physics and chemistry of the a tmosphere - brief overview on...

Remote sensing of the atmosphere [email protected] http://www.mpch-mainz.mpg.de/satellite

1

Basic properties of the atmosphere

Greenhouse effect

Stratospheric chemistry: ozone layer

Tropospheric chemistry:

- winter smog

- summer smog

- oxidation capacity

Physics and chemistry of the atmosphere- brief overview on important effects -


2

Basic properties of the atmosphere: composition


3

Basic properties of the atmosphere: composition

Trace gases are important. They control:

-radiation absorption/emission -energy supply for organisms

-chemical reactions -energy transport (latent heat)


4

Residence time of various atmospheric trace gases

Lebe

nsda

uer

1s10

0s1h

r1T

ag

10000km100km1km10m

Räumliche Skala

Transport Skala

kurz

lebi

gla

ngle

big

mod

erat

lang

lebi

g

mikro lokal regional global

OHNO3

HO2

CH3O 2

CH5H 8DMS

NOx CH5H 8

SO2

trop. O3

COCH3BR

CH3CCl3CH4

FCKWN2O

1 Ja

hr10

0 Ja

hre

Lebe

nsda

uer

1s10

0s1h

r1T

ag

10000km100km1km10m

Räumliche Skala

Transport Skala

kurz

lebi

gla

ngle

big

mod

erat

lang

lebi

g

mikro lokal regional global

OHNO3

HO2

CH3O 2

CH5H 8DMS

NOx CH5H 8

SO2

trop. O3

COCH3BR

CH3CCl3CH4

FCKWN2O

1 Ja

hr10

0 Ja

hre


5

Basic quantities for trace gas measurements:

Concentration, units: molecules / cm³, partial pressure

Examples:

-concentration of air under normal conditions: 2.51019 molecules / cm³

-maximum concentration of ozone in the ozone layer (~20 km): 51012

molec / cm³ (~8 mPa)

-concentration of CO2 under normal conditions: 11016 molec / cm³

-maximum BrO concentration close to the surface: 1109 molec / cm³


6


Mixing ratio, units: percent, parts per million (ppm), parts per billion (ppb), parts per trillion (ppt)

Mixing ratios are usually given ‚per volume‘ (e.g. ppmv): the fraction of air, which is occupied by a chemical substance. Similar to the fraction of molecules.

Alernatively, mixing ratios could be given ‚per weight‘ (e.g. ppmw)


7


Mixing ratio, units: percent, ppm, ppb, ppt

Examples:

-mixing ratio of air: 1

-maximum mixing ratio of ozone in the ozone layer (~30 km): 8 ppm(at 20 km: 3 ppm)

- mixing ratio of CO2: 407 ppm (pre-industrial: 260 – 280 ppm)

- maximum BrO mixing ratio close to the surface: 40 ppt


8


Column density, units: molecules / cm², Dobson unit (DU), g / cm²

The column density is the concentration integrated along a path s:

-a concentration integrated along the atmospheric light path is the SCD (Slant column density)

-The vertically integrated concentration is the VCD (vertical column density)

-The vertically integrated concentrations for specified atmospheric layers (e.g. the troposphere) is the partial VCD

s

dsdensitycolumn


9


Column density, units: molecules / cm², Dobson unit (DU), g / cm²

Examples:

-VCD of air: 21025 molecules / cm²

-Typical SCD of ozone for measurements at sunset/sunrise: 21020

molecules / cm² (~7500 DU)

-Typical VCD of ozone: 81018 molecules / cm² (~300 DU)

-Typical tropospheric (partial) VCD of ozone: 81017 molecules / cm²(~30 DU)

-Maximum H2O VCD in the tropics: 31023 molecules / cm² (~8 g / cm²)


10

For aerosols there are additional units:

-mass / cm³

-size distributions (as function of radius, mass, surface area, etc.)

