Introduction to noise pollution (II)&

Fundamentals of the atmosphere

Lecture TwoLecture Two

Road Traffic NoiseRoad Traffic NoiseSources - power train noises and rolling noises• Power unit noises

– Such as engine, air inlet, exhaust, and cooling system.

• Rolling noises – Such as wind turbulence

and tire/road surface, brakes, rattles, and load.

Power train vs. rolling noiseRoad Speed

(km/h)Vehicle

classRolling noise

dB(A)Power unit noise

dB(A)Total noise

dB(A)

20 Heavy* 61 78 78

Light 58 64 65

80 Heavy 79 85 86

Light 76 74 78

Note - * Heavy vehicles are > 1525 kg unladen weight

Rolling noise contributes little to the total noise for heavy vehicles operating at low speeds.

For cars running at a speed > 60 km/h, rolling noise is the dominant noise source.

Power unit noisePower unit noise• Combustion Engine noise

– mainly concerned with diesel engines.

• Mechanical Engine noise– mainly from

• piston slap, • bearing noise, • gear and timing drive noise, • valve train impact noise, • fuel injection pump and injector noise.

• Fan noise– Significant for large commercial vehicles

• Transmission noise– Not an important source of noise under normal conditions

Wind turbulence and other noise• Wind turbulence noise

– generally not significant source of external noise at normal road speeds. – but lower frequency wind flutter can be trouble some due to resonance of

the air space inside a car as air streams past an open window.

• Brake squeal– can be a significant source of noise.

• Tire / road noise– The most important component is that generated by action of the vehicles

tire rolling over the road surface.– The main factors affecting tire noise are

• the speed of rotation of the tire • type of tread pattern and material • texture applied to the road surface (which has a bigger effect)

Road Tire noiseRoad Tire noise

Railway Noise• The structure of a railway consists of train, track

and roadbed.– Noise sources include

• rolling noise• engine noise• body vibration of a train• the structure on the ground

• The rolling noise – generated from the interaction between the wheel and rail.

• There is a wide range of parameters affecting the noise level of the railway system – types of locomotive propulsion system– the compressors, motor generators, brakes etc.– the interaction of the wheels and rails– the noise radiated by vibrating structure such as steel bridges,

the speed of train and its length. – The generated airborne noise radiated into community, also

ground borne noise and vibration which travels through the track, support structure and the intervening soil to nearby buildings.

Railway Noise

Type of trains in Hong KongType of trains in Hong Kong

Wheel absorber to reduce squeal noiseWheel absorber to reduce squeal noise

Wheel absorber to reduce rolling and Wheel absorber to reduce rolling and squeal noisesqueal noise

Insulator for Light RailInsulator for Light Rail

Base Plate PadBase Plate Pad

Elastic sleeper pad and rubber bootElastic sleeper pad and rubber boot

Insulation matInsulation mat

Construction NoiseConstruction Noise

• Impact noise – Piling– Hand-held breaker– Excavator mounted breaker– Vibration hammer.

• Engine noise– Compressors– Generators– Trucks

Sound power levels of percussive piling

Piling Method* and Pile Type Sound Power Level (dB(A))Diesel hammer driving pre-stressed concrete pile 128

Diesel hammer driving steel pile 132

Diesel hammer driving steel sheet pile 132

Drop hammer driving concrete pile 116

Drop hammer driving steel pile 126

Drop hammer driving steel sheet pile 129

Hydraulic hammer (double acting) driving pre-stressed concrete pile 126

Hydraulic hammer (double acting) driving steel pile 129

Hydraulic hammer (double acting) driving steel sheet pile 129

Hydraulic hammer (single acting) driving pre-stressed concrete pile 122

Hydraulic hammer (single acting) driving steel pile 126

Hydraulic hammer (single acting) driving steel sheet pile 126

Internal drop hammer 113

Pneumatic or steam hammer (double acting) driving steel sheet pile 135

Pneumatic or steam hammer (single acting) driving steel pile 130

LegislationLegislation

• Piling work: – 5 hours per day max (daytime 07:00 – 19:00)

