18.2 What Pollutants Are of Interest for Model Performance?

There are a number of gas phase species that can be used to evaluate both ozone and

secondary PM2.5. Their presence may affect the response of ozone or secondary PM components

to emissions strategies. Also, the model's performance in predicting certain gaseous species may

provide diagnostic clues which help explain poor performance in predicting ozone or secondary

PM2.5. Gaseous pollutants of interest include:

- Ozone (O3)

- Nitric acid (HNO3)

- Nitric oxide (NO)

- Nitrogen dioxide (NO2)

- Peroxyacetyl nitrate (PAN)

- Volatile Organic Compounds (VOCs)

- Ammonia (NH3)

- NOy (sum of NOx and other oxidized compounds)

- Sulfur dioxide (SO2)

- Carbon monoxide (CO)

- Hydrogen peroxide (H2O2)

Some of the species listed above are currently available from either existing monitoring

network systems and/or special studies. However, it is important to note that many of the species

listed above are not routinely measured, (e.g. H2O2, HNO3, and NH3). Model performance can

best be assessed using extensive data bases, such as those obtained in major field studies.

However, we recognize that such data may not be available for every model application which

needs to be performed. At a minimum, a State should supplement its performance tests with

available data with a review of results from performance tests for the model(s) which were

completed elsewhere where extensive data bases were used.

Because PM2.5 is a mixture, a meaningful performance evaluation should include an

assessment of how well the model is able to predict individual chemical components that

constitute PM2.5. Components of PM2.5 of interest include:

- Sulfate ion (SO4) and/or Sulfur (S)

- Nitrate ion (NO3)

- Ammonium ion (NH4)

- Elemental Carbon (EC)

- Organic Carbon (OC) and/or Organic Carbon Mass42

- Crustal (weighted average of the most abundant trace elements in ambient air)

- Mass of “other” primary particulate matter43

- Mass of individual constituents of inorganic PM


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