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Lecture 1: Introduction

Lecture 1: Introduction. Ken Carslaw. A short history of aerosol and climate. 1783 Laki Eruption. Benjamin Franklin attributes global cooling to volcanic haze 1800’s aerosols are the smallest known sub-division of matter

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Lecture 1: Introduction

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  1. Lecture 1: Introduction Ken Carslaw

  2. A short history of aerosol and climate • 1783 Laki Eruption. Benjamin Franklin attributes global cooling to volcanic haze • 1800’s aerosols are the smallest known sub-division of matter • 1859 Tyndall explains blue colour of sky in terms of light scattering by particles • 1871 JW Strutt (3rd Lord Rayleigh) explains light scattering • 1880 Aitken discovered role of aerosol in cloud drop formation • 1898 Aitken: First evidence of new particle formation in the atmosphere. • 1950s: Aerosol as pollution • 1950s Aerosol is a regional pollution issue (LA, London…). Smog. • 1958 CE Junge "unpolluted areas... no longer exist" in Western Europe

  3. A short history of aerosol and climate • 1960s-70s: Anthropogenic aerosol and climate? • 1964 Nicolai Fuchs published The Mechanics of Aerosols • 1967 Aerosol turbidity spread over 1000’s km. McCormick and Ludwig "Climate Modification by Atmospheric Aerosols." • 1968-70. Aerosol cooling could counteract CO2 warming (Bryson). • 1970: First calculation of cooling by aerosol (JM Mitchell). 2/3 of cooling since 1940 due to volcanoes • 1970. Hubert Lamb “volcanic dust probably not main influence” • 1970 Journal of Aerosol Science founded • 1971 Potential aerosol cooling of 3.5K, bigger than CO2 (Rasool and Schneider) • BUT, discussion about whether aerosol cools or warms • 1976 Wide regional effect of sulfate aerosol on climate (Bolin and Charlson) • 1977 Aerosol effect on cloud albedo. Net cooling. (Twomey)

  4. A short history of aerosol and climate • 1980s: First global models with aerosol effects • Late 1970s. First global models including aerosol. James Hansen and others. • 1981. Climate model with volcanic aerosol, solar and CO2 forcings explains 20th C T changes (Hansen) • 1982 The American Association of Aerosol Research formed • 1990: First IPCC report: “neither the sign nor magnitude of the [aerosol] climatic feedback can be quantitatively estimated” • 1990s: Aerosol a central part of climate models. Increasing confidence • 1991: SO4 aerosols roughly balancing CO2 warming (Charlson et al., 1990, 1991, Hansen and Lacis, 1990) • 1991: Pinatubo eruption. Hansen et al (1992) predict 0.5K cooling. Roughly correct. • 1992. Biomass burning aerosol impacts (Penner) • 1994/5: Model of 20th century climate with CO2 and SO4 aerosol (Taylor and Penner, Mitchell et al.) • 1995. 2nd IPCC. Several aerosols in climate models. “Human influence on climate discernable”

  5. A short history of aerosol and climate • 2000s: Sophisticated models and observations • 2001. 3rd IPCC. “Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. Aerosol most uncertain forcing. • 2000/01: Potential large warming from soot aerosol • 2001: First “microphysical” global aerosol models • 2002: Term “Global dimming” • 2005: Global brightening! • 2007: 4th IPCC. Aerosol still most uncertain forcing…

  6. Aerosol distribution and properties • Spatial distribution • Mass, number • Size distribution • What’s important for climate?

  7. Remer et al., Global aerosol climatology from the MODIS satellite sensors, JGR, 2008 Global aerosol distribution Pollution Dust Sea spray Biomass burning Aerosol Optical Depth

  8. Seasonal variability • MODIS satellite aerosol optical depth climatology Remer et al., JGR, 2008

  9. Particle concentrations at the surface 1 mg m-3 ~ 0.75 parts per billion (ppbm) at STP European annual mean exposure limit European recommended limit

  10. European surface level particulate mass <10 mm From the European Air Quality monitoring network 2004, European Environment Agency

  11. Aerosol vertical profile • Profile of aerosol extinction: • Decays from boundary layer to ~3-4km, then follows molecular • Typical for surface sources constant exponential FREE TROPOSPHERE Well mixed BOUNDARY LAYER Sasano, Applied Optics, 1996

  12. Aerosol number vertical profile Remote Pacific • Number increases with altitude • Typical Z-shaped profile over continents • Numerous small particles are invisible CLEAN BOUNDARY LAYER Europe Cirrus Z POLLUTED BOUNDARY LAYER Clarke et al. Schroder et al.

