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The Beating Heart of Mercury Pollution in the West

Circles represent measurement stations, and are colored according to the monthly median mercury concentration of the precipitation they collect. States are colored according to the monthly median of the measurement stations within them. States that are gray had no data for the period. The animation can be stopped by clicking anywhere on the map; data for a given period can be viewed by adjusting the sliders. Mouse over states and measurement stations to read the mercury concentration.

Data Notes


I learned of the availability of this mercury deposition data when I was working on another diversion that depicts the history of acid rain in the United States. I didn't know that there was such a large amount of mercury in the precipitation in the United States, nor that it had this interesting seasonal pattern. It's worth noting that this graphic only relates to wet deposition of mercury, which is only a fraction of total mercury deposition. Note also that the majority of the mercury pollution, particularly in the western United States, comes from global sources 1.

Weaknesses of the Visualization

There are four primary problems with this graphic in my view:
  1. There is a lot of missing data.

    There's nothing I can do about missing data, but it might be more appropriate to perform some kind of regional aggregation rather than statewise aggregation.

  2. The graphic only accounts for wet deposition of mercury.

    The NADP has some data on dry deposition and methyl-mercury deposition, but unfortunately it's even sparser than the wet data.

  3. The concentration of mercury may be less important than the accumulated deposition of mercury.

    I would like to have made a graphic that accounts for the total deposition of mercury rather than the concentration of mercury, but I think that is quite difficult given both the missingness of data and the variation of the missingness.

  4. There is not enough context.

    Exactly how bad are these concentrations? It seems clear that pretty much any amount of mercury is toxic, but there are natural sources of mercury in the environment. Therefore, the environment must be capable of coping to some extent. It would be better if the graphic could represent harm rather than just concentration.

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Data Sources


Thanks to the NADP for making their data public. This visualization was created using R and D3. The following packages were particularly helpful:


1 Weiss-Penzias, P.S., et al., Trends in mercury wet deposition and mercury air concentrations across the U.S. and Canada, Sci Total Environ (2016),