Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 74

Note: This example problem points out the need for reporting temperature and
pressure when the results are present on a weight-to-volume basis.

Solution : Let parts per million equal µL/L, then 2.5 ppm = 2.5 µL/L. The molar
volume at 25°C and 760 mmHg is 24.46 L, and the molecular weight of SO 2 is 64.1
g/mole.

1. 25°C and 760 mmHg:

3

2.5 µL
L

1µmole
24.46 µL

64.1 µg
µmole

1000 L 6.6 × 10 µg

× × × = at STP

3 3

m m

2. 37°C and 752 mmHg:

310°K
298°K

760 mmHg
752 mmHg

24.46 µL × × = 25 72 . µL

3

2.5 µL
L

1µmole
25.72 µL

64.1 µg
µmole

100 00L

m

6.2 × 10 µg

× × × = at STP

3 3

m

Conversion Tables for Common Air Pollution Measurements
To assist the environmental engineer in converting from one set of units to another,
the following conversion factors for common air pollution measurements and other
useful information are provided. The conversion tables provide factors for

• Atmospheric gases

• Atmospheric pressure

• Gas velocity

• Concentration

• Atmospheric particulate matter

Following is a list of conversions from ppm to µg/m 3 (at 25°C and 760 mmHg) for
several common air pollutants. Also see Tables 2.11 to 2.15.

• ppm SO 2 × 2620 = µg/m 3 SO 2 (sulfur dioxide)

• ppm CO × 1150 = µg/m 3 CO (carbon monoxide)

• ppm NH 3 × 696 = µg/m 3 NH 3 (ammonia)

• ppm CO 2 × 1800 = µg/m 3 CO 2 (carbon dioxide)

• ppm NO × 1230 = µg/m 3 NO (nitrogen oxide)

• ppm NO 2 × 1880 = µg/m 3 NO 2 (nitrogen dioxide)

• ppm O 3 × 1960 = µg/m 3 O 3 (ozone)

• ppm CH 4 × 655 = µg/m 3 CH 4 (methane)

• ppm CH 4 × 655 = µg/m 3 CH 4 (methane)

• ppm CH 3 SH × 2000 = µg/m 3 CH 3 SH (methyl mercaptan)

• ppm C 3 H 8 × 1800 = µg/m 3 C 3 H 8 (propane)