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TROPOSPHERIC AEROSOLS. Part II: secondary aerosol. Aerosol properties. Species. Natural processes. anthropogenic. Present burden vs pre-industrial. Elements of climate affecting emissions. Primary particles. Mineral dust . Wind erosion. Land use change, industrial dust. Incr.

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tropospheric aerosols

TROPOSPHERIC AEROSOLS

Part II: secondary aerosol

aerosol properties
Aerosol properties

Species

Natural processes

anthropogenic

Present burden vs pre-industrial

Elements of climate affecting emissions

Primary particles

Mineral dust

Wind erosion

Land use change, industrial dust

Incr.

Changing winds and precipitation

Sea salt

Wind

Changing winds

Biolog. Part.

Wind, biolog. processes

Agriculture

???

Changing winds

Carb. Part.

Vegetation fires

Fossil fuel & biomass burning

Incr.

Changing precip.

Secondary

DMS

Phytoplankton degradation

More sulfate

Changing winds

SO2

Volc emissions

Fossil fuel comb.

More sulfate

NH3

Microbial activity

Agriculture

More ammonium nitrate

NOx

Lightning

Fossil fuel comb.

Incr. nitrate

Change in convective activity

VOC

Vegetation

Industrial processes

Incr. Org. aerosol

gas emissions leading to secondary aerosol
Gas emissions leading to secondary aerosol
  • Dimethylsulfide (DMS)
  • SO2 emissions from volcanoes
  • Industrial SO2 emissions
  • Nitrogen oxides and ammonia
  • Volatile Organic compounds (VOC)
dms ch 3 2 s is the major one of biogenic gases emitted from sea
DMS, (CH3)2S,is the major one of biogenic gases emitted from sea
  • mean residence time is about 1-2 days - most of S from DMS is also re-deposited in the ocean
  • is produces during decomposition of dimethyl-sulfonpropionate (DMSP) from dying phytoplankton
  • only small fraction lost into the atmosphere
dimethylsulfide
Dimethylsulfide
  • Recent global estimates of DMS flux from the oceans range from 8 to 51 Tg S a-1
  • This is 50% of total natural S-emissions (presently nearly equivalent to anthropogenic emissions, 76 Tg S a-1)

- Differences in the transfer velocities in sea-to-air calculations

  • Uncertainties are due to:

- DMS seawater measurements (paucity of data in winter months and at high latitudes)

dms and climate
DMS and Climate
  • DMS is emitted by phytoplankton as a natural biproduct of metabolism
    • Possibly related to radiation protection
  • Gives sea water its characteristic smell
  • Forms much of the natural aerosol (sub-micron particles) in oceanic air
  • DMS is the major biogenic gas emitted from sea and the major source of S to the atmosphere. It contributes to the sulfur burden in both the MBL and FT.
the claw hypothesis charlson lovelock andreae and warren 1987
The CLAW Hypothesis(Charlson, Lovelock, Andreae and Warren, 1987)
  • DMS from the ocean affects cloud properties and can feedback to the plankton community
  • This acts to regulate climate by increasing cloud albedo when sea-surface temperatures rise.

Figure adapted from Charlson et al. (1987)

“Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate”

Nature, vol. 326, pp. 655-661

dms oxidation
DMS oxidation
  • The atmospheric oxidation pathways that lead from DMS to ionic species (essentially sulfate and methanesulfonic acid, MSA, CH3SO3H) are complex and still poorly understood
  • The first step to sulfate is SO2
  • SO2 is largely dominant vs MSA, except at high latitudes (reasons unclear)
  • MSA is unique for tracing marine biological activity, since it has no other source
about atmospheric so 2
About atmospheric SO2
  • SO2 has several sources:
  • either natural: marine MSA and volcanism
  • or anthropogenic: mining and fossil fuel burning
  • Its oxidation ways to SO4-- are still matter to investigation, in particular with the aid of S & O stable isotopes
  • This can occur either in the gaseous phase by OH radicals or in the liquid phase by O3 or H2O2 .
  • Generally gaseous phase process is dominant, except in regions of high sea salt concentrations
slide10
0%

