MONTPELIER, Vt. — Vermont ranked among the five worst states in the country for acid rainfall last month, according to the National Audubon Society.

In data to be released this week, the society’s Citizens’ Acid Rain Monitoring Network says Vermont’s April rainfall was at least 10 times more acidic than normal rainfall. The state’s April rainfall had a pH content below 4.0, the worst category for acidic content.

“Wow,” said Rich Poirot, an air quality planner with the state Department of Environmental Conservation.

The other four states in this category for April were Maine, Pennsylvania, West Virginia, and Virginia.

But Audubon Society and state officials said Wednesday that the pollutants causing Vermont’s high acid rain readings are coming from other states, particularly those in the Midwest. They said Vermont does contribute to the problem through its utilities and automobiles, but not enough to warrant the high readings alone.

“Vermont falls in the path of pollutants that are coming from Michigan, the Midwest and Ohio,” said Christine Indoe, an Audubon Society spokeswoman. “It’s unlikely that these pollutants are coming from Vermont.”

“Half or more of the acidity in our precipitation comes from Midwestern sources,” Poirot said. “That puts us right at the end of the tailpipe of the emitting regions.”

Unpolluted rain has a pH of 5.6, Indoe said. The lower the pH number of rainfall, the higher its acidic content.

Because the pH scale is logarithmic, there is a tenfold difference in acid concentrations between one whole number and the next. For example, rain with a pH of 4.0 is 10 times more acidic than rain with a pH of 5.0, and 100 times more acidic than that with a pH of 6.0.

The society’s monitoring network, which has volunteer-manned stations in every state, has measuring stations in Milton and West Burke. Milton’s reading for April was below 4.0 and West Burke’s was 4.1.