Transcript Poor Visibility, Its Causes and Its Measurement

Effects of Pollution on Visibility and
the Earth’s Radiation Balance
John G. Watson ([email protected])
Judith C. Chow
Desert Research Institute
Reno, NV, USA
Presented at:
The Workshop on Air Quality Management,
Measurement, Modeling, and Health Effects
University of Zagreb, Zagreb, Croatia
24 May 2007
Based on a Critical Review of Science
and Policy Interaction (www.awma.org)
High uncertainties for aerosol effects on global
radiation balance IPCC (2001)
Many aerosol effects are common for visibility
and climate change
Questions
 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?
 Haze is the visually perceived
degradation of humanly appreciated
views caused by polluting particles
and gases.
What is Haze?
Plume Blight: Attribution to a Single Source
Regional Haze
(Not directly attributable to a single source)
Poor and Natural Visibility at the
Grand Canyon
WINHAZE (webcam.srs.fs.fed.us/winhaze.htm)
The human eye is more sensitive to
sharp changes in constrast
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?
 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
absorb light
How is haze quantified?
Visibility 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?
Other 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?
 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
scattering
Optec NGN-2 measures
wet (total) particle
scattering
Radiance R903 with
smart heater measures
dry particle scattering
Temporal variability of particle scattering at
nearby sites
1000
100
FREM bsp
HELM bsp
FSF bsp
FSF RH
FRES bsp
800
80
600
60
400
40
200
20
0
0
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)
Nephelometer RH (%)
-1
Partilcle Scattering (Mm )
1/30/2001
Chemical extinction
Battery-powered minivol PM2.5/PM10 sampler
AirMetrics
impactors
Sampler
Configuration in
Tong Liang, China
PM10
PM2.5
PM2.5/scattering(dry) relationships
200
FREM
PM2.5 = 0.21 bsp
Relationship
R2 = 0.93
100
50
0
0
200
400
600
200
1000
800
Particle Scattering, bsp (Mm-1)
FRES
Relationship
PM2.5 = 0.19 bsp
R2 = 0.92
150
PM 2.5 (µg/m3)
PM 2.5 (µg/m3)
150
100
50
0
0
200
400
600
800
-1
Particle Scattering, bsp (Mm )
1000
Chemical Extinction
bext (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
distribution, pure substances, and
spherical particles
8
7
2
Scattering or Absorption Efficiency (m /g)
Organics, 4 m2/g
6
5
Ammonium
Sulfate, 3 m2/g
4
3
Black Carbon,
10 m2/g?
Soil, 1 m2/g
2
1
Coarse Mass, 0.6 m2/g
0
0.01
0.1
1
Mass Median Geometric Particle Diameter (µm)
10
Scattering efficiency depends on RH,
assuming an initial size distribution.
High RH measurements are inaccurate
25
IMPROVE, 2001
0.3 µm
0.7 µm
0.1 µm
0.5 µm
1.0 µm
Range in which RH is
inaccurately measured
2
Scattering Efficiency (m /g)
20
15
Range of Sulfate & Nitrate
Efficiencies in EPA Guidance
10
5
0
30
40
50
60
70
Relative Humidity (%)
80
90
100
Chemical extinction equals measured
extinction
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 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 Areas
Reasonable Progress Glide Path
35
Great Smoky
Denali
Visibility (deciview)
30
25
20
Baseline
15
10
Natural Visibility
5
0
2005
2015
2025
2035
Year
2045
2055
2065
Chemical Contributions to Extinction
Average of Highest 20% bext, 1995-1999
250
35
31
Clear Air
Organics
30
Sulfate
Soot
Nitrate
Soil
-1
Chemical Extinction (Mm )
200
24
150
22
21
19
19
19
18
Deciviews
100
13
12
12
10
50
G
re
a
tS
m
ok
y
M
Sh
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an
do
ah
Sa Ac
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G
or
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ey
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B
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P
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N
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w
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Yo od
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on
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Ja
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B
ry
i
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C
an
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D
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i
0
0
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 bext (Mm-1)
1988-1999
re
a
tS
m
ok
Sh y M
en nt
an n N
do P
a ,T
A
Sa c h N N
n adi P, (GR
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M int on , M (SH )
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nt ey S E (A N)
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R
ai s N CA CA
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(S D)
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Bi r N , C AG
A
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Be P, W (P O)
G nd A OR
R laci NP (M E)
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O
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w
N TX RA
o
Yo od P,
(B )
se N MT IB
P
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Pi mit , C (G )
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B
da ad les , C ED
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La pe and M (Y )
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Vo ns , S (PI )
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(B N)
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Ba Lak NM (L O)
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ky ed lier , O (C )
M Fo NM R HIR
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(
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nt st , NM CR
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M ws P 2 AZ ND
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Sa Ja e N W M
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A)
G
Visibility (Deciviews)
Comparison with Natural Conditions
35
Average Poorest 20%
30
Average Best 20%
Average Natural Visibility
25
20
15
10
5
0
IMPROVE Site
10,000
Silicon
Calcium
Potassium
1,000
100
10
5/
27
5/
20
5/
13
5/
6
4/
29
4/
22
4/
15
4/
8
4/
1
3/
25
3/
18
3/
11
3/
4
1
Day in 1998
10,000
25
OC
EC
Burned Area
20
6,000
15
4,000
10
2,000
5
0
0
1/
9
4/ 1
9
7/ 1
10 91
/9
1/ 1
9
4/ 2
9
7/ 2
10 92
/9
1/ 2
9
4/ 3
9
7/ 3
10 93
/9
1/ 3
9
4/ 4
9
7/ 4
10 94
/9
1/ 4
9
4/ 5
9
7/ 5
10 95
/9
1/ 5
9
4/ 6
9
7/ 6
10 96
/9
6
2
8,000
Burned Area (km )
b) Carbon at
Yosemite NP
3
Organcic & Elemental Carbon (ng/m)
Natural emitters
(Asian dust and
wildfires) affect
visibility as well
as manmade
sources
Aluminum
Iron
Titanium
Asian Sand
Storm Period
3
Concentration (ng/m )
a) Geological Elements at
Yosemite NP
Month and Year
Conclusions
 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