Environmental Chemistry
Chapter 2:
Ground-Level Air Pollution—
Outdoors and Indoors
Copyright © 2007 by DBS
Cartoon
Part 1 – Ground Level Air Pollution
Ozone (smog) and particulate pollution (soot) are two of
the biggest pollution hazards for public health in the US
The main sources of harmful smog and soot are
tailpipes and smokestacks – from factories and power
plants, dieselpowered trucks, buses, ships, boats,
locomotives and tractors
http://www.environmentaldefense.org
Smog
This 1963 photo shows
a massive smog
episode in New York
City
(Photo: AP/Wide World Photo,
EPA Journal Jan/Feb 1990.)
Industrial pollution
around the Siberian city
of Troitsk
(54.0N, 61.0E).
Troitsk is the smallest of
a group of three heavy
industrial cities east of
the Urals, the other
being Magnitogorsk and
Chelyabinsk.
All have been cited as
being some of the worst
industrial polluted cities.
http://www.ametsoc.org
Photochemical Smog
Photochemical Smog
NASA October 2000
In China, Cloud-free Days Do
Not Mean Sunshine; Smog Is
To Blame
China
January 18, 2006
China has darkened over the
past half-century. Where has all
the sunshine gone? Eliminating
clouds from the dimming
equation now leaves little doubt
that human activity, in the form
of a nine-fold increase in fossil
fuel emissions over the same
half-century period, has
entrenched China in a foggy
haze that absorbs and deflects
the sun's rays
Qian et al., 2006
Over the past half century, sunlight reaching the
surface in China has decreased (upper left),
along with surface evaporation (upper right).
Without an extenuating circumstance,
climatologists would expect to find increased
cloudiness. But, in fact, they found the opposite
(lower left), along with more frequent clear skies
for the same period (lower right).
The likely culprit: a sun-choking haze from a
nine-fold increase in air pollution.
(Source: Pacific Northwest National Laboratory)
Concentration Units for Atm. Pollutants
•
•
Commonly expressed as ppm, ppb, ppt
Also expressed in terms of
– molecules cm-3
– mol L-1
– Microgramsof a substance per cubic meter µg m-3
See page 68, 69 for inter conversion of units. We already worked through
problems in earlier class
Primary pollutants
– NOx Oxides of nitrogen (NO and NO2)
– SOx Oxides of sulfur (SO2) and VOCs Volatile organic compounds
(hydrocarbons, ethene etc.)
Secondary pollutants
– O3, HNO3, H2SO4, peroxyacetylnitrate (PAN)
Table 2-1
Question
Which of the following gases found in troposphere
are primary pollutants?
O3
NO
HNO3
CH4
PAN
H2C=O
H2C=CH2
VOC
HOO
NO2
H2SO4
SO2
CO
CH3Br
NH3
O
Oxidation by OH
•
The naturally released gases are eventually oxidized to oxides
-but not by direct reaction with O2
•
Hydroxyl Radicals (•OH) produced in the environment serves as an oxidant (Conc.
In the atmosphere is small and it is very shortlived)
O3 + UV-B → O2 + O*
O* + H2O → 2 •OH
Formation via O* occurs
far quicker than with O
•
OH radical is referred as Troposphere vacuum cleaner or detergent
e.g.,
CH4 + 4 •OH → CO2 + 2H2O
•
Because the lifetime of hydroxyl radical is short (~1s) constant regeneration is
essential
- OH radical concentration drops quickly at night
Auto Pollution
•
Burning a gallon of gasoline releases 8.9 kg
of CO2 into the atmosphere.
•
Carbon emissions make up 84 percent of the US
emissions of greenhouse gases, and motor vehicles
•
It accounts for 20 percent of U.S. carbon emissions
•
HC’s, NOx, and CO emitted during combustion of gasoline constitute other
major pollutants
Carbon dioxide emissions differ from several other vehicle pollutants in that
they are unregulated. For emissions of HC’s and CO, for example, the federal
government sets a limit of so many grams per mile driven. Vehicles must have
pollution-control equipment (and, in some states, periodic emission
inspections) to meet those limits.
Emissions from Cars,
Power Plants and Industry
Emissions from N. America
Source: EPA National Emissions Inventory (NEI) Air
Pollutant Emissions Trends Data
Air Pollution
•
•
Historic air pollution problem was high levels of
smoke and SO2 arising from the combustion of
sulfur-containing fossil fuels
Major threat now posed by automobiles, principally
CO, NOx, VOCs and particulates (PM10)
– Photochemical reactions of NO2 and VOCs
from vehicles leads to the formation of O3, a
secondary long range pollutant
– Acid rain is another long-range pollutant
influenced by vehicle NOx emissions
SO2
CO
NOx
Pb
HC’s/VOC’s
PM
O3
Smog
Acid Rain
Toxic Organics
CO2???
