Title: Fundamentals of air Pollution
1Fundamentals of air Pollution Atmospheric
Photochemistry Part B
- Yaacov Mamane
- Visiting Scientist
- NCR, Rome
- Dec 2006 - May 2007
- CNR, Monterotondo, Italy
2 Stratospheric Ozone
- Chapman Reactions (1931)
- O2 hn ? 2O (1)
- O O2 M ? O3 M (2)
- O3 hn ? O2 O (3)
- O O3 ? 2O2 (4)
- Reactions (1) plus (2) produce ozone.
- O2 hn ? 2O (1)
- 2 x ( O O2 M ? O3 M ) (2)
- 3 O2 hn ? 2 O3 NET
3- While Reactions (3) plus (4) destroy ozone.
- O3 hn ? O2 O (3)
- O O3 ? 2O2 (4)
- 2O3 hn? 3 O2 NET
- Reactions (3) plus (2) add up to a null cycle,
but they are responsible for converting solar UV
radiation into transnational kinetic energy and
thus heat. This cycle causes the temperature in
the stratosphere to increase with altitude. Thus
is the stratosphere stratified. - O3 hn? O2 O (3)
- O O2 M ? O3 M (2)
- NULL NET
- By way of quantitative analysis, we want O3ss
and Oss and Oxss where Ox is defined as odd
oxygen or O O3. The rate equations are as
follows.
4- (a)
- (b)
- (ab)
- From the representation for O atom chemistry
- In the middle of the stratosphere, however, R3
gtgt2 R1 and R2 gtgt R4 thus - (I)
- (R4 can be ignored in an approximation of Oss
). - The ratio of O to O3 can also be useful
5- (II)
- Reactions 2 and 3 set the ratio of O to O3, while
Reactions 1 and 4 set the absolute
concentrations. Now we will derive the steady
state ozone concentration for the stratosphere.
From the assumption that Ox is in steady state it
follows that - R1 R4
- or
- j(O2)O2 k4OO3
- Substituting from (I), the steady state O atom
concentration - or
6- SAMPLE CALCULATION
- At 30 km
- This is almost a factor of ten above the true
concentration! What is wrong? There must be
ozone sinks missing.
7- Bates and Nicolet (1950)
- Odd hydrogen HOx is the sum of OH and HO2
(sometimes H and H2O2 are included as well). - HO2 O3 ? OH 2O2 (5)
- OH O3 ? HO2 O2 (6)
- 2O3 ? 3O2 NET
- The following catalytic also destroys ozone.
- OH O3 ? HO2 O2 (6)
- HO2 O ? OH O2 (7)
- O O3 ? 2O2 NET
8- Crutzen (1970) Johnston (1971) NOx
- Odd nitrogen or NOx is the sum of NO and NO2.
Often NOx is used as odd nitrogen which
includes NO3, HNO3, 2 N2O5, HONO, PAN and other
species. This total of odd nitrogen is better
called NOy or total reactive nitrogen. N2
and N2O are unreactive. - NO O3 ? NO2 O2
- O NO2 ? NO O2
- O O3 ? 2O2 NET
- This is the major means of destruction of
stratospheric ozone. The NOx cycle accounts for
about 70 of the ozone loss at 30 km.
9- Stolarski Cicerone (1974) Wofsy McElroy
(1974) ClOx - Cl O3 ? ClO O2
- ClO O ? Cl O2
- O O3 ? 2O2 NET
- This reaction scheme is very fast, but there is
not much ClOx in the stratosphere yet. - Today ClOx accounts for about 8 of the ozone
loss at 30 km. If all these catalytic
destruction cycles are added together, they are
still insufficient to explain the present
stratosphere O3 level.
10Stratospheric ozone destruction cycles Stratospheric ozone destruction cycles Stratospheric ozone destruction cycles Stratospheric ozone destruction cycles
Cycle Sources Sinks Reservoirs
HOx H2O, CH4, H2 HNO3, H2SO4nH2O H2O, H2O2
NOx N2O O(¹D) HNO3 HO2NO2, ClONO2
ClOx CH3Cl, CFC HCl HCl, HOCl
The sinks involve downward transport to the
troposphere and rainout or other local loss.
