Outdoor air pollution fundamentalsOutdoor air pollution fundamentals

Air pollutantsAir pollutants Air pollution standards and measurementAir pollution standards and measurement Air pollution problemsAir pollution problems Air pollution in Hong KongAir pollution in Hong Kong Air pollution meteorologyAir pollution meteorology

1. Definition of air pollutants1. Definition of air pollutants Air pollution may be defined as the presence in the Air pollution may be defined as the presence in the

atmosphere of substance(s) added directly or indirectly in atmosphere of substance(s) added directly or indirectly in such amounts as to affect living and non-living things such amounts as to affect living and non-living things adversely. adversely.

What is classified as a pollutant therefore depends upon What is classified as a pollutant therefore depends upon recognition of which recognition of which substances cause adverse effectssubstances cause adverse effects. It . It is an is an ever-changing definitionever-changing definition..

Centuries ago only soot or odoured gases may have been Centuries ago only soot or odoured gases may have been considered air pollutant. Now we recognize that pollutants considered air pollutant. Now we recognize that pollutants can cause more subtle effects than producing unpleasants can cause more subtle effects than producing unpleasants smells. Even COsmells. Even CO22 is now considered a pollutant. is now considered a pollutant.

Air Pollution ?

The key points of air pollution: i) The key points of air pollution: i) substancesubstance; ii) ; ii) man-made man-made or naturally producedor naturally produced; iii) with ; iii) with adverse effects to living and adverse effects to living and non-living thingsnon-living things; and iv) ; and iv) high concentrations or large high concentrations or large amountamount..

Questions arise: How do we define the above vague Questions arise: How do we define the above vague points? How is adversity defined? At what concentration points? How is adversity defined? At what concentration should a pollutant be considered high? What are the should a pollutant be considered high? What are the substance that should be considered as pollutants? substance that should be considered as pollutants?

Particulate matterParticulate matter::– total suspended particulate (TSP) (typical size < 100 total suspended particulate (TSP) (typical size < 100

m)m)

– respirable suspended particulate (RSP) (typical size respirable suspended particulate (RSP) (typical size < 10 < 10 m) (PMm) (PM1010, particulate matter of size < 10 , particulate matter of size < 10 m)m)

Gaseous pollutantsGaseous pollutants::– Primary gaseous pollutants: SOPrimary gaseous pollutants: SOxx, NO, NOxx, CO, volatile , CO, volatile

organic compound (VOC), Pb;organic compound (VOC), Pb;– Secondary gaseous pollutants: peroxyacetylnitrate Secondary gaseous pollutants: peroxyacetylnitrate

(PAN), ozone (O(PAN), ozone (O33))

Photochemical pollutantsPhotochemical pollutants::– VOC, OVOC, O33, PAN, CFC, greenhouse gases (CO, PAN, CFC, greenhouse gases (CO22, H, H22O)O)

2. Common air pollutants2. Common air pollutants

2.1 Air pollutants sources and 2.1 Air pollutants sources and propertiesproperties Natural pollutant sourcesNatural pollutant sources

Volcano eruption: emitting smoke, particulate Volcano eruption: emitting smoke, particulate matter, SOmatter, SO22, H, H22S, CHS, CH44……

Fires: emitting smoke, unburnt hydrocarbons, Fires: emitting smoke, unburnt hydrocarbons, CO, COCO, CO22, NO, NOxx... ...

Dust or sand storms dispersing dust Dust or sand storms dispersing dust Oceans are emitting corrosive salt aerosols Oceans are emitting corrosive salt aerosols Lightning produces NOLightning produces NOxx and O and O33

Normal human respiration produces CONormal human respiration produces CO22

Artificial or anthropogenic sourcesArtificial or anthropogenic sources Stationary sources: combustion, fuel usage, Stationary sources: combustion, fuel usage,

waste incineration, industrial processes…waste incineration, industrial processes… Mobile sources: all emissions and exhausts from Mobile sources: all emissions and exhausts from

transportationtransportation

2.2 Sources of air pollutants in Hong 2.2 Sources of air pollutants in Hong KongKong

Particulate matter

Aircraft

0.5% Marine

4.3%Fuel combustion

3.7%

Pow er generation

36.7%

Vehicle

54.8%

Sulphur dioxide

Vehicle

1.7%Marine

5.0%

Pow er generation

86.4%

Fuel combustion

6.6%

Aircraft

0.3%

Nitrogen oxides

Marine

13.1%

Aircraft

3.6%

Pow er generation

42.9%

Vehicle

35.8%

Fuel combustion

4.6%

Carbon monoxide

Aircraft

2.5%Vehicle

89.3%

Fuel combustion

3.2%Marine

2.1%Pow er generation

2.9%

2.2 Particulate matter2.2 Particulate matter typical size varies: gravel typical size varies: gravel

2000µ, sand 20 ~ 1000µ, hair, 2000µ, sand 20 ~ 1000µ, hair, 50µ, RSP with health effects 50µ, RSP with health effects 0.1 ~ 10µ0.1 ~ 10µ

Sizes that cause significant air Sizes that cause significant air pollution problems are 0.01 ~ pollution problems are 0.01 ~ 50µ, as larger particles tend to 50µ, as larger particles tend to settlesettle

Sources of PM: Natural: wind, Sources of PM: Natural: wind, sandstorm, forest fires, sandstorm, forest fires, volcano eruption; volcano eruption; Anthropogenic: industry, Anthropogenic: industry, automobilesautomobiles

Size of particlesSize of particles Large particlesLarge particles (2.5 ~ 250µ): produced in mechanical, crushing, (2.5 ~ 250µ): produced in mechanical, crushing,

crashing, milling or grinding processes. Most mechanical crashing, milling or grinding processes. Most mechanical processes cannot produce particles of size smaller than 10µprocesses cannot produce particles of size smaller than 10µ

Fine particles Fine particles (0.1 ~ 10µ): produced in combustion, evaporation, (0.1 ~ 10µ): produced in combustion, evaporation, condensation, settling, e.g. tobacco smoke contains particles of condensation, settling, e.g. tobacco smoke contains particles of condensed hydrocarbons at 0.01 ~ 1µ. As usual the finer the condensed hydrocarbons at 0.01 ~ 1µ. As usual the finer the size, the more volatile the material.size, the more volatile the material.