Photochemical Smog
Photochemical smog formation
1) Nitrogen oxides generate oxygen atoms
2) Oxygen atoms form ozone and hydroxyl radicals
3) Hydroxyl radicals generate hydrocarbon radicals
4) Hydrocarbon radicals form hydrocarbon peroxides
5) Hydrocarbon peroxides form aldehydes
6) Aldehydes form aldehyde peroxides
7) Aldehyde peroxides form peroxyacylnitrates
Urban atmospheres have been
referred to as chemical soups!
Photochemical Smog
• NO and unburnt hydrocarbons (VOCs) are the primary reactants
of photochemical smog formation
VOCs + NO + O2 + sunlight → mixture of O3, HNO3, organics, free radicals
• More free radicals are formed than consumed in smog because
of the reaction of VOCs
• Reaction products such as aldehydes absorb UV-B and some
UV-A to produce additional free radicals
NOx Production
Combustion or Thermal NO: N2 + O2 ⇌ 2NO
H = +180 kJ mol-1
(Occurs only at high temp. (lightning/engines) because of high activation energy)
Fuel NO: NX + O2 → yNOx
(Occurs during combustion of nitrogen compounds)
•
•
NO slowly oxidizes (+O2) to NO2 – takes other routes
Collectively NO and NO2 are referred as NOx
NO2 absorbs in the UV-visible
(absorption in the 400 nm region is
visualized by yellow color)
NO2 + UV→ 2NO + O
O + O2 + → O3
Thus Ozone becomes the main
product of smog
Steady-State Analysis
NO2 → NO + O
O + O2 → O 3
NO + O3 → NO2 + O2
(1)
(2)
(3)
At steady state for ozone: d[O3]/dt = 0 = k2[O][O2] – k3[NO][O3]
At steady state for oxygen atom d[O]/dt= 0= k1[NO2] -k2 [O][O2]
Adding the two expressions:
0 = k2[O][O2] – k3[NO][O3] + k1[NO2] -k2[O][O2]
k3[NO][O3] = k1[NO2]
k3[O3]/k1 = [NO2] / [NO]
Summary of PC Smog Reactions
Sunlight, NOx and VOCs contribute to the smog by undergoing a series of
chemical reactions involving free radicals as catalysts
…We will revisit again when we discuss Chapter 3
Daily Variation
Oxidant = O3 does not rise until NO has been
reduced due to reaction with O3
•
A.M. traffic increases NOx and
VOCs as we drive to work
•
Later, traffic dies down and the
NO and VOC’s begin to react
forming NO2
•
As sunlight becomes more intense
NO2 is broken down and its
byproducts form increasing O3
•
As the sun sets, the production of
O3 is halted
•
O3 that remains in the atmosphere
is then consumed by several
different reactions
Ninetieth percentiles
of summer afternoon
ozone conc, in ppb
(conc. higher than
this 10% of the time)
Maximum surface
ozone levels in ppm
In Mexico city ozone levels
reached as high as 400 ppb
(310 days in1992)
Ground Level O3 Formation
•
The same O3 molecules that protect us
from UV high in the stratosphere can
cause health problems for people and
animals near the Earth's surface
•
Ground-level O3 is formed when
vehicle/power plant exhaust and some
other chemicals commonly use in
industry mix in strong sunlight
•
When the O3 concentrations get high
enough, they can make breathing
difficult, especially for people with
asthma and other respiratory diseases
•
EPA's O3 mapping site provides
information on ozone levels in many US
cities
O3 in the Troposphere
•
O3 concentrations in the troposphere vary widely over the Earth’s surface. The
more direct the angle of sunlight, the greater its intensity. Where O3 precursors
exist, more O3 tends to occur in regions closer to the Equator (lower latitudes)
than in regions at the poles (higher latitudes)
•
O3 concentrations also vary through time, throughout the day and through the
year. The highest O3 concentrations of the year generally occur during summer,
when sunlight is most intense
Ozone tolerance levels:
In clean air
30 ppb
WHO limit 75-100 ppb (50/60 for 8hr)
Canada
82
US
80 ppb/8hr period
The ozone levels in West coast and east coast cites, midwest and texas reach as
high as 300 ppb at peak
…The Bad
•
•
•
Damages forests and crops; destroys nylon, rubber, and other
materials; and injures or destroys living tissue
A threat to people who exercise outdoors or with respiratory problems
High concentrations of O3 cause plants to close their stomata ( cells on
the underside of the plant that allow CO2 and H2O to diffuse into the
tissue. This slows down photosynthesis and plant growth. O3 may also
enter the plants through the stomata and directly damage internal cells
Rubber, textile dyes, fibers,
and certain paints may be
weakened or damaged by
exposure to ozone.
