Effects of Pollution on Visibility andEffects of Pollution on Visibility and the Earth’s Radiation Balance the Earth’s Radiation Balance

John G. Watson (john.watson@dri.edu)Judith C. Chow

Desert Research InstituteReno, NV, USA

Presented at:The Workshop on Air Quality Management, Measurement, Modeling, and Health Effects

University of Zagreb, Zagreb, Croatia24 May 2007

Based on a Critical Review of Science Based on a Critical Review of Science and Policy Interaction and Policy Interaction (www.awma.org)(www.awma.org)

High uncertainties for aerosol effects on global High uncertainties for aerosol effects on global

radiation balanceradiation balance IPCC (2001)IPCC (2001)

Many aerosol effects are common for visibility Many aerosol effects are common for visibility and climate changeand climate change

QuestionsQuestions What is poor visibility or “haze”?

Why is visibility important?

What causes haze?

How is haze quantified?

How can haze be measured?

How can visibility be improved?

What is haze?What is haze?

Haze is the visually perceived degradation of humanly appreciated views caused by polluting particles and gases.

What is Haze?What is Haze?Plume Blight: Attribution to a Single SourcePlume Blight: Attribution to a Single Source

Regional Haze Regional Haze (Not directly attributable to a single source)(Not directly attributable to a single source)

Poor and Natural Visibility at the Poor and Natural Visibility at the Grand CanyonGrand Canyon

WINHAZE (WINHAZE (webcam.srs.fs.fed.us/winhaze.htm)webcam.srs.fs.fed.us/winhaze.htm)

The human eye is more sensitive to The human eye is more sensitive to sharp changes in constrastsharp changes in constrast

Why is haze important?Why is haze important?

Poor visibility is the most publicly accessible indicator of air pollution.

Haze is associated with adverse pollution levels that affect public health.

Tourists and homeowners pay much for highly prized views.

The same pollutants that affect haze also affect global radiation balance.

What causes haze?What causes haze?

Particles and gases that remove light from a sight path and scatter light into a sight path, thereby obscuring the contrast of a target with background air.

Particles and gases in the air scatter and Particles and gases in the air scatter and absorb lightabsorb light

How is haze quantified?How is haze quantified?Visibility MetricsVisibility Metrics

Perceived visual air quality: What people think they see.

Light extinction (bext), I(x)/I(0) = e-bextx

Contrast=I(x)target/I(x)background

Visual range (VR=4/bext or furthest observed distance)

Spatial frequency (Modulation Transfer Function)

Δbext=4/x

Deciview (dv=10ln(bext/10)

[I(x)=light intensity at distance x from target]

How is haze quantified?How is haze quantified?Other considerationsOther considerations

Long-term averages (e.g., annual, seasonal).

Averages of highest and lowest values (e.g., poorest 20%, lowest 20%).

Frequencies above a threshold.

Willingness to pay or be paid.

How can haze be measured?How can haze be measured? Human observations – viewing targets at various

distances Photographs – measuring distance to targets or

visual enjoyment Contrast transmittance – teleradiometers measure

intensity of target and background) Sight path extinction – transmissometers measure

light removed from a path Point extinction – nephelometers for particle

scattering, aethalometers for particle absorption, NOx analyzer for gas absorption, elevation for clear air scattering

Chemical extinction – weighted sum of major chemical components in fine and coarse particles

Nephelometers for particle light Nephelometers for particle light scatteringscattering

Radiance R903 with smart heater measures dry particle scattering

Optec NGN-2 measures wet (total) particle

scattering

0

200

400

600

800

1000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Hour (PST)

Par

tilc

le S

catt

erin

g (

Mm

-1)

0

20

40

60

80

100

Nep

hel

om

eter

RH

(%

)

FREM bsp FSF bsp FRES bsp

HELM bsp FSF RH

1/30/2001

Temporal variability of particle scattering at Temporal variability of particle scattering at nearby sitesnearby sites

