The atmospheric envelope that encompasses the Earth is finite with 99%
of its mass lying within 20 miles of Earth’s surface. A convenient division
od atmosphere in subshperes is based on its temperature characteristics.
The first region , closest to the Earth’s surface, where temperature falls
with increasing latitude (since heating at the surface is due to re-radiation
of sunlight) is Troposphere. In the mid-latitudes its upper limit of about
15 Km, where the minimum temperature is about 2100K, is “tropopause”. Above
the tropopause is the clean, dry, and stable stratosphere where the temperature
starts rising with altitude. The troposphere contains most of the atmosphere’s
water and ,therefore, nearly all clouds, storms, and winds. Of the gases
contained in the lower troposphere nitrogen amounts to about 78%
and oxygen about 21% by volume. The other compounds present include all
the known compounds of hydrogen, nitrogen, and oxygen with carbon monoxide,
carbon dioxide, and methane. There are also many free radicals and ions.
Atmospheric lapse rate: The rate of decrease in atmospheric temperature
with altitude is called the lapse rate. In dry atmosphere it is 5.40F/Km.
During late Fall and winter, when days are getting shorter, the evening
temperature at the surface fall faster than the air above. This inverted
condition is called “thermal inversion”. This inversion layer prevents
the rise of any warm air through it. In the absence of strong winds the
pollutants released under this ceiling may remain trapped there with increasing
concentrations with time. Many industrial and air pollutant releasing sources
can create serious local pollution problems under these conditions.
In addition to these overhead inversions, the upward movement of large
masses of air, such as cyclone, can create a vacuum and cold air can slide
in again reversing the lapse rate. These subsidence inversions are at much
higher level and may occur in the presence of overhead inversions, thus
magnifying the local air pollution problems in cooler seasons. The height
of these inversions determines how much air is available for the dispersion
and dilution of air pollutants and this is called “maximum mixing depth/height.
Winds. The movement of air masses related with temperature differences occurs at global, regional, and local levels. These can determine the transport of air pollutants. Familiarize with this material in a geography or environment book. The vertical barrier to the movement of air, such as tall buildings in cities, mountains in certain regions, etc. Many cities in valleys may have serious pollution problems in cool months.
The local turbulance related with the above factors determines the dispersion and transport of pollutants. Consider a smoke stack from a factory. The shape of the plume and its horizontal and vertical dispersion will be governed by the lapse rate and the prevalent wind. Master the material in the handouts.
Fate of a chemical in air
Familiarize yourself with the physical shape of the pollutant as described
below..
The fate depends on the input (source, kind, rate, etc.), dispersion
(mixing due to advection, turbulance, and wind), transport (vertical and
horizontal by wind), reactions (physical and chemical, such as photolysis,
hydrolysis, adsorption, absorption, etc. This may produce secondary pollutants)
and removal (in precipitation, washout, etc.). The sink/receptor is the
end of this chain. The residence time of a chemical is determined by “
production rate/removal rate”. The time for removal of half of the amount
of the chemical is called “half-life or t1/2.
If half-life is < 6 months then the concentration decreases with time
and distance and local effects are important; if it is more than 6 months
then long-distance transport and regional and global effects, especially
of gaseous pollutants, are more important. In troposphere one coircuit
around the globe takes 15-25 days in kid-latitudes. In stratosphere, due
to lack of rain or snow, the gases can remain for months to years, such
ad CFCs.