Agglomeration of fine particlesAgglomeration of fine particles: Fine particles tend to stick : Fine particles tend to stick together when they get close together due to electrostatic and together when they get close together due to electrostatic and Van Der Waal’s forces.Van Der Waal’s forces.

AerosolsAerosols: Particles small enough to remain suspended in the : Particles small enough to remain suspended in the atmosphere for a long time are referred to as aerosolsatmosphere for a long time are referred to as aerosols

Effects of particulate matter pollutionsEffects of particulate matter pollutions VisibilityVisibility: Particles are able to scatter lights with wavelengths : Particles are able to scatter lights with wavelengths

close to the particle size. Because of this particulate matter close to the particle size. Because of this particulate matter pollutions usually yield hazy days and visible smog. Since pollutions usually yield hazy days and visible smog. Since visible lights have wavelength between 0.4 ~ 0.8µ, hazy visible lights have wavelength between 0.4 ~ 0.8µ, hazy days are caused by secondary particles.days are caused by secondary particles.

HealthHealth: Inhalable lung-damaging dust ranges from 0.5 ~ 5µ; : Inhalable lung-damaging dust ranges from 0.5 ~ 5µ; asthma, respiratory syndromes, bronchitis, decreased lung asthma, respiratory syndromes, bronchitis, decreased lung functions.functions.

ClimateClimate: Fine particles can be called condensation nuclei in : Fine particles can be called condensation nuclei in meteorology. When wet air reaches saturation condition, the meteorology. When wet air reaches saturation condition, the existence of fine particles makes it easier for water vapour to existence of fine particles makes it easier for water vapour to condense and form tiny droplets, forming fog and mist. It condense and form tiny droplets, forming fog and mist. It also leads to formation of clouds.also leads to formation of clouds.

2.3 Gaseous pollutants2.3 Gaseous pollutants Both N and S are essential to our bodies. However Both N and S are essential to our bodies. However

N and S oxides are strong irritants that cause health N and S oxides are strong irritants that cause health damage at high concentrations. They also undergo damage at high concentrations. They also undergo atmospheric reactions to form PMatmospheric reactions to form PM1010 in urban areas. in urban areas.

N and S oxides react with water and ON and S oxides react with water and O22 to form to form

nitric and sulphuric acid, which are principal nitric and sulphuric acid, which are principal contributors to contributors to acid rainacid rain..

Both N and S have many sources, the main of them Both N and S have many sources, the main of them being combustion or chemical plants.being combustion or chemical plants.

S oxides are formed from the sulphur contaminants S oxides are formed from the sulphur contaminants in fuels or incomplete in fuels or incomplete combustion combustion in sulphur ores. in sulphur ores. N oxides come mainly from atmospheric nitrogen N oxides come mainly from atmospheric nitrogen due to due to lightninglightning..

Anthropgenic sources of NOx and SOx

Effects of NOx pollutionsEffects of NOx pollutions smog problems: smog problems: respiratory respiratory

problems, visibility issuesproblems, visibility issues acid rainacid rain nutrient overload in water: nutrient overload in water:

decreasing water qualitydecreasing water quality toxic atmospheretoxic atmosphere global warmingglobal warming

Since 1970, all air pollutants Since 1970, all air pollutants have shown a decreasing have shown a decreasing trend except NOx, which has trend except NOx, which has increased around 10%.increased around 10%.

Effects of SOx pollutionsEffects of SOx pollutions PM formationPM formation acid rainacid rain respiratory problemsrespiratory problems

2.4 VOC2.4 VOC VOCs are those organic compounds whose room temperature VOCs are those organic compounds whose room temperature

vapour pressures are greater than about 0.0007 atm. It usually vapour pressures are greater than about 0.0007 atm. It usually contains carbon bonded with H, N or S and can vaporise at contains carbon bonded with H, N or S and can vaporise at significant ratessignificant rates

VOCs are contributors to the problem of VOCs are contributors to the problem of photochemical oxidantsphotochemical oxidants (smogs, ozone): (smogs, ozone): xx + O + O22 + VOC + VOC OO33 + smog + smog

Some VOCs are infrared absorbers and thus contribute to Some VOCs are infrared absorbers and thus contribute to greenhouse effects. Other are known to be toxic or carcinogenic.greenhouse effects. Other are known to be toxic or carcinogenic.

Most VOCs are emitted from Most VOCs are emitted from smaller sourcessmaller sources like automobiles, like automobiles, paints, solvent usage, nail polish and vanish, correcting fluids. paints, solvent usage, nail polish and vanish, correcting fluids. Plants, due to stringent laws, produce comparatively less VOC as Plants, due to stringent laws, produce comparatively less VOC as emissionsemissions

sunlight

2.5 Ozone2.5 Ozone

OO33 layer absorbs ~3% of UV radiation. It controls the layer absorbs ~3% of UV radiation. It controls the

amount of incoming and outgoing solar radiation to and amount of incoming and outgoing solar radiation to and from the Earth surface, thus maintaining a normal evolution from the Earth surface, thus maintaining a normal evolution of global climate.of global climate.