50%

100%

Effect of sea-salt chemistry on SO2 and SO42- concentrations

Percent (%) change in concentrations (yearly average)

Case A: SO2/SO42- concentration without sea-salt chemistry

Case B: With sea-salt chemistry

SO2 (decrease)

SO42- (small increase)

slide11
0%

100%

50%

Effect of sea-salt chemistry on gas-phase sulfate production rates

Percent (%) decrease (seasonal average):

Mar/Apr/May

Jun/Jul/Aug

Sep/Oct/Nov

Dec/Jan/Feb

slide12
Aqueous-phase

O3

Aqueous versus Gas Phase Oxidation

Biological regulation of the climate?

(Charlson et al., 1987)

H2O2

Aqueous-phase

Gas-phase

CCN

OH

DMS

SO2

H2SO4

New particle formation

NO3

OH

Light scattering

so 2 emissions from volcanoes 1
SO2 emissions from volcanoes (1)
  • Volcanoes are a major natural source of atmospheric S-species
  • Injections are generally occurring in the free troposphere
  • Most active volcanoes are in the Northern Hemisphere (80%)
  • The strongest source region is the tropical belt, in particular Indonesia
  • Emissions are in the form of SO2, H2S and SO4--
so 2 emissions from volcanoes 2
SO2 emissions from volcanoes (2)
  • 560 volcanoes over the world are potential SO2 sources, but only a few have been measured
  • Volcanic activity is sporadic, with a few cataclysmic eruptions per century
  • Cataclysmic eruptions inject ash particles and gases (mainly SO2) into the stratosphere, where H2SO4 formed forms a veil (« Junge layer »)
atmospheric impact of volcanoes
Atmospheric impact of volcanoes

SO2 relatively insoluble, resists tropospheric washout

Injected into the stratosphere in large quantities (Pinatubo, 1991 ~20 Tg)

In stratosphere, SO2 oxidises to produce sulfuric acid aerosols (H2SO4)

Conversion of SO2 to H2SO4 slow (months), aerosol cloud replenished months after eruption

slide18
The total amount of volcanic tropospheric S-emissions is presently estimated at:

14 +/- 6 Tg a-1

Mean volcanic sulfur emissions are of comparable importance for the atmospheric sulfate burden as anthropogenic sources because they affect the sulfate concentrations in the middle and upper troposphere whereas anthropogenic emissions control sulfate in the boundary layer.

S-isotope measurements in central polar regions (i.e. in the free troposphere) seem to support the important role of volcanic sulfur

volcanic aerosol and global atmospheric effects
Volcanic aerosol and global atmospheric effects

Acid aerosols reside in the stratosphere for several years

Aerosol veils increase optical depth of the atmosphere

(inc. optical depth of 0.1% = 10% reduction sunlight reaching Earth surface). Spread around the globe by stratospheric winds

Injection of acid aerosols into stratosphere is the

fundamental process governing the atmospheric impact of volcanic eruptions

atmospheric effects of volcanic eruptions
Atmospheric effects of volcanic eruptions

1. Tropospheric cooling due to increased albedo

Effects of aerosols can be direct or indirect

Albedo increased indirectly when aerosols fall out of the stratosphere

Nucleate clouds in troposphere - increase albedo

Recent major volcanic eruptions produced significant cooling anomalies (0.4-0.7oC) in the troposphere for periods of 1 to 3 years

Magnitude of volcanic effects masked by natural variations (e.g. El Nino)

2.Stratospheric warming

Acid aerosols absorb incoming solar radiation, heating the tropical stratosphere, e.g. Mt. Agung (1963), El Chichon (1982), and Pinatubo (1991) all caused warming of the lower stratosphere of ~2oC

3. Enhanced destruction of stratospheric ozone

stratospheric warming
Stratospheric warming

+3oC

0oC

El Chichon

Pinatubo

-3oC

Lower stratospheric temperature (global mean)

Localised heating in the stratosphere can influence how far volcanic aerosol veils spread, by influencing stratospheric wind patterns

enhanced destruction of stratospheric ozone
Enhanced destruction of stratospheric ozone

Volcanoes do not inject chlorine into the stratosphere.

