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Is there is a way to calculate or predict how far a certain organic molecule will travel from an oil refinery on any given day? Are there any models or sites out there that could answer that question?

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The answer for any particular pollutant will depend on three factors:

1. what happens to the compound in air (e.g., chemical reactions, wet and dry deposition);
2. how high the compound is released;
3. details of the meteorology (wind speeds, temperatures, precipitation, etc.) downwind of the release point.

For the first issue, please see a report I did several years ago for a group of compounds of concern in the Great Lakes. This report and others are on the web site at the bottom of my contact info. One number I've seen is that absent any chemical reactions and deposition, a compound could travel -- on average -- on the order of 400 km per day. Of course this will vary quite a bit from day to day. Some days it might not go very far at all -- stagnant air conditions -- and some days it might go further. But this is about the right order of magnitude on average. This can be much shorter if, for example, the compound reacts very quickly in the atmosphere. Some compounds do react very quickly, and they get "killed off" in less than a day -- in some cases much less than a day. On the other hand, some compounds can last much longer. For example, some compounds are very water soluble and if it rains they get washed out of the atmosphere. If that happens right after they are emitted, then they don't go very far! However, a number I've seen is that on average, a particular parcel of air will only see rain about once a week -- on average -- in the U.S. This obviously is a rough average.

If you want to do a simple calculation, you can use the HYSPLIT model on the NOAA READY web site and run 24-hr forward trajectories. For any given day, this will tell you how far the compound might have traveled in the absence of any other factors. You can input the starting height (e.g. effective stack height). Note that hot gases rise once emitted and so the effective stack height will generally be higher than the stack height. And actually, no matter what happens, as long as the chemistry or deposition is not extremely fast, there will be some of the compound left at the end of the day -- but not necessarily all of it.

Dr. Mark Cohen