Can I use visual Methods 9 and 22 for opacity monitoring under my air permit?

Posted by Earl Parker on May 16, 2017 2:30:00 PM

New solutions for air permit monitoring

For generations opacity monitoring was essentially the only monitoring option for dust collector operators across all industries. Many plants continue to operate that way, allowing older air permits to just renew without any changes if possible. Because of this, opacity monitoring still forms a key part of their compliance monitoring, even though there may be better methods of monitoring available.  But when it comes to opacity monitoring what kind of options are available? 

Stack Monitoring for Air PermitsOpacity-Emissions-Example.jpg

The basic idea of a stack observation of opacity is to try to quantify how much particulate is emitted from the stack by determining how much light it blocks from passing through the plume. This measurement of the plumes light blocking power is called opacity. The more dust in the air the more light is scattered/blocked. Prior to 1974 all emissions monitoring was based on the Ringelmann system first developed in the late 19 century to monitoring coal emissions. This system outlined a set of procedures on how an observer could take a visual reading of opacity by viewing the emission source (e.g. stack) from a distance during daytime.  In 1974, the EPA revised the test into the current EPA opacity observation standard methods in an attempt to make the test more reliable and less prone to observer bias. These methods or instructions for conducting the test are known as EPA Methods 9 and 22. 

Opacity Observation Methods 9 and 22

It is key to understand the fundamental difference between Method 9 and Method 22. Method 9 is designed for regular compliance monitoring whereas Method 22 calls for a less rigorous process and is mainly suited to quickly confirm major issues such as filter failure or other upset conditions. As such, Method 9 is a quantitative test (objective is to determine amount of particulate concentration in the plume) and Method 22 is a qualitative test (objective is to determine whether or not a major upset condition has caused the plume concentration to spike quickly). 

Method 9 requires that the observer (sometimes called a smoke reader) be trained and certified by an accredited training organization in the method. Often these organizations refer to this training as “smoke school”. Only certified personnel are legally allowed to conduct the test. Further the observer must keep a careful record outlining the observation and how it was conducted according to the method. To begin the test the observer identifies a location that will allow him to observe the stack emissions in accordance with the method’s guidelines for mitigating factors that can affect the test. These can include viewing angle, sun location, background (e.g. other buildings, geographic features such as mountains, trees, etc.). Then the observer will begin the test by viewing the plume and recording the approximate opacity level ever y15 seconds for 6 minutes. With this data he then calculates an average opacity level after correcting for factors such as weather and color of the smoke. 

Method 22 follows some of the same basic steps above but is much less rigorous. It essentially is done simply to determine whether an excursion has occurred. The individual conducting a method 22 test does not need to be certified to do so. 

Both methods are a form of manual monitoring requiring personnel time and labor to conduct the methods properly. Depending on the number of stacks at a facility this can become a costly way of meeting compliance requirements.

New Call-to-action

Still Useful But Surpassed by Triboelectric Monitoring3600-3200-3400.jpg

While Methods 9 and 22 are still useful in some instances, for the most part they have been surpassed as primary monitoring methods for air permits by alternatives that use continuous monitoring equipment.. Opacity meters such as used in CEM Systems or more extensively triboelectric dust monitoring systems provide significant advantages over Methods 9 and 22 observations, both in compliance as well as maintenance and operational ways. Additionally, as air emissions standards become stricter, visual based opacity monitoring for  air permit monitoring no longer proves adequate capability in nearly all applications. 

Methods 9 and 22 still provide some benefit. Method 22 can be useful for confirming that a major excursion has occurred. Method 9 can also be used as a backup compliance monitoring method during maintenance or issues involving the primary monitoring system. 

Does your facility still make use of Method 9 and 22 as its primary PM monitoring method? Click here to learn more about how modern triboelectric monitoring systems can help you more reliably achieve compliance as well as provide operational and maintenance savings. 

For more information view the EPA quick guide to Methods 9 and 22:


Topics: Air Permits, Environmental Monitoring