Air Quality: Criteria Pollutant

Lect-6

Detailed of Criteria Pollutant

1.Carbon monoxide, CO Carbon monoxide, CO, is a colorless odorless flammable

gas, major pollutant of an urban air, produced from incomplete combustion of fossil fuel and biomass.

2C + O2→ 2CO and 2CO +O2 → 2CO2 Anthropogenic sources: IC engine, cigarette smoke,

biomass burning Natural sources: biomass burning, atmospheric oxidation

of methane gas and other hydrocarbons. Concentrations: Background concentration 50 – 110

ppbv, closely associated with traffic density and meteorological conditions

Sinks: Atmospheric photochemical processes: CO +OH → CO2 +H; H+O2 +M → HO2 +M; HO2 +NO →NO2+OH; NO2 subsequently oxidize to produce O3; Residence time: 2 months

As a result of these reaction CO is oxidized to CO2CO +2O2 + hν → CO2 +O3---- important source of O3 in atmosphere

2.Sulfur dioxide, SO2 Sulfur dioxide, SO2, is a colorless gas with a sharp odor,

primary pollutant, has anthropogenic (man-made) and natural sources.

Oder detected: 0.38 ppm; At 3 ppm –pungent irritating odor Anthropogenic sources: industries burning sulfur-containing

fossil fuels, ore smelters, oil refineries. - Sulfur is present in many fuels (e.g., coal, crude oils) over a

wide range of concentrations. Combustion causes its oxidation to sulfur dioxide.

Natural sources: marine plankton, sea water, bacteria, plants, volcanic eruption.

SO2 effects:- At relatively high concentrations SO2 causes severe

respiratory problems.- Sinks: - Sulfur dioxide is an acid precursor, which is a source of acid

rain produced when SO2 combines with water droplets to form sulfuric acid, H2SO4

- Sulfur dioxide is an precursor of sulfate particulates (sulfates) which affect the radiation balance of the atmosphere and can cause global cooling

Residence time: 2 to 4 days: Trans- boundary problem

Health effects of Sulphur Dioxide

Concentration of SO2 (ppm) Effects

0.52ppm with particulate (24-hr avg.) Increase death

0.25 ppm with smoke (3-4 days;24-hr avg.)

Increase death

0.25 ppm with particulates (24-hr avg. 3-4 days exposure)

Increase illness for elderly

0.11 to 0.19ppm with low particulate levels(episode of several days duration)

Increase hospitalization

0.037 to 0.092ppm with smoke (chronic exposure)

Increase respiratory symptoms and lung diseases

3. NO2 Nitrogen, N2, is a dominant gas of the atmosphere

about 78% by volumeNOx stands for an indeterminate mixture of nitric oxide, NO,

and nitrogen dioxide, NO2Nitrogen oxides, NOx, are formed mainly from N2 and O2

during high-temperature combustion of fuel in cars.Anthropogenic sources: motor vehicles, biomass burningNatural sources: bacteria, lightning, biomass burningNOx effects:causes the reddish-brown haze in city air, which contributes

to heart and lung problems and may be carcinogenic NOx is an acid precursor, which is a source of acid rain

produced when nitrogen oxides combines with water to produce nitric acid, HNO3

Nitrogen oxides are the precursors of nitrate particulates (nitrates) which affect the radiation balance of the atmosphere and can contribute to global cooling

Nitrogen oxides are major contributors to the formation of ground level ‘bad’ ozone.

Health Effects of NO2Concentration of NO2 (ppm) and exposure period

Effects

150 (5-8 minutes) Potentially fatal50-100 (<1-hr) May cause bronchopneumonia- but

recovery probable10 - 40 (intermittent exposure) May cause chronic fibrosis and

Emphysema0.05 to 0.10 (chronic exposure) Increase chronic bronchitis<0.05 (long-term average) Increase in heart and lung disease

ingeneral population with increase in an ambient concentration

4. OzoneOzone, O3, is a gas.At ground level, ozone is a hazard (‘bad’ ozone) - it

is a major constituent of photochemical smog. However, in the stratosphere, it serves to absorb some of the potentially harmful UV radiation from the sun, which is believed to cause skin cancer, among other things (‘good’ ozone).

Sources: ozone is not emitted into the atmosphere; ozone is formed from the ozone precursors, VOCs, and nitrogen oxides (will be discussed in several Lectures).