• Ozone occurs in two layers of the atmosphere. • The layer surrounding the earth's surface is the

troposphere. • Here, ground-level or "bad" ozone is an air pollutant • that damages human health, vegetation, and many

common materials. It is a key ingredient of urban smog. • The stratospheric or "good" ozone layer extends upward

from about 10 to 30 miles and protects life on earth from the sun's harmful ultraviolet rays (UV-b).

Any chlorofluorocarbon (CFC) molecule in the upper Any chlorofluorocarbon (CFC) molecule in the upper atmosphere tends to become stripped of a chlorine atom atmosphere tends to become stripped of a chlorine atom photochemically, by bombardment with radiation. That photochemically, by bombardment with radiation. That loose atom combines readily with any nearby ozone loose atom combines readily with any nearby ozone molecule, to form normal oxygen and chloro-monoxide:molecule, to form normal oxygen and chloro-monoxide:

Cl + OCl + O33 ClO + OClO + O22

The monoxide then combines with any available atom of The monoxide then combines with any available atom of oxygen in the atmosphere to form normal oxygen and oxygen in the atmosphere to form normal oxygen and chlorine: ClO + Ochlorine: ClO + O Cl + OCl + O22

So the outcome is a chlorine atom, as at the So the outcome is a chlorine atom, as at the beginning, once again available to destroy more beginning, once again available to destroy more ozone. The chlorine thus acts as a catalyst. ozone. The chlorine thus acts as a catalyst. This catalytic process occurs most effectively on This catalytic process occurs most effectively on a foreign surface, for instance on an ice crystal. a foreign surface, for instance on an ice crystal. Since the lower stratosphere is cold over Since the lower stratosphere is cold over Antarctica in winter, the little water vapour Antarctica in winter, the little water vapour there is forced to condense in polar there is forced to condense in polar stratospheric clouds. There is good evidence stratospheric clouds. There is good evidence that every winter the catalytic process of CFCs that every winter the catalytic process of CFCs virtually totally consumes the ozone between virtually totally consumes the ozone between 15~25 km over Antarctica. Any CFC has a 15~25 km over Antarctica. Any CFC has a lifetime in the troposphere of ~100 years, so it lifetime in the troposphere of ~100 years, so it can remain available to destroy ozone for a long can remain available to destroy ozone for a long time. Even if CFC production were stopped time. Even if CFC production were stopped today, what is in the atmosphere already would today, what is in the atmosphere already would damage the ozone layer for decades.damage the ozone layer for decades.

Nitric oxide, NO, is a catalyst in the same way. Nitric oxide, NO, is a catalyst in the same way. First it reacts with ozone to form oxygen and First it reacts with ozone to form oxygen and nitrogen oxide NOnitrogen oxide NO22, and then that reacts with , and then that reacts with loose atoms of oxygen to create Oloose atoms of oxygen to create O22 and NO once and NO once more: more:

NO + ONO + O33 NO NO22 + O + O22

NONO22 + O + O NO + O NO + O22

The reactions occur most readily on the surface of The reactions occur most readily on the surface of ice particles found in the winter stratosphere ice particles found in the winter stratosphere above Antarctica, where temperatures are ~ -80 above Antarctica, where temperatures are ~ -80 °C.°C.

One common misconception: One common misconception: OO33 is is poisonouspoisonous. Its only function is to . Its only function is to block block radiationradiation..OO33 is also a pollutant itself, it is the chief reason for is also a pollutant itself, it is the chief reason for smogsmog

In 1985, a team led by British In 1985, a team led by British scientists J. Farman (1985) scientists J. Farman (1985) shocked the scientific shocked the scientific community by reporting community by reporting massive annual decreases of massive annual decreases of stratospheric ozone over stratospheric ozone over Antarctica in the polar spring.Antarctica in the polar spring.

In fact such phenomenon has In fact such phenomenon has been detected as early as been detected as early as 1977 aboard Nimbus-7 1977 aboard Nimbus-7 satellite, only that the satellite, only that the observations were being observations were being discarded as wrong data.discarded as wrong data.

Same thing actually happen in Same thing actually happen in Arctic. However, since temperature Arctic. However, since temperature is slightly higher in Arctic, ozone is slightly higher in Arctic, ozone depletion is less.depletion is less.

The effect of a compound on The effect of a compound on stratospheric ozone depletion is stratospheric ozone depletion is assessed by the unit assessed by the unit ozone ozone depletion potentialdepletion potential (ODP). ODP is (ODP). ODP is usuallyusually defined as the total steady- defined as the total steady-state ozone destruction, vertically state ozone destruction, vertically integrated over the stratosphere, integrated over the stratosphere, that results per unit mass of species that results per unit mass of species ii emitted per year relative to that of emitted per year relative to that of CFC-11.CFC-11.

11CFC,3

,3

O

OODP

ii

In September 1987, Montréal Protocol on In September 1987, Montréal Protocol on Substances that Deplete the Ozone Layer, each Substances that Deplete the Ozone Layer, each signer agreed to reduce the production of CFC-11 ~ signer agreed to reduce the production of CFC-11 ~ CFC-114 and halons. Consumption of these FCFs CFC-114 and halons. Consumption of these FCFs was frozen at 1986 level from 1989 and is to be was frozen at 1986 level from 1989 and is to be reduced to 80% and then 50% of these values at reduced to 80% and then 50% of these values at 1994 and 1999.1994 and 1999.

