Air Polution Control

Applied Chemistry 0505Applied Chemistry 0505HanHaoHanHao

18thJune18thJune, 2007, 2007

Physical Chemistry Physical Chemistry PresentationPresentation

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Air Pollution Control Engineering

United Nations Environment Programme



Contents Air Pollution Control Engineering

5.Particulate pollution and health.

2.Air pollution meteorology

4.Thinking of air pollution control

3.The concentration model of air pollution

1.Chief introduction

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Introduction

In our daily life, it is the fact that most of people don’t treat the air pollution as seriously as water pollution or other kinds of pollutions.

But it is really easy for us to ignore the bad effect on our health caused by air pollution because it seems that there are few examples to be seen directly.

* Now let’s have a look at the report of the general condition of our country in the year of 2005 which is written by State Environmental Protection Administration of China.





Lead-in Diagram

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Background knowledge

According to the report, we can see that the main pollutant in the air is particulate. It is for sure that if we want to make the sky over us clean, we must find some efficient and possible ways to reduce the concentration of particulate to a acceptable level.

* First of all, we have to get some information and background knowledge about the meteorology…




Density of the atmosphere

Stability of the atmosphere

Height of the mixed layer

Polar heating and cooling

Rotation of the Earth

Land and Ocean

Knowledge of atmosphere

AtmosphericAtmosphericlayerlayer

BB

EE

CC

DD

AAHorizontal movement

Vertical movement

Wind

Smog & Stranded

Atmospheric inversion(逆温)

** I really want to share this part with you just because it is very interesting, and maybe the next thing will even surprise you …


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Vertical movement

The density of the atmosphere will change while the temperature and humidity are changing.

According to the ideal gas equation:

So, at certain height, the density is depended on M and T. If we take the fundamental equation of hydrostatic into consideration:

then we can get: (z is the height)

M pR T

ρ =

dp gM dzp RT

= −

dp gdz

ρ= −




Vertical movement

Heig

ht ab

ove t

he se

a lev

el, z

Trop

osph

eric

laye

r St

rato

sphe

ric

laye

r

65.840ft

20.061m

36.150ft

11.021m

-92.8℃

-135℉

15℃

59℉

-56.5℃

-69.7℉Temperature

Adiabatic air

Standard air


While a air block is While a air block is rising up, if we rising up, if we ignored the heat ignored the heat exchanged between it exchanged between it and other air, the and other air, the process can be process can be regarded as adiabatic regarded as adiabatic and reversible. and reversible. OOf f course we are familiar course we are familiar with such a process, with such a process, we have the equation: we have the equation:

TThen we get an hen we get an important equation:important equation:

pC dTdpp RT

= −

,adiabatic ideal p

dT gMdz C

= −

dT/dz is just the slop of the line.



The stability of the airHe

ight

abov

e the

sea l

evel

, z

Temperature

6000ft

1000ft

50℉ 90℉


Standard air: dT/dz=-6.5℃/km=-3.6℉/1000ft

Adiabatic air: dT/dz=-9.8℃/km=-5.4℉/1000ft

3.00 P.M

Dawn+4hDawn+2h

Dawn

When z ≤1000ft, we can see that the temperature of the air will rise up when it is higher and higher, such a phenomenon is calledtemperature inversion.

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Why should we know that?

It’s very important for us to know how the atmosphere moves everyday, if we want to find some available ways to solve the air pollution.

Hover Fly There is something interesting: hovering is really different from flying, because if you want to hover, you must keep agitating your wings, but if you are flying, you can feel the real freedom.

But it is impossible for angle to fly at dawn or cloudy day. It is also very dangerous for people to glide in that situation. Do you know why?

There is something interesting: hovering is really different from flying, because if you want to hover, you must keep agitating your wings, but if you are flying, you can feel the real freedom.

But it is impossible for angle to fly at dawn or cloudy day. It is also very dangerous for people to glide in that situation. Do you know why?


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What forms temperature inversion

TemperatureTemperatureInversionInversion

Cooling air form bottom to top

Heating air form top to bottom

Making a warm air layer over a cool air layer

Making a cool air layer Under a warm air layer


Stable atmosphere

Reduce the energy exchange between lower and upper air layers

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Smog & Stranded

If there is very strong surface temperature inversion at the disposal of pollutants area, the plume of the pollutants will be stopped from diffusing.

9:00 A.M

8:00 A.M

6:00 A.M

No temperature inversion layer

Surface temperature rises. Unstable layer comes out

The highest pollutant density of ground

Strong inversion of terrestrial surface radiation


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The concentration model Air Pollution Control Engineering

The ideal pollutant concentration model can predict the discharge of any pointed pollutant and the pollutant concentration under any climate condition, in any positions and at any time area correctly.

We can use an equation to express the amount equilibrium of some certain pollutant:

Accumulating rate = all flow of flowing into – all flow of flowing out + speed of producing – speed of cutting down



Air pollutant concentration model

Fixedbox

Diffusion model

The concentration model of the air pollution


Two main kinds of air pollutant concentration model

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Fixed box model Air Pollution Control Engineering

The fixed box model is the simplest model with the lowest reliability. Before we use it to calculate the pollutant concentration of a city, we have to make some necessary hypothesis.

z

xy

LW

Wind speedu City

H



Fixed box model

8 hypothesis to the fixed box model:1. The shape of city is rectangle with W and L as its width and length respectively. One

side of city parallels with the wind direction.

2. The atmospheric rapids makes the pollutants to mix completed under the mixed layer.

3. The pollutants over the city distribute uniformly.

4. The wind speed never changes.

5. The concentration of the pollutants which are just getting into the city is a constant b.

6. The speed of pollutant emission is Q. Q=qA, in which q means the speed of unit area emission and A means the area of city.