Some elastic materials can
become brittle and crack,
while paints and fabric dyes
may fade more quickly
Source: http://www.ucar.edu
Health Effects
Ozone can
inflame the
lung's lining
Ozone can irritate your respiratory system
Ozone can reduce lung function and make it more difficult for you to
breathe as deeply and vigorously as you normally would
Ozone can aggravate asthma. When ozone levels are high, more
people with asthma have attacks that require a doctor's attention or the
use of additional medication. Also, asthmatics are more severely
affected by the reduced lung function and irritation that ozone causes in
the respiratory system
Healthy Lung
Ozone can inflame and damage cells that line your lungs. Within a
few days, the damaged cells are replaced and the old cells are shedmuch in the way your skin peels after a sunburn
Ozone may aggravate chronic lung diseases such as emphysema
and bronchitis and reduce the immune system's ability to fight off
bacterial infections in the respiratory system
Ozone may cause permanent lung damage. Repeated shortterm
ozone damage to children's developing lungs may lead to reduced lung
function in adulthood
Lung Lining
Inflamed by O3
Source: http://airnow.gov
AQI
•
•
•
The Air Quality Index is a
scale used to report actual
levels of O3 and other
common pollutants
The higher the AQI value,
the greater the health
concern
As shown in the table, the
AQI scale is divided into
categories that correspond
to different levels of health
concern
Action days are usually called when the AQI gets into the unhealthy ranges. Different air
pollution control agencies call them at different levels. In some places, action days are
called when the AQI is forecast to be Unhealthy for Sensitive Groups, or Code Orange
Source: http://airnow.gov
Limiting VOC and NOx Emissions to
Reduce Ground Level O3
•
If NOx is 0.20 ppm
reduction in VOC
of 0.5 to 0.4 ppm
will result in
decrease of O3
from 160 to 80
ppb
•
Decreasing VOCs
from 1.6 to 1.0 has
little effect on O3
concentration
Laws
•
In 1955, after many state and local governments had passed legislation
dealing with air pollution, the federal government decided that this
problem needed to be dealt with on a national level. This was the year
Congress passed the Air Pollution Control Act of 1955, the nation's first
piece of federal legislation on this issue. The language of the bill identified
air pollution as a national problem and announced that research and
additional steps to improve the situation needed to be taken. It was an act
to make the nation more aware of this environmental hazard.
Eight years later, Congress passed the nation's
Clean Air Act of 1963. This act dealt with reducing
air pollution by setting emissions standards for
stationary sources such as power plants and steel
mills
Clean air act was amended in 1970 and 1990
Source: http://www.ametsoc.org/sloan/cleanair/
Principal provisions :
1970: Clean Air Act
1. Establishing National Ambient Air Quality Standards (NAAQS). The law requires
that EPA identify and set standards for pollutants identified as harmful to human
health and the environment
The six "criteria" pollutants are:
Carbon monoxide
Nitrogen dioxide
Ozone
Sulfur dioxide
Particulate matter with aerodynamic size less than or equal to 10 μm (PM-10)
Lead.
2. Primary and Secondary Standards. The Clean Air Act establilshes two categories
of air quality standards: Primary standards set limits to protect public health.
Secondary standards set limits to protect against public welfare effects, such as
damage to farm crops and vegetation
3. Leaded gasoline phasedown. The law requires leaded gas to be phased out by
the mid-1980s — one of the single most important and successful environmental
health initiatives of the last century
Economy vs. Regulation
New Source Review. In 1970 Congress had assumed that older industrial facilities, such as
power plants and refineries, would be phased out of production, so they were exempted
from the legislation. But when these big polluters continued to operate and emit pollution
at much higher levels than new facilities that were built with modern pollution-control
equipment, lawmakers knew they had to act
2002: NSR Rollback Initiative
On Dec. 31, 2002 the Bush administration announces significant rollbacks to New Source Review
pollution control provisions
1. New rules will allow virtually all pollution increases from old, high-polluting sources to go unregulated.
EPA will allow companies to avoid updating emission controls if their plant’s equipment has been
reviewed at any time within the past decade, and the measures used to calculate emissions levels will be
reconfigured
2. The review process built into NSR will be drastically scaled back. Communities will now not know
when a nearby power plant is increasing the amount of pollutants pumped into their backyards
2003: Senate Rolls Back NSR
An attempt by Sen. John Edwards (D-NC) to postpone a rollback of the New Source Review rules is
defeated in the Senate (46-50) during amendment votes on the 2003 budget bill; a competing
amendment by Sen. James Inhofe (R-OK) wins (51-46), clearing the way for the Clean Air Act rollback.