For undeveloped countries, production must not For undeveloped countries, production must not exceed 110% of the 1986 levels. exceed 110% of the 1986 levels.

compound ODP

CFC-11 (CFCl3) 1.00

CFC-12 (CF2Cl2) 0.82

CFC-113 (CFCl2CF2Cl) 0.92

CFC-115 (CF2ClCF3) 0.40

HCFC-22 (CF2HCl) 0.04

HFC-225ca (CF3CF2CHCL2) 0.02

2.6 Greenhouse effect2.6 Greenhouse effect

The atmosphere absorbs a high fraction of long-wave The atmosphere absorbs a high fraction of long-wave radiation of the earth. radiation of the earth. Greenhouse effectGreenhouse effect

Water Water in in vapourvapour form is the principal agent for this effect. form is the principal agent for this effect. CO CO22 is the next in importance only. CO is the next in importance only. CO22 is not as is not as

important because its concentration is much lower and important because its concentration is much lower and its main infrared absorption is localized in a narrow band its main infrared absorption is localized in a narrow band near 1.5 x 10near 1.5 x 1044 nm. nm.

However the amount of water in the atmosphere is fairly However the amount of water in the atmosphere is fairly constant, whereas the amount of COconstant, whereas the amount of CO22 is increasing is increasing

quickly due to rapid growth in industrial activities for the quickly due to rapid growth in industrial activities for the past century.past century.

3. Local air pollution problems3. Local air pollution problems

Air pollution problems appear in 3 main effects:Air pollution problems appear in 3 main effects: Effects on healthEffects on health

Smoke particles that enter and deposited on the alveoli Smoke particles that enter and deposited on the alveoli can cause tuberculosis. Other particles might adsorb can cause tuberculosis. Other particles might adsorb gas which causes more intensive irritation. Gases gas which causes more intensive irritation. Gases and particles might also penetrate into the and particles might also penetrate into the bloodstream, e.g. suspended lead from vehicle bloodstream, e.g. suspended lead from vehicle exhausts can causes significant nervous problems.exhausts can causes significant nervous problems.

Ecological effectsEcological effects

Plants and animals are also susceptible to air pollution Plants and animals are also susceptible to air pollution effects. Fluorine emitted by factories can damage effects. Fluorine emitted by factories can damage plants nearby and significantly lowers the value and plants nearby and significantly lowers the value and vitality of the crop nearbyvitality of the crop nearby

Effects on materialsEffects on materials

Many acidic gases, like fluorine, chlorine, SOx, NOx can Many acidic gases, like fluorine, chlorine, SOx, NOx can attack metals and concrete and etch glass attack metals and concrete and etch glass

3.1 Some severe air pollutions3.1 Some severe air pollutions London smog (1952)London smog (1952)

– Peak daily concentrations nearly 4000 µgmPeak daily concentrations nearly 4000 µgm-3-3 of SO of SOxx and 6000 and 6000

µgmµgm-3-3 of smoke of smoke

Los Angeles photochemical smog (1940s)Los Angeles photochemical smog (1940s)– Huge amount of OHuge amount of O33 found by photochemical reactions between found by photochemical reactions between

NONOxx from automobile emissions, peroxyacetyl nitrate (PAN) and from automobile emissions, peroxyacetyl nitrate (PAN) and

solar radiationsolar radiation

Acid rain (1968)Acid rain (1968)– Buildings damage and ecological changes in ScandinaviaBuildings damage and ecological changes in Scandinavia

Bhopal chemical plant accident (1984)Bhopal chemical plant accident (1984)– 3300 people died and more than 200000 suffered from respiratory 3300 people died and more than 200000 suffered from respiratory

and eye diseases when 40 tonnes of methyl-isocyanate (MIC) and eye diseases when 40 tonnes of methyl-isocyanate (MIC) were accidentally released were accidentally released

Chernobyl radiation accident (1986)Chernobyl radiation accident (1986)– More than 250 curies of radioactive isotopes were More than 250 curies of radioactive isotopes were

released in a nuclear power plant explosion. Entire released in a nuclear power plant explosion. Entire Northern and Eastern Europe were affected. 30 Northern and Eastern Europe were affected. 30 casualties, countless radiation sicknesscasualties, countless radiation sickness

Antarctica ozone hole (since 1983)Antarctica ozone hole (since 1983)– Ozone depletion at Antarctica due to CFCOzone depletion at Antarctica due to CFC

Forest fire in Indonesia (1997)Forest fire in Indonesia (1997)– More than 30000 people suffered from respiratory More than 30000 people suffered from respiratory

problems, visibility often less than 30 m, it was problems, visibility often less than 30 m, it was reported that breathing the air was the same as reported that breathing the air was the same as smoking 100 cigarettes per day.smoking 100 cigarettes per day.

4. The atmosphere4. The atmosphere

78.084%78.084%

20.946%20.946%

0.934%0.934%

0.036%0.036%

0.002%0.002%

0.001%0.001%

Average composition of Average composition of dry clean air by volumedry clean air by volume NN22

OO22

ArAr COCO22

NeNe HeHe

......

0 ~0 ~ 7000070000

360360

1.51.5

0.10.1

0.020.02

0.010.01

0.0010.001

0.00020.0002

0.00020.0002

Typical concentrations ofTypical concentrations ofvarious gases in clean air (ppm)various gases in clean air (ppm) HH22OO

COCO22

CHCH44

COCO OO33

NHNH33

NONO22

SOSO22

HH22SS

Concentrations are usually expressed ‘Concentrations are usually expressed ‘by volumeby volume’ ’ because there is a direct relationship between the because there is a direct relationship between the volume, partial pressure and the number of volume, partial pressure and the number of molecules present. (molecules present. (Dalton’s lawDalton’s law))

In ambient air at 1 atm, there are ~2.693 x 10In ambient air at 1 atm, there are ~2.693 x 101919 molecules / cmmolecules / cm33 ( (Loschmidt numberLoschmidt number))

Two concentration units are commonly used in Two concentration units are commonly used in reporting atmospheric species abundancereporting atmospheric species abundance

air and species of memoles/volu are C and C where

10CC

ppmin species ofion concentrat 6

i

i

i

i

iM

M

mm

i

i

iii

species ofweight molecular theis where

10 C ,gmin ion concentrat mass 6- 3-

The legislative basis for air pollution abatement in the USA is the The legislative basis for air pollution abatement in the USA is the 1963 Clean Air Act and its amendments1963 Clean Air Act and its amendments. The Act and its . The Act and its amendments provide for the establishment of two kinds of amendments provide for the establishment of two kinds of national ambient air quality standards.national ambient air quality standards.