-optical parameters, e.g. the extinction (in units of 1/km) or the vertically integrated extinction (the aerosol optical depth, unitless)


11

Basic properties of the atmosphere: pressure profile

dzzdpzg )()(

z

z + dz

p(z)

p(z+dz)

Hydrostatic equation


12

Basic properties of the atmosphere: pressure profile

z

z + dz

p(z)

p(z+dz)

NpV AWith ideal gas law

it follows:

and:

VM

dzzdpzg )()( Hydrostatic

equation

RT

N ARTMp

V


13

For isothermal atmosphere (t=const):

zRTMg

epzp

)0()(

Scale height z0:0zMg

RT

0)0()( zz

epzp

8 km

=> Scale height is different for different molecules


14-100 -50 0 50Temperatur [°C]

0

20

40

60

80

100

120

Höh

e [k

m]

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

1E+2

1E+3

Dru

ck [m

b]

Troposphäre

Stratosphäre

Mesosphäre

Thermosphäre

Tropopause

Stratopause

Mesopause

Ozonschicht

Basic properties of the atmosphere: temperature profile


15

The temperature profile in the troposphere is controlled by convective circulation. The energy originates from the warm surface which is heated by solar irradiation.

For the calculation of the temperature change with altitude it is assumed that the air parcels move adiabatically. That means they don’t exchange energy with their environment. This assumption is justified by comparison with the rates of radiative cooling with the transport times within the tropospere.

When an air parcel ascends it expands and thus does work against the air pressure.


16

The first thermodynamical law is:

(U = internal energy, Q = obtained heat, W = work done to the gas, p =pressure, V = volume)

For adiabatic processes: dQ = 0 and we get:

For an ideal gas the internal energy only depends on the temperature T it is:

It follows:

with

orwith

It follows:

It follows:with


17

With barometric height formula: It follows:

And we get the dry adiabatic temperature gradient:

Values for air:


18

With barometric height formula: It follows:

And we get the dry adiabatic temperature gradient:

Values for air:

Moist adiabatic temperature gradient:

If air ascends and cools, it will eventually reach the temperature at which water vapor condenses. The condensation process releases latent heat which provides energy to the airparcel. Thus, the temperature decrease with height is smaller than for the dry adiabatic temperature gradient.


19

Saturation humidity W (left) or partial pressure (right) over liquid water or ice as function of temperature Ordinate rechts, ist der zugehörige Wasserdampf-Partialdruck E eingezeichnet

The typical temparture gradient in the lower atmospere (up to about 10km) is determined

by the moist adiabatic temperature gradient. Typical values are 0.6K/100m


20

Long time it was known (e.g. from mountain climbing) that the temperature decreases with height. It was also assumed that the temperature decrease would continue until the‚upper edge‘ of the atmosphere.

About more than 100 years ago, several important observations were made, which showed that the actual temperature gradient differs from this expectation:

1880 - 1908: Discovery of the ozone absorption (especially in the UV)

1902: Balloon borne temperature measurements (Teisserenc de Bort and Richard Assmann) showed a temperature increase at about 11km.

1913: Balloon borne observations (Wigand) of the ozone absorption show nosignificant increase of the UV intensity up to 10km

1926: Umkehr-Effekt (Paul Götz): Maximum of the ozone layer at about 25km


21-100 -50 0 50Temperatur [°C]

0

20

40

60

80

100

120

Höh

e [k

m]

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

1E+2

1E+3

Dru

ck [m

b]

Troposphäre

Stratosphäre

Mesosphäre

Thermosphäre

Tropopause

Stratopause

Mesopause

Ozonschicht

Basic properties of the atmosphere: temperature profile


22

200 400 600Wavelength [nm]

1E-23

1E-22

1E-21

1E-20

1E-19

1E-18

1E-17

[cm

]

Hartley Hug

gins

Chappuis

310 330 3501E-22

1E-21

1E-20

1E-19

O2 absorption cross section

O3 absorption cross section

Note: there is ~105 times more O2 than O3

O2 shows strong absorption at small wavelengths


23

http://www.cas.manchester.ac.uk/documents/hughcoe/lecture22007[1].pdf


24but Treal = +15°C Greenhouse effect T = +33°C

The solar irradiation is S = 1368 W/m² (Solar constant). The earth cuts a cross section of r² off the solar beam. It reflects a fraction A (albedo) back into space.The absorbed power (1-A)Sr² has to be compensated by the terrestrial IRradiation to avoid a heating of the earth. From the Stefan-Boltzmann-law it follows that the terrestrial radiation is T4 · 4r² = (1-A)Sr²

It follows: Taverage = -18°C

© W. Roedel

Greenhouse effect


25


26

Atmospheric radiation budget


27Antarctica

Sahara

Mediteranean


28

Contribution of differentgreenhouse gases to the natural greenhouse effect(IPCC, 1995)

63.5%

22.5%

7.2%4.2% 2.7%


29

(C) ICCP 2013

Stärke verschiedener Klimaantriebe (Radiative Forcing, Differenz zur Zeit vor der Industrialisierung).


