Developing a Framework for Effective Air Quality Management

3.7 Implementation of Air Quality Plans

3.7.7 Programs to Determine Compliance Large Emissions Through a Stack

There are no simple approaches to verify compliance at a stationary source. The reason for this is the variety of ways that air pollution can be released into the air and the range of emissions (small to large) that are released. There are general approaches that are typically applied for each type of release. These are discussed in the following sub-sections.

Emissions through a single emission point are the most straight forward emission source for determining compliance. In the case of a source that emits large amounts of pollutants (more than 100 tons per year without control), continuous emission monitors (CEMS) are typically required. The emissions recorded by the continuous monitors are recorded onto some type of secure medium that is difficult to alter and available to the compliance agency. In the past, the recording medium was typically strip-chart paper. With the advent of digital electronics, large amounts of inexpensive memory, and the internet, the recording mechanisms have changed. There are now secure methods for storing data electronically and/or it can be transmitted to the compliance agency. In the special case of sulfur emissions, the amount of sulfur in the fuel can be monitored to reliably establish the sulfur emissions from a source.

Requirements must be set for the frequency of maintenance and calibration of continuous monitors and this information must be recorded in a secure manner that is accessible to the compliance agency. This is an expensive alternative, but is the easiest and surest approach to ensuring compliance through a stack. Actual installation costs of a single CEMS in large stack frequently exceeds US$500,000 each and can be substantially more where significant weather protection is required.

If a continuous monitor is not reasonable for a large emissions point, then annual or semi-annual stack tests become the next best alternative. Most compliance agencies do not conduct their own stack tests. Instead, they arrange for certified stack testing companies that are independent from the emissions source. It is also typical for the compliance agency to send knowledgeable staff to observe the conduct of the stack test. The greatest challenge for this approach is ensuring that the testing agency is truly independent and can be relied upon to provide honest data. However, this approach is used successfully in developed and developing countries.

It is possible to estimate emissions based on process parameters. This approach is used more often with smaller sources of emissions, but the ARCO refinery in Los Angeles (now the BP Refinery) demonstrated that it could estimate its stack emissions using process parameters to a degree that was as accurate as the stack monitors. While this is an exceptional case since many businesses do not maintain the same amount of process information as does a refinery, it can not be assumed that an estimation of emissions based on input parameters is not accurate. In this case, the same data storage security must be achieved. The relevant process data must be stored for review by the compliance agency. While the ARCO demonstrations were impressive, the South Coast Air Quality Management Agency did not allow them to remove their continuous stack monitors. If sufficient process information can be obtained and retained to verify emissions, it would likely be significantly less costly for the facility to use that methodology than online analyzers, which are more costly for initial installation and require significantly more preventive maintenance and calibration to operate reliably. Low Emissions Through a Stack

There are many cases where the emissions from a stack are too low to warrant the use of a continuous stack monitor or even a stack test. An example might be a coal boiler at a small business. In this case, process information is used to estimate emissions and compliance is assured by requiring that the equipment used by the business meet certain design standards. If the equipment meets design standards, it is assumed to be in compliance. Fortunately, the energy suppliers for this type of equipment are often independent of the business being regulated, such as the natural gas supplier, so that independent records exist as to the amount of gas being used or the amount of coal being used.

The U.S. EPA maintains an extensive set of emission factors for various types of equipment, which can be accessed through the internet at This web site also includes other information on maintaining compliance.

There are cases where emissions through a stack do use energy or other materials from an independent source. An example might be a furniture manufacturer which paints furniture under a hood that vents to the atmosphere or a woodworking operation that vents particulate matter through a stack. The only compliance approach here short of a stack test is to require record keeping of the products used. This is discussed further with respect to Fugitive emissions. Fugitive and Intermittent Emissions

The most difficult case for determining compliance is in the case of fugitive emissions and intermittent emissions. Emissions from leaking valves, emissions from storage tanks, emissions from open painting operations, and emissions from flares usually fall into this category. Flares can come in all forms. Some flares are actually contained within a stack and can be treated as emissions through an emission point, which can be monitored and tested. Most flares however are in the form of open flames at the top of a stack and must be relatively unconstrained due to the wide range of fuel that might be fed to the flares in cases of emergency. This makes emissions testing or monitoring extremely difficult if not impossible. In all of the aforementioned cases, some process monitoring information is often required. For example, records are required to be kept concerning the amount of paint that is used or the amount of wood that is processed. Unfortunately, no effective continuous measurement system has been developed to monitor most flaring systems. In this case, the temperature of the flame and opacity might be monitored along with visual observation of the amount of time that a flare might operate. In the case of storage tanks, equipment specifications are usually required along with inspections of the condition of the seals that keep emissions from leaking from the tanks. In the case of leaking valves, flanges, pumps and compressor seals, the only proven approach is to monitor hydrocarbon levels near the valves. A leaking valve will raise the amount of hydrocarbons in the vicinity of a valve. In this case standards are set for maintenance based on hydrocarbon concentrations measured near the valves.

The record keeping requirements are the most hated requirements by small business. This record keeping can be onerous and care should be taken to require only what is needed to ensure compliance. With the advent of much cheaper computers and data processing systems, businesses and compliance agencies should work together to streamline this data collection process. Remote Monitoring and the Use of Ambient Monitors for Enforcement

Remote monitors have been an option for consideration in recent years. These include fence-line monitors that use a beam of light to measure the emissions as they cross the fence line and remote Raman scattering monitors that look directly at smoke stack emissions. These approaches have been used only in limited situations for enforcement actions due to accuracy and source definitions questions. They are good tools for building emission inventories and finding sources of emissions but are less useful in most direct enforcement applications.

Ambient monitors are also problematic for use in enforcement situations especially in urban areas. In urban areas, multiple sources can contribute to the values measured at an ambient monitor. Also, to establish actual stack emissions, some form of modeling must be used to calculate back to the actual emissions coming from a source to establish a stack emissions violation. Existing models, especially short-range models, have been found to be very inaccurate. While progress is being made with respect to short-range modeling, most agencies use ambient monitors for general determination of air quality levels and to define which sources should be further investigated rather than as an enforcement tool. Collection and Review of Emissions Information

No stack monitoring or record-keeping requirement is of any value if that information is not reviewed within a reasonable time frame to ensure compliance. The requirement of a stack monitor or records do have some deterrent effect on emissions from a business, but eventually, if there are no significant checks on that information, the business might decide that it is worth the risk to ignore the requirement and then beg forgiveness once they are caught after potentially several years.

For businesses that produce significant air pollution, multiple inspections each year are in order by persons trained to look for flaws. A facility such as a refinery can have thousands of emission points, which cannot be adequately checked in less than two weeks worth of inspection and information review. It has been the goal of the South Coast Air Quality Management District in Los Angeles to visit every permitted source no less than once per year. Since there are 20,000 permitted businesses in the region, 100 inspectors are involved in the inspection program.

The proper training of inspectors is an important task. Most training at the larger agencies in the United States is handled by on-the-job experience. Inspector trainees are taken on inspection tours along with experienced inspectors and taught the best approaches for carrying out inspections. Inspection managers from developing countries have visited air quality management programs in the United States and spent up to two months accompanying inspectors as they visit various sources to gain the necessary experience.

The U.S. EPA offers enforcement training for U.S. air quality related officials from state and local air quality agencies ( This training can be of moderate value. It might be possible for non-U.S. air agencies to arrange for this training.