Air Pollution (unit measurement)

1. Air Pollution
Ms Noor Rosyidah Binti Sajuni
School of Engineering
rosyidah@ucsi.edu.my

2. Unit of Measurement
• Air quality measurement are commonly reported in terms of:
– micrograms per cubic meter (μg/m3)
– parts per million (ppm) or parts per billion (ppb)
• For particulate matter, sizes are expressed in micron or micrometer.
– ppm is a volume-to-volume ratio, which makes it independent of local
temperature and pressure.
ppmx xMWx L m x g g
MW gram molecularweight of the gas
V P
2 2
2
V P
1 1
1
6 3 3 6
3
:
10 10 / 10 /
( / )
/
T
T
V L mol
g m


 

2
Standard conditions: V=22.4 L/mol @ 273K & 760 mmHg

3. Converting μg/m3 ppm
• The conversion between μg/m3 and ppm is based on the fact that at standard
conditions (00C and 101.325 kPa), one mole of an ideal gas occupies 22.414 L.
• We may write an equation that converts the mass of the pollutant Mp in grams to its
equivalent volume Vp in liters at standard temperature and pressure (STP).
GMW = g MW of the pollutant
Vp = equivalent volume
Mp = mass of the pollutant

4. • REMEMBER!!
• For readings made at T & P other than standard conditions, the standard
volume, 22.414 L/GM must be corrected.
• Use Ideal law to make correction
• T2 and P2 (absolute temperature and absolute pressure at which the
readings were made.
• ppm is a volume ratio,
• Where Va = volume of air in cubic meters at T,P of the reading.

5. • Final equation:
Where
GMW = gram MW of the pollutant
Vp = equivalent volume
Mp = mass of the pollutant (μg)
Va = volume of air in cubic meters at T,P of the reading
T2 = absolute temperature at which the readings were made
P2 = absolute pressure at which the readings were made
• Factors converting μg to g and L to million of L to millions of L cancel
one another.
• Unless otherwise stated, assumed that Va =1.00 m3

6. Example
• A one-cubic-meter sample of air was found to contain 80 μg/m 3 of SO2.
The temperature and pressure were 25◦C and 102.193 kPa when the air
sample was taken. What was the SO2 concentration in ppm?
Given; S = 32.07
O = 16.00
Answer; SO2 = 0.03 ppm

7. Solution
1. Determine the GMW of SO2 .
GMW of SO2 = 32.07 + 2(16.00)
2. Convert temp to absolute temp.
250C + 273K = 298K
3. Solve the equation
Answer ; 0.0300 ppm of SO2