"Bad" ozone effects: diverse effects on human health ecological effects: damage vegetable and trees,

Criteria Air Pollutants: Ozone

Unpleasant appearance in urban cities photochemical smog

Deterioration of synthetic rubber, textiles, paints

Gates Corporationhttp://www.gates.com/brochure.cfm?brochure=2833&location_id=3369

US EPA in How Stuff Works Website, http://science.howstuffworks.com/ozone-pollution.htm

Criteria Air Pollutants: Ozone

Leaf damage◦ Chlorophyll damage: “flecks”◦ Discoloration

Reducing crop yields and forest growth

Tobacco leaf which has sustained ozone damage http://www.lambtonwildlife.com/nature_notes_98/tobac.fld/tobacp.htm

Ozone damage on white pine (Photograph courtesy of A. Heagle) NC State, http://www.ces.ncsu.edu/depts/pp/notes/Ornamental/odin19/od19.htm

Ponderosa Pine (left: undamaged; right: damaged)Image from Miller et al (1996) USFS PSW-GTR-155http://www.cbesurvey.org/aplv/panek/research.htm

5. LeadLead alkyls (ethyl and tetra methyl lead) is

the additives in the fuel to boost the octane rating.

Metals (such as lead, mercury, cadmium, chromium, nickel) found as impurities in fuels.

Anthropogenic sources: emitted by metal mining and processing facilities; motor vehicle.

Example: lead is a very useful metal, has been mined for thousand of years

Main effect: They are highly toxic

6.Particulate matters (PM)Particulate matters (aerosols) are solid or

aqueous particles composed of one or several chemicals and small enough to remain suspended in the air

Examples: dust, soot, smoke, sulfates, nitrates, asbestos, pesticides, bio-aerosols (e.g., pollen, spores, bacterial cells, fragments of insects, etc.)

Name: Aerosol, SPM- Suspended particulate matter;

TSP- Total Suspended particulate matter; PM10 are particles with diameter < 10 micrometers (μm), PM2.5

Effectsdiverse health effects (e.g.,

harmful to human respiratory system)

contribute to urban haze, cause visibility reduction

play a key role in the Earth’s radiative budget and global change

Health Effects of SPM Concentration of Particulate (µg/m3)

Effects

2000 µg/m3 with 0.4 ppm of SO2 (24-hr avg) of several days duration.

Increase in death due to bronchitis

1000 µg/m3 with 0.25 ppm of SO2 (24-hr avg) during episodes

Increase mortality from all causes including respiratory and cardiac disease

300 µg/m3 with 0.21 ppm of SO2 (24-hr avg)

Significant increase in bronchitis symptoms

100-200 µg/m3 with 0.05 to 0.08 ppm of SO2 (average seasonal level)

Increase in incidence of bronchitis reported

Some discussion pointsWhy particulate pollutants are more

common and their concentration is high in SA countries?

What are their sources and how we can control them?

How can we solve transboundary problem?

How CO affect human health?

Atmospheric Aerosols

SourcesNatural Origin: sea spray, dust from

arid/semiarid areas, volcanic eruption, forest fire, interplanetary meteors, gas-phase chemistry

Man-made: combustion, gas-phase chemistry

Sinks Coalescence of tiny aerosols due to air

motions Cloud formation; aerosols as nuclei Precipitation scavenging

Aerosols - CharacteristicsPhysical; size,

mode of formation, settling and optical properties

Chemical: Organic or inorganic

Biological: bacteria, viruses, spores, pollens

Fig. 17-8 p. 426

Aerosol Composition

Water-soluble: sea salt, sulfate, nitrate, organic carbon (optical properties are largely unknown)

Sulfate Particles (natural and anthropogenic): mainly reflect sunlight

Soot, carbonaceous materials (black carbon): mainly absorb sunlight

Dust-like substance (mineral): reflect and absorb sunlight

Particulate Matter

Human Hair (70 µm diameter)

Hair cross section (70 mm)

PM2.5(2.5 µm)

PM10

(10µm)

Source: US EPA

Composition of PM

PMSulfate:• Ammonium sulfate ((NH4)2SO4), Ammonium Bisulfate (NH4HSO4) and sulfuric acid (H2SO4)

• Water soluble• ≤PM2.5

Geological material:•Oxides of Al, Si, Ca, Ti, Fe and other metals•Typically about 50% of PM10 and 5 – 15% of PM2.5

Nitrate:• Mostly ammonium nitrate (NH4NO3)

• Easily evaporates with changes in temp and RH.

Organic carbon:• Includes hundreds of compounds containing more than 20 Carbon molecules (> C20)

• Semi-volatile

Elemental carbon:• Pure carbon• Also known as “soot”

Liquid Water:• Soluble compounds absorb water when RH is > 70%.