  13. Particle size distributions Nucleation • Modes • Nucleation, Aitken, accumulation and coarse • Not always present • Air quality • Particulate matter (PM), particulates • PM1 – mass less than 1 mm aerodynamic diameter • PM2.5 and PM10 • Air quality and health • Coarse > 2.5mm • Fine <2.5mm • Ultrafine < 0.1mm • Cloud Physics: • Giant > 2mm • Ultra giant > 10 mm Aitken 8e3 Accumulation 4e3 cm-3 Coarse 0 100 mm2 cm-3 50 0 8 Ultrafine fine coarse mm3 cm-3 4 PM2.5 PM1 PM10 0 10.0 1.0 0.01 0.1 Diameter / mm

  14. Size distribution representation 1e5 6000 cm-3mm-1 cm-3 5e4 3000 0 0 600 200 mm2 cm-3mm-1 mm2 cm-3 300 100 0 0 16 120 mm3 cm-3mm-1 mm3 cm-3 8 60 0 0 10.0 1.0 8 10 4 0.01 0.1 0 2 6 Diameter / mm Diameter / mm

  15. Urban • Dominated by emissions 2.105 105 0 1000 500 0 60 40 20 0 10.0 1.0 0.01 0.1 Diameter / mm

  16. Polluted continental • Emitted particles plus complex regional processes 8000 Accum. mode 4000 0 100 50 0 8 4 0 10.0 1.0 0.01 0.1 Diameter / mm

  17. Remote continental • Remote doesn’t mean clean! 8000 4000 0 200 100 0 8 4 0 10.0 1.0 0.01 0.1 Diameter / mm

  18. Free troposphere and stratosphere 20 100 UT 10 50 0 0 2 20 20 Volcanically perturbed 1 10 0 0 0.1 4 3 0.05 2 0 0 10.0 1.0 0.01 0.1 10.0 1.0 0.01 0.1 Diameter / mm Diameter / mm

  19. Arctic • Very aged aerosol • Two periods: • Spring: polluted (Arctic haze) • Summer: clean 200 Arctic haze 100 0 3 2 0 0.4 0.2 0 10.0 1.0 0.01 0.1 Diameter / mm G. Shaw, Bull. Am. Meteorol. Soc., 76, 2403-2413, 1995.

  20. Marine • Varies strongly between clean and polluted • Multiple modes from sea spray production processes • …but there are other sources even in clean regions 200 100 0 100 50 0 20 10 0 10.0 1.0 0.01 0.1 Diameter / mm Heintzenberg et al., Size distribution and chemical composition of marine aerosols: a compilation and review, Tellus, Ser. B, 52B, 1104–1122, 2000.

  21. Desert • Dominated by emissions 200 100 0 1000 500 0 2000 Aged dust plume 1000 0 10.0 1.0 0.01 0.1 Diameter / mm

  22. Composition COARSE Dust (CaCO3, Mg, Si, Al, Fe) Coal dust NaCl Pollen, spores Biological debris FINE H, NH4, SO4, NO3 Organic carbon Elemental carbon Metals (Fe, Pb, Cd, V, Zn etc) 10.0 1.0 0.01 0.1 Diameter / mm See lectures by Sandro Fuzzi.

  23. What’s important for climate?

  24. 8000 4000 0 200 200 Arctic haze 100 100 Light extinction Continental volume • Light scattering efficiency depends in a complex way on • size distribution of particles • chemical composition (refractive index) • particle shape (sphere or not) • Light absorption efficiency depends on • mass of absorbing material • mixing of absorber with other material Arctic volume Marine volume Number Area n = 1.5-0.005i n = 1.37-0.01i Extinction Efficiency 10.0 1.0 0.01 0.1 Diameter / mm See later lectures

  25. Cloud drop formation • Cloud drop number depends on (in order of importance): • Particle numbers and sizes • Cloud dynamics • Particle chemical composition cloud condensation nuclei Only a subset of particles affect climate 10.0 1.0 0.01 0.1 10.0 1.0 0.01 0.1 Diameter / mm Diameter / mm See lectures by Graham Feingold

  26. Long term change IPCC, 2001

  27. CCN change? 1850 2000 Leeds GLOMAP model

  28. Next 2 lecturesSources and sinksFactors that control the size distribution

  29. Definition • An aerosol is a dispersion of solid and liquid particles suspended in gas • It is a singular noun describing the mixture of particles. E.g. “the aerosol over Asia…” • Refer specifically to aerosol particles or particles. • E.g., the “the particle growth rates…” rather than “the aerosol growth rate…”.

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