2010 Average Fine Particulate Matter (PM 2.5) (µg/m³) By County

Today’s map of the day shows the average fine particulate matter (PM 2.5) (µg/m³) by county for the year 2010. From the map we can see clusters with a higher average indicated by the darker shading. For instance, we can see a cluster consisting counties within for Colorado, Nebraska, Kansas and Wyoming. It is also apparent there are higher concentrations in many Southern, Midwestern and Northeastern states. It is interesting to note some states had higher averages in 2010 when compared to our previous map of particulate matter (PM 2.5) (µg/m³) by county for the year 2011. Why might this be?