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Re: Rainwater pH

>From: IDMiamiBob at aol_com
>It should be 7.0, because it is a s close to pure as water gets in nature.  So
>pollution is hurting your water supply.

Pure rainwater, or, more accurately, rainwater unpolluted by any man-made
products, has a pH of 5.5 to 6 or so, rather than 7, because it absorbs
some carbon dioxide from the air.  Part of the dissolved CO2 reacts with
the water to produce carbonic acid.

A number of years ago, I was part of a nationwide survey of rainwater
conducted by the Audubon Society.  They supplied me with materials for
collecting rainwater and measuring its pH with little dye-indicator sticks
that had three different pH indicators, giving a range from over 7 to below
3, accurate to 0.5 pH unit.  My results indicated that the rain in central
Mississippi was unpolluted with a pH around 5.5 from late fall through late
spring.  During this period rain falls from warm, moist air brought up from
the Gulf of Mexico.  During the summer and early fall period, rain can fall
from air that has been over land for some time and become polluted.  On
several occasions I got pH's as low as 3 during this period, and the
typical value was between 5.5 and 4.0.

Paul Krombholz, in cool central Mississippi, with warm air on the way.