Prof. Jiakuan Yang

Huazhong University of Science and Technology

Air Pollution Control Air Pollution Control EngineeringEngineering

Questions for the Last Lecture

1 Please give three or more Abbreviations about American environmental organizations or air pollution laws.

2 Please explain the four air pollution control philosophies.

Answer

EPA : Environmental Protection AgencyNAAQS: National Ambient Air Quality StandardsACGIH: American Conference of Governmental Industrial Hygienists

NESHAP: National Emission Standard for Hazard and Air pollutions

CAA: Clean Air Act

four air pollution control philosophies

Emission standards philosophy cleanest possible air philosophy, the best technology Air quality standards philosophy zero-damage philosophy Emission taxes philosophy suitable tax for emitter Cost-benefit standards philosophy minimizing the sum of control cost and damage cost and damage cost, get maximum benefit

Lecture Lecture 4 4 Air Pollution Measurements, Emission Estimates

Ⅰ The components of monitoring or sampling deviceⅡ How to get a representative sample?Ⅲ How to determine the concentration correctly?Ⅳ How to select the sampling flow rate?Ⅴ How to select correct analytical methods? Ⅵ How to estimate emissions?

Ⅰ The components of monitoring or sampling device

Two kinds of air pollution measurements methods

ambient monitoring concentrations of pollutants in the air the public breathes

source testingconcentration and emission rates from air pollution sources

Ⅰ The components of monitoring or sampling device

Detector to quantify instantaneous or cumulative amount of pollutant

Gas meter

Sample Gasflow

Inlet device to exclude unwanted

sampling probe heated to prevent condensation

Devices for positioning the sampling probe

Air mover(pump)

Vent to air

Gas sourcesampling determining power

Flow rate

Ⅱ How to get a representative sample?

(1) selecting a suitable sampler site

Generally the ambient air sampler should be located at the place to which the public has free access where the pollutants concentration is the highest.

For ambient sampling

Ⅱ How to get a representative sample?

For source testing

In source testing , for most such stacks the velocity and concentration in the stack vary from point to point and from time to time , so that many separate measurements must be made and averaged.

The section near the bend, less uniform

The section far away the bend, more uniform

Ⅱ How to get a representative sample?

For source testing

Page 66, Figure 4.3

(2) Excluding unwanted materials

a bug screen (昆虫网） PM10 ( particulate matter 10 microns or smaller )

PM2.5 (particulate matter 2.5 microns or smaller )

Ⅱ How to get a representative sample?

(3) Probes are normally heated to prevent condensation of gases on the walls of sampling probe

Ⅱ How to get a representative sample?

Ⅲ How to determine the concentration correctly?

(1) Eliminating the interference effect

For example Determining SO2 concentration passes the gas through a dilute solution of NaOH.

if not considering of CO2 , Cdeterming > Ctrue

Measuring the change in NaOH concentration by simple acid-base titration.

SO2 + NaOH NaSO3 +H2O

CO2 + 2NaOH Na2CO3 + H2O

(2) Averaging the concentration

Ⅲ How to determine the concentration correctly?

Real –time instruments can memorize a lot of values during a period of time .

Time

0 t

Con

cent

ratio

n Average concentration =Cavg = (1/t)∫Cdt

C=area of the shadow t = the time of measurement

(2) Averaging the concentration

Averaging instruments of the concentration of particles.

Average C = Cavg = Total volumeTotal mass

Example4.2Page 69

A PM2.5 sampler ran for 24 hours, average flow of 16.7 L /min , fresh filter : 0.1400 g , gross weight of used filter : 0.1405 g , what is the average PM2.5 concentration ?

335

33

8.201008.2

min6024min

)107.16(

)1400.01405.0(

mg

mg

mgCavg

Ⅳ How to selecting the sampling flow rate?

isokinetic flow sampling for particulates in stack.

Vn : gas velocity inside the sampling probe

Vs : gas velocity in the stack

Vn= Vs

nozzlestack

(1) Vs < Vn

Density of particulate is much larger than density of air, so particulates are more inertial and keep direct.

Cdeterming < Ctrue

Mass keep constant, Vn> VsC =mass

flow nozzle volume

(2) Vs > Vn

Mass keep constant, Vn< VsC =mass

flow nozzle volume

Cdeterming > Ctrue

Ⅴ How to selecting correct analytical methods?

P27, Table 4.1

According to standard sampling methods by EPA

Test methods for major air pollutants in ambient air.

Ⅵ How to estimate emissions?

Emission factors

Page 74~78Sections 4.8~4.9 are studied by yourselves.

This Lecture and the Next Lecture

This Lecture: Chapter 4 Page 63~82

The Next Lecture: Chapter 5 Page 83~118

Homework

Page 794.44.8

DISCUSSION

Topics about Air pollution:

Introducing yourself

Interesting news or information about air pollution your

having read or heard

Your opinions on this Air Pollution course

Your suggestions for Chinese Air Pollution

Other familiar issues about Air Pollution