GLOBAL SULFUR BUDGET [Chin et al., 1996](flux terms in Tg S yr-1)

Phytoplankton

(CH3)2S

SO2

1.3d

DMS1.0d

OHNO3

Volcanoes CombustionSmelters

SO42-

3.9d

22

10 64

OH

cloud42

8184

dep27 dry20 wet

dep6 dry44 wet

H2SO4(g)

GLOBAL SULFUR EMISSION TO THE ATMOSPHERE

[Chin et al. 2000]

2001 estimates (Tg S yr-1): Industrial 57 Volcanoes 5 Ocean 15 Biomass burning 1

FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS

2

2

2

22 4 4

3 4

3 3

3 3 4 3

( ) 2

( )

( )

( ) ( ) ( )

H O

H O

H O

H SO g SO H

NH g NH OH

HNO g NO H

NH g HNO g NH NO aerosol

Sulfate always forms an aqueous aerosol

Ammonia dissolves in the sulfate aerosol totally or until titration of acidity, whichever happens first

Nitrate is taken up by aerosol if (and only if)excess NH3 is available after sulfate titration

HNO3 and excess NH3 can also form a solid aerosol if RH is low

Thermodynamic rules:

Highest concentrations in industrial Midwest(coal-fired power plants)

Observed aerosolacidity in US

GLOBAL EMISSIONS OF AMMONIA

GLOBAL UNITED STATES

Ammonia,Tg N yr-1

55 2.8

[Bouwman et al., 1997]

SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S. (2001)

Highest concentrations in industrial Midwest(coal-fired power plants)

Sulfate Nitrate

Ammonium

STRATOSPHERIC AEROSOL

TROPOPAUSE

Transport of long-lived S

gases (eg. COS)

Injection of volcanic ash

(SiO2, Al2O3, Fe2O3) as well as gases (H2S, SO2, HCl)

Aerosols in the stratosphere are long-lived due to absence of precipitation and “layered” transport (due to stability)

PSCs (nitric acid / water vapor)

PSCs (nitric acid / water vapor)

HOW COMPOSITION AND SIZE FIT TOGETHER…

Image from: C. Leck

SURFACE AEROSOL NUMBER CONCENTRATION

Dec July

Continental: > 250 cm-3

Urban/polluted: > 2000 cm-3

Marine BL: ~ 200 cm-3

[Spracklen et al., 2006]

GLOMAP: 2 moment sectional model simulating sulfuric acid / sea salt

RAOULT’S LAW

water saturation vapor pressureover pure liquid water surface

water saturation vapor pressureover aqueous solution of watermixing ratio xH2O

2 ,oH O SATP 2 , 2 2 ,

oH O SAT H O H O SATP x P

An atmosphere of relative humidity RH can contain at equilibrium aqueous solution particles of water mixing ratio 2 ,

22 , 100

H O SATH O o

H O SAT

P RHx

P

HOWEVER, AEROSOL PARTICLES MUST ALSO SATISFY SOLUBILITY EQUILIBRIA

Consider an aqueous sea salt (NaCl) particle: it must satisfy

2

(solubility equilibrium)

(electroneutrality)

1 (closure)

Na Cl s

Na Cl

Na Cl H O

x x K

x x

x x x

This requires:1

2100(1 2 ) "deliquescence RH"sRH K

At lower RH, the particle is solid at equilibrium, though it can also remain in metastable aqueous state

UPTAKE OF WATER BY AEROSOLS

RELATIVE HUMIDITIES FOR DELIQUESCENCE/CRYSTALLIZATION OF AEROSOLS

IN CONTRAST TO OZONE, HEMISPHERIC AEROSOL BACKGROUND IS NOT AN AIR QUALITY ISSUE (wrt NAAQS)

TRACE-P aircraft observations over NW Pacific (Mar-Apr 2001) and GEOS-Chem model simulations

…because of efficient precipitation scavenging in continental outflow

P3B DATA over NW Pacific (30 – 45oN, 120 – 140oE)

[Park et al. 2005]

HOWEVER, DESERT DUST CAN BE TRANSPORTED ON INTERCONTINENTAL SCALES

GlenCanyon, Arizona

clear day April 16, 2001: Asian dust!

Annual mean PM2.5 dust (g m-3), 2001

Asia

Sahara

Most fine dust in the U.S. (except in southwest) is of intercontinental origin

LONG RANGE TRANSPORT OF DUST FROM AFRICA TO THE AMAZON (2008)

[Prenni et al., 2009]

Timeseries of dust @ field site N of Manaus

Model simulation of the African dust plume

[IPCC 2007]

AEROSOL CLIMATE FORCING

SCATTERING OF RADIATION BY AEROSOLS:“DIRECT EFFECT”

By scattering solar radiation, aerosols increase the Earth’s albedo

Scattering efficiency is maximum when particle diameter = particles in 0.1-1 msize range are efficient scatterers of solar radiation

Mt. Pinatubo eruption

1991 1992 1993 1994

-0.6

-0

.4

-0.

2

0

+0

.2Te

mp

era

ture

C

ha

nge

(oC

)

Observations

NASA/GISS general

circulation model

Temperature decrease following large volcanic eruptions

EVIDENCE OF AEROSOL EFFECTS ON CLIMATE:

SCATTERING vs. ABSORBING AEROSOLS

Scattering sulfate and organic aerosolover Massachusetts

Partly absorbing dust aerosoldownwind of Sahara

Absorbing aerosols (black carbon, dust) warm the climate by absorbing solarradiation

AEROSOL “INDIRECT EFFECT” FROM CLOUD CHANGES

Clouds form by condensation on pre-existing aerosol particles (“cloud condensation nuclei”) when RH>100%

clean cloud (few particles):large cloud droplets• low albedo• efficient precipitation

polluted cloud (many particles):small cloud droplets• high albedo (1st indirect)• suppressed precipitation (2nd indirect)

Particles emitted by ships increase concentration of cloud condensation nuclei (CCN) Increased CCN increase concentration of cloud droplets and reduce their avg. size Increased concentration and smaller particles reduce production of drizzle Liquid water content increases because loss of drizzle particles is suppressed Clouds are optically thicker and brighter along ship track

N ~ 100 cm-3

W ~ 0.75 g m-3

re ~ 10.5 µm

N ~ 40 cm-3

W ~ 0.30 g m-3

re ~ 11.2 µm

from D. Rosenfeld

EVIDENCE OF INDIRECT EFFECT: SHIP TRACKS

AVHRR, 27. Sept. 1987, 22:45 GMTUS-west coast

NASA, 2003Atlantic, France, Spain

SATELLITE IMAGES OF SHIP TRACKS

Aircraft condensation trails (contrails) over France, photographed from the Space Shuttle (©NASA).

OTHER EVIDENCE OF CLOUD FORCING:CONTRAILS AND “AIRCRAFT CIRRUS”