# Presentation: 685019

## Ion-Induced Nucleation of Atmospheric Aerosols

_*Peter H. McMurry*_*, PI*
_*Kenjiro (Ken) Iida*_*, Graduate Student*
*Department of Mechanical Engineering*
*University of Minnesota*
_*Fred Eisele*_*, co-PI*
*Atmospheric Chemistry Division*
*National Center for Atmospheric Research*

- R82962001

## Frequency of Regional Nucleation Events at Three Locations1

- Finnish Boreal
- Forest

- Continental
- Europe

- Major U.S. City

- 1Kulmala, M., H. Vehkamäki, T. Tetäjä, M. dal Maso, A. Lauri, V.-M. Kerminen, W. Birmili,
-  P. H. McMurry, 2004, “*Formation and growth of ultrafine atmospheric particles: *
* **A review of observations*,”_ J. Aerosol Sci_., **35(2)**:143-176.

## Environmental Importance of Atmospheric Nucleation

- Effects of nucleation on climate
- Formation of cloud condensation nuclei
- Effects on aerosol size distribution
- Albedo and optical extinction
- Dry deposition
- Effects on human health
- Lung deposition of nanoparticles

## Number Distributions During Nucleation Event in Boulder, CO

- _Nano-SMPS Data_
*Size distribtions of *
*All particles*
*(neutral+positive *
*+ negative)*

- _IGMA Data:_
*Size distributions of*
*Positive (top) or *
*Negative (bottom)*
*particles*

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Nucleation Mechanisms

- Neutral molecule
- Involves clustering of neutral molecules
- Typically multicomponent, e.g., H2O, H2SO4 & NH3
- Ion-Induced
- Involves clustering of various molecules about ions
- Different Chemistries for +ve and -ve ions

**Notes:**
Our DOE-supported research focuses on homogeneous nucleation.  This EPA STAR grant focuses on Ion-Induced nucleation.  The two projects complement each other.

## Project Objectives

- To determine whether or not ion-induced nucleation leads to the formation of significant numbers of particles in the atmosphere
- To learn about the physics and chemistry of ion-induced nucleation in the atmosphere

## Atmospheric Measurements

- Measurements supported by EPA Star Grant
- Composition of +ve and -ve ions during nucleation events
- Ion mobility distributions (0.5 to 5 nm)
- Complementary measurements supported by DOE
- [H2SO4]
- Aerosol size distributions (3 nm to 2 μm)
- NanoTDMA: water uptake and volatility of 3 to 1- nm particles
- Composition of 3-10 nm particles by TDCIMS

## Charge Distributions of Particles formed by Neutral Molecule and Ion-Induced Nucleation

- Neutral Molecule Nucleation

- (Positive) Ion-Induced Nucleation

*nucleus*

*growth*

- -1  0 +1

- -1  0 +1

- +

- 0

## Positive Ion-Induced Nucleation:Size at which Initial Charge is “Remembered”

- Significant Fraction
- Of Particles <7 nm
- Retain Initial
- Positive Charge

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Distinguishing between Positive Ion-Induced and Neutral Molecule Nucleation

- Positive Ion-Induced Nucleation
- Fraction of Growing Particles
- That are Positively Charged

- Neutral Molecule Nucleation:
- Fraction of Growing Particles
- That are Positively Charged

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Size Below Which Charge Distributions Must be Measured to Identify Nucleation Process

*At higher growth rates,*
*particles “remember” their *
*initial charge longer*

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Selected Size Distributions from June 1, 2004

*IGMA Data:*
*Positive Particles*

- _Nano-SMPS Data:_
*All Particles*

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Charge Fractions for 3-5 nm Particles

- _Measured_

- Positive Particles

- Negative Particles

- _Calculated:_
*Ion-Induced *
*Nucleation*

- _Calculated:_
*Neutral *
*Nucleation*

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## IGMA Data: Positive and Negative Particle Size Distributions and +/- Ratio

- +/-
- Ratio

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Conclusions

- IGMA enables measurements on *nucleated particles* as small as 2 nm (~30 molecules)
- Nucleation in Boulder, CO, is dominated by neutral molecules, *not* ions.

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Other Ongoing Work

- Measurement of Ion Composition During Nucleation Events
- Design of new nano-SMPS for measuring *total size distributions* of particles down to 1 nm

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Mass Spectrometer Measurements of Negative Ion Composition in Boulder, CO , March, 2004

## Improved Nano-SMPS: Total (neutral, +, -) Distribution functions down to 1 nm

## Selected Size Distributions from June 1, 2004

*Calculated From IGMA Data:*
*All Particles*

- _Nano-SMPS Data:_
*All Particles*

**Notes:**
Example of an ion mobility spectrum measured in Atlanta on August 2, 2002.  

## Inclined Grid Ion Mobility Analyzer:For 0.5 nm to 5 nm ions: An Improved Instrument

- _Hannes Tammet_, Atmospheric Electricity Laboratory,
- Department of Phyiscs, University of Tartu, Estonia

**Notes:**
Inclined Grid Ion Mobility Analyzer developed by Professor Hannes Tammet for the University of Minnesota group.  This new design offers significant advantages over previous designs.