Air Pollution

Ms Noor Rosyidah Binti Sajuni

School of Engineering

rosyidah@ucsi.edu.my

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.

2

22

1

11

63363

:

)/(

/10/1010/

T

PV

T

PV

gastheofweightmoleculargramMW

molLV

ggxmLxMWxppmxmg

2

Standard conditions: V=22.4 L/mol @ 273K & 760 mmHg

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

• 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.

• 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

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

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