http://www.environmentaldefense.org
Nitrogen Oxides Control Strategies
1. Install catalytic converters:
catalytic converters in
automobiles can remove 76% of
NOx from tailpipes
2. Lower the combustion
temperature of the furnace in
electric power plants
Efficiency of CC’s
An O2 sensor & computer
chip monitor the intake of
air/fuel ratio
After the engine warm up
catalytic converter removes
80-90% of CO, NOx and
HC’s
Dependence on the air:fuel ratio
3-way catalytic converter for automobile
exhaust (Remove CO, NO and HC)
Control of Nitrogen Oxides (NOx) from Smoke Stacks
Emisson from power plants is almost equal to the amounts of NOx emitted
by vehicles! Regulations require to control the emission of power plants
Measures to reduce NOx include
- Combustion of fuel in stages
- Addition of Ammonia to the cooled gas stream
4NH3 + 4NO + O2 → 4N2 + 6H2O
- Wet scrubbing of exhaust gaes with aqueous solution more
effective with NaOH
2NaOH + NO + NO2 → 2NaNO2 + H2O
- Urea reduction of NO
2CO(NH2)2 + 6NO → 5 N2 + 2 CO2 + 4 H2O
Summary
http://jan.ucc.nau.edu/~doetqp-p
Question
Deduce the balanced equation in which ammonia reacts with
nitrogen dioxide to produce molecular oxygen and water. How much
ammonia is needed to react 1000 L of air containing 10 ppm NO2?
8 NH3 + 6NO2 → 7N2 + 12H2O
10 ppm of NO2 corresponds to 10 L of NO2 in 106 L of air
Or
(10L NO2/106 L air) x 1000 L = 0.01 L of NO2
For 6 parts of NO2 we need 8 parts NH3
Or
0.01 L x (8L NH3/6L NO2) = 0.0133 L of NH3
From the ideal gas law, n = PV/RT
n= (1 atm x 0.0133L)/(0.082 L atm mol-1 K-1 x 300 K) = 0.00054 moles of NH3
Or 0.00054 x 17 = 0.0092 grams of ammonia is needed for neutralization
Some Successful Results and Future
Reductions
Five of six components of direct emission
(CO,VOCs,SO2, partculate matter and lead) in
the US fell significantly during 1970 – 2000
•
NOx on the other hand grew by 20% with half
that increase during 90’s
•
Energy consumption in 90’s increased by 45%
and vehicle traveled distances by 143%
•
This increase in NOx has resulted in some
increase in ozone concentration
•
US committed to reducing NOx 35% by 2007
•
Sulfur levels will also be decreased – this
should improve the efficiency of catalytic
converters
http://www.epa.gov
New weapon in fight against smog
STOCKHOLM, Sweden (AP) -- From catalytic converters to alternative
fuels, the fight against big-city smog has for years been fought inside
combustion engines and exhaust pipes
Now, scientists are taking the fight to the
streets by developing "smart" building
materials designed to clean the air with a
little help from the elements
TiO2 photocatalyst can oxidize VOCs and
thus minimize ozone production
Its use as smog abating tool is a new
concept and yet to be used widely
http://www.cnn.com/2005/TECH/07/22/smog
.scrubbing.surface.ap/
Source: http://www.photocatalyst.co.jp/e/index.htm
Indoor Air Pollution
Indoor air quality is important since people spend more times indoors than
outdoors
Source: burn coal & wood; carpet, tobacco smoke
Formaldehyde: H2C=O,
– Stable intermediate of oxidation product of methane
– Can reach up to 1000 ppb (1 ppm) ……as compared to 10 ppb outdoors
Nitrogen Dioxide: NO2
– Homes that burn of natural gas (stove, heater, furnace) or kerosene have
higher level of NO2
Carbon Monoxide: CO
– Colorless, odorless gas whose concentration indoors increases from
incomplete burning of carbon based fuels.
Tobacco Smoke
– Refers to a family of six naturally occurring silicate minerals that are
fibrous. ……causes lung cancer
Read more about indoor pollutants in the textbook p127-135)
Question
Carbon monoxide binds to hemoglobin 320 times more effectively than oxygen does. Continuous
exposure of more than 50 ppm CO is accompanied by some observable impairment, 250 ppm results in
loss of consciousness and 750 ppm can result in death. A room having the dimension 4 m x 3 m x 8 m
is kept at 20°C by a natural gas (CH4) space heater.
Write the two balanced chemical equations for the combustion of CH4 to produce (1) CO2 and
water and (2) CO and water
CH4 + 2O2 → CO2 + 2H2O
(1)
CH4 + 3/2 O2 → CO + 2H2O (2)
The fuel-air mixture of the heater is running slightly rich (CH4:O2 ratio of 1.00:1.92)
resulting in some incomplete combustion to CO2. Calculate what percent of the total
carbon oxides produced is carbon monoxide
CH4:O2 is 1:1.92
A combination of the two reactions above (Eq. (1) and (2)) occurs. Let x represent the
contribution of Equation (2) and 1-x the contribution of Equation (1)
1.92 = 2(1-x) + 1.5(x)
x = 0.16
 16% of the total carbon oxide gases are CO.
