Check out this map that shows the average fine particulate matter (PM 2.5) (µg/m³) by county for the year 2011. 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 compared to western states. States such as, Indiana, Ohio, Tennessee and Kentucky predominantly have a higher average.
By Julia Watson