Composition andshape of soot

Different forms

Dusts:Solid aerosols generated by the handling, grinding,

abrasion, or cutting of a bulk material Dust particle size is related to the amount of energy

involved in creation; the higher the energy—the smaller the particle created; the lower the energy—the larger the particle created

Examples: Saw dust, coal dustSmoke:Fine, solid particles resulting from incomplete combustion

of organic particle such as coal, wood or tobacco, consists mainly of carbon and other combust able material. Size -0.1 to 1 micron

Fumes: are fine solid particles formed by condensation of vapors of solid material.

Other formFly ash: It consists of finely divided non combust able particles contained in

flue gases arising from combustion of coal. Fly ash shows properties of dust, smoke, and fumes.

Like dust it has particle range 1-100 micronLike smoke: it results from burningLike fumes: It consists of inorganic metallic or mineral substance

Mists: Liquid aerosols generated by condensation from a

gaseous state or by the breaking up of a bulk liquid into a dispersed state

Droplet size related to energy input as in dusts and fibers Examples: Metal working fluid from lathe, paint spray,

liquid mixing operations Spray: consists of liquid particles formed by atomization of

parent liquids such as pesticides and herbicides. 

Effectsdiverse health effects (e.g.,

harmful to human respiratory system)

contribute to urban haze, cause visibility reduction

play a key role in the Earth’s radiative budget and global change

Climate Effects of Black Carbon Aerosols in China and India

Surabi Menon, James Hansen, Larissa Nazarenko, Yunfeng Luo

In recent decades, there has been a tendency toward increased summer floods in south China, increased drought in north China, and moderate cooling in China and India while most of the world has been warming. We used a global climate model to investigate possible aerosol contributions to these trends. We found precipitation and temperature changes in the model that were comparable to those observed if the aerosols included a large proportion of absorbing black carbon ("soot"), similar to observed amounts. Absorbing aerosols heat the air, alter regional atmospheric stability and vertical motions, and affect the large scale circulation and hydrologic cycle with significant regional climate effects (Science, 27 September 2002).

Particle removal ProcessMost important process1. Coagulation2. Sedimentation3. WashoutLess important process4. Diffusion (through air to ground

or to upper atmosphere)5. Impaction (Attachment to

obstacle)

1. CoagulationCoagulation occurs when two particles

collide and then coalesce resulting in fewer but larger particles i.e smaller particles tend to disappear.

Consider aerosols consisting of identical particles at a number density N. The rate at which each particle strike other is proportional to the number density of target N

The rate of coagulation α N2

Non uniform sizeIf N consists of two size groups r1

and r2

Then rate of coagulation can be shown to be

dN/dT = c (2 + r1/r2 +r2/r1)N2

Monodisperse aerosol : r1/r2 = 1

Rate = 4 c N 2

Polydisperse aerosol : Rate = c(2 + r1/r2 ) N2

If r1/r2 = 100 Rate = 102 c N2

2. Sedimentation Settling is the major natural self cleansing

process for removal of particles from the atmosphere.

Particle classified as: Suspended particles: 1µm to 20 µmSettle-able or dust fall > 10µmAirborne behavior, such as settling velocity, is a

function of Size, Specific gravity, Shape Surface properties: Using Stokes’ law

Vt = g D2 (ρp- ρair)/18µHolds for 1µm to 100 µm

Assumptions1. The fluid is continuous2. The flow is laminar, Cd = 24/ Re3. Newton,s law of viscosity holds4. In the resulting equation the term that

involves square of velocity is negligibleParticle too large for stokes law:Flow becomes turbulent i.e. Cd> 0.4 and

assumption 4 does not hold good.Particles too small for Stokes law: Fluid will

not be continuous; Cunnigham correction is required.

ScavengingWash out by precipitation q = qo exp (-wp t)wp : washout coefficient depends

on rainfall rate and size of the droplet.

Size distributionCoagulation

determines lower end of the size distribution

And Sedimentation determine the upper end of the size spectrum

Size distribution of natural aerosols measured at a number of locations in Germany (data taken from Junge, 1963).

Junge size distributionN(r) = dn/dlogr = cr -ν and dN/dr = c r -(ν +1) Where n(r)= no of particles per unit volume per

log size interval

N= No of particles per unit volume

dN = No of particle per increment in log r

C= is a constant whose value depends on concentration

ν= the slope of the distribution curve

ProblemIf a continental aerosol contains

10 4 particles of radii ≥0.1µ m per cm3, how many particles would you expect to have with radii ≥0 .5 µm and ≥ 1µm