The heater combusts 10.0 g of methane per hour. Assuming all
the carbon monoxide from the heater is expelled into the room
Question
and there is no ventilation,
how long will it take before there is a
danger of losing consciousness?
Moles (CH4) = mass(CH4) = 10.0 g
M(CH4)
= 0.623 mol
16.042 g/mol
Moles (CO) = (0.623 mol)(0.16) = 9.97 x 10-2 mol
P(CO) = nRT/V = 9.97 x 10-2 mol x 0.0821 atm K-1 mol-1 x 293K = 2.5 x 10-5 atm
9.6 x 104 L
At 1 atm.
ppm (CO) = 2.50 x 10-5 atm x 1000 mb = 0.025 mb (ppt)
1 atm
Time to reach 250 ppm = 250 ppm
=10 hr
X 1000/1000 =
ppm
25 ppm/hr
In 10 hrs there is a danger of an occupant losing conciousness
President Bush on Energy and Environment
STATE OF THE UNION ADDRESS
January 31, 2006
President Bush on Energy and
Environment
Keeping America competitive requires affordable energy. Here we have a
serious problem: America is addicted to oil, which is often imported from
unstable parts of the world.
So tonight, I announce the Advanced Energy Initiative a 22-percent increase in
clean-energy research at the Department of Energy, to push for breakthroughs
in two vital areas. To change how we power our homes and offices, we will
invest more in zero-emission coal-fired plants; revolutionary solar and wind
technologies; and clean, safe nuclear energy.
We will increase our research in better batteries for hybrid and electric cars, and
in pollution-free cars that run on hydrogen. We will also fund additional research
in cutting-edge methods of producing ethanol,
Audio: http://www.pbs.org/newshour/indepth_coverage/white_house/sotu2006/
Part 2 – Acid Rain
Review
• Combustion of sulfur-containing fossil fuels such as coal is the
major source of SOx
• Gasoline and diesel-powered motor vehicles emit a wide variety
of pollutants, CO, NOx, VOCs and particulates (PM10)
• NO and unburnt hydrocarbons (VOC) are the primary reactants
responsible for photochemical smog formation
VOCs + NO + O2 + sunlight
→ mixture of O3, HNO3, organics, free radicals
Atmospheric Deposition
Wet Deposition
The process of removing gases and
particles from the atmosphere by
rain, snow, sleet, or fog
Dry Deposition
The process through which gases
and particles are removed from the
atmosphere in the absence of
Precipitation
http://nadp.sws.uiuc.edu
The National Atmospheric Deposition Program (NADP) monitors wet atmospheric deposition at
250 National Trends Network sites throughout the United States. The USGS supports 74 of the
roughly 250 active NADP/NTN sites. A fundamental NADP program objective is to provide
scientific investigators world-wide with a long-term, high-quality database of atmospheric
deposition for research support in the areas of air quality, water quality, agricultural effects, forest
productivity, materials effects, ecosystem studies, watershed studies and human health.
Acid Rain
• Natural rain water has dissolved CO2 which forms carbonic acid
(weak acid)
CO2 + H2O ⇌ H2CO3
Ka = 10-1.5
H2CO3 ⇌ H+ + HCO3-
Ka = 10-6.4
• Natural rain water pH of 5.6. Rain water with pH < 5 is acid rain
• Two predominant acids responsible for the acid rain are
H2SO4 and HNO3
• This pollution is not limited by state or country boundaries!
Acid Rain
Cross-boundary Pollution
•
Results from technological fix of local
air pollution – build taller chimneys
•
A large portion of SO2 and NO2
produced in one country is exported
to others by prevailing surface winds
•
More than half the acid deposition in
heavily populated southern Canada
originates from seven central and
upper midwestern states –
OH, IN, PA, IL, MO, WV, and TN
http://nadp.sws.uiuc.edu
SOx
Sulfur dioxide emissions are
highest in regions with
many coal-fired electric
power plants, steel mills,
and other heavy industries
that rely on coal.
SOx and NOx
Allegheny County, in
western Pennsylvania, is
just such an area, and in
1990 it led the United
States in atmospheric SO2
concentration.
NOx
The highest NOx emissions are generally found in states with large urban areas,
high population density, and heavy automobile traffic. Therefore, it is not
surprising that the highest levels of atmospheric NO2 are measured over Los
Angeles County, the car capital of the country.
Total US Emissions
Source: “Acid Rain Revisited”,
A Science Links™ Publication of the Hubbard Brook Research Foundation
Effects of Acid Rain
•
•
Acidification of surface water (lakes, rivers, etc), and subsequent
damage to aquatic ecosystems.