Note that some sinks are also reservoirs HCl
OH ? H2O Cl
11The Greenhouse Effect
12SOLAR IRRADIANCE SPECTRA
1 ?m 1000 nm 10-6 m
13TOTAL SOLAR RADIATION RECEIVED BY EARTH
- Solar constant for earth 1368 W m-2
- Solar radiation received outside atmosphere
- per unit area of sphere
- (1370) x (? re2)/(4 ? re2) 342 W m-2
14EFFECTIVE TEMPERATURE OF EARTH
- Effective temperature of earth (Te)
- Temperature detected from space
- Albedo of surfaceatmosphere 0.3
- 30 of incoming solar energy is reflected by
clouds, ice, etc. - Energy absorbed by surfaceatmosphere 1-0.3
0.7 - 70 of 342 W m-2 239.4 W m-2
- Balanced by energy emitted by surfaceatmosphere
- Stefan-Boltzman law Energy emitted ? Te4
- ? 5.67 x 10-8 W m-2 K-4
- Solve ? Te4 239.4
- Te 255 K
15GLOBAL TEMPERATURE
- Annual and global average temperature 15 C,
i.e. 288 K - Te 255 K --gt not representative of surface
temp. of earth - Te is the effective temp. of the earth
atmosphere system - that would be detected by an observer in space
16ENERGY TRANSITIONS
- Gas molecules absorb radiation by increasing
internal energy - Internal energy ? electronic, vibrational,
rotational states - Energy requirements
- Electronic transitions
- ? UV (lt 0.4 ?m)
- Vibrational transitions
- ? Near-IR (lt 0.7-20 ?m)
- Rotational transitions
- ? Far-IR (gt 20 ?m)
- Little absorption in visible range (0.4-0.7 ?m)
- Gap between electronic and vibrational
transitions - Greenhouse gases absorb in the range 5-50 ?m
- Vibrational and rotational transitions
17GREENHOUSE GASES
- Vibrational transitions must change dipole
moment of molecule
- Important greenhouse gases
- H2O, CO2, CH4, N2O, O3, CFCs
- Non-greenhouse gases
- N2, O2, H2, Noble gases
18ATMOSPHERIC ABSORPTION OF RADIATION
- 100 absorption of UV
- Electronic transitions of
- O2 and O3
- Weak absorption of visible
- Gap in electronic and
- vibrational transition energies
- Efficient absorption of terrestrial radiation
- Greenhouse gas absorption
- Important role of H2O
- Atmospheric window between 8 and 13 ?m
19A SIMPLE GREENHOUSE MODEL
239.4 W m-2
(1-f)? To4
f? T14
absorbed f ? To4
f? T14
? To4
- Incoming solar radiation 70 of 342 W m-2
239.4 W m-2 - IR flux from surface ? To4
- Assume atmospheric layer has an absorption
efficiency f - Kirchhoffs law efficiency of abs. efficiency
of emission - IR flux from atmospheric layer f ? T14 (up and
down)
20RADIATION BALANCE EQUATIONS
239.4 W m-2
(1-f)? To4
f? T14
absorbed f ? To4
f? T14
? To4
- Balance at top of atmosphere
- f ? T14 (1-f) ? To4 239.4
- Balance for atmospheric layer
- f ? T14 f ? T14 f ? To4
21THE GREENHOUSE EFFECT
239.4 W m-2
(1-f)? To4
f? T14
f? T14
absorbed f ? To4
? To4
- To 288 K
- f 0.77 T1 241 K
- Greenhouse gases ? gases that affect f
- As f increases, To and T1 increase
22THE IPCC THIRD ASSESSMENT
23CONCEPT OF RADIATIVE FORCING
239.4 W m-2
(1-f)? To4
f? T14
absorbed f ? To4
f? T14
? To4
- Consider increase in concentration of a
greenhouse gases - If nothing else changes
- ? f increases ?outgoing terrestrial radiation
decreases - Change in outgoing terrestrial radiation
radiative forcing
24RADIATIVE FORCING AND TEMPERATURE CHANGE
239.4 W m-2
(1-f)? To4
f? T14
absorbed f ? To4
f? T14
? To4
- Response to imbalance
- To and T1 increase ? may cause other
greenhouse gases to - change ? f ? (positive feedback) or ?
(negative feedback) - ?To and T1 may ? or ? ? ?f ? ?T ? ? Rad.
balance - Radiative forcing is measure of initial change
in outgoing flux
25RADIATIVE FORCING
- Permits assessment of potential climate effects
of - different gases
- Radiative forcing of a gas depends not only on
change in - concentration, but also what wavelengths it
absorbs - Aerosols can exert a negative radiative effect
(i.e. have a - cooling effect) by reflecting radiation (direct
effect) and - by increasing reflectivity of clouds (indirect
effect)
26GLOBAL WARMING POTENTIAL
- Index used to quant.
- compare radiative forcings
- of various gases
- Takes into account lifetimes,
- saturation of absorption
27FORCINGS AND SURFACE TEMPERATURE
- Climate sensitvity parameter (?) ?To ? ?F
- Global climate models ? ? 0.3-1.4 K m2 W-1
28THE TEMPERATURE RECORD
29RECENT CHANGES IN SURFACE TEMPERATURE
- Trend differences due to
- differences in spatial av.,
- diff. in sea-surface temps.,
- and handling of urbanization
- Same basic trend over last
- 100 years
- Increase in T by 0.6-0.7 C
30POTENTIAL CAUSES OF TEMPERATURE CHANGES
239.4 W m-2
absorbed f ? To4
- Variations in solar radiation at top of
atmosphere - Changes in albedo (e.g. due to changes in cloud
cover) - Changes in greenhouse gas forcing (i.e., change
in f) -
31SOLAR VARIABILITY
- Changes in sunspots and surface conditions
32CHANGES IN CLOUD COVER
- Incoming solar radiation 0.7 x 342 W m-2
239.4 W m-2 - Consider albedo change of 2.5
- Albedo 0.3 x 1.025 0.3075
- Incoming solar radiation 0.6925 x 342 W m-2
236.8 W m-2 - Radiative forcing 236.8 239.4 - 2.6 W m-2
- ? Comparable but opposite to greenhouse gas
forcing - Clouds are also efficient absorbers of
terrestrial radiation - ? Positive forcing
- Cloud effects are larege source of uncertainty
in climate - projections
33MODEL SIMULATIONS OF RECENT PAST
34CLIMATE PROJECTIONS
35POTENTIAL IMPACTS
36JULY HEAT INDEX FOR South-East U.S.