FATE
* INPUT
*ATMOSPHERIC FACTORS
DISPERSION : mixing due to advection, turbulance & wind
TRANSPORT : vertical & horizontal wind
REACTIONS : photolysis, hydrolysis
PHYSICAL REACTIONS: adsorption, absorption
REMOVAL : pptation, washout
*OUTPUT : to receptor/ sink
100 I*
I *
I *
I *
I
*
50 I_________ *
(%) I
*
I
*
I
*
I
*
--I------------- ---------------*-------------------
0 1
10
100
Time
Production rate
RESIDENCE TIME (t1/2) = ----------------------------
Removal rate
if >1/2 yr....(gases, small particles)...global/ troposphere
if < 1/2 yr...concn. decrease with time and/ distance...local
t1/2 in:
TROPOSPHERE: a few days to a month
one cicuit around the globe = 15-25 days (mid-latitudes)
STRATOSPHERE: 3 months to 5 yr
(depending on height of injection, particle
size, latitude, season)
The U.S.A. has about 3x1015 tons of air. There are only 12,000 ft available and most pollutants do not rise above 2000 ft. If 0.7 million tons of air pollutants are released daily and uniformly distributed then the concentration will be only a few parts per billion (70 ppb). But, these pollutants are not uniformly released and are concentrated in urban centers. Also, there may be local barriers to dispersion and transport and most of these never rise above 200 feet. So, very high local concentrations are not uncommon, such as 5-10 ppm and in certain areas up to 100 ppm.
In USA 65% people in congested cities are showing serious effects 42%
of these die of diseases caused or worsened by pollution; there are about
30, 000 premature deaths each year because of this. Global city population
has showed increase in death due to emphysema, lung cancer, and chronic
bronchitis.
AIR POLLUTANTS
RURAL: agricultural dusts, particulates, smoke, combustion products,
farm chemicals, and natural products (pollen, terpenes, ,arsh gases, odors,
etc.)
These sources are distributed over large land area with very few people
who live there to get exposed. But certain pesticides are highlt toxic
and can be transported by air, water, and food.
URBAN: About 70% of US population (200 million) lives in cities= 0.75% of US land area. The high density of people produce lot more pollutants on area basis and also get exposed to high levels/capita basis. Situation gets worst if city is close to industrial sources and also has topographic disadvantages. Dirtiness of our cities is proportional to their size.
PHYSICAL NATURE OF AIR POLLUTANTS
Particulates: dust, smoke, fog, smog, etc.
Gases: NOx, SOx, COx, fog
Miscellaneous: noise, heat, radiation, radioactivity, etc.
Another way to classify air pollutants is
Primary pollutants
vapors, gases, mists, fog, aerosols, smoke, smog,
haze, fumes, dusts, radiation, noise, heat
Organis: hydrocarbons, chlorinated
hydrocarbons, etc.
Inorganics: nitrogen, sulfur,
carbon, radiactive metals
Secondary Pollutants
Ozone, formaldehyde, peroxyacyl nitrates
Find out
* How much, as well as where, when, and how the pollutants will reach
the environment
* Fate of the pollutants in the atmosphere (see above)
* Effects on man, animals, plants, and materials
* Inters with other substances to affect their toxicity and fate
FIVE MAJOR CHEMICALS ACCOUNT FOR 98% OF AIR POLLUTION
CO= 48%, SOx= 18%, HC= 12%, particles=12%, NOx=16%
FIVE MAJOR SOURCES OF ABOVE
.....Transportation=60, industries= 18, power plants= 13, space heating=
16, refuse incineration= 3% of total
SOURCES OF LOCAL AIR POLLUTION
...City & Highways....CO, HC, NOx, PAH
...Steel mills, construction...particles
...smelters, refineries, power plants, paper plants..SOx
IN USA: mi tons/yr
...gases= 230, particles 30
TRANSPORTATION noise, gases, vapours, particles
INDUSTRY increase in
size ,unsuitable location
Commercial Combustion gases, particles,
fumes
Power plants 80 % use fossil fuel
56 % coal, 20 % nuclear, l0 % hydro,
5 % oil.
