Future plans in this area, summarized by the questions below, fall into four general areas:

1.  Particle nucleation and growth processes
2.  Phase transformations and water uptake and evaporation
3.  Chemical mechanisms and transformations
4.  Characterization of aerosol particles at a microscopic level

1. Particle Nucleation and Growth

a. What are the precursors to nucleation, and what determines the nucleation rate? For example, what is the role of H₂SO₄, H₂O, NH₃, organics and ions?

b. What determines the rate of growth of freshly nucleated particles?

c. What is the chemical composition of the particles? What are the implications of the composition for particle growth rates? What are the implications for the nucleation mechanism?

d. What is the role of reactions at interfaces in particle growth?

e. What is the effect of homogeneous nucleation on the concentration of CCN?

f. How can nucleation be parameterized in models, given that it does not occur uniformly throughout the atmosphere? What are the effects of perturbations such as clouds, diurnal variations in light and local emissions of precursor gases?

a. What are the phase transformations that occur in mixed composition (organic, inorganic, insoluble solid inclusions) aerosols and how do they change with temperature? What are the effects on their chemistry and radiative properties?

b. How do these processes change from bulk to submonolayer levels?

c. How is water uptake and evaporation affected by such factors as temperature, the presence of an insoluble solid core and the mixture of organics and inorganics?

d. What are the cloud-nucleating capabilities of particles consisting of internal-external mixtures of inorganics, organics and mineral dust?

e. To what extent are aerosol particles coated with sub-monolayer coatings of H₂O? How does this depend on particle composition and relative humidity? What are the implications for reactions on particle surfaces and for particle growth?

3.1 Aqueous Phase:

a. How do reactions in the aqueous phase affect gas phase oxidants and trace species?

b. How do aqueous phase reactions of gaseous trace species affect living organisms?

c. What free radical chemistry occurs in the atmosphere in the aqueous phase and what are the overall impacts on atmospheric chemistry?

d. What is the role of heterogeneous chemistry in NO_x-NO_y interconversions? What are the implications for NO_x production in remote atmospheres? What are the implications for HONO production in source regions?

e. What are the aqueous phase bulk chemistry and properties (e.g., solubility and reaction kinetics) needed to understand processes at interfaces?

 a. How do reactions of NO_y and organics affect the tropospheric oxidant cycle?

 b. Do halogen atoms play a significant role in tropospheric chemistry?

 c. Is the chemistry at surfaces of one species affected by the presence and reactions of others (e.g. saturation of reactive sites)?

 d. What is the interaction of gas phase organics with aerosol surfaces?

 e. What is the interaction of inorganic gases with organic surfaces?

 f. Is there unique photochemistry at surfaces?

a. What are the organics present in particles? How should sampling of particles containing organics be done to avoid artifacts? How do we analyze all the complex species present? What should be used for standards for organics in particles?

b. What is the particle morphology and phase(s) of multi-component aerosol particles? What do the surface and bulk phase look like, chemically and morphologically?

c. How do particles "age" in terms of both chemistry and morphology and how does this affect subsequent chemistry?

d. How is the particle composition (both bulk and surface) and morphology related to health effects of respirable particles observed in epidemiological studies? Can ACP work help to address this?

There are a number of interactions and collaborations involving both the modeling and field studies communities. These include modeling efforts involving scientists at combinations of BNL, PNNL, Battelle Columbus, Univ. of Calif at Irvine, and Univ. of Iowa. In addition, a number of scientists (e.g. McMurry, Imre, Lee) in the aerosols and heterogeneous chemistry research community are actively involved in field programs.

 
Table. Summary of DOE ACP Efforts on aerosols and heterogeneous processes, where "X" denotes an effort funded by ACP and "L" indicates a link between ACP and research funded by other DOE programs or by other agencies.
 

Area	Topic (Investigators)	Laboratory Studies	Modeling	Instruments	Field Studies	Theoretical Studies
Particle Nucleation & Growth	Nucleation, (Garrett,Laulainen, Mikheev,Barlow)	X				X
	Aerosol Growth Mass Spectrometry (Worsnop, Kolb, Jayne, Davidovits)	X		L
	Nanoparticle Size Distribution (Weber)			X	L
	Composition (McMurry)			X	X
Phase Transformations & Water Uptake & Evaporation	Phase transformations as function of T (Imre)	X				X
	Role of organics in aerosols and CCN (Novakov)	X			X
	Nucleation of efflorescence (Martin)	L				L
Chemical Mechanisms and Kinetics	Uptake of gases (Davidovits, Jayne, Worsnop, Kolb)	L				X
	Aqueous phase processes (Lee)	X		X	X
	NOy Heterogeneous Chemistry (Berkowitz, Spicer, Bischof, Cowen)	X	X			X
	VOC Heterogeneous Chemistry (Carmichael,  Grassian)	X	X
	Heterogeneous sea salt halogen chemistry (Finlayson-Pitts)	X	X
Characterization	No direct ACP efforts?