pollution

Lecture No. 10

Noise and Air Pollution

Part I Noise

1. Sound and Hearing Noise is unwanted sound Sound is caused by the presence of mechanical airwaves in matter. Sound waves are longitudinal—the atoms transmitting the wave oscillate in the

direction that the wave is travelling. Waves are characterized by alternating region of compression and rarefaction of

matter.

Intensity through unit area perpendicular to the direction of the wave, Speed of sound in air at sea level, 340 Equation:P(t) = Pa + p(t)P(t) = instantaneous pressurePa = atmospheric pressurep(t) = pressure due to sound

cyclic function, therefore, Pavg = P root mean square = PrmsP(t) = Prms =

Lecture No. 10 Noise and Air Pollution Page No.2

P(t) = Pa + PrmsSound pressure refers to the RMS value. One bar = 100kPa 1.013 bar = 1 atmosphere Sound pressure, 2 talkers 1 meter apart = 1x10-6 bar, 1 micro bar, 1 bar, small. Too add RMS, square the individual values, add and then take the square root.

Example:Given: Two sounds are received simultaneously: 3.8 bar and 5.2 bar.Find: Combined pressure in bar dB

Pcombined = = Pcombined = 6.44 bar

2. Human Hearing 15-20,000Hertz, Hz, cps, Maximum sensitivity 3000Hz Sound pressure, .0002 bar to 10,000 bar Non-linear with respect to pressure and frequency, therefore, a weighted log scale is

in order.

SPL = 10 log10

SPL = Sound pressure, decibels, dBP = sound pressure, barP0 = preference pressure, threshold of human hearing, .0002 bar = 0 dB = 2x10-5Pa, To combine dBs:

Convert dB to bar Add squares Convert sum to sound pressure

Examples:Given: Two sounds from the previous example: 3.8 bar and 5.2 bar.Find: Combined pressure in dB

Pcombined = 6.44 barSPL = 10 log10 SPL = 10 log10

SPL = 10(9.02)SPL = 90.2 dB

Given: A garbage truck, 100dB, is passed by a motorcycle, 110dB.Find: The combined effect, dBSPL1 = 100dBSPL = 10 log10


100 = 10 log10 log10 = 10 = 1010

SPL2 = 110dBSPL = 10 log10 110 = 10 log10 log10 = 11 = 1011

= 1010 + 1011

= .1x1011 + 1x1011

= 1.1 x1011

SPLsum = 10 log10 = 10 log10 (1.1 x1011)SPLsum = 10(11.04)SPLsum = 110.4 dB combined effect of truck and motorcycle

3. Occupational Noise Exposures 120 dB threshold of pain, humans 150 dB rupture ear drum See handout for various dB levels. Prolonged exposure to noise leads to gradual deterioration of inner ear and deafness. Hearing loss associated with aging presbycusis Hearing loss:

Begins at higher frequencies Difficult to distinguish fricative consonants: f,v,s,z,th,ch,sh, etc.

Constant 90 dB is dangerous; 80 dB is not. OSHA requires controls: 90 dB, maximum daily exposure, 8 hours 95 dB, maximum daily exposure, 4 hours 100 dB, maximum daily exposure, 2 hours Sound is a function of distance and dissipates very quickly. Equation:SPL2 = SPL1 - 20 log10

Example:Given: An automobile registers a sound level of 74 dB at a distance of 20’.Find: The same sound level at 80’.

SPL2 = SPL1 - 20 log10 = 74 - 20 log10

SPL2 = 74 – 12.04SPL2 = 62 dB


4. Noise Controls Reduction of noise at the source, muffler Substitute different machine or operation, electric motor vs. gas Reduction of noise at listener, ear plugs. Education

5. Sonic Boom Objects travelling faster than the speed of sound, air at sea level=740 Boom is produced constantly- not just when object reaches the speed of sound.


The sonic boom cone would appear as follows:


Part II Air Pollution

1. GeneralAir pollution is related to 2 factors: Man’s use of energy Increased concentration of human beings in urban areas.See handout entitled "National Ambient Air Quality Standards"

2. Emission Sources

A. 5 Major Pollutants1.) Hydrocarbons (HC) Partial combustion of fossil fuels.

2.) Carbon Monoxide (CO)Colorless, odorless, tasteless gas. Lessens bloods ability to carry oxygen.

