Transcript Document

The roles of H2SO4 and organic species
in the growth of newly formed particles
in the rural environment
Wu Zhijun
Leibniz-Institute for Tropospheric Research (Ift), Leipzig,
Germany
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Talk outline
• Introduction: Nucleation and New particle
formation and growth.
• Experimental: Measurements performed at
Melpitz, Germany
• Case study: Growth rate and condensable
vapor concentration
• Summary
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Nucleation
• Nucleation is the onset of a phase transition in a
•
small region.
The phase transition can be the formation of a
bubble or of a crystal from a liquid. Creation of
liquid droplets in saturated vapor or the creation
of gaseous bubble in a saturated liquid is also
characterized by nucleation. Nucleation of
crystalline, amorphous, and even vacancy clusters
in solid materials is also important.
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What is new particle formation?
Theories:
(1) Binary (H2SO4+H2O)
(2) Ternary (H2SO4+NH3+H2O)
(3) Ion-induced nucleation
New Particle Formation
Condensable
(4) Organics
Vapors
(5)….
Nucleation
Coagulation
Subsequent growth
CCN
Stable clusters
1 nm
3 nm detectable Size
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Kulmala, Science, (2003); Kulmala, Science, (2004); McMurry et al., JGR, (2005)
How important are they?
New particle formation is considered as an
Global climate
important source of particles (e.g. Stanier et al.
2004).
Air quality
In particular: Play Particles
an important role in determining
Visibility
the concentration of cloud condensation nuclei
(CCN), and may change the extent of cloud cover
[Laaksonen et al., 2005].
Health effects
What are the chemical mechanisms controlling nucleation ?
What are the vapors causing the particle growth?
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Up to now: The mechanisms of new particle
formation and growth are still not understood very well.
• Several different nucleation theories
available, but do not work to all the
different geographical locations .
• The characteristics of species
contributing to particle nucleation and
growth are still an open question .
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Talk outline
• Introduction: New particle formation and
growth.
• Experimental: Measurements performed at
Melpitz, Germany
• Case study: Growth rate and condensable
vapor concentration
• Summary
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Measurement site
Ift’s research station
Field campaign: May, June, 2008
Melpitz
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Measurements ---instruments
• Twin Differential Mobility Particle Sizer
(with and without Thermodenuder): (3-800
nm)
20-100 nm
3-20 nm
Kr85
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Measurements ---instruments
• Atmospheric Pressure Chemical
•
•
•
•
•
Ionisation Mass Spectrometry: H2SO4
Air Ion Spectrometer: Air ion mobility
distribution
Hydroxyl radical (OH), Ozone
VOCs
Meteorological parameters
et al.
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New particle formation event at Melpitz
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Growth rate of newly formed particles
2008/05/07
n
 (log Dp  log Dpi ) 2 
N t ,i
dN
Multiple lognormal function:

exp

2
d log Dp i 1 2 log i
2
(log

)
i


Dm
Growth Rate (GR): GR 
t
Dm :Mean geometric diameter
of lognormal ultrafine particle mode
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Condensational growth
4mv  M DC

GR=
dt
Dp 
dDp
Sulfuric acid
Dp : particle diameter;
mv : molecular mass of condensable vapor;
D : the diffusion coefficient;
C : the condensable vapor concentration;
 : particle density;
M : transitional correction factor for the mass flux;
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Condensable vapor concentration
2
2

D

D
2  D p 
  p
 2

p,0
2

C
   0.312 D p  D p ,0   0.623 ln
tDmv 
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2  D p ,0 
 3

 : The mass accommodation coefficient
 : The mean free path of the gas molecules.
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Results from the calculation
H2SO4 available
Observed Growth Rate=4.9 nm h-1
condensable vapor conc. = 6.8107 molec. cm-3
H2SO4 conc. = 2.3 107 molec. cm-3
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Potential candidates (1)
• Non-volatile compounds (at 300 C)
Without Thermodenuder
What
the non-volatile compounds?
Withare
Thermodenuder
(at 300C)
Polymers (Kalberer et al., 2004);
HULIS substances (Limbeck et al., 2003);
(Heterogeneous reactions)
EC?
?
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Potential candidates (1)
Non-volatile compounds (at 300 C)
GR=1.2 nm h-1
C=1.7 107 molec. cm-3
H2SO4 conc. = 2.3 107 molec. cm-3
(Observed) Growth Rate=4.9 nm h-1
condensable vapor conc. = 6.8107 molec. cm-3
Coagulation growth < 5% (Wehner et al., 2005)
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Potential candidates (2)
• Semi-volatile compounds: oxidation
products of Biogenic VOC
VOC, OH, O3: Production rate of semivolatile organic compounds.
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Summary
• The sulphuric acid concentrations are
too low to explain particle growth in the
rural environment, at least for Melpitz.
• The non-volatile compounds contributed
to the particle growth, and formed
parallel to the growth of newly formed
particles.
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Three take-home messages
• NPF events constitute an important
source of CCN.
• H2SO4 concentration can only explain
part of the growth rate of newly formed
particles.
• Non-volatile compounds contribute the
growth of newly formed particle.
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Acknowledgments:
Dr. Wolfram Birmili
Aerosol group in ift
EUCAARI project
Organizers of summer school
Thanks!!
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