Air Pollution 1

AIR POLLUTION Dr. B. B. Ale Department of Mechanical Engineering Pulchowk Campus, Institute of Engineering Tribhuvan University 2008

AIR POLLUTION • Accumulation of any substances in the air in sufficient concentration to effect man, animals, vegetation or other materials. • Air + contaminants => Air pollution • These contaminants include gases (SOx, NOx, CO, HC etc), particulate matters (smoke, dust, fumes, aerosols), radioactive materials and many others.

National Ambient Air Quality Standards for Nepal

S.N.

Parameters

Units

1

TSP (Total Suspended Particulates)

µg/m

2

PM10

µg/m

3

Sulphur Dioxide

µg/m

4

Nitrogen Dioxide

3

Averaging Time Annual 24-hours*

3

3

3

µg/m

5

Carbon Monoxide µg/m3

6

Lead

3

µg/m

Annual

7

Benzene

µg/m

230

High Volume Sampling

-

24-hours*

120

Annual

50

24-hours**

70

Annual

40

24-hours**

80

Low Volume Sampling Diffusive sampling based on weekly averages To be determined before 2005. Diffusive sampling based on weekly averages To be determined before 2005.

8 hours**

10,000

To be determined before 2005.

15 minute

100,000

Indicative samplers *** Atomic Absorption Spectrometry, analysis of PM10 samples****

Annual 24-hours

3

Concentration in Test Methods Ambient Air, maximum

Annual 24-hours

0.5 20*****

Diffusive sampling based on weekly averages

-

*Note: 24 hourly values shall be met 95% of the time in a year. 18 days per calendar year the standard may be exceeded but not on two consecutive days. **Note: 24 hourly standards for NO2 and SO2 and 8 hours standard for CO are not to be controlled before MoPE has recommended appropriate test methodologies. This will be done before 2005. ***Note: Control by spot sampling at roadside locations: Minimum one sample per week taken over 15 minutes during peak traffic hours, i.e. in the period 8am - 10am or 3pm - 6pm on a workday. This test method will be re-evaluated by 2005. ****Note: If representativeness can be proven, yearly averages can be calculated from PM10 samples from selected weekdays from each month of the year. *****Note: To be re-evaluated by 2005.

Kath AQMM: National AAQS Parameter

AVG Time

Conc., Max.

Conc., Max. (WHO,2005)

TSP

24 hour

230 µg/m3

PM2.5

Annual 24 hour

10 µg/m3 25 µg/m3

PM10

Annual 24 hour

120 µg/m3

20 µg/m3 50 µg/m3

NO2

Annual 24 hour

40 µg/m3 80 µg/m3

40 µg/m3 200 µg/m3 (1-hour)

SO2

Annual 24 hour

50 µg/m3 70 µg/m3

20 µg/m3 500 µg/m3 (10-min)

CO

8 hour 15 minute

10,000 µg/m3 100,000 µg/m3

Lead

Annual

0.5 µg/m3

Benzene

Annual

20 µg/m3

Ozone

8-hour

100 µg/m3

AIR QUALITY AND HEALTH - WHO Key Facts: • Air pollution is a major environmental risk to health and is estimated to cause approximately 2 million premature deaths worldwide per year. • Exposure to air pollutants is largely beyond the control of individuals and requires action by public authorities at the national, regional and even international levels. • The WHO Air quality guidelines represent the most widely agreed and up-to-date assessment of health effects of air pollution, recommending targets for air quality at which the health risks are significantly reduced. • By reducing particulate matter (PM10 ) pollution from 70 to 20 micrograms per cubic metre, we can cut air quality related deaths by around 15%. • By reducing air pollution levels, we can help countries reduce the global burden of disease from respiratory infections, heart disease, and lung cancer. • The WHO guidelines provide interim targets for countries that still have very high levels of air pollution to encourage the gradual cutting down of emissions. These interim targets are: a maximum of three days a year with up to 150 micrograms of PM10 per cubic metre (for short term peaks of air pollution), and 70 micrograms per cubic metre for long term exposures to PM10 . •

More than half of the burden from air pollution on human health is borne by people in developing countries. In many cities, the average annual levels of PM10 (the main source of which is the burning of fossil fuels) exceed 70 micrograms per cubic metre. The guidelines say that, to prevent ill health, those levels should be lower than 20 micrograms per cubic metre.