7. No pollutant get through the top of box, nor passing the side paralleling with the wind direction.

8. Pollutants stay in atmosphere for a long enough time.




Diffusion modelAir Pollution Control Engineering

The fundamental model is Gauss Plume Model, which is also a model of mass equilibrium.

△h

hHy xWind directi

on

z

X=y=z=0(at the bottom of the chimney）



Gauss Plume Model

In the picture, H is called the efficient height of the chimney, h is the physical height of the chimney, △h is the lifting height of the pollutant plume.

H = h + △hWe suppose that the wind speed won’t change, then the

question is to calculate the pollutant concentration c at any point (x,y,z,x＞0) caused by the point source.


我们开始从排放点沿下风向运动，则认为大气污染物背景浓度b＝0，经过烟囱口后，就进入高浓度区。经过烟囱口后，受污染的空气在湍流的作用下开始扩散。若对烟羽轴线附近小的立方体列物料平衡方程则：

∑ ∑累积率＝所有流入的量－所有流出的量



累积率是污染物的量对时间求导数。

根据湍流的作用，所研究的小立方体的六个面都有空气穿过，因此借助物质通量进行估计。通量中，c表示污染物浓度，n表示所研究方向上的距离，K表示湍流扩散系数。方程中负号表示烟流由高浓度流向低浓度。

立方体沿x轴共有两个面，每个面面积为△y △x则湍流扩散在两个面的净通量为：

Gauss Plume Model

c )t

c cV V x y zt t

∂ ∂ ∂= =∆ ∆ ∆

∂ ∂ ∂＝（累积率

cKn

∂∂

通量＝－




Air Pollution Control EngineeringGauss Plume Model

y y yx x x z z z

K cK c K cy yx z z

x y z+∆+∆ +∆

∂ ∂∂ ∂ ∂ ∂ −− − ∂ ∂∂ ∂ ∂ ∂ ∂ + +∂ ∆ ∆ ∆

K cK c K c

c x＝t

同样还可以得到另外四个面的式子，从而我们得到:

xx x x

K cx +∆

∂ − ∂ − ∆ ∆ ∂ ∂

- K c方向的流入量＝ y z

x

2

2 20lim x x x

x

K c K cK cx x

x x+ ∆

∆ →

∂ ∂ − ∂∂ ∂ =∆ ∂

＝

又有：



Gauss Plume Model Air Pollution Control Engineering

最终我们得到高斯烟羽模式方程：

2 2 2

2 2 2x y zc c c cK K Kt x y z

∂ ∂ ∂ ∂= + +

∂ ∂ ∂ ∂

这里我们只考虑高斯烟羽模式的一维扩散结果：

2

1/ 2 1/ 2

1exp2( ) 4x x

X xct K t Kπ

= −

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The model used in daily life Air Pollution Control Engineering

In fact, because the situation around us is so complexed that none of the models we use nowadays can forecast the concentration of the pollutants correctly.

So maybe we can only say :”All of the models are wrong, but some of them can be used in certain aspects.”

It is impossible for us to use only one model to deal with all kinds of pollutants. But if we take many different sorts of models into consideration, we can get the result which is the most efficient one.



Thinking of air pollution control

Promote diffusionPromote diffusion

Change process of producing.Change process of producing.Cutting down the discharging to prevent from polluting.Cutting down the discharging to prevent from polluting.

Application of the downstream pollution control equipments.Application of the downstream pollution control equipments.


When we want to deal with the problems caused by air pollution, we should know some common thinking of air pollution control.

There are three kinds of available control plans when we confronted with the air pollution…

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Where will they finally go?

Burning them to be ashes

Transform theminto other forms

Stack them in thelandfill yard


Pollutants

?

?

?

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Particle pollution

What is particle pollution?

Particle pollution is a mixture of microscopic solids and liquid droplets suspended in air. This pollution, also known as particulate matter, is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mold spores).




The size of particles Air Pollution Control Engineering

The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs.

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The size of particles

PM10 "Inhalable coarse particles," such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.

Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

PM2.5 "Fine particles," such as those found in smoke and haze, are2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobilesreact in the air.




Primary and Secondary particles Air Pollution Control Engineering

* These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some particles, known as primary particles are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires.

* Others form in complicated reactions in the atmosphere of chemicals such as sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles. These particles, known as secondary particles, make up most of the fine particle pollution in the country.

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How can particles affect your health?

Long-term exposures,such as those experienced by people living for many years in areas with high particle levels, have been associated with problems such as reduced lung function and the development of chronic bronchitis and even premature death.

Particles

Short-term exposures to particles (hours or days) can aggravate lung disease, causing asthma attacks and acute bronchitis, and may also increase susceptibility to respiratory infections. In people with heart disease, short-term exposures have been linked to heart attacks and arrhythmias.

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How can you avoid unhealthy exposure?


Particle levels can be elevated indoors, especially when outdoorparticle levels are high. Certain filters and room air cleaners can help reduce indoor particle levels. You also can reduce particle levels indoors by not smoking inside, and by reducing your use of otherparticle sources such as candles, wood-burning stoves, and fireplaces.

Your chances of being affected by particles increase the more strenuous your activity and the longer you are active outdoors. If your activity involves prolonged or heavy exertion, reduce your activity time or substitute another that involves less exertion. Go for a walk instead of a jog, for example. Plan outdoor activities for days when particle levels are lower. And don't exercise near busy roads; particle levels generally are higher in these areas.

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