Primary ambient air quality standardsPrimary ambient air quality standards: those measures to protect : those measures to protect public healthpublic health with an adequate margin of safety with an adequate margin of safety

Secondary ambient air quality standardsSecondary ambient air quality standards: specify a level of : specify a level of pollutant concentrations requisite to the pollutant concentrations requisite to the public welfarepublic welfare from any from any known or anticipated adverse effects associated with the known or anticipated adverse effects associated with the presence of such air pollutants in the air. These effects include presence of such air pollutants in the air. These effects include damage to crops and vegetation, wildlife, visibility, climate and damage to crops and vegetation, wildlife, visibility, climate and economy.economy.

5. Air quality standards5. Air quality standards

Air quality standards are based solely on the Air quality standards are based solely on the effects of air pollutioneffects of air pollution, , not by scientific or economical standards.not by scientific or economical standards.

Three kinds of studies have been conducted: animal testing, short-Three kinds of studies have been conducted: animal testing, short-term exposures to human volunteers, and epidemiological studies.term exposures to human volunteers, and epidemiological studies.

National air quality standards (1997): standards not to be exceeded National air quality standards (1997): standards not to be exceeded once a yearonce a year

Pollutant Averaging time Primary (µgm-3) Secondary (µgm-3)SOx annual 80

daily 365PM10 annual 50 50

daily 150 150PM2.5 annual 15 15

daily 65 65CO 8 hours 10 10

1 hour 40VOC 3 hours 160 160NOx annual 100 100Pb 3 months 1.5 1.5O3 8 hours 80 80

Air quality objectives of Hong Kong (1987): daily threshold not more Air quality objectives of Hong Kong (1987): daily threshold not more than once a year, hourly threshold not more than 3 times a yearthan once a year, hourly threshold not more than 3 times a year

Pollutant

Concentration in Microgrammes per Cubic Metre (i)

Health Effects of Pollutant at Elevated Ambient Levels

Averaging Time

1hr 8hrs 24hrs 3mths 1yr

Sulphur Dioxide 800 350 80Respiratory illness; reduced lung function; morbidity and mortality rates increase at higher levels.

Total Suspended Particulates 260 80 Respirable fraction has effects on health.

Respirable Suspended Particulates (v)

180 55Respiratory illness; reduced lung function; cancer risk for certain particles; morbidity and mortality rates increase at higher levels.

Nitrogen Dioxide 300 150 80Respiratory irritation; increased susceptibility to respiratory infection; lung development impairment.

Carbon Monoxide 30 000 10 000 Impairment of co-ordination; deleterious to pregnant women and those with heart and circulatory conditions.

Photochemical Oxidants (as ozone) (vi)

240Eye irritation; cough; reduced athletic performance; possible chromosome damage.

Lead 1.5

Affects cell and body processes; likely neuro-psychological effects, particularly in children; likely effects on rates of incidence of heart attacks, strokes and hypertension.

The The Air Pollution IndexAir Pollution Index ( (APIAPI) of USA is the compact ) of USA is the compact expression of the air quality levels referring to expression of the air quality levels referring to five major five major pollutantspollutants: PM: PM1010, SO, SO22, CO, O, CO, O33, and NO, and NO22, based on the , based on the

National Ambient Air Quality Standards (NAAQS).National Ambient Air Quality Standards (NAAQS). The Hong Kong API is based upon the Hong Kong Air The Hong Kong API is based upon the Hong Kong Air

Quality Objectives (HKAQO). Our API is slightly more Quality Objectives (HKAQO). Our API is slightly more sophisticated and is comprised of sophisticated and is comprised of 9 sub-indices9 sub-indices: TSP : TSP (daily average), RSP/PM(daily average), RSP/PM1010 (daily average), SO (daily average), SO22 (daily (daily

average), SOaverage), SO22 (hourly average), NO (hourly average), NO22 (daily average), (daily average),

NONO22 (hourly average), CO (8-hour average), CO (hourly (hourly average), CO (8-hour average), CO (hourly

average) and Oaverage) and O33 (hourly average). (hourly average).

5.1 Air pollution index5.1 Air pollution index

Calculations of API:Calculations of API: 1) Calculate sub-index 1) Calculate sub-index IIii of the of the iith pollutantth pollutant

APIvalues

TSPDaily

RSPDaily

SO2

DailySO2

HourlyNO2

DailyNO2

HourlyCO8-hour

COHourly

O3

Hourly0 0 0 0 0 0 0 0 0 0

50 80 55 80 400 80 150 5 15 120100 260 180 350 800 150 300 10 30 240200 375 350 800 1600 280 1130 17 60 400300 625 420 1600 2400 565 2260 34 90 800400 875 500 2100 3200 570 3000 46 120 1000500 1000 600 2620 4000 940 3750 57.5 150 1200

XXii observed concentration for the observed concentration for the iith pollutantth pollutant

XXi,ji,j concentration for the concentration for the iith pollutant and the th pollutant and the jjth breakpointth breakpoint

XXi,j+i,j+11concentration for the concentration for the iith pollutant and the (th pollutant and the (j+j+1) breakpoint1) breakpoint

IIi,ji,j API value for the API value for the iith pollutant and the th pollutant and the jjth breakpointth breakpoint

IIi,j+i,j+11 API value for the API value for the iith pollutant and the (th pollutant and the (jj+1)th breakpoint+1)th breakpoint

The maximum of all sub-indices are then selected as the APIThe maximum of all sub-indices are then selected as the API

],...,,Max[API 921 III

Air Quality StatusAir Quality Status Air Pollution Air Pollution

LevelLevel APIAPI Health Implications Health Implications [1] [1]

Air quality significantly Air quality significantly worse than both short-term worse than both short-term and long-term AQOs. and long-term AQOs. 