Chemical extinctionChemical extinctionBattery-powered minivol PMBattery-powered minivol PM2.52.5/PM/PM1010 sampler sampler

AirMetrics impactors

PM10 PM2.5

Sampler Configuration in

Tong Liang, China

PMPM2.52.5/scattering(dry) relationships/scattering(dry) relationships

PM2.5 = 0.21 bsp

R2 = 0.93

0

50

100

150

200

0 200 400 600 800 1000

Particle Scattering, bsp (Mm-1)

PM

2.5 (

µg

/m3 )

FREMRelationship

PM2.5 = 0.19 bsp

R2 = 0.92

0

50

100

150

200

0 200 400 600 800 1000

Particle Scattering, bsp (Mm-1)

PM

2.5 (

µg

/m3 )

FRESRelationship

Chemical ExtinctionChemical Extinctionbext (Mm-1) = Σdry extinction efficiency (m2/g) x

humidity multiplier x species concentration (µg/m3)

= 3 x f(RH) x (NH4)2SO4

+ 3 x f(RH) x NH4NO3

+ 4 x Organics+ 10 x Soot+ 1 x Soil+ 0.6 x Coarse Mass+ 10 (Clear Air Scattering)

f(RH)=extinction efficiency increase with RH dv=10ln(bext/10)

Extinction efficiencies assume size Extinction efficiencies assume size distribution, pure substances, and distribution, pure substances, and

spherical particlesspherical particles

0

1

2

3

4

5

6

7

8

0.01 0.1 1 10

Mass Median Geometric Particle Diameter (µm)

Sca

tter

ing

or

Ab

sorp

tio

n E

ffic

ien

cy (

m2 /g

)

Black Carbon,

10 m2/g?

Soil, 1 m2/g

Organics, 4 m2/g

Ammonium

Sulfate, 3 m2/g

Coarse Mass, 0.6 m2/g

Scattering efficiency depends on RH, Scattering efficiency depends on RH, assuming an initial size distribution. assuming an initial size distribution.

High RH measurements are inaccurateHigh RH measurements are inaccurate

0

5

10

15

20

25

30 40 50 60 70 80 90 100

Relative Humidity (%)

Sca

tter

ing

Eff

icie

ncy

(m

2 /g)

IMPROVE, 2001 0.1 µm0.3 µm 0.5 µm0.7 µm 1.0 µm

Range of Sulfate & Nitrate Efficiencies in EPA Guidance

Range in which RH is inaccurately measured

Chemical extinction equals measured Chemical extinction equals measured extinctionextinction

How can visibility be improved?How can visibility be improved?

Quantify where and when poor visibility occurs

Measure PM2.5 chemical components

Determine sources of PM2.5 components

Separate natural from manmade contributions

Reduce emissions from manmade emitters

US Regional Haze RuleUS Regional Haze Rule

Sets ten year goals along line between baseline and “natural visibility conditions”

Uses IMPROVE aerosol measurements to monitor progress

Attains natural visibility conditions by 2065

Uses deciview as indicator of haze

Uses 2000-2004 as baseline

Allows Regional Planning Organizations (RPOs) to develop regional emissions strategies (e.g., emissions trading)

156 U.S. Mandatory Class I Areas156 U.S. Mandatory Class I Areas

Reasonable Progress Glide PathReasonable Progress Glide Path

0

5

10

15

20

25

30

35

2005 2015 2025 2035 2045 2055 2065

Year

Vis

ibil

ity

(d

eciv

iew

)

Great Smoky Denali

Baseline

Natural Visibility

Chemical Contributions to ExtinctionChemical Contributions to ExtinctionAverage of Highest 20% bAverage of Highest 20% bextext, 1995-1999, 1995-1999

3130

2422

2119 19 19 18

13 12 1210

0

50

100

150

200

250

Great

Sm

oky M

ntn

Shenan

doah

Acadia

San G

orgonio

Point R

eyes

Big B

end N

P

Glaci

er N

P

Redwood

Yosem

ite

Yello

wstone

Jarb

idge

Bryce

Can

yon

Denal

i

Ch

emic

al E

xti

nct

ion

(M

m-1

)

