NEW PARTICLE FORMATION: MECHANISMS AND

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NEW PARTICLE FORMATION MECHANISMS AND INFLUENCE
ON ATMOSPHERIC AEROSOL PROPERTIES
Robert McGraw Atmospheric Sciences
Division Brookhaven National Laboratory Upton, NY
11973
Program Objectives Characterization of new
particle formation mechanisms Evaluation of
subsequent growth/loss processes in the
consideration of new particle formation as a
source for climate- important aerosol, including
light-scattering accumulation mode particles and
CCN Support interpretation of measurements
during ASP field campaigns (e.g correlation of
new particle formation events with measurements
of atmospheric composition and weather conditions)
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OBSERVATIONS OF NEW PARTICLE FORMATION
Global map showing locations of observations of
new particle formation. The dots indicate
observation sites, the dashed lines indicate
regions where airborne or ship observations have
been made (from Kumala et al., 2004).
How important are such new particle formation
events to climate?
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NEW PARTICLE FORMATION IN THE ATMOSPHERE (LIST OF
PROPOSED MECHANISMS)
Homogeneous nucleation of binary mixtures of
water and sulfuric acid (most well understood
system) Homogeneous ternary nucleation of
water, sulfuric acid and ammonia (insufficient
laboratory data CNT models have been
developed) Ion-induced nucleation of binary,
ternary, or organic vapors (upper troposphere /
lower stratosphere as limited by the ion
production rate) Homogeneous nucleation of
iodide species (seen in coastal environments)
Homogeneous ternary nucleation involving water,
sulfuric acid, and organic acids (good laboratory
data by Zhang et al., 2004)
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APPROACH TO CHARACTERIZATION OF NEW
PARTICLE FORMATION (NUCLEATION THEOREM)
2 components
1 component
3 components
HIGHLIGHTS OF APPROACH NT based on law
of mass action and principle of detailed balance
(not a model) nucleation stoichiometry a, b,
and c are approximately the number of molecules
(sulfuric acid, water, and organic,
respectively) in the critical nucleus
related to direction of nucleation path
through critical nucleus region parameterized
rate form is especially convenient for
correlation of field data and for use as
source term in atmospheric models
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EXAMPLE TERNARY NUCLEATION INVOLVING AN ORGANIC
ACID
Data of Zhang et al., 2004
NT motivated replot on log-log scale
H2SO4 (109 molecule cm-3)
(a da 8.2) (b db 17-18) (c dc 1.7)
H2SO4 8 molecules H2O 17 molecules
(approx) p-toluic acid 1 molecule!
CRITICAL NUCLEUS MOLECULAR CONTENT (from slopes
or relative sensitivities ? Log J / ? Log Si )
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REQUIREMENTS FIELD MEASUREMENTS FOR IMPROVED
UNDERSTANDING OF NEW PARTICLE FORMATION AND
LIFECYCLE
Input for event/lifecycle analysis using
Lagrangian trajectory models Measurements of
new particle (3nm) formation events (free
atmosphere plumes) Atmospheric
composition/meteorology, including potential
nucleation/growth species concentrations, upwind
of a new particle event (1-3 hr) SOA growth
rates for correlation with model estimates of
particle growth (nm/hr) Background aerosol
measurements (size distribution and loading)
important for determining competing rates of
coagulation removal Downwind measurements of
new particle lifecycle (1-12 hr) (e.g. size,
composition, loss rate) Correlation of new
particle formation events with increased CCN
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DELIVERABLES
NT-based parameterizations for nucleation rate
(source term for new particle formation)
(Year 1) Improved quantification of particle
growth rates/processes through correlation of
air parcel trajectory calculations with field
measurements (Years 2 and 3) New particle
formation /aerosol growth modules for input to
climate models (Years 2 and 3)