30

Ohne Rückkopplungen

Klima-system

Störung der Klimabilanz, z.B. doppelte CO2 Konzentration

3.7 W/m2

T = 1.2°C


Klima-system


3.7 W/m2

T = 1.2°C

Rükkopplungen verstärken oder dämpfen ursprüngliche Klimaeinflüsse

without feedbacks


31


Klima-system


3.7 W/m2

T = 1.2°C

Mit Rückkopplungen

Klima-system


3.7 W/m2

T = 1.5°C - 5.5°CVerstärkung der Störung durch Rückkopplungen

+1.9 W/m2

+0.3 W/m2

+1.6 W/m2

bis -0.2 W/m2

-0.8 W/m2

Rüc

kkop

plun

gen

Temperatur-Gradient

Wasser-dampf

Albedo

Wolken


Klima-system


3.7 W/m2

T = 1.2°C

Mit Rückkopplungen

Klima-system


3.7 W/m2

T = 1.5°C - 5.5°CVerstärkung der Störung durch Rückkopplungen

+1.9 W/m2

+0.3 W/m2

+1.6 W/m2

bis -0.2 W/m2

-0.8 W/m2

Rüc

kkop

plun

gen

Temperatur-Gradient

Wasser-dampf

Albedo

Wolken

Rükkopplungen verstärken oder dämpfen ursprüngliche Klimaeinflüsse

without feedbacks

with feedbacks


32

Report of the Intergovernmental Panel of Climate Change (IPCC), http://www.ipcc.ch/


33

IPCC 2013


34

IPCC 2013

Sulfate aerosols deposited in Greenland ice


35

IPCC 2013

MLO: Mouna Loa, Hawai

SPO: South Pole

MHD: Mace Head, NH

CGO: Cape Grimm, SH


36

1880 1900 1920 1940 1960 1980 2000

Solare EinstrahlungRuspartikel & KondensstreifenStratosphärischer WasserdampfTroposphärisches OzonMethan, Lachgas, FCKWCO2

-4-3-2-101234

Forc

ing

[W/m

2 ]

Direkte AerosolefffekteIndirekte AerosolefffekteLandnutzungStratosphärisches OzonVulkane

Zeitlicher Verlauf verschiedener Störungen des Strahlungsgleichgewichts (Radiative Forcing) seit 1880. Positive Beiträge durch Treibhausgase und negative Beiträge durch Aerosole zeigen eine systematische Zunahme.


37

-1012

Forc

ing

[W/m

2 ]

Summe künstliche AntriebeSumme alle Antriebe

1880 1900 1920 1940 1960 1980 2000

MessungenSimulationen mit allen KlimaantriebenSimulationen mit natürlichen Klimaantrieben

-0.5

0

0.5

1

Tem

pera

tura

nom

alie

[C

]

Oben: Zeitlicher Verlauf der Summe der künstlichen (positiven und negativen) Klimaantriebe sowie aller Klimaantirebe. Unten: Werden die verschiedenen Störungen in Klimaberechnungen miteinbezogen, so lässt sich der beobachtete zeitliche Verlauf der Temperaturen an der Erdoberfläche sehr gut beschreiben. Daten aus Myhre et al., 2013.


38

IPCC 2014


39

1970 1980 1990 2000 2010-100

0

100

200

300

Ener

giea

ufna

hme

[102

1 J] Summe

Oberer OzeanTiefer OzeanEisLandAtmosphäre

Aus Temperaturmessungen und Modellsimulationen bestimmte Wärmeaufnahme von Ozeanen, Kontinenten, Atmosphäre und Eisflächen von 1971 bis 2010. Der größte Anteil wird von den Weltozeanen, und hier insbesondere von den oberen Schichten (bis 700 m Tiefe) aufgenommen. Der für den Zeitraum 1971 – 2010 gemittelte Energiefluss in die Ozeane wird mit 0,55 W/m² abgeschätzt. (IPCC 2013)


40

Average near surface temperature as function of latitude

Global circulation patterns redistribute energy

Why not at the equator?


