Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 73

TABLE 2.10
Conversion for Parts per Million in Proportion and Percent

Parts per Million Proportion Percent Parts per Million Proportion Percent

0.1 1:10,000,000 0.00001 25.0 1:40,000 0.0025

0.5 1:2,000,000 0.00005 50.0 1:20,000 0.005

1.0 1:1,000,000 0.0001 100.0 1:10,000 0.01

2.0 1:500,000 0.0002 200.0 1:5,000 0.02

3.0 1:333,333 0.0003 250.0 1:4,000 0.025

5.0 1:200,000 0.0005 500.0 1:2,000 0.05

7.0 1:142,857 0.0007 1550.0 1:645 0.155

10.0 1:100,000 0.001 5000.0 1:200 0.5

15.0 1:66,667 0.0015 10,000.0 1:100 1.0

The expression “parts per million” is without dimensions; that is, no units of
weight or volume are specifically designated. Using the format of other units, the
expression may be written as

Parts
Millionparts

“Parts” are not defined. If cubic centimeters replace parts, we obtain:

Cubic centimeter
Millioncubic centimeters

Similarly, we might write pounds per million pounds, tons per million tons,
or liters per million liters. In each expression, identical units of weight of volume
appear in both the numerator and denominator and may be canceled out, leaving a
dimensionless term. An analog of parts per million is the more familiar term “per-
cent.” Percent can be written as

Parts
Hundred parts

To convert from parts per million by volume (µL/L) to µg/m 3 at standard tem-
perature (25°C) and standard pressure (760 mmHg), known as STP, it is necessary
to know the molar volume at the given temperature and pressure and the molecular
weight of the pollutant. At 25°C and 760 mmHg, 1 mole of any gas occupies 24.46 L.

■ Example 2.135
Problem : 2.5 ppm by volume of sulfur dioxide (SO 2 ) was reported as the atmospheric
concentration. What is this concentration in micrograms (µg) per cubic meter (m 3 ) at
25°C and 760 mmHg? What is the concentration in µg/m 3 at 37°C and 752 mmHg?