KEY FINDINGS IN 2005 AIR QUALITY GUIDELINES - WHO •

• •

•

There are serious risks to health from exposure to PM and O3 in many cities of developed and developing countries. It is possible to derive a quantitative relationship between the pollution levels and specific health outcomes (increased mortality or morbidity). This allows invaluable insights into the health improvements that could be expected if air pollution is reduced. Even relatively low concentrations of air pollutants have been related to a range of adverse health effects. Poor indoor air quality may pose a risk to the health of over half of the world’s population. In homes where biomass fuels and coal are used for cooking and heating, PM levels may be 10–50 times higher than the guideline values. Significant reduction of exposure to air pollution can be achieved through lowering the concentrations of several of the most common air pollutants emitted during the combustion of fossil fuels. Such measures will also reduce greenhouse gases and contribute to the mitigation of global warming.

AMBIENT AIR QUALITY STANDARDS LEVEL 3 S/N POLLUTANTS COUNTRY AVERAGE TIME ppm mg/m Japan 24 h 10 11.5 8h 20 23 USA 8h 8.6 10 1h 35 40 1 CO Germany 24 h 8.6 10 15 min 100 WHO 30 min 60 1h 30 8h 10 Japan 24 h 0.02 0.04 USA 1 year 0.05 0.1 NO2 2 Germany 30 min 0.05 0.1 WHO 24 h 0.15 1h 0.35 Japan 24 h 0.04 0.1 USA 1 year 0.03 0.08 24 h 0.14 0.365 1h 0.5 1.3 SO2 3 Germany 24 h 0.06 0.15 WHO 24 h 0.125 1h 0.3 0.35 10 min 0.43 0.5 Japan 24 h 0.1 1h 0.2 USA 1 year 0.06 4 SPM 24 h 0.15 Germany 1 year 0.1 24 h 0.2 WHO 24 h 0.12 PM10 5 24 h 0.07 Sources: The World"s Air Quality Management Standards, EPA, 1974 WHO/UNEP, 1992

3

microgram/m 11,500 23,000 10,000 40,000 10,000 100,000 60,000 30,000 10,000 40 100 100 150 400 100 80 365 1300 150 125 350 500 100 200 60 150 100 200 120 70

CRITERIA POLLUTANTS • Six pollutants have been identified as criteria pollutants as they are the contributors to both sulfurous and photochemical smog problems. • They are – – – –

Carbon monoxide (CO) Oxides of nitrogen (NOx) Oxides of sulphur (SOx) Lead (Pb) – Ozone (O3) – Particulate matter (PM)

4- SCALE OF CONCENTRATION • Mass concentration scale • Volume concentration scale • Volume concentration scale in parts per million • Mass-volume concentration scale

MASS CONCENTRATION Mass concentration scale, wp Wp = mp/ (ma+mp) Where; mp – mass of pollutant Ma – mass of pure air in a given volume of air-pollutant mixture

VOLUME CONCENTRATION SCALE • Volume concentration scale, Yp Yp = Vp/(Va+Vp) Where; Vp – volume of the pollutants Va – volume of the pure air

VOLUME CONCENTRATION SCALE

in ppm

• Volume concentration scale in parts per million (ppm) – Yppm = Yp x 10^6

MASS-VOLUME CONCENTRATION SCALE

• It is ratio of the mass of the pollutant to the volume of the air and pollutant combined

• ρp = Mp/(Va+Vp), µg/m3 • ρp = Mp/Vp x Ypp x 10^(-6) Notes:

• ρp = Mp / [(Va+Vp)/Vp x Vp] x Ypp/(Ypx10^6) = Mp/[1/Yp x Vp] x Ypp/ (Ypx10^6) = Mp x Yp x 1/Vp x Ypp/(Ypx10^6) = Mp/Vp x Ypp x 10^(-6)

CLASSIFICATION OF AIR POLLUTANTS • • • •

Depending upon the process of formation Based on the types of pollutants Based on the nature of source Based on the source types