particles, gases, heat,radioactivity,
(C,Si,Fe,Al) (CO ,NO , SO ,CO ,HC,
RCHO, F
Field Burning
Refuse Incineration
NO ,SO , HCl, florides, acids,
plastics, dioxins
Construction gases, dust, particles, mist, fibers,
noise, mists
Chemical : acids, fertilizer, rubber, soap,solvents,
pesticides, paper. leather, textile,oil
toxic & reactive gases, dust, mist,
odours, particles
Metallurgica particles, acids, reactive gases
Agriculture & Food
odours, dust, smoke, poisons, trash,
fungi
Waste-Water & Sewage Treatment
odours, vapours
Space Heating gases
*How much of, as well as where, when, and how, the pollutant will reach the environment
*Fate of the pollutant in the atmosphere (physical, chemical, biological interactions)
*Effects on man, animals, plants, and materials
*Interactions with other substances to make it more or less toxic
Carbon emissions: mi tons in 1990
__________________________________
N.America
1400
Europe
1100
Soviet Union
990
China
510
__________________________________
AIR POLLUTION IN USA
Table. Trends in local average concentrations of air pollutants
__________________________________________________________________________
ppm
1975
1982
1990
_____________________________________________________________________________
NO2
ppm: annual
.34
.31
(.053)
Auto emission(Fed): g/mi
4
.4
production
O3
ppm: daily, l hr (2nd highest) .165
.131
(.12)
SO2
ppm: daily, 24 hr (2nd highest) .08
.048
(.14)
industrial output: tons
7000
5000
CO
ppm: 8 hr (2nd highest)
13
9
(9)
transport: tons
88000
75000
Fed. Std: g/ mile
80
5
TSP
ug/ m3: 24 hr
69
50
mi. tons
10,000
8000
Fed. Std: g/ mile
.3
.03
HC
Fed. Std: g/ mi
11
.25
____________________________________________________________________________________
Table. Emissions in million tons/yr of air pollutants in USA
_____________________________________________________________________________________________
SOURCE
CO
HC
Nox
Sox
Particulate
______________________________________________________________________________________________
COMBUSTION
1. FUEL
Transportation
80 (75)
12
11
1
1
Stationary
1
1
12
26
7
2. INDUSTRIES
9
4
1
7 (5)
10 (8)
3. SOLID WASTE
3
1
0.2
0.1
1
MISCELLANEOUS
5
13
0.2
0.1
1
TOTAL
95
31
24
33
19
_________________________________________________________________________________________
Auto-exhaust limit:ppm (gm/mile)
1976
15
1.5
3.1
(0.6)
1982
3.4(4.7)
0.41(.25)
1.0(.4) (0.03)
HEALTH EFFECTS OF AIR POLLUTANTS
TABLE. LIMITS OF EFFECTS OF AIR POLLUTANTS ON HUMANS
__________________________________________________________________________________________
EFFECT
O3
SO2
NO2
CO
___________________________________________________________________________________________
Absorption
LRT
URT
LRT
Blood
Toxicity: ppm
0.05
0.50
0.25
32
Odor perception: ppm
0.02
0.12
0.09
NONE
Dark adaptation: ppm
0.05
0.075
0.21
NONE
TLV: ppm
0.10
5.0
5.0
50
Severe distress: ppm/
1.5/2h
5-10/10 min
20
100
PULMONARY:
Breathing
up
Tidal Volume
down
down
down
Diffusion
down
down
Compliance
down
down
down
down
Airflow resistance
up
up
up
Other
down=FEV,
cough,
Met-Hb
CO-Hb
Vit.cap
sputum
Chronic
Fibrosis
yes
yes
yes
Bronchiolitis
yes
yes
Pneumonia
yes
yes
Emphysema
yes
Bronchogenic CA yes
Edema
yes
yes
______________________________________________________________________________________________
OZONE
Pulmonary effects
Other effects
premature aging, calcification of thoracic
cartilage, body fat depletion,
dull cornea, sagging conjuctiva