41

Global circulation patterns redistribute energy


42

Complex atmospheric circulation patterns

Convection-heat gradient-gravitation

Solar irradiance

cold

cold

hot


43

Tropopauserapid mixing

CFC + h -> Cl+ O1D

wintersummer

Schematic diagram of the Brewer-Dobson Circulation (adapted from Solomon et al. [1998]). Because the stratosphere contains only about 10% of the total atmosphere, the circulation must turn over many times to exchange the whole air of the troposphere. This is e.g. important for the destruction of the CFCs, which are only destroyd in the stratosphere, resulting in a long atmospheric live time of these species.

Altitude profiles of CFC-11 (bottom) and CFC-12 (top) [NASA, 1994].


44

Ozone in the stratosphere

Chapman Cycle [1930].

O2 + h 2 O ( 240nm)

O + O2 + M O3 + M

O3 + h O2 + O(1D) ( 320nm)

O(1D) + M O + M

O3 + h O + O2 ( 1180nm)

O + O +M O2 + M

O + O3 2 O2

odd oxygen is produced

odd oxygen is conserved

odd oxygen is destroyed

odd oxygen = O + O3


45

0 5 10 15 20Ozone mixing ratio [ppm]

10

20

30

40

Hei

ght [

km]

Chapman-cycle

measurements

Comparison of measured ozone profiles and modelled ones taking into account only the reactions of the Chapman-cycle (adapted from Röth [1994]).


46

Additional (catalytic) Ozone destruction mechanisms:

X + O3 XO + O2

XO + O X + O2

Net: O + O3 2O2

with:

X = OH, NO, Cl, Br


47

Organic chlorine (mostly CH3Cl)

Industrial emissionsBiomass

burningVolcanoes

CFCsTroposphericaccum.: 0.56

Inorganic chlorine compounds (mostly HCl)

Chloride ion in sea salt aerosol

Stratospheric Chlorine compoundsaccumulation: 0.08

600

Sedimentation, Precipation 5400

Wave generation 6000

Precipitation 610

HCl 73

0.81

1.5Oceanic emissions 2.5

Precipitation,HO-reaction 5

0.030.24 0.19 Precipitation

units:1012 g Cl yr-1

Global atmospheric chlorine cycle (adapted from Graedel and Crutzen [1993]).

Until the mid 1990s the stratospheric Clorine load increased


48

Organic chlorine (mostly CH3Cl)

Industrial emissionsBiomass

burningVolcanoes

CFCsTroposphericaccum.: 0.56

Inorganic chlorine compounds (mostly HCl)

Chloride ion in sea salt aerosol

Stratospheric Chlorine compoundsaccumulation: 0.08

600

Sedimentation, Precipation 5400

Wave generation 6000

Precipitation 610

HCl 73

0.81

1.5Oceanic emissions 2.5

Precipitation,HO-reaction 5

0.030.24 0.19 Precipitation

units:1012 g Cl yr-1

Global atmospheric chlorine cycle (adapted from Graedel and Crutzen [1993]).

Until the mid 1990s the stratospheric Clorine load increased

Today these fluxes are reversed


49

NOAA Earth System Research Laboratory (http://www.esrl.noaa.gov/gmd/aggi/)

Concentrations of CFC in the troposphere (left) and chlorine compounds in the stratosphere (right) decrease


50

Ozone hole, Antarctica

1. Nov. 20071. Nov. 1979

1. März 20071. März 1979

100 200 300 400 500[DU]

Ozongesamtsäule aus Satellitenmessungen über dem Nord- und Südpol im polaren Frühling 1979 und 2007. (Daten vom NASA Goddard Space Flight Center, http://toms.gsfc.nasa.gov/index_v8.html)


51

Ground based measurements,Halley, Antarctis (Farman et al. 1985; Johnes et al., 1995 und SPARC, 2009, British Antarctic Survey (BAS), https://www.bas.ac.uk/)

Ozone hole, Antarctica

0 5 10 15 20Ozon Partialdruck [mPa]

10

15

20

25

Hoe

he [k

m]

Ozonprofile am Südpol

Oktobermittelwerte 1967 - 1971:

282 DU

7. Oktober 1986: 158 DU

8. Oktober 1997: 112 DU

(from Hoffmann et al., 1997)

1950 1960 1970 1980 1990 2000 2010 2020Zeit

0

50

100

150

200

250

300

350

Ozo

n G

esam

tsae

ule

[DU

]


52

Polar Stratospheric Clouds over Kiruna (Sweden), © Carl-Fredrik Enell.