– kills aquatic plants, fish and microorganisms in lakes and streams
by releasing ions of Al, Pb, Hg and Cd from soils and sediments.
Damage to forests and vegetation
– Weakens or kills trees, especially conifers at high elevations;
– Makes trees more susceptible to diseases, insects, drought, and
fungi and mosses that thrive under acidic conditions;
– Stunts growth of crops such as tomatoes, soybeans, spinach,
carrots, broccoli and cotton
Damage to Buildings and Statues
1944
CaCO3(s) + H+ → Ca2+ + HCO3- (aq)
HCO3-(aq) + H+(aq) → H2CO3 (aq) → CO2 (g) + H2O(aq)
2004
Ions in Pure Water
Review of pH
•
•
•
The pH of a solution is a measure of the concentration of the H+ ions
present in that solution
The mathematical expression for pH is a log-based scale and is
represented as:
pH = -log10[H+]
So for a solution with:
[H+] = 1.0 x 10-3 M, the pH = -log [1.0 x 10-3], or -(-3.00) = 3.00
Since pH is a log scale based on 10, a pH change of 1 unit represents a power of 10
change in [H+]
That is, a solution with a pH of 2 has a [H+] ten times that of a solution with a pH of 3
Review of pH
•
SF when taking logarithms: The log of a number should have the same
number of SF in its mantissa as there are SF in the number you are taking the
log of
Given [H+] = 4.29 x 10-5 M, what is the pH (expressed with the correct # SF?
- log[4.29 x 10-5] = 4.3675427 (not rounded yet)
Correct answer: pH = 4.368
•
SF when taking antilogs: The antilog of a number should have the same
number of SF as appears in the mantissa of the number you are taking the
antilog of.
Given a pH = 8.72, what is [H+]?
antilog [-8.72] = 10-8.72 = 1.9054607 x 10-9 (not rounded)
Correct answer: [H+] = 1.9 x 10-9 M
pH Value of Pure Water
KW = [H+][OH-]
-logKW = -log[H+] – log[OH-]
pKW = pH + pOH
In pure water, autoionization is the only source of ions, therefore:
[H+] = [OH-] = 10-7 M
pH = 7
A pH of 7 defines neutrality, pH < 7 means acidic and pH > 7 is
basic
What is the pH of natural rain water?
pH of natural rain water is determined by acidic and basic species that are
naturally present in the atmosphere.
CO2: 370 ppm = 370 x 10-6 atm
CO2(g) + H2O ⇌ H2CO3 (aq)
Ka1 = 10-1.5
H2CO3(aq) ⇌ H+(aq) + HCO3-(aq)
Ka2 = 10-6.4
[H+] ~ [HCO3-]
Ka1 = [H2CO3]
[CO2]
Ka2 = [H+][HCO3-]
[H2CO3]
Ka1 = [H2CO3]
PCO2
Ka2 = [H+]2
[H2CO3]
10-1.5 = [H2CO3]
370 x 10-6
[H+]2 = Ka2[H2CO3] = 10-6.4 x 1 x 10-5 = 4 x 10-12
[H+] = 2 x 10-6
[H2CO3] = 1 x 10-5 M
pH = -log10[2 x 10-6] = 5.7
Rainwater
•
•
•
Rainwater has a pH of 5.7. If CO2 is
the only species that affects its acidity
When additional acidic species are
present at appreciable levels as a
result of man-made activities, pH of
rain water becomes lower than 5.7 →
Acid rain
H2SO4 and HNO3 are the major
contributors to acid rain.
Both substances are formed in the air
– Precursor to H2SO4: SO2
– Precursor to HNO3: NO2
Concentrations of the precursors SO2 and NO2 are greatly
increased by fossil fuel combustion
The Source and the Cause of Acid Rain
Example:
The burning of coal.
Coal contains 1-3% sulfur
S(s) + O2(g)
2 SO2(g) + O2(g)
SO2(g) + H2O(l)
SO3(g) + H2O(l)
SO2(g)
2 SO3(g)
H2SO3(aq)
H2SO4(aq)
And then: H2SO4(aq)
2 H+(aq) + SO42-(aq)
sulfurous acid
sulfuric acid
Note:
Note:
• NO is not very soluble in H2O
• H2SO3 formed from the dissolution of SO2 in water is a weak
acid
• Thus primary pollutants themselves do not directly increase the
acidity of rain water. However over periods of hours and days
these weak acids get converted to string acids, HNO3 and
H2SO4
Problem 9
If the pH of the rainfall is 4.0 and half the acidity is due to HNO3 and half
due to H2SO4, calculate the mass of the primary pollutants NO and SO2
that are required to acidify 1L of rain
Since pH is 4.0, [H+] = 10-4 M (Recall pH = -log10[H+])
H+ obtained from dissociation of HNO3 and H2SO4 is 10-4/2 = 5 x 10-5 M
[HNO3] = 5 x 10-5 M and [H2SO4] =2.5 x 10-5 M (two H+ for 1 H2SO4)
Since 1 mole of HNO3 results from 1 mole of NO
5x10-5 moles of NO = 5x10-5 mol x (30g mol-1) = 0.0005 g NO
Since 1 mole of H2SO4 results from 1 mole of SO2
2.5 x 10-5 mols of SO2 = 2.5 x 10-5 mol x (64.1g mol-1) = 0.0016 g SO2
The Ecological Effects of Acid Rain
Major problems in Europe
and East Coast.