Aerosols improve efficiency with which CFC`s destroy ozone,

by activating anthropogenic bromine and chlorine, indirectly leading to

enhanced destruction of stratospheric ozone

Relatively short lived - aerosols last only 2-3 years in the stratosphere

Reduction in ozone following the June 1991 eruption of Pinatubo

atmospheric effectiveness
Atmospheric “effectiveness”

Several factors combine to determine whether a volcanic eruption has the

potential to influence the global atmosphere

1. Eruption style

Energetic enough to inject aerosols into the stratosphere

Larger eruptions do not necessarily have greater effects

Increased SO2 results in larger particles, not more

Fall from the stratosphere faster, smaller optical depth per unit mass

volcanic effects on the atmosphere may be self-limiting

2. Magma chemistry

Importance of acid aerosols means that large eruptions of sulphur-poor

magma less significant than sulfur-rich magmas

e.g. Mt St Helens - sulfur poor - negligible global effects

atmospheric effectiveness1
Atmospheric“effectiveness”

3. Latitude

Proximity to the stratosphere:smaller eruptions at high latitude can inject as much SO2 into the stratosphere as larger eruptions at lower latitudes

Stratospheric dispersal:Aerosols from tropical eruptions have the potential to spread around the globe (e.g Pinatubo). Atmospheric influence of eruption outside the tropics is contained within the middle and polar latitudes of the hemisphere of origin

volcanic eruptions and climate
Volcanic eruptions and climate

Atmospheric processes are complex !

Understanding how an atmospheric perturbation influences climate and weather is still problematic, even for largest eruptions

However, understanding how volcanoes effect climate necessary to isolate other forcing processes

Comparison of chronology of known eruptions and climatic data shed light on the ways climate responds to large volcanic eruptions

making the connection
Making the connection

1. The written record

Compare eruption chronologies with written records of unusual

climatic events

e.g. Benjamin Franklin (1784) ``During several months of the summer of the year 1783, when the effects of the Sun`s rays to heat the Earth should have been the greatest, there existed a constant fog over all of Europe, and great parts of North America.`` => 1783 - Laki fissure eruption, Iceland

Disadvantages: record only a couple of thousand years, humans unreliable, eruption chronologies incomplete, geographical bias (e.g. no humans = no record)

making the connection1
Making the connection

2. Ice cores

Acid aerosols fall on ice fields

Accumulation of ice preserves

information - acidity profile

Climatically significant eruptions

can be identified with great precision

Advantages: objective, precise, records

`climatically significant` eruptions only

Disadvantages: Which eruptions and why?

Only those with high sulfur contents.

Geographical bias.

HALF of known large eruptions not recorded in Greenland ice cores

making the connection2
Making the connection

3. Tree rings

Proxy witnesses to eruptions

Temperate trees record passage of seasons in growth rings - dendochronology

Changes in ring spacing, frost damage correlate with known eruptions

Advantages: Trees, are old! Record extends back thousands of years. Objective, precise

