effects of degraded air-quality on precipitation and

MGWA Simcik 04.12.06

Effects of degraded air-quality on precipitation and recharge

quality

Matt F SimcikDivision of Environmental Health Sciences

School of Public HealthUniversity of Minnesota


USGS website


Percolation• Volatilization

– Henry’s Law• Adsorption

– Kd• Absorption

– fOM

– KOW

• Biodegradation

sw

l

x

x

Cp

CPH

0

≈=Low H

water

soild C

CK =Low Kd

omomneutw

omomOC fK

CfCK ⋅=

⋅=

,

14.0log82.0log +≅ owom KKLow fOM

Low KOW

Recalcitrant


Precipitation/Deposition

• Precipitation– Solubility– Particulate– Surface adsorption

• Dry Deposition– Particle size distribution– Gas-Particle Partioning


Wet Deposition

C

C

C

C

C

CHenry’s

Law

Air-icepartitioning

or

Absorptioninto organic film

impaction

Browniandiffusion

interceptionimpaction

interceptionfiltration

Brownian diffusion

aq

p s,rain

g s

org

Simcik, 2001 In: Persistent Organic Pollutants: Environmental Behavior and Pathways of Human Exposure


Washout of Air Pollutants

( )φφ −+= 1GPT WWWAir

ecipT C

CW Pr= ( )

( )

3

3

mng

mng

air of volumeair in SOC of mass

rain of volumerain in SOC of mass

gasAir,

gas Precip,

C

CWG =

particle Air,

particle Precip,

C

CWP =


Gas ScavengingHenry’s Law Partitioning• partitioning to bulk dissolved phase• equilibrium is reached in 10m fall of raindrop• equilibrium described by Henry’s Law:

wCP

H =

RTH

H ='Dimensionless HLC:

',

, HC

C gAdR =

Partitioning to surface

gas Air,

surface water

CC

K ia =

( )( )air of volume

air in SOC of mass waterof area surface

surface on SOC of mass

2

3

mm

K ia =

Kia is inversely proportional to pL

0 just as K from gas-particle partitioning


Gas ScavengingHenry’s Law Partitioning Partitioning to surface

( )'bulk , H

WG

φ−=

1 ( )φ−= 16000

dKW iaG surface ,

( )φ−

+= 1

60001d

KH

W iaG 'Partitioning to surface becomes important only for compounds with high Kia values and low enough F


Particle Scavenging• Particle washout ratio not so easily calculated from theory• Dependent on both particle size and raindrop size, but more so particle size• Generally 104 – 106, but often operationally defined


Dry Deposition

•Particle phase pollutants depositing on terrestrial aquatic surfaces•Gravitational settling•Molecular diffusion

Turbulence

Boundary layer = no turbulence

Well-mixed Bulk Air


Transfer Depends on:

• Meterology– T, atmospheric stability, relative humidity,

wind speed, pollutant concentration• Particles

– Size, electrostatic effects, density, shape• Surface

– Type (terr vs. aquatic), canopy structure, pH effects, roughness


Removal Rate = Flux, F

F = Vd Ca,p Vd – Deposition velocityCa,p – Air particle concentration of

pollutant

0.0001

0.001

0.01

0.1

1

10

100

Vd (cm sec )

0.001 0.01 0.1 1 10 100Particle Diameter ( m)µ

BrownianDiffusion

GravitySedimentationInertial forces

-1


Physi-chemicalsorptionAd

sorptioninto Liquid-like MatrixAb

Surfaces:MineralElemental CarbonIce

Liquid-like Matrices: Organic Carbon Water


What determines whether a HAP will be a gas, particle or both?

Vapor Pressure = partial pressure of a compound above the pure substance at STP

p0 < 10-7 Pa

10-7 < p0 < 10Pa

p0 > 10 Pa

particles

both

gas

Metals and some large organics

SOCs

Hg0, radon, VOCs


Precipitation/Deposition

• Precipitation– Solubility High Solubility/Low H– Particulate Particulate– Surface adsorption air-water afinity

• Dry Deposition– Particle size distribution larger/smaller– Gas-Particle Partioning low volatility


Atmospheric transport

• Gas-Particle– Gases transport farther– Particles greater potential for deposition

• Reactions– Reactive compounds won’t make it very far– Reaction products may – Gas-particle partitioning


Physical Chemical Properties• Low H• Low Kd• Low Kow• Recalcitrant• Low vapor pressure

• Non-Reactive• High aqueous

solubility

Large sources are necessary to be significant


Candidate Chemicals

• BTEX• Ammonia• Metals• Pesticides• Perfluorochemicals


BTEX

• High H• Low solubility• Moderate Kd• High vapor pressure


Ammonia

• Gas/particle– Relative humidity

• Large sources• Present in precipitation• Biodegradation?• Adsorption?


Metals (Se, Al, Zn etc.)

• Low H• Low vapor pressure• Low Kow• Kd?• Solubility?


Pesticides

• Long-range transport• Low H• High solubility• Moderate Kow• Kd?• Reactive?


PerfluorochemicalsPFOS

PFOA

F3C

F2C

COOH

n

Other perfluorinated acids

n = 4-10

F3C

F2C

CCF2

F2C

CF2

F2C

CF2

COOH


Perfluorochemicals

• Surface active molecules• Stain protectant• Non-stick surfaces• AFFF – Aqueous Film Forming Foam• Residual by-products


Physical/Chemical Properties

• Extremely low H• Low Kd• Kow?• Extremely recalcitrant & non-reactive• Low vapor pressure• Relatively high aqueous solubility (mg/L)


Transport

• Global distribution– Biota– Water

• Atmospheric transport– Precursors

• Direct discharge– WWTP– Landfill leaching


PFCPlant

MajorMidwestern

River

High PFCContamination

In Groundwater

effects of degraded air-quality on precipitation and

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