....what had been ignored before:


53

Polar Stratospheric Cloud over Kiruna (Sweden), © Thomas Wagner

....what had been ignored before:


54

Abun

danc

e

Time

Surface reactions

Gas phasereactions

ClONO2

HCl

ClO + 2 Cl2O2

Fall Early winter Late winter Spring

End of polar nightphotochemical ozone destruction

DenitrificationDehydration

Dynamical and photochemical development in the stratosphere during polar winter

CFC Stratosphere Reservoir compounds active comp. OClO(HCl, ClONO2) (Cl, ClO)

Ozone destruction

Transport hv (UV) PSC BrO


55

2(Cl + O3 ClO + O2)

ClO + ClO + M Cl2O2 + M

Cl2O2 + h Cl + ClOO

ClOO + M Cl + O2 +M

Net: 2O3 3O2

Catalytic ozone destruction cycle through chlorine

Quadratic dependence on ClO

Dependence on sun light


56Envelope of minimum temperature 1980-1988 at about 90 mb from MSU measurements [WMO 1991].

Temperature differences between both hemispheres


57

Predicted future atmospheric burden of chlorine (adapted from Brasseur [1995]).


58

Aus Messungen von Bodenstationen gewonnene Zeitserien der atmosphärischen Ozongesamtsäule in mittleren und tropischen Breiten (Abweichungen bezüglich der Mittelwerte 1965 –1980, modifiziert nach Pawson et al., 2014)

1970 1980 1990 2000 2010-9

-6

-3

0

3

6Ab

wei

chun

g [%

]35°N - 60°N

-9

-6

-3

0

3

6

Abw

eich

ung

[%]

20°S - 20°N

1970 1980 1990 2000 2010Zeit

-9

-6

-3

0

3

6

Abw

eich

ung

[%]

35°S - 60°S


59

-9

-6

-3

0

3

[% p

ro D

ekad

e]Ozontrend 1979 - 1997

-60 -40 -20 0 20 40 60Latitude [°]

-3

0

3

6

9

[% p

ro D

ekad

e] Ozontrend 2000 - 2013

Aus Bodenmessungen bestimmten Ozontrends (2-Sigma-Bereiche) für zwei Zeitäume als Funktion der geographischen Breite (Modifiziert nach Pawson et al., 2014).


60

Ozone trends derived from combining satellite trend estimates for the periods before 1998 (top row) and after 1998 (bottom row). The error bars show the 95 % confidence level calculated in three ways, See Harris et al., 2015, for further details. Harris et al., 2015: Past changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends, Atmos. Chem. Phys., 15, 1-19.


61

Questions:

• When will ozone hole close?(influence of climate change)

• How important are bromine compounds?

• Will there be an ozone hole over the Arctic?

• How strong does ozone change in mid-latiudes?


62

’London Smog’ (John Evelyn, Fumifugium, 17th century)

‘It is this horried smoake which obscures our churches and makes our places look old, which fouls our cloth and corrupts the waters, so as the very rain, and refreshing dews which fall in the several seasons, precipate to impure vapour, which, with its black and tenacious quality, spots and contaminates whatever is exposed to it.

But without the use of calculations it is evident to every one who looks on the yearly bill of mortality, that near half of the children that are born and bred in London die under two years of age. Some have attributed this amazing destruction to luxury and the abuse of spirituos liquors: these, no doubts, are powerful assistants; but the constant and unremitting poison is communicated by the foul air, which, as the town still grows larger, has made regular and steady advances in its fatal influence.’

