Slide 3 of 28
Notes:
pH is the scale used to measure degree of acidity for solutions in water. It ranges from 0 to 14, with values less than 7 being called acid, and those greater than 7 called alkaline. The neutral point is thus 7 and increasing acidity extends downwards from there. Rain from clean air is also slightly acidic, with a pH around 5.7, from the effects of carbon dioxide dissolved from the air to form a weak solution of carbonic acid.
This map shows large areas in the western U.S. where the air is fairly clean (green), though there is a tongue of greater acidity (yellow) from Arizona, to New Mexico to the Colorado mountains. However, east of the Mississippi are large areas (red) with pH below 4.5. These patterns clearly show the effects of downwind transport by the prevailing westerlies in the mid-troposphere.
The plume originating in Arizona is largely associated with electricity which is generated there but exported to California.
This problem first became apparent in the U.S. during the 1970's *** check *** when stories began circulating in Pennsylvania and New England of fisherman complaining that their favorite lake had gone barren, or of owners discovering after a shower of rain that their automobile had developed a case of measles and needed a paint job. In those days maps like this did not exist, because the measurements were not routinely made, and it took years of research to establish the facts as we now know them.