• General construction work:– Nighttime permit after 19:00

• Product label:– Noise level specified for the product

Chemical CompositionChemical CompositionConstituent Chemical

FormulaPercent by

VolumeParts per Million by

Volume

Nitrogen N2 78.084

Oxygen O2 20.946

Argon Ar 0.934

Neon Ne 18.2

Helium He 5.2

Krypton Kr 1.1

Hydrogen H2 0.5

Xenon Xe 0.09

Nitrous oxide N2O 0.3

Water vapor H2O 0.01-7

Carbon dioxide CO2 0.036

Methane CH4 1.72

Carbon Monoxide CO 0.11

Ozone O3 0.02

Ammonia NH3 0.004

Nitrogen dioxide NO2 0.001

Sulfur dioxide SO2 0.001

Hydrogen sulfide

H2S 0.00005

Constant

Varied temporally and spatially

1. Raw material for green plants to make food molecules.

2. Greenhouse gases

Ideal Gas LawIdeal Gas Law

RTPM

VW

RTMWnRTPV

Where ρ= density of gas, kg/m3

P = absolute pressure, kPa

V = volume of gas, litre (L)

W = weight of gas, gram

M = molecular mass, grams/mole

T = absolute temperature, K

R = universal gas constant = 8.3143 J/K·mole

Dalton’s Law of Partial Dalton’s Law of Partial PressuresPressures

Pt = P1 + P2 + P3 + …

Where Pt = total pressure of mixture

P1, P2, P3 = pressure of each gas if it were in container alone, that is, partial pressureIt may also be written in terms of the ideal gas law:

VRTnnn

VRTn

VRTn

VRTnPt

...)(

...

321

321

Units of MeasureUnits of Measure• Concentration

– the amount (mass, moles, molecules, etc) of a substance in a given volume divided by that volume.

– The example concentration units are mg/m3, mol/m3, molecules/cc, and etc.

• Mixing ratio – the ratio of the amount of the substance in a given

volume to the total amount of all constituents in that volume.

Expressions of Mixing RatioExpressions of Mixing Ratio

• Mixing ratio: based on volume-volume ratios

1 ppmv =1 gas volume

106 air volume

1 ppbv =1 gas volume

109 air volume

1 pptv =1 gas volume

1012 air volume

Concentration ExpressionsConcentration Expressions

• Metric unit:Metric unit: expressed as mass per unit volume– microgram per cubic meter (µg/m3)– milligram per cubic meter (mg/m3)

Conversion between the two units

– M is molecular weight of the pollutant– R = 62.36 (mm Hg-L)/(mol-K) – P is pressure (mmHg) – T is temperature (°K) at reference, respectively

• Standard condition: 760 mmHg; 25 °C

X (ppbv) = Y (µg/m3)62.36 T

M P

Important!

The electromagnetic spectrumThe electromagnetic spectrum

Adapted from The Atmosphere, Eighth edition, by F. Lutgens and Tarbuck, Prentice Hall

Solar radiation spectra

• Solar radiation at the top and bottom of the earth’s atmosphere (blackbody radiation at ~ 6000 K)

• O2, O3 and H2O absorbing some portions of the radiation• Radiation concentrated in the visible light region (green)

Air pollutionAir pollution• “Clear” air becomes polluted when it is

changed by addition of particles, gases or energy forms such as heat, radiation, or noise so that the altered atmosphere is less useful to mankind or poses some harm because of its impact on weather, climate, human health, animals, vegetation and materials.

Natural and Anthropogenic Natural and Anthropogenic pollutionpollution

• Natural Pollution– Volcanic eruption:

• particulate matter, SO2, H2S– Wild forest fires:

• smokes, hydrocarbon, CO, CO2, NOx

– Emission from trees, lightning 1. levels of pollutants are normally low2. often far from large population3. transient (short-term)

• Anthropogenic Pollution– Significant environmental problem because of its impact on human

health and welfare

Effects of air pollutantsEffects of air pollutants1. Effects on materials1. Effects on materials

Mechanisms of deteriorationAbrasion – large enough size solid particles with high enough speed

Deposition and removal – For most surfaces, it is the cleaning process that causes the damage.

Direct chemical attack – oxidation/reduction reactions

Indirect chemical attack – pollutants are absorbed and then react with some component of the absorbent to form a destructive compound.

Electrochemical corrosion – results from the potential that develops in the microscopic batteries.

Factors that influence deteriorationFactors that influence deteriorationMoisture – essential for most of the mechanisms of deterioration to occur.

Temperature – higher air temperatures generally result in higher reaction rates.

Sunlight – Oxidation effect of its UV wave lengths, providing energy for pollutant formation and cyclic reformation.

