This presentation talks about types of air pollution measurement : ambient measurement and source measurement

2. Contents
INTRODUCTION
A REPRESENTATIVE SAMPLE
CONCENTRATION DETERMINATION
AVERAGING
STANDARD ANALYTICAL METHOD
DETERMNING POLLUTANT FLOW RATE
ISOKINETIC SAMPLING
EMISSION FACTORS
VISIBLE EMISSIONS

3. 1-INTRODUCTION
➢there are two kinds of air pollution measurements ambient measurements or
ambient monitoring and source measurement.
• Ambient measurement : concentrations of pollutant in the air that public breathe
Concentrations in the ambient air must be measured to determine whether the air is safe
to breath ( meet the NAAQS)
• Source measurement : concentrations and / or emission rates from pollution
sources
➢Emission rates of various sources of air pollutants must be measured to control pollution
concentrations

4. The components of any ambient –monitoring or source
sampling –device.

5. 2-A representative sample
➢ Any air pollution measurement involves two problems :
1- the first is to obtain a suitable place
2- the second is to determine the concentration of pollutant of
interest in it correctly
➢An ambient air sampler should be located at the place to
which the public has free access where the pollutant has the
highest concentration
An ambient monitor must be placed where it has power ,
shelter from rain , a constant temperature environment , easy
access for monitoring and personal protection.
there are EPA guidelines for the proper placement of intake for
air samples
➢in source testing, gas flow in a large industrial flue or
smokestack with various velocities and concentrations so that
many separate measures must be made and averaged.
▪ in newer plants designer consider the problem of obtaining a
uniform flow gas and provided for the source sampler to place
the required instruments

7. The components of any ambient –monitoring or source
sampling –device.

8. The components of any ambient –monitoring or source
sampling –device.

9. 3-GETTING THE REPRESENTATIVE SAMPLE TO THE DETECTOR
➢sampling instruments have a device on their inlet to exclude unwanted materials like
insects and large dust particles
➢the EPA has modified its particulate samplers in 1987-1997
1-before 1987 the sampler inlet was designed to exclude all particles larger than 50
microns the quantity sampled was called (TSP total suspended particulate)
2- in 1987 the inlet design changed to exclude particles larger than 10 micron the quantity
sample is called PM2.5
3- in 1997 the inlet design changed to exclude particles larger than 2.5 micron the
quantity sample is called PM2.5
➢ the sampling probe is heated to prevent the condensation of water vapor on its walls
➢acid gases like so2 will react with alkaline solids on a filter thus increasing the weight of
solids on a filter
➢For grab sample that taken in the field , then brought to the lab for analysis , the
sample container must not react or modify its contents during transit.

10. 4-CONCENTRATION DETERMINATION
the sample passes through a cell in which a light beam of a suitable wave length is
absorbed by the pollutant
 the pollutant enter a fast light producing chemical reaction with some reagent and the
resulting light emission is measured
THE PROBLEM OF INTERFERENCES
➢Interference : other pollutants that absorb or emit the same wavelength of interest
or can go with the same reactions for the pollutant to be measured
for example measuring SO2 in nitrogen gas. one passes the gas through a dilute solution
of NaOH in which reaction is 2NaOH+ SO2 → 𝐍𝐚 𝟐 𝐒𝐎 𝟑+ 𝐇 𝟐 𝐎
then measure the change in concentration of NaOH by acid - base titration
• if the problem is to measure SO2 in the air , CO2 in the air will also react and cause
interference by the reaction 2NaOH+CO2→ 𝐍𝐚 𝟐C𝐎 𝟑+ 𝐇 𝟐 𝐎
if the concentration of CO2 is known a correction could be made
➢in other cases the concentration of the interfering component may not be known so that
the uncertainty in the resulting measurement is also unknown

11. 5- AVERAGING
➢to find the average concentration of a pollutant to compare it with the applicable standard it
is found by 𝐶 𝑎𝑣𝑒 =
1
Δ𝑡
‫׬‬ 𝐶 ⅆ𝑡 C: the instantaneous concentration indicated by the instrument
t : the time of measurement
➢there are two type of instruments : real-time instruments and averaging instruments
real-time instruments: present their results as an electronic signal that can be averaged be
easily averaged by built in electronics.
Averaging instruments :represent the old type instruments for gases as well as current
type for particulates
For example PM2.5 sampler that consists of a special inlet exclude all particles larger than 2.5
micron
Filter , fan and floe measuring device and a suitable housing .
A pre-weighed filter is placed in the filer holder and air is sucked through it for 24 hours at a
measured rate
The concentration is computed through 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑐 𝑎𝑣𝑒 =
increase in filter weight
air flow rate x time

12. ➢ High- quality weighing and sample humidity control are needed
➢ For this example If the weighings are only reliable to ±100 μg then our confidence in the difference of the two
measurements is ±200μg and our confidence in the ambient concentration is only 40%
➢ This type of instruments is not suitable for determining hourly variations as are the real time instruments

13. ➢efforts to develop a suitable real time instruments for PM2.5 have so far not been
completely successful , mostly because of this small sample size
➢older measuring schemes for gas pollutants operated somewhat like the following :
passing a measured volume of gas through a bubbler that contained a solution that reacted
specifically with the gas to be measured and then titrating the solution to determine the
concentration of the pollutant in the gas or measuring the color of the solution.
For example the EPA sampling train for measuring the concentration of SO2 gas in stack

14. The components of any ambient –monitoring or source
sampling –device.
EPA sampling train for SO2

15. 5-standard analytical method
➢EPA has standard sampling methods for various pollutants
➢This methods are different for ambient monitoring than for source sampling
➢In EPA for each major air pollutant there is a reference method and equivalent
method
Reference method is the test method that is considered the standard against other
methods can be tested
Equivalent methods which are checked against the reference method and found to
similar result

16. The components of any ambient –monitoring or source
sampling –device.

17. 6-determining the pollutant flow rate
➢the mass flow rate of a pollutant is the product of the concentration in the gas and the
molar mass or mass flow rate of the gas
➢ pollutant flow rate = molar flow rate of gas x pollutant molar concentration in the gas

18. The components of any ambient –monitoring or source
sampling –device.

19. 6-isokinetic volumetric
In stacks sampling for particulates , one
must maintain isokinetic constant flow
into the sampling probe.

20. 8-emission factors
➢Emissions testing is expensive
➢For simple, will-defined sources(power plant sources) it can be tedious but it is not difficult
➢Often we want to know the emission from facility before it is built
➢To meet this needs the EPA has produced a very useful set of emissions factors
documents
➢This are summaries of the results of past emission tests, organized to make them easy
to apply

22. The components of any ambient –monitoring or source
sampling –device.

23. The components of any ambient –monitoring or source
sampling –device.

24. 8-visible emissions
➢Airborne particles can scatter and absorb light,
so if the particles concentration in the plume is
high enough, the plume will be visible.
➢As the plume flows downstream and mixes
with the surrounding air the plume opacity
decrease

25. The components of any ambient –monitoring or source
sampling –device.