An annual cycle of size-resolved aerosol

hygroscopicity at a forested site in Colorado

Ezra LevinA.J. Prenni, S.M. Kreidenweis, M.D.

Petters, R.C. Sullivan, S.A. Atwood, J. Ortega, P.J. DeMott and J.N. Smith

Funded by: NSF (ATM-0919042)

AMS Annual Meeting 1/24/12

(Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen)

BEACHON

What are the impacts of biogenic emissions on aerosol hygroscopicity and CCN concentrations?

[Levin et al, 2009; Schichtel et al, 2008]

Regional aerosol

21%45%

Modern C

Fossil C

We expect biogenic organics to be important, especially in the summer

Size resolved cloud condensation nuclei

Total NCCN

Dc

Hygroscopicity parameter: kappa

DRT

M

DD

DDDS

w

Was

d

d

/

33

33 4exp

1)(

κ = 0.1

κ = 0.6

[Petters and Kreidenweis, 2007]

SOA

Ammonium Sulfate

0.13 ± 0.04

0.14 ± 0.05

0.15 ± 0.05

0.17 ± 0.06

0.22 ± 0.12

48 ± 3

54 ± 5

66 ± 2

85 ± 3

147 ± 14

KappaActivation Diameter

Kappa timeline

Low kappa indicates large organic component

Kappa and CCN have a seasonal cycle

Why do kappa and CCN change with season and size?

Largest particles are more variable.

Smallest particles consistently low.

New particle formation

New particle formation

At larger diameters, New particles have lower hygroscopicity.

New particle formation

NPF affects aerosol hygroscopicity and CCN concentration.

SOA

Conclusions

The aerosol in Manitou Forest is highly organic dominated.

New particle formation appears to depress kappa but increase CCN.

It is likely that the new CCN have a large biogenic organic component, thus linking the biosphere, hydrosphere and atmosphere.