SevereSevere 201 to 500201 to 500 People with existing heart or respiratory illnesses People with existing heart or respiratory illnesses will experience significant aggravation of their will experience significant aggravation of their symptoms and there will be also widespread symptoms and there will be also widespread symptoms in the healthy population. These symptoms in the healthy population. These include eye irritation, wheezing, coughing, include eye irritation, wheezing, coughing, phlegm and sore throat.phlegm and sore throat.

Air quality worse than both Air quality worse than both short-term and long-term short-term and long-term AQOs. AQOs. 

Very HighVery High 101 to 200101 to 200 People with existing heart or respiratory illnesses People with existing heart or respiratory illnesses will notice mild aggravation of their health will notice mild aggravation of their health conditions. Generally healthy individuals may conditions. Generally healthy individuals may also notice some discomfort.also notice some discomfort.

Air quality within the short-Air quality within the short-term AQOs but worse than term AQOs but worse than the long-term. the long-term. 

HighHigh 51 to 10051 to 100 Very few people, if any, may notice immediate Very few people, if any, may notice immediate health effects. Long-term effects may, however, health effects. Long-term effects may, however, be observed if you are exposed to such levels for be observed if you are exposed to such levels for a long time.a long time.

Air quality within all AQOs.Air quality within all AQOs. MediumMedium 26 to 5026 to 50 None expected for the general population.None expected for the general population.

Air quality well within all Air quality well within all AQOs.AQOs.

LowLow 0 to 250 to 25 None expected.None expected.

5.2 Measurement of air pollution5.2 Measurement of air pollution

The air quality monitoring network in Hong Kong of the The air quality monitoring network in Hong Kong of the Environmental Protection Department (EPD) comprises Environmental Protection Department (EPD) comprises fourteen fixed monitoring stations as of July 1999 to meet the fourteen fixed monitoring stations as of July 1999 to meet the following objectives:- following objectives:-

– To understand air pollution problems in order that cost-effective To understand air pollution problems in order that cost-effective policies and solutions can be developed; policies and solutions can be developed;

– To assess how far standards and targets are being achieved or To assess how far standards and targets are being achieved or violated; violated;

– To assist the assessment of public's exposure to air pollution; and To assist the assessment of public's exposure to air pollution; and

– To provide public information on current and forecast air quality. To provide public information on current and forecast air quality.

Other stations have been used in the past and there are Other stations have been used in the past and there are more planned for the future. In addition to the EPD's stations, more planned for the future. In addition to the EPD's stations, other independent monitoring units are operated, for other independent monitoring units are operated, for example, those being operated by the power companies in example, those being operated by the power companies in order to assess the air quality impact of their power stations. order to assess the air quality impact of their power stations.

A typical sampling urban sampling station

High volume RSP and TSP samplers

Solar radiation detector

tapered element oscillating microbalance - continuous RSP

Wind anemometer

Acid rain collector

Mobile air samplerGaseous pollutants analyzer

6. Air Pollution in Hong Kong6. Air Pollution in Hong Kong

Chiefly vehicular emission related - TSP, RSP & Chiefly vehicular emission related - TSP, RSP & photochemical pollutionphotochemical pollution

Large industrial sources are relatively under controlLarge industrial sources are relatively under control Hong Kong is extremely mountainous. This makes Hong Kong is extremely mountainous. This makes

trapping of air pollutants easy. Modelling and prediction of trapping of air pollutants easy. Modelling and prediction of air pollutants dispersion also becomes difficult.air pollutants dispersion also becomes difficult.

Pollution events usually happen in hot summer or winter.Pollution events usually happen in hot summer or winter.

CARBON MONOXIDE(8-hour Maximum)

0

5000

10000

15000

20000

25000

San F

ranc

isco

Hong

Kong

New Yo

rk

LosA

ngele

s

Sydne

y

Lond

on

Bangk

ok

Co

nce

ntr

atio

n (

g/m

3)

Air Quality Objective: 10,000 g/m3

19991999

1999 1999

1997

1998

1999

SULPHUR DIOXIDE(Annual Average)

0

10

20

30

40

50

60

70

80

90

100

San F

ranc

isco

Sydne

y

Los A

ngele

sBer

lin

Mac

au

Taipe

i

Lond

on

Toro

nto

Toky

o

Hong

Kong

Singap

ore

Bangk

ok

New Yo

rk

Mex

ico C

ity

Co

nce

ntr

atio

n (

g/m

3)

Air Quality Object: 80 g/m3

1999 19971999

1998 1997 1999 1999 19971997

1999 1998 1999 1999

1998

RESPIRABLE SUSPENDED PARTICULATES(Annual Average)

0

10

20

30

40

50

60

70

80

90

Co

nce

ntr

ati

on

(g

/m3 )

Air Quality Objective: 55g/m3

1998

1999

19971999

199719991999

19981998

1996

199919991999

1997

NITROGEN DIOXIDE(Annual Average)

0

20

40

60

80

100

120

140

Sydne

yBer

lin

San F

ranc

isco

Singap

or

Toro

nto

Taipe

i

Bangk

ok

Toky

o

Mac

au

New Yo

rk

Los A

ngele

s

Lond

on

Hong

Kong

Mila

n

Man

ila

Mex

ico C

ity

Co

nce

ntr

atio

n (

g/m

3)