CLASSIFICATION OF AIR POLLUTANTS • Depending upon the process of formation: – Primary pollutants: they are emitted directly from the source (volcanic ash, CO from motor vehicle) • • • • • •

Oxides of S, N, & C Organic compounds (fuel vapors & solvent like HCs) Particulate matters (smoke, fumes and dust) Metal oxides of Pb, Cd, Cu & Fe Odors Toxic substances

Among the large number of primary pollutants emitted into the atmosphere, only a few are present in sufficient concentrations to be of immediate concerns. They are Particulate matters, Sox, NOx, CO, HC – Secondary pollutants

CLASSIFICATION OF AIR POLLUTANTS • Depending upon the process of formation: – Primary pollutants: they are emitted directly from the source (volcanic ash, CO from motor vehicle) – Secondary pollutants: they are formed from the primary pollutants by chemical interaction with some constituent present in the atmosphere (SO3, NO2, O3, peroxyacetyl nitrate (PAN), aldehydes, various sulphates and nitrate salts etc.)

• Based on the types of pollutants: – Gaseous pollutants: SOx, NOx, CO, HCs, etc. – Particulates: smokes, dust, fumes, aerosols etc.

CLASSIFICATION OF AIR POLLUTANTS • Based on the nature of source – Point source or single source: steel mills, power plants, oil refineries, paper & pulp mills – Spread sources or multiple or area sources: an entire residential area – Line source: highways carrying moving vehicles

• Based on the source types – Combustion – Industrial – Power plants

TYPES OF SOURCES • Natural sources: – Volcanic ash and gases – Smoke and harmful trace gases fro forest fires – Dust storms

• Anthropogenic sources: – Combustion: • combustion of fossil fuels: SO2, NOx, CO, PM, water vapor and traces of metal oxides of mercury, lead & cadmium • incineration of solid combustible wastes: aldehydes, benzo-α-pyrene, CO, NOx, SO2, HCs, NH3, PM

TYPES OF SOURCES • Anthropogenic sources: – Combustion: – Chemical & metallurgical industries: • Iron & steel industry: dust, fumes, HC, H2S, SO2 • Non-metallic mineral industries (cement, glass, ceramics, refractories): hazardous dust • Chemical process industries: SO2, SO3, NH3, NO2, HF, HCl, H2S; C6H6, C6H5CH3, CCl4 • Petroleum refining operations: oxides of S and S containing vapors, particulates from catalyst regenerations and recycling, H2S & mercaptans • Pulp & paper industry: H2S, methyl mercaptan, methyl sulphides, particulates • Food processing industries: dust, odors, nitrates & phosphates, pesticides, arsenic & lead particulates

PROPERTIES OF AIR POLLUTANTS – PARTICULATE MATTER • Particulate matter: they are suspended droplets or solid particles or mixture of the two. • Particulates can be composed of inert or extremely reactive materials, ranging in size (i.e. diameter) from 100 µm to 0.1 µm or less. • The inert materials do not react readily with the environment nor do they exhibit any morphological changes as a result of combustion r any other processes whereas the reactive materials could be further oxidized or may react chemically with the environment. • They may reduce visual amenity and adversely impact health.

PARTICULATE MATTER • PM may either be primary pollutant such as smoke particles, or a secondary pollutant formed from the chemical reaction of gaseous pollutants such as dust, smoke, plant spores, bacteria, salt, fumes, mist, fog, aerosol • Human activities resulting in PM in air includes: mining, burning of fossil fuels, transportation, agriculture & hazard reducing burning, the use of incinerators, the use of solid fuel for cooking and heating

PARTICULATE MATTERS • PM can be usefully classified by size: – Large particles settle out f the air quickly while smaller particles may remain suspended for days r months – Rainfall is an important mechanism for removing particles from the air

• The size of particles also determine its potential impact on human health. – Large particles are usually trapped in the nose and throat and swallowed – Smaller particles may reach the lungs and cause irritation there

CLASSIFICATION OF PMS Dust: • It contains particles of size ranging from 1 to 200 µm • It is formed by natural disintegration of rock and soil or by the mechanical processes of grinding and spraying • They have large settling velocities & are removed from the air by gravity and other inertial processes • Fine dust particles act as centers of catalysis for many of the chemical reactions taking pace in the atmosphere