0

35

Clear Air Sulfate NitrateOrganics Soot Soil

Deciviews

How can haze be improved?How can haze be improved? Technology-based emissions limitations

Ambient standards

Air quality maintenance

Regional emissions caps and trading zones

Goals and demonstration of reasonable progress

Trends in 20% highest bTrends in 20% highest bextext (Mm (Mm-1-1))1988-19991988-1999

Comparison with Natural ConditionsComparison with Natural Conditions

0

5

10

15

20

25

30

35

Great

Sm

oky M

ntn

NP, TN (G

RSM)

Shena

ndoa

h NP, V

A (SHEN)

Acadia

NP, M

E (ACAD)

San G

orgo

nio S

, CA (S

AGO)

Point R

eyes

NS, C

A (PORE)

Mou

nt R

ainier

NP, W

A (MORA)

Big Ben

d NP, T

X (BIB

E)

Glacier

NP, M

T (GLA

C)

Redwoo

d NP, C

A (REDW

)

Yosem

ite N

P, CA (Y

OSE)

Pinnac

les N

M, C

A (PIN

N)

Badlan

ds N

P, SD (B

ADL)

Guada

lupe

Mnt

ns N

P, TX (G

UMO)

Lass

en V

olcan

ic NP, C

A (LAVO)

Chirica

hua

NM, A

Z (CHIR

)

Crate

r Lak

e NP, O

R (CRLA

)

Bande

lier N

M, N

M (B

AND)

Petrif

ied F

ores

t NP, A

Z (PEFO)

Rocky

Mou

ntain

NP 2

, CO (R

OMO)

Yellow

stone

NP, W

Y (YELL

)

Mes

a Ver

de N

P, CO (M

EVE)

Jarb

idge

W, N

V (JARB)

Great

San

d Dun

es N

M, C

O (GRSA)

Canyo

nland

s NP, U

T (CANY)

Bryce

Can

yon

NP, UT (B

RCA)

Wem

inuch

e W

, CO (W

EMI)

Bridge

r W, W

Y (BRID

)

Denali

NP, A

K (DENA)

IMPROVE Site

Vis

ibili

ty (

Dec

ivie

ws)

Average Poorest 20%

Average Best 20%

Average Natural Visibility

Natural emitters Natural emitters (Asian dust and (Asian dust and wildfires) affect wildfires) affect visibility as well visibility as well

as manmade as manmade sourcessources

1

10

100

1,000

10,000

3/4

3/11

3/18

3/25 4/

14/

84/

154/

224/

29 5/6

5/13

5/20

5/27

Day in 1998

Co

nce

ntr

atio

n (

ng

/m3 )

Silicon AluminumCalcium IronPotassium Titanium

Asian Sand Storm Period

a) Geological Elements at Yosemite NP

0

2,000

4,000

6,000

8,000

10,000

1/91

4/91

7/9110

/911/

924/

927/

9210

/921/

934/

937/

9310

/931/

944/

947/

9410

/941/

954/

957/

9510

/951/

964/

967/

9610

/96

Month and Year

Org

anci

c &

Ele

men

tal

Car

bo

n (

ng

/m3 )

0

5

10

15

20

25

Bu

rned

Are

a (k

m2 )

OC EC Burned Areab) Carbon at Yosemite NP

ConclusionsConclusions Haze is the most publicly accessible evidence of air pollution Poor visibility is related to all other pollution problems Haze is best quantified in terms of contributions from

different types of pollution Progress is tracked through long-term measurements Much of our current knowledge of regional haze comes from

PM monitoring with chemical speciation and special studies within its framework

Each of the aerosol components can be quantified reasonably accurately, with the exception of organic and elemental carbon

Haze improvements will result in general emission reductions that also mitigate against global warming