# Can I convert from an emission amount (in tonnes per area) to a concentration (in ppbv)?

Hi, I was wondering if it is possible to estimate the concentration of SO2 given the total mass of SO2 emissions?

Europa's EDGAR has a resource called "Global Emissions EDGAR v4.2" (see http://edgar.jrc.ec.europa.eu/overview.php?v=42). A database of SO2 emissions in Metric Tons per Area is provided, but I need concentration instead.

Currently I am determining the volume of the gas by assuming it's at STP, then I am dividing this by the estimated total containing volume, which I tried to estimate as follows.

Total Containing Volume = (11120 m*11120 m)*altitude

or

Total Containing Volume = (apprx. area of 1° latitude by 1° longitude "square")*altitude

I calculated an altitude that makes the calculation match another database of SO2 concentrations that I have. Unfortunately the other database of SO2 concentrations is limited in the area that it covers, so it is not suitable.

Is this estimation attempt misguided or is there a better way to do it? If there is another database that contains global or continental SO2 concentration grids that would also fix the problem.

What you are doing seems reasonable but there are many hidden assumptions in your technique:

• The data source you are using actually provides a rate, i.e. metric tons per area per year.

• Thus your calculation is also implicitly a rate: the results will be in tons per volume per year.

• You are assuming that the only source of atmospheric $\ce{SO2}$ is the emissions quantified by your data source. It may well be that there are other, natural sources of $\ce{SO2}$, or more likely, natural sinks of $\ce{SO2}$.

• If you want to know actual concentrations, you will need to quantify all the other sources and sinks of $\ce{SO2}$, and integrate all sources and sinks over time.