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Effects of Pollution on Visibility andEffects of Pollution on Visibility and the Earth’s Radiation Balance the Earth’s Radiation Balance
John G. Watson ([email protected])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