Developing a Framework for Effective Air Quality Management

3.5 Understanding the Sources of Air Quality Problems

3.5.1 Overview
As the levels of air pollutants in a region are better understood, it becomes critical that the air quality manager understand the sources of the air quality problem. While the development of such information seems intuitive, it is surprising how many air pollution control programs initiate the control of sources with only guesses about the sources of their problems. It follows then that the implementation of control measures without the proper understanding of emissions may lead to bad policy choices and may not improve air quality as anticipated.

In the case of rural areas, the cataloging of the sources of an air quality problem can be relatively simple. However, in urban areas with many sources of air pollution the issue can become exceedingly complex. Chapters 5 and 6 of this manual focus on the processes associated with identifying the sources of air quality problems in a region of interest and quantifying their impact. This section is intended only to summarize the topic.

The sources of a region’s air quality problems can be established using three approaches. The first approach relies on the development of a wind rose. A wind rose is a drawing that illustrates the frequency of wind from different directions at a particular location. A wind rose can be developed for the area near a specific monitoring station and the average air pollution levels can be studied during the times when the wind is coming from a certain direction. There are potential errors with this approach that are discussed in Chapter 5. However, this type of a review can be useful to defining the sources of an air pollution problem. A second approach is the use of “finger printing” to determine the source of a problem. In this case, studies of emission sources such as automobiles or trucks or point sources such as coal fired power plants can be used to define unusual compounds that are released by these sources or unusual ratios of compounds that are released. The research can look at the ambient monitoring data to see if these unusual compounds or ratios show up in the data. Finally, an emission inventory can be developed to indicate the major sources of emissions. Normally all three approaches are used to some extent in the source identification process.

In the case of region wide air pollution problems such as ozone and secondary particulate matter, there are no specific sources of the problem. In these cases, the emission inventory is the best indicator of the sources of the problem. Simply, the sources that produce the greater amount of emissions are the greatest contributor to the problem.

For this reason and the fact that an emission inventory is needed to make air quality projections, the use of an emissions inventory is the more common approach to identifying the sources of an air pollution problem. Even in cases where a single source or source category does produce a larger portion of the problem, the remaining sources cannot be ignored if the air quality problem is to be solved.

If only a limited group of sources are singled out for inclusion in an emissions inventory there are issues of fairness and consistency since the sources to be controlled are identified based on the inventory. This does not mean that priority should not be given to controlling the major contributors, but it does argue that all contributors should be included and that all sources should contribute to the solution in some way.