Monitoring Study
between pork and egg producers and EPA calls for a 2-year national
air monitoring study on animal feeding operations that agree to
participate in the study. The study will use state-of-the-art technologies
and standardized procedures to monitor emissions from barns and
lagoons. These data will help State and Federal regulators and farmers
identify farm sizes and manure handling systems that exceed thresholds
for regulated pollutants. For farms that participate, EPA has agreed
to provide certain legal protections for past and current emissions
violations. EPA has invited other sectors of the animal industry
(broilers, dairy, and fed beef) to participate.
The information gathered during the study will be valuable for
both farmers and regulators. Many producers are not aware of their
operation's contribution to emissions or whether they are subject
to existing air quality regulations. Knowing the legal and financial
risks for different types of operations would help farmers make
decisions about reducing emissions to protect them from possible
lawsuits or enforcement actions and still remain profitable.
Information on atmospheric emissions from agriculture can help
regulators identify the emission thresholds that meet air quality
goals at minimum cost to the sector and develop coordinated incentives
to help farmers simultaneously protect air and water quality. This
would reduce unintentional harm to the environment because of unconsidered
cross-media effects and minimize the cost to producers who change
their production practices to comply with emerging environmental
regulations.
Confined Animal Production
and Manure Nutrients, by Noel Gollehon, Margriet Caswell,
Marc Ribaudo, Robert Kellogg, Charles Lander, and David Letson,
AIB-771, USDA, Economic Research Service, June 2001.