Pollution Air II
Where does air pollution come from?
How can it be reduced?
(Ch. 1: Chemistry in Context)
Problem Set #1 Chemistry 100
Do the following problems in your text:
Chapter 1: 8, 12, 15, 20, 21, 35, 36, 42, 43*
Procedure:
1. Bring your answers to class on paper in a form that is ready to turn in. Do not use red color
pen/pencil when writing your answers.
2. Prior to turning in the problem set, we will discuss the answers in class. Red pens will be
distributed in class for you to write corrections and other notations as you wish.
3. Grading will be based on your initial answers, i.e. material that is not written in red. A total of
25 points will be split among the assigned problems.
4. A star denotes a web exercise. When completing this exercise, you must cite the web pages
you used to develop your answer. While you may go to wikipedia to obtain some basic
information, you must visit and cite other web pages.
Clean Air Act, 1970
(Amendments in 1990 and 1997)
Criteria pollutants:
Regulated by first developing health-based criteria as
the basis for setting permissible levels
Each State must develop an implementation plan
(SIP) to achieve National Ambient Air Quality
Standards (NAAQS)
Hazardous Air Pollutants
Known to cause cancer and/or other major health
effects
Regulation based on Maximum Available Control
Technology (MACT), i.e. reducing levels as much as
is technologically and economically feasible
Revisions to Criteria Pollutant Standards
1987: PM10 replaces Total Suspended Particulates
1997: PM2.5 standard added; PM10 standard
retained
2008: PM standards under final review
PM2.5 daily average set to 35 g/m3
PM10 standard removed
PMcoarse (2.5-10 m size) set to 70 g/m3
New PM2.5 standard: How low is low enough?
Health effects scale with exposure.
Health studies suggest that each 1 g/m3 reduction
in PM2.5 will prevent 25,000 premature deaths
worldwide.
There is no such thing as zero exposure.
What is a low enough exposure? (Cost-benefit)
Past and future PM2.5 standards:
Current US standard (annual average): 15 g/m3
World Health Organization recommendation: 10 g/m3
American Lung Association recommendation: 12 g/m3
Current EPA suggestion for new standard: 14 g/m3
See: Nature, Vol 444 (16 Nov 2006) pp. 249-250
Sources of Atmospheric Particles
Source
Natural /
Anthropogenic
Emission Rate
(Tg/yr)
Size range
Sea spray
N
1000-1500
PM coarse
Dust
N
100-750
PM coarse
Forest fires and
volcanoes
N, (A)
85-150
PM 2.5
Combustion
A
50
PM 2.5
A, (N)
1500
PM 2.5
(soot from cars, etc)
Condensation
(ammonium sulfate,
nitrate; organic C)
1997:
Ozone standard set to 0.085
ppm
2007:
Bush administration
recommends 0.075 ppm
2009:
EPA recommends setting limit
between 0.06 and 0.07 ppm;
EPA states it will not
implement 0.075 ppm
standard
2011:
Pres. Obama asks EPA to
withdraw new standard, has
not ruled on whether 0.075
ppm will be implemented
Combustion:
Definition: Rapid combination of oxygen with a substance (fuel).
Coal:
C(s) + O2(g) CO2(g) (+ heat)
Equation is balanced (conservation of matter):
Atoms on left = Atoms on right
Note: CO2 is a greenhouse gas!
Natural Gas:
__ CH4(g) + __ O2(g) __ CO2(g) + __ H2O(g) (+ heat)
Equation is not balanced!
Atoms on left Atoms on right
Natural Gas:
__ CH4(g) + 2 O2(g) __ CO2(g) + 2 H2O(g) (+ heat)
Equation is balanced!
Atoms on left = Atoms on right
Note: Fuel oil works by the same general principle, only with
larger hydrocarbons (i.e. more C and H atoms per molecule).
Incomplete Combustion
Not enough time to
react completely.
Not enough oxygen
to react with all of
the fuel.
__ C(s) + __ O2(g) __ CO(g)
Remember:
CO is a criteria pollutant!
(Another product is PM2.5)
Incomplete Combustion
Not enough time to
react completely.
Not enough oxygen
to react with all of
the fuel.
2 C(s) + __ O2(g) 2 CO(g)
Remember:
CO is a criteria pollutant!
(Another product is PM2.5)
Impurities: Sulfur in Fuel
S + O2(g) SO2(g)
Primary (also Criteria) Pollutant
SO2(g) + O2(g) SO3(g)
Secondary Pollutant
SO3(g) + H2O(g) H2SO4(g)
Secondary Pollutant
H2SO4 condenses and reacts with ammonia (NH3) to produce
ammonium sulfate particles (PM2.5)
Ammonia is emitted from human/livestock waste and other
anthropogenic sources.
NH3 + H2SO4 (NH4)2SO4
Secondary Pollutant
(Equations on this slide are not balanced!)