Air Quality Objective: 80 g/m3

1997

1998 1999 1998

19971999

19991997 1997 1999 1999 1999

1999

1996

19951998

OZONE(Hourly Maximum)

0

100

200

300

400

500

600

700

Berlin

San F

ranc

isco

Bangk

ok

Lond

on

Toro

nto

Singap

ore

Sydne

y

Los A

ngele

s

Toky

o

New Yo

rk

Hong

Kong

Rome

Houst

on

Texa

s City

Athen

s

Mex

ico C

ity

Co

nce

ntr

atio

n (

g/m

3)

Air Quality Objective: 240 g/m3

1998 19991999

1999 1996 19961996

19991997

19991999 1997

1999 1999

1998

1996

7. Atmospheric stability7. Atmospheric stability

adiabatic

subadiabatic

superadiabaticA

C

B

T0T0 - dT T0 + dT

z0 + dz

z0 - dz

z0

7.1 Lapse rates7.1 Lapse rates

A A lapse ratelapse rate is the change of temperature with unit rise is the change of temperature with unit rise of elevation.of elevation.

Under adiabatic condition, the lapse rate near the Earth Under adiabatic condition, the lapse rate near the Earth surface is ~-9.8 K kmsurface is ~-9.8 K km-1-1. If the numerical value of the . If the numerical value of the lapse is lapse is greater in magnitudegreater in magnitude than this value, than this value, superadiabaticsuperadiabatic lapse; lower, lapse; lower, subadiabatic subadiabatic lapse.lapse.

For calculation purposes, meteorologists and For calculation purposes, meteorologists and engineers have defined a standard atmospheric lapse engineers have defined a standard atmospheric lapse of about by ~-6.5 K kmof about by ~-6.5 K km-1-1 by the approximate average of by the approximate average of all observations. It simply indicates the the adiabatic all observations. It simply indicates the the adiabatic assumption is not too appropriate.assumption is not too appropriate.

What does not the atmosphere always have an What does not the atmosphere always have an adiabatic lapse rate as its actual profile?adiabatic lapse rate as its actual profile?

It is because other processes such as winds and solar It is because other processes such as winds and solar heating leading to the dynamic temperature heating leading to the dynamic temperature behaviour is seldom adiabatic. Other processes behaviour is seldom adiabatic. Other processes exert an equal influence on the prevailing exert an equal influence on the prevailing temperature profile than does the adiabatic rising and temperature profile than does the adiabatic rising and falling of air parcels.falling of air parcels.

One common fallacy: Cold air is more dense, One common fallacy: Cold air is more dense, and therefore heavier than warm air. and therefore heavier than warm air. Therefore, when the air aloft is colder than the Therefore, when the air aloft is colder than the air near the ground, the atmosphere is air near the ground, the atmosphere is unstable: the cold air will sink and the warm unstable: the cold air will sink and the warm air will rise.air will rise.

7.2 Temperature-elevation curve7.2 Temperature-elevation curve

The temperature-elevation curve is the principal The temperature-elevation curve is the principal determination of atmospheric stability.determination of atmospheric stability.

Suppose an air parcel is at point A on the figure. If Suppose an air parcel is at point A on the figure. If it is displaced suddenly upward or downward, fast it is displaced suddenly upward or downward, fast enough to be considered reversible and adiabatic. enough to be considered reversible and adiabatic. It would then move to B or C.It would then move to B or C.

If the air parcel is displaced slowly, then it could If the air parcel is displaced slowly, then it could transfer heat to or from the air around it. The transfer heat to or from the air around it. The process is then unadiabatic.process is then unadiabatic.

If the surrounding air has adiabatic lapse rate, If the surrounding air has adiabatic lapse rate, wherever the air parcel moves, it will reach the same wherever the air parcel moves, it will reach the same temperature and pressure as the surrounding air. temperature and pressure as the surrounding air. Because of this, further movement is prohibited. This Because of this, further movement is prohibited. This condition is condition is neutral stabilityneutral stability: simple displacement do : simple displacement do not lead to restoration to original position, nor do they not lead to restoration to original position, nor do they make the parcel move further.make the parcel move further.

When the sun comes up and heats the ground When the sun comes up and heats the ground surface and the air above it, there will be a layer of surface and the air above it, there will be a layer of warmed air near the ground, where the lapse rate is warmed air near the ground, where the lapse rate is practically adiabatic.practically adiabatic.

If the surrounding air has a subadiabatic lapse rate, If the surrounding air has a subadiabatic lapse rate, then if it is moved upwards, it will follow the adiabatic then if it is moved upwards, it will follow the adiabatic curve, making itself colder and denser than the curve, making itself colder and denser than the surrounding. Gravity will then drive it back down. If it is surrounding. Gravity will then drive it back down. If it is moved downwards, it becomes warmer and less dense, moved downwards, it becomes warmer and less dense, and gravity will push it upwards. For whatever and gravity will push it upwards. For whatever disturbance, the parcel will be restored to its original disturbance, the parcel will be restored to its original position. The atmosphere is position. The atmosphere is stablestable..

When the ground cools at evening, temperature When the ground cools at evening, temperature increases with height near the ground. This is called increases with height near the ground. This is called inversioninversion. Because of the difference is temperature . Because of the difference is temperature gradient, the situation inside the inversion is extremely gradient, the situation inside the inversion is extremely stable.stable.