‘Es ist dieser schreckliche Rauch, der unsere Kirchen verdunkelt und unsere Paläste alt aussehen läßt; der unsere Kleider verdreckt und unser Wasser verdirbt. Insbesondere den Regen und den erfrischenden Tau, die sich zu unreinem Dunst niederschlagen, der schwarz und zäh alles benetzt, das ihm ausgesetzt ist. Aber ohne zu rechnen ist es auch für jeden offensichtlich, der in die Jährliche Todesstatistik liest, daßfast die Hälfte der in London geborenen Kinder im Alter von nicht einmal zwei Jahren stirbt. Manche glauben daß diese erschreckende Entwicklung auf Luxus und Mißbrauch von alkoholischen Getränken zurückzuführen sei. Diese Faktoren mögen die Entwicklung sicherlich begünstigen, aberdas wahre Gift erreicht uns durch die verdorbene Luft, die, solange die Stadt stetig wächst, ihren verderblichen Einfluß beständig erhöht.


63

’London Smog’ (also wintersmog, sulfur smog)

• In the 13th century coal (with high sulfur content) began to replace wood for domestic heating and industrial use in London

• Earliest massive human impact on the atmosphere

• The effects of smog on human health were evident, particularly when smog persisted for several days. Many people suffered respiratory problems and increased deaths were recorded, notably those relating to bronchial causes.

• The first smog-related deaths were recorded in London in 1873, when it killed 500 people. In 1880, the toll was 2000. London had one of its worst experiences with smog in December 1892. It lasted for three days and resulted in about 1000 deaths.

• London became quite notorious for its smog. By the end of the 19th century, many people visited London to see the fog.

• Despite gradual improvements in air quality during the 20 th century, another major smog occurred in London in December 1952. This ‘Great London Smog’lasted for five days and resulted in about 4000 more deaths than usual.


64Hazardous driving conditions due to smog(see also http://www.met-office.gov.uk/education/historic/smog.html)

The London smog disaster of 1952. Death rate with concentrations of smoke


65

Environmental damage due to sulfur emissions Anthropogenic sulfur emissions were in particular responsible for the first non-local pollution

At the end of the 1960s in Scandinavia a massive fish-dying occurred in inland waters. It was found out that the reason was an acidification of the soil. Finally it turned out that it was caused by strong industrial SO2 emissions from Great Britain.

The Waldsterben was also mainly caused by SO2 emissions

Since the mid of the 1980s the SO2-emissions were strongly reduced in ‘western countries’ due to effective filter techniques.

Today very strong smog events in China, India


66

SO2 reacts rapidly with OH to form HSO3 (1), which reacts with O2 to form SO3 (2). It is soluble in clouds and aerosols, where it reacts with H2O2. As a result of these processes, SO2 is converted to H2SO4 (3), consequently causing Acid rain and deforestation. In general the maximum concentration of SO2 is close to its source and the amount of SO2 decreases rapidly as the distance from the source increases, indicating a short tropospheric lifetime of typically a few days.

SO2 + OH HSO3 (1)

HSO3 + O2 SO3 + HO2 (2)

SO3 + H2 O2 H2SO4 (3)

In the dry stratosphere, particularly in the lower stratosphere where the concentration of OH is relatively small, the lifetime of SO2 is longer than in the troposphere being of the order of several weeks.

M

M


67

Typical conditions for winter smog:

-primary pollution: SO2, soot particles

-secundary pollution : H2SO4, Aerosols

-Temperature: 2°C

-Relative humidity: high, typically foggy

-kind of inversion: ground inversion

-time of maximum pollution: early morning


68


70

Los Angeles Smog

(Sommersmog, Ozonsmog)

• Ozone affects health

• Ozone damages plants

• Ozone destroys material

• Ozone determines the oxidation capacity of the atmosphere

Impact of Ozone on Rubber


71DeMore et al., 1997

UV radiation at different altitudes

Ozone production in the troposphere, summer smog

-In the troposphere, not enough UV radiation is available for ozone formation through O2photolysis

-where does troposphericO3 originate from?