Impurities: Metals in Coal
Al, Fe, Ca, K, Mg, Na, Tl, Zn, V, Pb, As, Cd, Hg
Impurities: Metals in Coal (PM2.5)
Fraction Particles
Al, of Fe, Ca, K, Mg, Na, V, Zn, Pb, As, Cd
Normalized Intensity
K+
0.0018
0.0016
0.0014
0.0012
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
Zn+
Fraction of Particles
Na+
50
110
220
440
770
Dva (nm)
Pb+
0
`50
100
150
m/z
200
250
0.005
0.004
0.003
0.002
0.001
0.000
0.001
0.002
0.003
0.004
0.005
330
0
30
300
60
270
90
240
120
210
180
Particles from a coal combustion
source in Wilmington, Delaware
150
Mobile Vehicle Emissions
What goes in?
Gasoline, motor oil
(CxHy)
Air
What comes out?
CO
CO2
VOC (volatile organic
compounds) (CxHyOz)
Soot (C(s))
NOx (NO and NO2)
How are motor vehicle pollutants formed?
Combustion of gasoline (e.g. octane = C8H18)
CO2
Incomplete combustion of gasoline
CO, VOC, Soot
Other reactions requiring high temperature
NOx = NO + NO2
N2(g) + O2(g) 2NO(g) NO(g) + O(g) NO2(g)
A question for later: why does NO form only at high temperature?!
How are motor vehicle pollutants formed?
Combustion of gasoline (e.g. octane = C8H18)
CO2
Incomplete combustion of gasoline
CO, VOC, Soot
VOC
Other reactions requiring high temperature
NOx = NO + NO2
NO
N2(g) + O2(g) 2NO(g) NO(g) + O(g) NO2(g)
A question for later: why does NO form only at high temperature?!
Photochemical Smog from Mobile
Vehicle Emissions
VOC + NOx very little reaction
VOC + NOx + sunlight smog!! = PM2.5 + O3
1. Vehicles emit NO, NO2 and VOC; lots
of VOC from biogenic sources, too
2. Sunlight decomposes NO2 to
produce oxidants and NO
3. Oxidants react with VOC; some of
the VOC products go on to react with
NO to regenerate NO2 and others
form PM2.5
(A)
(VOC)
(OH and O3)
4. Steps 2-3 continue to cycle; O3 and
PM2.5 levels build up over time
5. Process stops when sun goes down
Van Loon and Duffy, Environmental Chemistry,
Oxford University Press, 2005, Fig. 4.2
Photochemical Smog:
NOx + VOC + sunlight O3 + Particulate Matter (PM)
Photochemical formation of oxidants from NO2:
(A)
NO2 + sunlight NO + O
O + O2 O3
O3 + sunlight O2 + O
O + H2O 2 OH
Reactions of VOC:
VOC + NO NO2
VOC (CxHy) + OH or O3 A (CxHyOz)
(VOC)
(OH and O3)
PM2.5 in Photochemical Smog
Secondary organic aerosol (SOA)
VOC + (OH or O3) A (CxHyOz)
A + (particle) (A+particle)
Particles grow in size and mass (PM2.5 increases)
Sulfate aerosol
SO2 + (OH or O3) SO3 (faster in polluted air)
SO3 + H2O H2SO4
H2SO4 + NH3 + (particle) [(NH4)2SO4 + particle]
Particles grow in size and mass (PM2.5 increases)
If VOC and NOx emissions occur all the time, why is
smog worse some days and places than others?
Answer: A solution to pollution is dilution
Normal temperature profile
High mixing height
Temperature inversion
Low mixing height
Cold
Cold
Cool
Hot
Hot
Cold
Diurnal Variation of Ozone Concentration
If VOC and NOx emissions occur all the time, why is
smog worse some days and places than others?
Another Answer: A solution to air pollution is dissolution
P, G
(P)articles, (G)ases
Back to Earths surface
Homework:
What are the current and forecast AQI in Delaware and
around the country? www.airnow.gov
What are current pollutant levels in Delaware?
http://www.dnrec.state.de.us/air/aqm_page/airmont/air.asp
Major sources of VOC and NOx
www.epa.gov
Reducing Pollution: Remove them at the Source
Emission Reduction via Catalytic Converters
Removes NO, CO and VOC by reaction on metal surface
The surface is a catalyst:
Example of a surface catalyzed reaction: 2NO + 2CO N2 + CO2
What is the source of PM2.5 in Wilmington?
80%
Secondary particles (smog) composed of ammonium sulfate,
ammonium nitrate, secondary organic compounds (A)
- 38% from regional gas emissions (Ohio River Valley, etc.)
- 29% from local gas emissions (industry, motor vehicles, etc.)
- 13% from biomass burning (regional and local)
7%
Locally produced carbonaceous particle emissions (diesel vehicles,
industry, food processing, etc.)
13%
Locally produced inorganic particles (coal combustion, refinery, etc.)
Policy question: How do we control air pollution in Delaware (i.e.
develop a state implementation plan) if half of it comes from out of state?
Data from: Reinard, Adou, Johnston, Atmospheric Environment (2007) 41, 9397-9409
General Chemistry Concepts
Balancing chemical equations
Periodic table chemical properties by
location (metals, nonmetals)
Types of chemical reactions
Combustion (generates energy, i.e. heat)
Catalysts (make reactions go faster)
Photochemistry (light is a reactant)