Mice: fewer implants in matings from O3-exposed males, litter size
lower, neonatal survival lower
Free radicals, peroxides-related damage
*SH-oxidation……….GSH depletion
*Lipid peroxidation…..fatty acid ozonides, membrane damage, membrane
enzymes (P450) reduced
*Blood: sphering of rbc, breakage of lynphocytes, Hb oxygenation lowered
*Brain: serotonin lowered
*Parathyroid: alteration
NITROGEN DIOXIDE
Less soluble, but 4-time more toxic, than SO2
Initial latent period to reach alveoli
+ other pollutants (SO2, particles, smoke, cigarette
smoke, etc.)..additive
ACUTE
Odor perceived at 1 ppm
5-10 ppm / 10 min…narrowing of
airways…flow resistance
13 ppm……………….mucus membranes irritated
100-150 ppm/30 min bronchiole obliteration
fatal, pulmonary edema..death (silo fillers)
CHRONIC
Russia…..Trainees in Fertilizer Cos….3-5 yr
exposure….COPD, blood changes,
bronchioneumonia, inflammation, respiratory
infections
USA……Chitanooga, TN
Children more sensitive to respiratory
infection later in life
SULFUR DIOXIDE
Low concn..< 1ppm LRT
Very high concn…URT
Asthma, chronic bronchitis, ENT irritation…as warning symptoms
10-30 min exposure
1 ppm: 10% airflow resistance
<5 ppm…39% air flow resistance (over the controls)
..chronic mild respiratory irritation
>5 ppm..slight decrease in pulmonary spasm,
in sensitives* ..severe spasm < 1ppm
13 ppm..72% airflow resistance..reversible
20 ppm..water logging…..respiratory paralysis
*= aged, sick, smokers ( 0.2 ppm= ER, physician calls,
absentees, deaths)
Rat
Chronic exposure
Thickening (in trachea) & hypertrophy of mucus cells (in
bronchi)
= chronic bronchitis, ciliary mucus transport decreased
Acute exposure
10 ppm : cilia paralyzed in 5 min
50 ppm/ 6hr: tracheal epithelium damaged, mucus cells destroyed
Dogs, cats, guinea pigs
Mild bronchial constriction, airflow resistance.. compliance (deep
breathing)
SO3 + H2O = H2SO4
ratio of sulfuric acid to sulfur dioxide
varies from 0.03-0.25
depends on amounts of: misture, sunlight, pptation, SO2 half-life
in air, catalytic particles
SO2 synergism= NaCl, KCl, Va salts
LONDON
Jan. 1956: 0.4 ppm of SO2 + H2SO4 + smoke
4,000 deaths of 70 + olds
diary kept: chronic broncitis worst on
0.19 ppm
CHICAGO
Oct-Dec.: increase coughing, breathing difficulty, purulant sputum
57+ year olds sensitive
socioeconomic groups, sick
*atropine can relieve spasm (cat) and histamine can aggravate (Guine
pigs)
Airway resistance: mostly in medium-sized bronchioles < 2mm dia..cause
20% of resistance
Large airway irritation(flow), peipheral lung irritation (compliance),
cigarette smoke, irritants, chronic bronchitis, asthma
FEV(closing volume) change: indicates restrictive or obstructive
flow
Fibrosis: trachea, bronchi: interstitial &
endothelial
Impaired Ventilation: breathing rate & depth
Diffusion: perfusion & ventilation, blood pH
increased alveolar thickening: interstitial fibrosis, increased
thickenening of epithelia, replaced with cuboidal cells, fibroblasts, muscle
cells, collagen fibers
due to: asbestosis, alveolar cell CA, sarcoidosis
area decreased: alveolar cells & connective tissue destroyed, alveolar
ducts & terminal bronchioles distended, emphysema
COMPLIANCE: lung expansion/elasticity
caused by: pulmonary fibrosis, pleural thickening, scarring, atelactasis,
LV failure,
emphysema, old age
More information about Natural Air Pollutant Emition Trends, Ambient Air Quality Status, and Criteria pollutants are available at the following Web Sites.