Data Preparation For Kriging

[RichardMassatti]

I???ll be using ordinary kriging to create a surface of air pollution for Ohio. My data from the Toxic Release Inventory are annualized, so each case represents the amount of pollutant XYZ given off over an entire year.

My question is this: Should I aggregate (with the sum command) in cases where I have multiple chemicals given off by one facility at the exact same lat/long coordinates to create a total pollution score ??? or ??? should I allow for multiple chemical releases at the same location. I ask because I???m afraid I???ll bias the nearby values if I use the total score. Yet, the total score is a reflection of what was released there ??? so I don???t know what to do.

Thanks!

[EricKrause]

You need to ask yourself what an interpolation would mean for your data.  If you used your data to predict a value at an unmeasured location, how would you interpret the value of the prediction?  If your data is about the amount of pollution released, then the interpretation of the prediction would be "the amount of pollution released at this location over the year."  But what if there is no factory at the new location?  In the case of pollution release, it's only being released from particular locations.  It doesn't really make sense to interpolate a variable that only occurs at discrete points on the map.

If you want to make a map of pollution levels, your data needs to be random samples of pollution levels, not measurements of pollution release from discrete locations.  There may be physics models that can predict pollution levels from data about pollution release, but ordinary kriging is not the way to do this.

[RichardMassatti]

I wanted to roughly measure potential exposure within Ohio. Ideally, I would use air modelling software (e.g., AERMOD or CALPUFF), but this software really isn't built to take into context the vast number of chemicals and sites that exist in Ohio.

[EricKrause]

If you just want a rough measure of relative pollution exposure, consider using the Kernel Density tool in Spatial Analyst.  Sum up the pollution released from each location, and use it as the Population field.

You won't be able to actually estimate the total exposure at a given location, but you'll be able to say that certain locations are more exposed than others.  As for estimating the actual amount of exposure, I don't know how you would do that.  You would probably need to talk to a physicist.

[EricKrause]

http://getthegistofit.blogspot.com/2012/04/pollution-exposure-risk-in-washington.html

Give that a read.  They start with Kernel Density, then they do post-processing on the results.  I can't really comment on the legitimacy of the methodology, but it's a good place to start.