Position of the exposed material –

- Vertical or horizontal or at some angle affects deposition and wash-off rates;

- Upper or lower surface may alter damage rate

2. Effects on vegetation2. Effects on vegetation

NO2 - inhibit plant growth and produce surface spotting.

SO2 – cause surface spotting and bleaching.

Air pollutants – reduce the surface area –> lead to less growth and small fruit reduction in income for the farmer.

Cause early death of vegetation

Fluoride deposition on plants causes them damage and results in a second untoward effect

3. Health Effects Caused by Air Pollution 3. Health Effects Caused by Air Pollution

Yosemite Valley, visual range 234 km

Yosemite Valley, visual range 35 km

4. Effects on visibility4. Effects on visibility

Primary versus Secondary air pollutantsPrimary versus Secondary air pollutants

• Primary: the pollutants directly from sources of emissions, – such as NO, SO2 and CO

• Secondary: the pollutants that are formed through chemical reactions of the primary pollutants, – such as O3 and H2SO4

Hong Kong Air Quality Objectives Hong Kong Air Quality Objectives (HKAQO) µg/m(HKAQO) µg/m33

Air Pollutants 1-hour 8-hour 24-hour 3-month 1-year Sulphur dioxide 800 -- 350 -- 80 Nitrogen dioxide 300 -- 150 -- 80 Carbon monoxide 30000 10000 -- -- -- Ozone 240 -- -- -- -- Total suspended particulate

-- -- 260 -- 80

Respirable suspended particulates

-- -- 180 -- 55

Lead -- -- -- 1.5 --

Sources and sinks of air pollutantsSources and sinks of air pollutantsSources: the places from which pollutants emanate.Sinks: the places to which pollutants disappear from the air.

• Hundreds of air pollutants found in the atmosphere• Only a small number of them identified as being at levels significantly enough

to pose a threat to human health and welfare– Carbon (C) oxides– Sulfur (S) compounds– Nitrogen (N) compounds– Hydrocarbon (HCs) and their derivatives– Photochemical oxidants (O3 etc)– Halogenated hydrocarbon– Particulate matter

• It is important to know – the sources, – atmosphere conversions, – sinks of these compound.

Carbon Oxides: CO and COCarbon Oxides: CO and CO22• CO:

– colorless, odorless, and tasteless, mainly from the incomplete burning of fossil fuel and other organic matter:

2C+ O2 2CO(CO is a major air pollutant because of its health effects, and is regulated under an ambient air quality standard.)

• Sources: – transportation, solid waste disposal, agricultural burning, and

steel production; (Natural sources include CH4 and HCs oxidation, forest fire, microbial processes in ocean and soil.)

• Sinks– chemical reaction with OH in the air (CO+ OH CO2 + H)

and uptake by microorganisms

Carbon Oxides: CO and CO2• CO2:

– relatively nontoxic but contributes to climate warming– CO2 has been increasing in the past 50 years due to the large use fossil

fuel. – It is a major “greenhouse” gas.

• Source:– produced from when organic matter is burned, weathered, or

biologically decomposed.C + O2 CO2

– combustion of fossil fuels (coal and oil) and biomass burning.

• Sinks – uptake by plants (photosynthesis) and oceans.

Sulfur compounds: SOSulfur compounds: SO22• SO2

– colorless with odor– SO2 has important health and environmental implications, and is regulated

under an air quality standard.• Source:

– mainly from burning of sulfur containing fossil fuel such as coal and oil, as well as roasting metal sulfide ores in steel and iron industries. (Major natural source is volcanoes and oxidation of reduced S compounds.)

• Sinks: – by wet and dry deposition and conversion to H2SO4 and sulfate (then

removed from wet and dry deposition)

SO2 + OH HOSO2

HOSO2 + O2 HO2 + SO3

SO3 + H2O H2SO4

Nitrogen compounds:Nitrogen compounds:• N2, N2O, NO, NO2, NO3, N2O5, HNO3, HNO2, CH3COO2NO2,

NO3, HCN, NO3-, NO2

-, NH4-

• Nitrous Oxide(N2O): colorless, nontoxic, slightly sweet, relatively non-toxic (widely used as an anesthetic), greenhouse gas

• produced naturally from soils by anaerobic bacteria. It can dessociate by short UV in the stratosphere to produce NO, thus can influence ozone in the stratosphere.

Nitrogen compounds:Nitrogen compounds:• Nitric Oxide (NO):Nitric Oxide (NO):

– colorless, odorless, tasteless, and relatively nontoxic; important in smog chemistry

• Source:Source: – high temperature combustion from automobile exhaust and stationary

sources such as power plants; (Major natural source is anaerobic biological processes in soil and water.)