CLASSIFICATION OF PMs Smoke: • It contains fine or very small liquid or solid particles • Size ranges from 0.01 to 1µm in diameter • It is formed b incomplete combustion or by other chemical processes • It may have different colors depending upon the nature of other materials burnt

CLASSIFICATION OF PMs Fumes: • They are solid particles of sizes ranging from 0.1 to 1µm. • They are released from chemical and metallurgical processes Mist: • It is made up of liquid droplets having size less than 10µm. • It is formed by condensation in atmosphere or is released from industrial operations

CLASSIFICATION OF PMs Fog: • It is air-borne liquid having size of 1 to 100µm. • It is the mist in which the liquid is water & is sufficiently dense to obscure vision. Smog: • It implies an air mixture of smoke particles, mists and fog droplets of such concentration and composition as to impart visibility in addition to being irritating or harmful • The composition varies widely between the different locations and times (0.01 to 0.1µm) • Smog + fog + mist => visibility reduced

CLASSIFICATION OF PMs Aerosol: • It includes all air-borne suspensions either sold or liquid having size smaller than 1µm.

SIZES OF ATMOS PHERIC PM

HEALTH EFFECT OF PM The toxic effect of particles can be grouped into three categories: • Interference of the inert particles with the clearing mechanisms of the respiratory tracts • Particles act as the carriers of adsorbed toxic gases such as SO2 and produce synergistic effects • Particles may be intrinsically toxic because of their physical or chemical characteristics.

MAJOR HEALTH IMPACTS • Acute respiratory infection (ARI) – damages lung’s defense mechanisms and causes cardiovascular disease & lung cancer • Triggers asthma • Causes irritation in the eye • Low birth weight

HEALTH IMPACT DUE TO SIZE AND NUMBER • Particles in the size range 1-10µm have measurable settling velocities but are readily stirred by air movement • Particles of size range 0.1-1µm have small settling velocities • Particles of size below 0.1µm, s submicroscopic size found in urban air, undergo random Brownian motion resulting from collisions among, individual molecules • Most urban particulates have size in the range 0.1 to 10µm • The smallest and the finest particles are the ones which cause significant damage to health

HEALTH IMPACT DUE TO SIZE AND NUMBER • Ultrafine particles tend to behave more like gases and hence travel to the lower region of the lungs as compared to the larger particles which tend to deposited in the upper or middle region of the respiratory tract • Ultrafine particles are extremely toxic to the lungs, even when they comprise materials that are not toxic when present in the larger particles • The smaller the particle, the greater the fraction of particles deposited in airways and lungs, and the greater the surface area available for interaction with biological systems

HEALTH IMPACT DUE TO COMPOSITION OF PM • Organic compounds lead to mutations & even lung cancer • Materials of biological origin (fungal spores & pollens) induce a variety of allergic responses • Sulphates and nitrate ions lead to significant impairment of the respiratory tract because of their acidic potential • Carbonaceous materials in core lead to lung irritation & damage after chronic exposure

DIESEL PARTICLES • Size: mostly smaller than 1µm in diameter • They have carbonaceous core with a large surface area to which various organic compounds are adsorbed, including carcinogenic polycyclic and nitro-polycyclic hydrocarbons • They also adsorb allergens from grass pollen, thus potentially increasing allergen deposition in the respiratory tract

MECHANISMS OF HEALTH EFFECTS OF PM • Dose: a quantity of materials that reaches a target • Adult human lung: surface are 40-120m2; inhales 10,000 to 20,000 liters of ambient air per day • Lung defenses: The lung has evolved a multilayered defense mechanism to counter inhaled particles and it responds particulate pollution with the same defense mechanism as it does to pollens and spores

CONCLUSIONS ON PM • While a large body of studies links adverse health effects of particles less than 10µm in diameter (PM10), the latest evidence strongly indicates that the fine (size < 2.5µm) and ultrafine (size < 0.1µm) fractions of PM are most harmful because of their ability to penetrate deeply into the lungs. • For a given mass, the surface area & the particle no. increase dramatically as the particle size decreases. As a result, a smaller mass of PM which happens to consist primarily of ultrafine particles can be more damaging than a greater mass of PM10 but with the significant fraction falling in the coarse range.