Disadvantages: Tree growth sensitive to things apart from climate. Local environmental factors significant

case study krakatau 1883
Case study: Krakatau, 1883

20 km3 of pyroclastic material in a Plinian column 40 km high

Aerosol veil circumnavigated the globe in ~2 weeks

Initially confined to the tropics, later spread to higher latitudes in

both hemispheres

Caused spectacular sunsets worldwide

20% fall in radiant energy reaching Europe after the eruption

Average Northern Hemisphere cooling of 0.25oC, more pronounced at

higher latitudes (-1oC)

case study tambora 1815
Case study: Tambora, 1815

50 km3 of pyroclasts, Plinian column 43 km high

Aerosol veil reached London in about 3 months

Many climatic effects attributed to Tambora

1816 - `the year without a summer`

inspired `Frankenstein`

Anomalously cold winter in North America and Europe

Widespread crop failures, famine

industrial so 2 emissions
Industrial SO2 emissions
  • During the last decade, researchers from different countries have prepared separate country-level inventories of anthropogenic emissions (GEIA= Global Emission Inventory Activity). In regions were local inventories were not available, estimates based on fossil fuel consumptions and population were calculated.
slide34
Anthropogenic sulfur emissions

In 1985: about 81% of anthropogenic sulfur emissions were from fossil fuel combustion, 16 % from industrial processes, 3 % from large scale biomass burning and 1% from the combustion of biofuels, but these figures have to be revised for more recent years.

The total amount for 1985 is estimated at :

76 Tg S a-1, accurate to 20-30%

sources of nitrogen oxides and ammonia
Sources of nitrogen oxidesand ammonia

Fluxes in

TgN/year

Aircraft

0.5

NOx: ~32 TgN anthropogenic

~11 TgN natural

nitrogen oxides
Nitrogen oxides
  • They are important in atmospheric oxidant chemistry
  • They are precursors for nitric acid which is a contributor to atmospheric acidity and reacts with NH3 and alkaline particles
a century of no x emissions van aardenne et al gbc 15 909 2001
A century of NOx emissions(van Aardenne et al., GBC, 15, 909, 2001)

1990: dominated by

northern hemisphere

industrialization

1890: dominated by

tropical

biomass burning

ammonia nh 3
Ammonia NH3
  • Ammonia is the primary basic (i.e. not acidic) gas in the atmosphere, and after N2 and N2O, the most abundant nitrogen containing gas in the atmosphere
  • The significant sources of NH3 are animal wastes, ammonification of humus, emissions from soils, loss of fertilizer from soils and industrial sources – see next table
  • The ammonium ion, NH4+ is an important component of continental tropospheric aerosols (as is NO3-) forming NH4NO3
  • NH3 is highly water soluble and therefore has a residence time in the troposphere of around 10 days
    • Consequently, atmospheric concentrations of NH3 are quite variable, typically ranging from 0.1 to 10 ppb
voc volatile organic compounds
VOC = Volatile Organic Compounds
  • Natural biogenic and anthropogenic sources
  • -Anthropogenic: alkane, alkenes, aromatics and carbonyls
  • -Biogenic: isoprene, mono-and sesquiterpenes, a suite of O-containing compounds
  • They produce secondary organic particles
  • Based on emission inventories and laboratory data, the production of secondary organic particulate from VOC is estimated to:

30 to 270 Tg a-1

spatial and temporal development of voc emissions klimont et al atmos environ 36 1309 2002
Spatial and temporal development of VOC emissions(Klimont et al., Atmos. Environ., 36, 1309, 2002)
slide46
Conclusion: Integrated observation and modeling programs like INDOEX, TRACE-P, and ACE-Asia improve our understanding of emissions …

Experimental

measurements

Theoretical

modeling

but we desperately need more source testing in the developing world
… but we desperately need more source testing in the developing world

Representativeness of entire

population of sources

Typical operating practices

Typical fuels and fuel characteristics

Relationship to similar sources in the

developed world

Daily and seasonal operating cycles

a few insights on air pollution and climate from ace asia
A Few Insights on Air Pollution and Climate from ACE-Asia

Barry J. Huebert

Department of Oceanography

University of Hawaii

[email protected]

The Real Authors:

Steve Howell, Byron Blomquist

Liangzhong Zhuang, Jackie Heath

Tim Bertram, Jena Kline

ACE-Asia Science Team

Supported by the US NSF

& 35 other agencies

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