If the surrounding air has a superadiabatic lapse rate, If the surrounding air has a superadiabatic lapse rate, then if it is moved upwards, it will follow the adiabatic then if it is moved upwards, it will follow the adiabatic curve, making itself warmer and less dense than the curve, making itself warmer and less dense than the surrounding. Gravity will then drive it further upward. surrounding. Gravity will then drive it further upward. If it is moved upwards, it becomes colder and denser If it is moved upwards, it becomes colder and denser than the surrounding, and gravity will push it further than the surrounding, and gravity will push it further downwards. Whatever disturbs it from its original downwards. Whatever disturbs it from its original position, the parcel will continue to move away from position, the parcel will continue to move away from its original position. The atmosphere is its original position. The atmosphere is unstable unstable and and vertical motion is spontaneous if any minute trigger vertical motion is spontaneous if any minute trigger exists.exists.

By afternoon, enough heat has been transferred from By afternoon, enough heat has been transferred from the warmed ground to the surrounding. The heated the warmed ground to the surrounding. The heated adiabatic air, extends to large height (~2 km) where it adiabatic air, extends to large height (~2 km) where it meets the stable air above. The air there has a meets the stable air above. The air there has a standard lapse rate and thus superadiabatic.standard lapse rate and thus superadiabatic.

7.3 Examples of instability7.3 Examples of instability

ThermalsThermals : A thermal is a column of warm-air : A thermal is a column of warm-air bubbles, expanding as they rise due to atmospheric bubbles, expanding as they rise due to atmospheric instability. Thermals commonly occur on warm, instability. Thermals commonly occur on warm, calm afternoons above hot grounds. The air lifts off, calm afternoons above hot grounds. The air lifts off, entrains more air and bubbles and form a column of entrains more air and bubbles and form a column of ~1 km vertical height. The lift is great enough to ~1 km vertical height. The lift is great enough to support soaring eagles without flapping their wings.support soaring eagles without flapping their wings.

rising hot air column

warm air columnnear groundlow

pressure

slowly falling warm air

Hot ground

TornadoesTornadoes : A tornado is the : A tornado is the result of extreme instability, result of extreme instability, consisting of a violent vortical air consisting of a violent vortical air flow and a tapering funnel of flow and a tapering funnel of twisting cloud. Although the twisting cloud. Although the formation of tornadoes is similar formation of tornadoes is similar to thermals, it depend on three to thermals, it depend on three conditions: 1) a sufficient amount conditions: 1) a sufficient amount of convective energy, 2) stable of convective energy, 2) stable PBL to prevent thunderstorms to PBL to prevent thunderstorms to release instability and 3) strong release instability and 3) strong increase of wind speed with increase of wind speed with respect to height.respect to height.

7.4 Mixing heights7.4 Mixing heights

Due to the thermals, there will be Due to the thermals, there will be vigorous vertical mixing from the vigorous vertical mixing from the ground at ~2 km, and then negligible ground at ~2 km, and then negligible vertical mixing above that. The rising vertical mixing above that. The rising air columns provide good vertical air columns provide good vertical mixing and induce large-scale three-mixing and induce large-scale three-dimensional turbulence, which induce dimensional turbulence, which induce horizontal mixing. Pollutants released horizontal mixing. Pollutants released at ground-level will be mixed uniformly at ground-level will be mixed uniformly up to that up to that mixing heightmixing height, but not above , but not above it. Mixing heights set a limit to air it. Mixing heights set a limit to air pollutants dispersions. pollutants dispersions.

clouds with irregulartops but flat bottoms

mixingheight

clouds tops nearmixing height

8. Effect of atmospheric stability on 8. Effect of atmospheric stability on

air pollutant dispersionair pollutant dispersion

LoopingLooping : The plume is formed in : The plume is formed in unstable condition. The flow unstable condition. The flow pattern follows closely that of a pattern follows closely that of a flow past bluff body forming a flow past bluff body forming a turbulent wake behind it. turbulent wake behind it.

ConingConing : A typical buoyant plume : A typical buoyant plume which grows by mixing. It is which grows by mixing. It is formed in neutral atmospheric formed in neutral atmospheric condition. The plume is usually condition. The plume is usually bifurcated and rises by its own bifurcated and rises by its own buoyancy.buoyancy.

natural adiabatic lapse

actual temperature lapse

FanningFanning : The plume is seen to reach : The plume is seen to reach its equilibrium level quickly. The its equilibrium level quickly. The plume starts off bifurcated by meets plume starts off bifurcated by meets strong inversion and travels stably. It strong inversion and travels stably. It is formed in stable atmospheric is formed in stable atmospheric condition.condition.

FumigatingFumigating : The plume is formed by : The plume is formed by being trapped by a strong stable being trapped by a strong stable inversion above and a well mixed inversion above and a well mixed unstable air below it. It occurs usually unstable air below it. It occurs usually in the morning when sunshine causes in the morning when sunshine causes the layer beneath the inversion to be the layer beneath the inversion to be mixed by convection.mixed by convection.

Lofting Lofting : If the inversion is : If the inversion is weak, the plume may weak, the plume may penetrate it and then continue penetrate it and then continue to spread upwards but not to spread upwards but not downwards due to the downwards due to the inversion.inversion.

ThermallingThermalling : It is formed : It is formed when the thermals are well when the thermals are well developed, and the plume is developed, and the plume is carried away by convection carried away by convection and is broken into lumps.and is broken into lumps.

FlaggingFlagging : When the efflux velocity of : When the efflux velocity of the plume is not large enough to the plume is not large enough to carry the effluent, some pollutants carry the effluent, some pollutants are trapped near the stack hole. This are trapped near the stack hole. This is then brought down by gravity.is then brought down by gravity.

BifurcationBifurcation : The buoyancy of a hot : The buoyancy of a hot plume generates a double vortex plume generates a double vortex circulation in the plume with an circulation in the plume with an updraught. This is due to internal updraught. This is due to internal convective motion of the plumeconvective motion of the plume