Ohio Valley pollution is
responsible or the acid
rain in Ontario
Global Pattern of acidity pattern
June 23 1980
Neutralization of Soil by Acid Rain
In North America most of
the acidity comes from
the burning of high sulfur
content coal in power
plants
The effect of acid rain on
biological life depends
upon the composition of
soil and bedrock in the
Area
– Acid Neutralizing Capacity
(ANC)
Regions of North America with low soil alkalinity
Neutralization of Acid Rain by soil
CaCO3(s) + H+ → Ca2+ + HCO3-(aq)
HCO3-(aq) + H+(aq) → H2CO3(aq) → CO2(g) + H2O(aq)
Acidity from the rain deteriorates soil by
removing plant nutrients:
K+, Ca2+, Mg2+ attached to –ve sites on
clay and organic matter
H+ trades places and is retained
‘Base cations’ K+, Ca2+, Mg2+ leached into
subsoil or washed away
Neutralization of Acid Rain by soil
Although SO2 emissions have
decreased over the years, rain
acidity remains high(lack of fly ash
emission which used to neutralize
acidity)
Thousands of lakes have become
strongly acidified
The acid rain problem of Northeast
now extends to southeast
Wet sulfate deposition
Neutralization of Acid Rain by soil
Hubbard Brook
New Hampshire experimental station
Half of Ca2+ and Mg2+ leached by 1996, vegetative growth almost stopped
Release of Aluminum into Soil and Water
Bodies by Acid Rain
Acidified lakes also possess elevated concentrations
of Al3+ ions - leached from rocks and soil (exchanged with H+)
Decreases fish populations
Havas and Jaworski, 1986
Thoughts for Future
Mandatory implementation of catalyst converter in automobiles enabled the
control of SOx and NOx emissions. No such requirement exists for home
heating systems. What is your thought on recommending only high efficiency
(95+%) home furnaces?
How to control CO2 emission?
Do you think using electric cars, Liquefied Natural Gas or Hydrogen fuel cell
driven cars can reduce the emission?
With increasing energy demand increased amount of coal and natural as
burning will be necessary. Do you think additional treatment of smokestack
emissions is necessary?
Should we consider nuclear energy as an alternative source to meet our energy
demand?
Part 3 – Particulate Matter
Glossary
Particulate Matter
A complex mixture of solid particles and liquid droplets found in the air
"Where Does Tread Rubber Go?"
“It is estimated that more than 600,000 metric tons of tire tread are worn off
American vehicles every year. Instead of leaving black smudges on the
highways, tiny particles of tread are worn off tires and are released into the air.”
by Peggy J. Fisher President of Fleet Tire Consulting, Rochester Hills, MI
Over 80% of respirable particulate matter (PM10) in
cities comes from road transport and that tire and
brake wear are responsible for the 3-7% emission of
it
10 μm
Tire debris eluates contain zinc, and we have
demonstrated that this metal can accumulate in
cells, and affect X. laevis embryos [frog]
Gualtieri et al., 2005
1 μm
http://www.particleandfibretoxicology.com/content/2/1/1
Sizes of Common Airborne Particles
e.g NH4Cl,
SO42- / NO3- salts
Mineral dust from
weathering of rocks
and soils
Fine
Coarse
1 nm
Natural: forest fires,
volcanoes etc.
Man-made: fossil-fuel
combustion, industry
Chemical composition
can be used to ID source
Course - basic
Fine - acidic
Sizes of Common Airborne Particles
Settling Velocity
Stoke’s Law
Equating this frictional force with the gravitational force:
vt = 2 r2 g (ρs - ρf )
9μ
where: Vt = settling velocity, r = radius, g = gravity, ρs = density
of the particles, and ρf = density of the medium,  = viscosity
Settling velocity increases with square of radius – smaller particles are
suspended
Sources of Coarse Particles
•
Most coarse particles are primary pollutants
•
Natural sources: Soil dusts, (similar composition to soil or rocks – Al, Ca, Si, O),
sand, sea salt spray, forest fire debris, leaf litter, pollen, volcanic eruptions
•
Man-made sources: vehicle exhaust , stone crushing, land cultivation
•
Basic due to high soil content
May begin
existence as
coarser matter
Sources of Fine Particles
•
Most fine particles are secondary pollutants – form via chemical reactions and
coagulation / nucleation of smaller species
•
Natural sources: similar to course particles + aerosols
•
Man-made sources: vehicle exhausts, tires, brakes, metal smelting
– Diesel engines produce majority carbon particles (soot), gasoline engines
produce majority VOC’s
•
The organic content of fine particles is greater than the coarse ones, e.g. urban
smog, they are also more acidic
Because of their small size their settling velocity is very small.