3.) Sulfur Oxides (SOx)SO2 and some SO3. Emitted when fossil fuels containing sulfur impurities are burned.

4.) Nitrogen Oxides (NOx)NO and NO2. Formed when N and O are combined under high temperatures, >2000F conditions e.g. automobile engines, power plants.

5.) ParticulatesSolid or liquid particles. Emitted during combustion or grinding of material. Size and/or chemical problem.

See handout labeled "Air Pollution Levels that Could Cause Significant Harm to the Health of Persons" for effects.

B. Sources Motor vehicles Power plants

3. Smog

A. London SmogCombination of sulfur oxides and particulates


B. Photochemical SmogChemical reactions between hydrocarbons, NOx and sunlight. Primary- NO and HC Secondary:

NO2

O3

Peroxyacetyl nitrate, PAN, CH3CO3NO2

Known as photochemical oxidants.

C. Results of Smog Eye irritant Headache Coughing Exhaustion Death Respiratory diseases:

Bronchitis Emphysema Asthma Lung cancer

4. Particulates Individual aggregates larger than a single molecule .0002 , but smaller than 500

, = 10-6 meters, a micron. Include:

Particulate Form SizeAerosols solid or liquid <1Fumes solids <1Dust solids small sizeMist liquid < 100Soot fine carbon small size

Particulates of interest are from .1 to 10 , about the size of a bacteria. <.1 exhibit Brownian movement and agglomerate to .1; >10 settle quickly as

dust, 7 inches/minute. <1 result largely from the condensation of vaporized material after combustion;

>10 result from mechanical processes. Equation:R = visible range, milesc = particulate concentration, , micro grams per cubic meter.


Example:Given: The California air quality standard is 100 Find: The visibility in miles, when the standard is reached.

R = R 7.5 miles

Adverse health conditions > 80

5. Hazardous Air Pollutants Asbestos- lung cancer, mesothelioma Beryllium – manufacture of beer, rocket firings Mercury – methyl mercury in food, paint, coal power plants.

6. Air Pollution Control Techniques

A. Mobile Sources (cars, etc.) Catalytic converters Minor modifications to internal combustion engines, Volvo > 100mpg Devices added to the exhaust Changes in fuels Unconventional engines e.g. GMs EV-1, and Honda’s new electrical car, H2O cars

B. Stationary Sources See handout entitled "Average Collection Efficiencies of Control Equipment…" 97% of the particulates Changing fuel so that fewer particulates are formed Control equipment:

Settling chamber Cyclone separator Scrubber, water spray Electrostatic precipitators, the particles are charged and removed by an electrical

field Fabric filter bag house

LECTURE NO. 10..........................................................................................................................................1

NOISE AND AIR POLLUTION...................................................................................................................1

PART I NOISE...............................................................................................................................................1

1. SOUND AND HEARING.....................................................................................................................1

2. HUMAN HEARING.............................................................................................................................2

3. OCCUPATIONAL NOISE EXPOSURES.........................................................................................3

4. NOISE CONTROLS.............................................................................................................................4

5. SONIC BOOM......................................................................................................................................4

PART II AIR POLLUTION..........................................................................................................................6

1. GENERAL..................................................................................................................................................6

2. EMISSION SOURCES..............................................................................................................................6

A. 5 MAJOR POLLUTANTS.......................................................................................................................61.) Hydrocarbons (HC).......................................................................................................................62.) Carbon Monoxide (CO)................................................................................................................63.) Sulfur Oxides (SOx).......................................................................................................................64.) Nitrogen Oxides (NOx)..................................................................................................................65.) Particulates...................................................................................................................................6

B. SOURCES.............................................................................................................................................6

3. SMOG..........................................................................................................................................................6

A. LONDON SMOG...................................................................................................................................6B. PHOTOCHEMICAL SMOG.....................................................................................................................7C. RESULTS OF SMOG..............................................................................................................................7

4. PARTICULATES.......................................................................................................................................7

5. HAZARDOUS AIR POLLUTANTS........................................................................................................8

6. AIR POLLUTION CONTROL TECHNIQUES.....................................................................................8

A. MOBILE SOURCES (CARS, ETC.)..........................................................................................................8B. STATIONARY SOURCES.......................................................................................................................8

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