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TROPOSPHERIC AEROSOLS

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

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  1. TROPOSPHERIC AEROSOLS Part II: secondary aerosol

  2. 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

  3. Gas emissions leading to secondary aerosol • Dimethylsulfide (DMS) • SO2 emissions from volcanoes • Industrial SO2 emissions • Nitrogen oxides and ammonia • Volatile Organic compounds (VOC)

  4. 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

  5. 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)

  6. 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.

  7. 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

  8. 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

  9. 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

  10. 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)

  11. 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

  12. 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

  13. 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--

  14. 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 »)

  15. Volcano locations

  16. Continuously erupting volcanoes

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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)

  27. 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

  28. 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

  29. 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)

  30. 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

  31. Global sulfur emissions

  32. GLOBAL SULFUR EMISSION TO THE ATMOSPHERE (1990 annual mean) Chin et al. [2000]

  33. 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.

  34. 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%

  35. Future SO2 emissions in Asia are likely to be much lower than the latest IPCC forecasts

  36. Sources of nitrogen oxidesand ammonia Fluxes in TgN/year Aircraft 0.5 NOx: ~32 TgN anthropogenic ~11 TgN natural

  37. 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

  38. Global NOx emissions (Tg/yr)

  39. 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

  40. Global NOx from lightning

  41. 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

  42. Global NH3 emissions

  43. Global NH3 sources

  44. 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

  45. Spatial and temporal development of VOC emissions(Klimont et al., Atmos. Environ., 36, 1309, 2002)

  46. Conclusion: Integrated observation and modeling programs like INDOEX, TRACE-P, and ACE-Asia improve our understanding of emissions … Experimental measurements Theoretical modeling

  47. … 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

  48. A Few Insights on Air Pollution and Climate from ACE-Asia Barry J. Huebert Department of Oceanography University of Hawaii huebert@hawaii.edu 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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