Most of them remain suspended in air
Most ultrafine particles in urban air are anthropogenic
Aerosol
•
•
•
•
Aerosol: A dispersion of
microscopic solid or liquid
particles dispersed in air
Sulfate aerosol from
volcano eruption, fuel
combustion and
microbial activities
Ammonium salts from
reaction with biologically
derived ammonia
Soot (C) from fuel
combustion
Secondary organic C
from volatile organic
compounds
Typical composition
Mt. Pinatubo Eruption
Largest eruption since 1912
1992 one of the Coolest Years
http://www.ngdc.noaa.gov/seg/hazard/stratoguide/pinfact.html
http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/description_pinatubo.html
PM Index
•
Total suspended particulates – TSP (no longer used)
•
Inhalable – PM10,
– diameter < 10 μm (coarse/fine)
– Typical urban concentration 10-30 μg m-3
– AQS: 24 hr 150 μg m-3, Annual ave. 50 μg m-3
•
Respirable – PM2.5,
– Deeply penetrating (fine and ultrafine)
– Typical urban concentration 10-20 μg m-3
– AQS: 24 hr 65 μg m-3 d-1, annual average 15 μg m-3
•
Since most of the fine particles in urban
air are secondary, their number can
only be controlled by reducing primary
pollutants (NO, VOCs and SO2)
Distribution of Particle Size
Nuclei Mode: Small particles (0.01 µm) are
formed by the condensation of vapors of pollutants
(Condensation of H2SO4 and soot particles)
Accumulation Mode: These small particles serve
as nuclei and undergo coagulation followed by
deposition of gas moecules
(Distribution peak 0.1 µm)
Coarse Particle Mode: Particles with distribution
peak around 1µm are mainly soot or materials
produced from mechanical grinding. Larger
particles quickly settle
Distribution of numbers of
aerosol particles in a typical
urban area
Peak in the m Region
Small particles
coagulate
Why no particles
down here?
cf. Fig. 2-17
Average Residence Time
Absorbed: dissolves
Adsorbed: stick to the surface
Distribution of Particle Mass
Ultrafine
•
•
•
•
Coarse
Number of particles
does not represent the
actual mass distribution
Mass (volume) ~
(radius)3
Larger particles
contribute more mass
Because of their small
mass, peak
corresponding to nuclei
mode is not seen
cf. Fig. 2-19
Health Effects of Outdoor Pollutants
•
•
Inferred from epidemiology
Main target organ – lungs
Health Effects of Outdoor Pollutants
Carbon monoxide: binds to hemoglobin
in red blood cells & reduces ability of
blood to carry oxygen
Sulfur dioxide: causes constriction of
airways & can cause bronchitis
Nitrogen oxides: irritate lungs, cause
conditions similar to bronchitis &
emphysema
Ozone: causes coughing, chest pain,
shortness of breath, & eye, nose & throat
irriation
Volatile organics: cause mutations,
reproductive problems, & cancer
Read p116-120
Health Effects of Particulates
•
Increase the risk of
cardiovascular diseases and
mortality
– Ultrafine may be especially
dangerous
(current drive to reduce
PM2.5 may be dangerous)
– Particles penetrate the
lungs, blocking and irritating
air passages
– Toxic substances present in
the particles
Health Effects
Relationship Between PM 2.5 and Daily Deaths in 6 Cities
Fine particles that originated
from auto emissions and
sulfate from burning of coal
are responsible for increased
mortality rate
Cities with high PM2.5
(~20 mg m-3) had 1.4% higher
death rate than cities with 10
mg m-3
A 10 mg m-3 drop results in
36000 fewer earlier deaths per
year
The shaded area represents
uncertainty in data points
NO THRESHOLD!!!
Schwartz et al., 2002
US Death Map
Mega Cities
Source: UNEP/WHO, 1992
Short-term Improvements in Public Health from Global
Climate Policies on Fossil Fuel: an Interim Report
If the world community
does nothing to reduce
the combustion of
fossil fuels, particulate
matter could cause up
to 8 million avoidable
deaths between the
years 2000 and 2020
Davis, DL. Working Group on Public Health and Fossil-fuel Combustion. Shortterm improvements in public health from global-climate policies on fossil-fuel
combustion: an interim report. The Lancet, 1997, 350(9088), 8 November 1997:
1341–1349.