Frequently Asked Questions

How do I contact another user?

Once you have registered, you can send private email messages to other users by clicking on the "contact" tab in their profile. You may access their profile by clicking on their username link, which is included at the bottom of everything that they have posted to the website. If they are currenlty logged in, then their username link is also included on the right sidebar under "Online users".


Why is the website sometimes not available?

Note that you must be registered to access all of the simulations. Unregistered users can access the more basic simulations and all of the general website content. Since the simulations can be computationally intensive, it makes sense for us to limit the number of simultaneous users. The number of users currenly online is always shown in the right sidebar. Currently, we have a limit of 200 anonymous users and 75 registered users -- for a total of 275 users at any time. If the website is slow or appears to not be available, then please try again later. The user limits may be reduced in the future, if the load on the system is too high.


Is secondhand smoke really bad for you?

In a word "yes". The weight of evidence shows that exposure to secondhand tobacco smoke (SHS) can lead to a variety of maladies some very severe, such as lung cancer and heart disease mortality.

See this description of the 2006 US Surgeon General's Report on the health effects of secondhand smoke.

The U.S. Environmental Protection Agency published a seminal report on respiratory illnesses due to SHS exposure in 1993. You may want to read an updated assessment of


Where did my graph go?

The graphics produced as part of simulations are purged from the website every 30 minutes. This means that a graphic you produce will only be available for download for a maximum of 30 minutes, but perhaps only for a few minutes or less. If you can't view or save a full-size graphic (for example, by right clicking and using the "View image" menu item), then rerun the simulation and you should have close to 30 minutes in which to access it.


Why are the units for quantities so confusing?

On this website we adhere to the common practice of writing units for all scientific quantities using positive or negative superscripts. For example, instead of writing micrograms per cubic meter as μg/m3, we write it as μg m-3. In this case the negative subscript indicates that there are a given number of micrograms of an air pollutant "per" cubic meter of air. Remember from algebra that negative subscripts indicate that one takes the reciprocal of the quantity.


Is there a glossary for the scientific terms?

In describing and interpreting results from the simulation of exposure to secondhand tobacco smoke (SHS), we make use of common scientific terms. Below is a list of some of these terms and their explanation.

The artificial depiction of events with the intention of closely mimicking reality.

Steady State
The condition that is reached when material entering a system is balanced by material leaving a system. When this happens the concentrations in the system do not vary over time, i.e., they reach a "steady state concentration".


What do you mean by "exposure"?

Human exposure to an environmental air pollutant is defined as contact between molecules of the pollutant and a given biological boundary, such as the breathing zone or the human lung. For the purposes of this website, we consider exposure as the concentration of airborne particles from secondhand smoke in the breathing zone of a person. We DO NOT consider any uptake or dose of the chemical components of secondhand smoke. You can learn more about the science of exposure on



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