72

Early assumption

Todays knowledge

Troposphere

Troposphere

Stratosphere

Stratosphere


73

Oxidation of methane yields CO, H2O and O3


74

Ozonsmog (Los Angeles, 1940s, Haagen-Smit, 1952)

Radical chemistry, Ozone production in the troposphere:

RO2 + NO RO + NO2

NO2 + h NO + O ( 410nm)

O + O2 + M O3 + M

The occurance of ozone smog depends on the concentrationsof volatile organic compounds (VOC) an nitrogen dioxid(NO2)

Without pollution, ozone is produced by oxidation of CH4 and CO => tropospheric background ozone

Oxidation of CO and VOC yields O3


75

A VOC to NOx ratio of 8 to 1 is often cited as an approximate decision point for determining the relative benefits of NOx vs. VOC controls. At low VOC to NOx ratios (< about 4 to 1), an area is considered to be VOC-limited; VOC reductions will be most effective in reducing ozone, and NOx controls may lead to ozone increases. At high VOC to NOx ratios (>about 15 to 1), an area is considered NOx limited, and VOC controls may be ineffective. When VOC to NOx ratios are at intermediate levels (4 to 15), a combination of VOC and NOx reductions may be warranted.

NOx limited

VOC limited


76

Typical conditions for summer smog:

-primary pollution: NOx, VOC

-secundary pollution : O3, Aerosols

-Temperature: >25°C

-Relative humidity: low

-kind of inversion: subsidence inversion

-time of maximum pollution: afternoon


77

Emissions of NMHC in GermanyAverage concentrations of NO2 in Germany

Days with

[O3] > 240 g/m³

in Germany

Importance of ‚local‘ effects?


78

© UBA


79

© UBA


80

© UBA


81(Volz and Kley, 1988)

Montsouris

Cape Arcona

What about tropospheric background ozone concentrations?

ozone concentrations increased between 1870 and 1970

What about the later years?


82Cooper, et al., Global distribution and trends of tropospheric ozone: An observation-based review. Elementa Sci. Anthropocene, 2, 000029, doi:10.12952/journal.elementa.000029, 2014.


83Cooper, et al., Global distribution and trends of tropospheric ozone: An observation-based review. Elementa Sci. Anthropocene, 2, 000029, doi:10.12952/journal.elementa.000029, 2014.

In European and US background stations O3 decreases after 2000

=> less VOC, less NOx

In very remote stations (e.g. Mauna Loa) still slightly increasing values => increasing CH4


84

CH4 largely increased during the last 200 years

IPCC

IPCC 2014

MLO: Mouna Loa, Hawai

SPO: South Pole


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Discovery of the ‘Cleansing agent’ of the atmosphere (OH-radical, Levi, 1971)

O3 + h O(1D) + O2 ( 310nm)

O(1D) + H2O 2OH•

OH• ist a (free) radical. Radicals are molecule fragments with unpaired electrons. Thus their bound conditions are not required and they are very reactive. The production of radicals depends on the fission of molecules and requires high energy. Typically, this energy is supplied by photons. Radicals are the ‘active players’ of photochemistry.

OH reacts with almost all atmospheric trace gases which is the prerequisite for their destruction. This ability to destroy atmospheric trace gases is called oxidation capacity.

OH is very reactive (within seconds). Although its concentrations are very low, it is the most important atmospheric reactand.

OH exists only during day. Will concentrations of atmospheric pollutants increase during night?


86

Discovery of the ‘Cleansing agent’ of the atmosphere (OH-radical, Levi, 1971)

O3 + h O(1D) + O2 ( 310nm)

O(1D) + H2O 2OH•

OH• ist a (free) radical. Radicals are molecule fragments with unpaired electrons. Thus their bound conditions are not required and they are very reactive. The production of radicals depends on the fission of molecules and requires high energy. Typically, this energy is supplied by photons. Radicals are the ‘active players’ of photochemistry.

OH reacts with almost all atmospheric trace gases which is the prerequisite for their destruction. This ability to destroy atmospheric trace gases is called oxidation capacity.

OH is very reactive (within seconds). Although its concentrations are very low, it is the most important atmospheric reactand.

OH exists only during day. Will concentrations of atmospheric pollutants increase during night?

Yes, but also during night reactive cleansing agents (in particular NO3) exist. Nevertheless, they are uually not as effective as OH during day.


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Summary (why atmospheric remotes sensing?) There are several major challenges (from local to global scale):-air pollution-climate change-ozone hole-undertstanding of the earth system (for future predictions, geo-engineering)

Remote sensing can provide information on locations which are not (easily) accessible (e.g. at high altitudes, polar regions, areas subject to political restrictions)

Remote sensing (and in-situ) observations help to quantify emission sources and to understand transport processes and chemical transformations in the atmosphere

physics and chemistry of the a tmosphere - brief overview on...

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