N2+O2 2NO– Nitrogen Dioxide (NO2): colored as light yellowish at low concentrations

to reddish at high concentrations, it is toxic and corrosive gas. (NO and NO2 play important roles in smog pollution and climate change.)

Hydrocarbons and oxygenated HCsHydrocarbons and oxygenated HCs• Sources:

– Anthropogenic • In major urban areas, motor vehicle exhaust, gasoline

spillage and evaporation, solvent use are often the major sources. Oxygenated HCs can be emitted from vehicle exhaust as well as produced during the atmospheric oxidation of HCs.

– Natural • emissions from forest trees (mainly isoprene and monoterpenes),

grassland (light alkanes and higher HCs) soils (mainly ethane), and ocean water (alkenes and C9-C28 alkanes).

Photo Courtesy of Richard Weisser and smokyphotos.com

Hydrocarbons and Oxygenated HCsHydrocarbons and Oxygenated HCs• SinkSink

– through the oxidation on reaction with OH (hydroxyl radical) and O3 to form various aldehydes and acids which are in turn removed from the atmosphere by wet and dry deposition.

– The oxidation processes involved on the degradation of HC and oxy-HCs are very complex. They are very important in smog chemistry that are responsible for the formation of major photochemical oxidants including O3.

Emissions of :Volatile Organic Compounds (VOCs)

Light hydrocarbons, alcohols, carbonyls, acids, halogenated

HC…

and NO + NO2 = NOx

The atmosphere is a The atmosphere is a giant photoreactorgiant photoreactor

+ h

+ O2

- carbonyls

- peroxides

- Ozone

- organic nitrates

- organic aerosols

In both developed and developing countries, the major threat to clean air is posed by traffic emissions in summer.

The archetype is the Los Angeles photochemical smog, first described in 1948 and now plaguing cities from Athens to Mexico City.

Photochemical SmogPhotochemical Smog

Ozone SinksOzone Sinks1. Surface destruction or deposition - reaction with plants, bare land, ice and snow, and man-made

structures

- deposition of O3 is at its greatest over forests and croplands during daylight hours.

2. Photochemical reactions

-photodissociation on absorption of UV light and subsequent formation of OH radicals.

- In polluted atmosphere, O3 reacts with NO to produce NO2 + O2

- during nighttime hours, it reacts with NO2 to produce HNO3

Particulate MatterParticulate Matter• Particulate matter is a collective term used to describe small solid and

liquid particles in the atmosphere.

• It is of a major air-quality concern because it is 1) an inhalation hazard to humans and animals, 2) reduces visibility, 3) affects climate on regional and global scales.

• Particle size is a very important characteristics because it determines atmospheric lifetime, effects on light scattering, deposition in human lungs.

• Most atmospheric particles are very small (<0.1 μm), whereas most aerosol mass is associated with particles > 0.1 μm.

Human Hair: 100 m

Bacteria: 10 m

Road Dust: 5 m

Viruses: 0.4 m

Vehicle Emission: 0.2 m

Relative Particle Size

Coal Dust: 2 m

Particulate MatterParticulate Matter• SourceSource

– PrimaryPrimary• Natural – volcanoes, forest fires, ocean sprays,

biologic sources (mold, pollen, bacteria etc.)• Anthropogenic – transportation, fuel combustion in stationary

sources, and other activities such as industrial processes, construction and agricultural activity

– SecondarySecondary• from chemical processes involving gases, aerosol particles and

moisture

Particulate MatterParticulate Matter• Chemical composition:Chemical composition:

– major components include organic and elemental carbon (OC and EC), sulfate, nitrate, and a variety of trace metal.

– In Hong Kong, C ~ 50% of PM10 mass; sulfate ~17%, nitrate~6%

• Sink:Sink: – wet and dry deposition

SummarySummary• Some basic knowledge on the atmosphere, including chemical composition,

radiation by sun and earth, and thermal structure of the atmosphere.

• Properties, sources and sinks of major air pollutants such as carbon oxides, sulfur compounds, nitrogen compounds and hydrocarbons. These can come from very complex sources, including natural and man-made, primary and secondary.

• Photochemical oxidants and particulate matter. Chemical reactions can be very complicated for photochemical oxidants.

• Understanding of above fundamental aspects is important for the management of air pollution.