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Prof. Production mechanism, number concentration, size distribution, chemical composition , and optical properties of sea spray aerosols. [Source: wikipedia ]. [Source: daily mail]. Wind entrains air into surface waters, leading to bubble formation.

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Presentation Transcript
slide1

Prof.

Production mechanism, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols

[Source: wikipedia]

[Source: daily mail]

Wind entrains air into surface waters, leading to bubble formation

Bubbles rise to the top and burst producing residual particles

Markus Petters

Workshop, Raleigh June 4-6 2012

the role of marine aerosols in determining cloud albedo precipitation and structure
The role of marine aerosols in determining cloud albedo, precipitation, and structure

[Petters et al., JGR, 2006]

quotes from an andreae et al 2009
Quotes from an Andreae et al. (2009).

“The number size distribution of the sea salt aerosol extends well down into the submicron range and indeed commonly peaks there”

It had long been thought that most marine sub-micron particles are primarily comprised of sulphate derived from the oxidation of dimethyl sulfide emitted from ocean surface and SO2 from long range transport of continental sources and ship emissions.”

“… numerous recent studies have revealed a substantial organic presence even in remote marine air.”

hygroscopicity diameter growth factor as a proxy for aggregate chemical composition
Hygroscopicity (diameter growth factor) as a proxy for aggregate chemical composition

Sulfates:

gf @ 80% = 1.5-1.6

Organics:

gf @ 80% = 1-1.2

Sea Salt:

gf @ 80% = 1.8

Internally mixed particle:

  • Low (< 0.6) measured hygroscopicities indicate substantial contribution of organic compounds
model prediction over remote oceans
Model prediction over remote oceans:

[Pringle et al., ACP, 2010, ECHAM/MESSy Atmospheric Chemistry (EMAC) model]

measurements show generally
Measurementsshow generally
  • Where is all the sea salt?
  • Does sea-spray contribute to aerosol number?
  • Does sea spray include a dominant organic source?

Growth factor data from DYCOMS-II

(remote Pacific, 7 flights in July

Histogram of growth factor measurement

taken over the ocean

[Snider and Petters , ACP 2008]

[Wex et al., GRL, 2010]

slide10

Bottom up approach: lab studies combined with bubble spectra

[Blanchard and Syzdek, JGR, 1988]

[Wu et al., 1992]

slide11

Bottom up approach: aerosol number production/bubble scatter widely – do we accept such large uncertainties?

[Lewis and Schwartz, 2004]

[Blanchard and Syzdek, JGR, 1988]

organic coatings on bubbles
Organic coatings on bubbles
  • The thickness of the organic coating for oceanic bubbles ranges from0.01 m for lipids to 1 m for proteins such as glycoproteins
  • Coating occurs within a few seconds for bubbles < 300 m
  • Coatings stabilize the bubble potentially through their surfactant properties
  • Large bubbles (mm size) are not completely coated
  • Important for ocean optical properties

[Chalmers and Bavarian, 1991]

[Thorpe 1982, Yount1979 and others]

trying to understand production of organics in the laboratory
Trying to understand production of organics in the laboratory

filtered air

Aerosol

measurement

[Bates et al., 2012, JGR in press]

slide14
Organic fractions from sea-spray are all over the map, but many studies show that it is difficult to emit organics

Keene et al., JGR 2007

Facchini et al., GRL, 2008

Wex, Fuentes et al., AMET/AMT, 2010

Bates al. JGR, 2012

Modini et al. ACP, 2010

slide15
To what level do we need to decompose the system? Single bubble, single plume, single whitecap, single model gridbox?

[Deane and Stokes, Nature, 2002]

field vs laboratory measurements
Field vs. Laboratory Measurements
  • Very challenging measurement environment
  • Difficult to isolate sea-spray from secondary aerosol and free- troposphere entrainment
  • Difficult to control for key variables (wind speed, sea-water composition, wind fetch, wet and dry deposition, evolution of size distribution, atmospheric turbulence …)
  • Studies in great detail are possible, working towards mechanistic understanding
  • Precise control over variables (bubble size, water composition, surface layer)
  • Main critique: experiments are not representative (bubble plume, atmospheric turbulence …)

http://termserv.casaccia.enea.it/term/brivido/brivido.html

Courtesy of Jeff Reid

different questions may need different foci
Different questions may need different foci
  • Mass emissions (optical properties)
  • Number emissions (CCN properties: size + chemical composition)
  • “Special” emissions (surfactants affecting CCN properties, ice nuclei emissions)