To understand the health risk from air toxics to the people living, working, going to school, or recreating in Oregon, you must first determine how much pollution is in the air. You can do this in one of two ways: modeling or monitoring.
Monitoring involves setting up a piece of equipment and directly measuring the pollution in the air at a specific location. Modeling involves collecting information on the emissions and the local weather patterns. For example, emissions from a facility are informed by the reported air toxics, source testing and monitoring. This information is run through computer models to estimate where the pollution will go over time.
The Portland Air Toxics Solutions study is an example of modeling for all sources of air toxics: mobile, area, and stationary sources.
The main benefit of monitoring is its accuracy because it directly measures the amount of pollution in the air. However, monitoring can only determine health risks at a single location – where the monitor is set up. Monitoring is also expensive and must be measured over a period of months to years to understand the changes that can happen under different weather conditions.
The main benefit of modeling is the ability to estimate the amount of pollution in areas all around, including at specific locations and facilities. Additionally, modeling can estimate pollution under a wide range of weather conditions and identify situations that may lead to higher amounts of pollution impacting people nearby. However, modeling can over- or underestimate the amount of pollution in the air. This depends on several factors, including how accurate the emissions inventory is and how the much is known about how the pollution leaves the site, including information such as facility stack height.
There are pros and cons to both modeling and monitoring. DEQ uses both techniques depending on the circumstances. For facilities going through Cleaner Air Oregon, DEQ uses modeling to understand how the facility impacts the community, including at homes, schools, business and parks. DEQ also sets up air toxics monitors to look at areas where many different sources of toxic air pollution may impact people's health.