TAMU Cotton Engineering & Management

AIR QUALITY ISSUES

Agricultural Air Quality

The state and federal regulation of air pollutants from agricultural operations has resulted in serious problems for concentrated animal feeding operations (CAFO), grain and fiber processing (cotton gins and textile mills, feed and oil mills, and grain elevators), prescribed burning, and agricultural field operations (disking, harvesting, etc.). The results of these problems are mandated, unwarranted implementation of expensive controls, inappropriate fines and fees, difficulty in obtaining a permit to operate, and an incorrect perception that agriculture is a major source of pollutants impacting the public. The solutions for the inappropriate regulations of agricultural operations and the long-term sustainability will be an air pollution regulatory policy and process that is based upon sound science and engineering. The above problems need to be addressed through careful research studies. In the area of agricultural air quality, these include resolving issues on particulate matter (PM10, PM2.5), gas emissions (NH3, H2S, VOC, NOx, SOx, Ozone, etc.), odors, evaluation of dispersion models, emission factor calculations, and abatement technologies among others.

Particulate Matter

A partial list of current issues for agricultural operations and state and federal air pollution regulatory agencies are as follows: 

(a) Accuracy of concentration measurements - The EPA has approved PM10, PM2.5 samplers that measure inaccurate concentration of regulated pollutant from rural sources compared to urban sources (Buser, 2002). This is a consequence of the particle size distribution of PM in the ambient air associated with rural sources having a larger mass median diameter (MMD) than urban PM. Errors with approved samplers are as high as 300%. 

(b) NAAQS as a property line concentration limit - Some states are using the NAAQS as a property line concentration limit that should not be exceeded. For agricultural sources, there may be no occupied residences near the property line. It can be argued that this concept of limiting concentrations of PM at the property line for agricultural sources is inappropriate and not the intent of Congress. In light of the fact that PM10 samplers may result in a three fold error, this is an inappropriate regulation of PM emissions from rural operations. 

(c) Characteristics of agricultural PM emissions - In most non-agricultural operations, the PM emission rates are relatively constant over time. As a consequence, reductions of emission rates can be achieved simply by a change in the controls used to limit emissions. In many and almost all AFO operations, the PM emission rates vary during the day, week, and year. As a consequence, the protocol used to measure concentrations must consider the sampling time: time during the day, week, month, and year that sampling occurred; and the abatement strategies installed at the time of sampling. In addition, the particle size distributions (PSD) of agricultural emissions will have a higher MMD (usually at least 15 to 30 μm) compared to urban emissions (typically 10 μm). 

(d) PM10 Pre-separator Performance Characteristics - The resulting measurement of PM10 is a function of the ambient PSD and the fractional efficiency of the sampler. Parnell et al (1999) reported the logic used by EPA in 1987 when changing from the regulation of total suspended particulate matter to PM10. The human respiratory system works like a pre-separator with a cut-point of 10mm AED and a slope of 1.5 (ISO, 1981). It is not possible to engineer a sampler having a pre-separator with exactly these performance standards, thus we must be concerned with EPA approved samplers for potential sampling errors. 

(e) Appropriate Units for PM10 concentrations - Prior to 1997, all measurements of air quality compared to the PM10 NAAQS were corrected to mass per standard volume[1] . The epidemiologists conducting the studies on PM2.5 exposures did not detect any health effects from changes in barometric pressure (elevation above sea level) and concluded that the PM NAAQS should not be corrected to a reference temperature and pressure. In reality, humans performing at the same level of physical activity at sea level and at one mile above sea level will require the same mass of oxygen but their exposure will be different due to larger air requirement at higher elevations. If the NAAQS were 150 μg/acm, the exposure experienced by the person in higher elevation would be as much as 3,060 μg (e.g. Denver). At sea level the value would be 2,535 μg (e.g. Houston). It would seem that the NAAQS for PM10 and PM2.5 should be based upon mass per dry standard volume. From the engineering perspective, this issue must be resolved.

Dispersion Modeling

The regulation of criteria air pollution sources has become more and more dependent upon the results of dispersion modeling with respect to predicted off-property/boundary line concentrations. When these predicted concentrations exceed the maximum ambient levels as defined by the state and EPA, the source is required to provide a solution that will result in lower predicted concentrations. In order to quantify the emissions from agricultural operations, net downwind concentrations are measured and the resulting concentrations are used to back into an emission flux using dispersion modeling. Emission fluxes can subsequently be reported as emission factors. The box model has been used in the past to estimate fluxes with the resulting fluxes being used in Industrial Source Complex–Short Term, Version 3 (ISC) to estimate downwind concentrations for regulatory purposes. We need to evaluate a process for estimating fluxes using the box model with the criterion that the subsequent concentrations with ISC will be conservative and not an over estimation.

Inaccurate or Non-Existent Emission Factor

The demand of more food at less cost has resulted in more agricultural products being supplied by large operations with fewer small operations. The perception that “factory” farms are less desirable than “family” farms has impacted public opinion and in many cases, large agricultural operations are being forced to implement controls that are not based upon accurate emission factors but on emotion. The air pollution regulatory process requires that controls mandated for large operations be used on smaller operations. Many small, agricultural businesses are going out-of-business. The reality is that inappropriate air pollution regulations of agricultural operations will likely impact the public with less production and higher prices at the supermarket. Numerous studies must be conducted to develop new and improved abatement technologies to consider changing scenarios in the agricultural sector.

Abatement Strategies for Samll and Large Agricultural Operations

The demand of more food at less cost has resulted in more agricultural products being supplied by large operations with fewer small operations. The perception that “factory” farms are less desirable than “family” farms has impacted public opinion and in many cases, large agricultural operations are being forced to implement controls that are not based upon accurate emission factors but on emotion. The air pollution regulatory process requires that controls mandated for large operations be used on smaller operations. Many small, agricultural businesses are going out-of-business. The reality is that inappropriate air pollution regulations of agricultural operations will likely impact the public with less production and higher prices at the supermarket. Numerous studies must be conducted to develop new and improved abatement technologies to consider changing scenarios in the agricultural sector.

Inappropriate Demands by Regulatory Agencies

Cotton gins are being required to comply with concentrations at the property line that are not feasible based upon current technology. In some cases, these concentrations limits are significantly less than the limit that would be required by an urban industry. In some states, measured PM10 concentrations are considered unacceptable for regulatory permitting purposes in deference to modeled concentrations. Some grain elevators are being required to meet a PM emission concentration limit of 0.01 grains per dry standard cubic foot (gr/dscf) while hazardous waste incinerators are allowed to emit PM at concentrations up to 0.08 gr/dscf. In effect, this grain elevator new source performance standard (NSPS) is potentially making the grain elevator more likely to have a grain dust explosion. This is a consequence of the abatement strategy (fabric filters) used to comply with the NSPS and will periodically have the minimum explosive concentration in its normal mode of operation. In effect a standard promulgated by USEPA could have a consequence of decreasing the safety of grain elevators.

Summary and Future Works of CAAQES

In the next five years, continued work in several areas of the air quality program will be pursued including 
(1) emission factor development for agricultural operations for ammonia, hydrogen sulfide, reactive VOCs, NOx, PM10 and PM2.5 emissions; 
(2) abatement strategies to reduce emission; 
(3) dispersion modeling to more accurately predict downwind concentrations; and 
(4) address new areas such as agricultural burning, pathogens, and emissions from agricultural engines. Additionally, there may be opportunities for us to collaborate with institutions other than those listed here, and more importantly, be involved in transferring our technical knowledge to institutions working in air quality but lacking a technical background in air quality characterization.