Dr. Marzuki Hj. IsmailDr. Marzuki Hj. Ismail

Semester I 2009/10 Semester I 2009/10

ENTECHENTECH

Gas % by volume

N2 78.08

O2 20.95

Ar 0.93

CO2 0.03

All other gases (Ne, He, Kr, H, etc)

0.01

Water Variable

Dry air

Concentration the amount (mass, moles, molecules, etc)

of a substance in a given volume divided by that volume.

The example concentration units are mg/m3, mol/m3, molecules/cc, and etc.

Mixing ratio the ratio of the amount of the substance in

a given volume to the total amount of all constituents in that volume.

Variety of ways to express gas concentrations, which can easily be converted from one type of units to another. They include the following:

Major Constituents Volume percent

Both Major and Minor Constituents Mole fraction

Minor Constituents Parts per million (ppm) Milligrams per cubic meter (mg/m3) Micrograms per cubic meter (ug/m3) Nanograms per cubic meter (ng/m3)

Volume and mass basis unit Volume basis % (1 in 100) ppm (1 in 106) ppb (1 in 109) ppt (1 in 1012)

Mass basis g/m3

mg/m3

g/m3

ng/m3

Concentration in volume percent have the same value at both actual and standard conditions, because any adjustments necessary to account for changes in T and P affect the numerator and denominator proportionally.

100% volume conc. = 1,000,000 ppm What is the concentration of sulfur dioxide, expressed as

ppm, in a combustion gas having the following composition?

Three different sets of units are used to express pollutant concentrations in terms of mass per cubic meter:

Milligrams per cubic meter (mg/m3) Micrograms per cubic meter (µg/m3) Nanograms per cubic meter (ng/m3)

The relationships between these three sets of units:

At STP mg/m3 = ppm *MW/ 22.4 ppm = (mg/m3)*(22.4/MW)

At NTP mg/m3 = ppm *MW/ 24.5 ppm = (mg/m3)*(24.5/MW)

Absolute and Relative Scales

Absolute Scale Relative Scale

Metric System K oC

English System

oR oF

From mg/m3 to ppmv

ppmv = (mg/m3)(273.15 + °C) / (12.187)(MW)

where: ppmv = ppm by volume (i.e., volume of gaseous

pollutant per 106 volumes of ambient air) mg/m3 = milligrams of gaseous pollutant per

cubic meter of ambient air MW = molecular weight of the gaseous pollutant °C = ambient air temperature in degrees

Centigrade (change to K)

For NOx, convert 20 mg/m3 to ppmv at 25 °C:

from ppmv to mg/m3

mg/m3 = (ppmv)(12.187)(MW) / (273.15 + °C)

where: mg/m3 = milligrams of gaseous pollutant per

cubic meter of ambient air ppmv = ppm by volume (i.e., volume of gaseous

pollutant per 106 volumes of ambient air) MW = molecular weight of the gaseous pollutant °C = ambient air temperature in degrees

Centigrade 

As an example, for gaseous pollutant NOx, convert 20 ppmv to mg/m3 at 25 °C:

)/( 3mgionConcentratpM

RTppm

i

Pressure unit and R Constant:

P= 1.01325x105 pascal

R= 8.314 J/K.mol for P in Pa and volume in m3

Example:The Hong Kong Air Quality Objective for ozone is 240 g/m3. The U.S. National Ambient Air Quality Standard for ozone is 120 ppb. Which standard is stricter at the same temperature (25oC) and the pressure (1atm)?

ppbppmmgxxx

xppm 122122.0/240

481001325.1

298314.8 35

Dioxin-furan compound concentrations are often expressed on a Toxic Equivalency Quotient (TEQ) basis rather than a total mass per cubic meter (nanograms per cubic meter basis).

The TEQ format is an adjusted form of the concentration data that takes into account the substantially different toxicities of some of the dioxin-furan compounds.

Data expressed in a TEQ basis are often considered to be more representative of the possible health impact of emissions than data expressed as total dioxin-furan compounds.

The TEQ basis is used because medical researchers believe that the compounds included in the calculation are considerably more toxic than the other dioxin-furan compounds.

Accordingly, dioxin-furan data calculated on a TEQ basis are more closely related to the possible adverse health effects of these emissions.