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Effects of Pollution on Visibility and the Earth

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University of Zagreb, Zagreb, Croatia. 24 May 2007 ... Poor and Natural Visibility at the Grand Canyon. WINHAZE (webcam.srs.fs.fed.us/winhaze.htm) ... – PowerPoint PPT presentation

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Title: Effects of Pollution on Visibility and the Earth


1
Effects of Pollution on Visibility and the
Earths Radiation Balance
  • John G. Watson (john.watson_at_dri.edu)
  • 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

2
Based on a Critical Review of Science and Policy
Interaction (www.awma.org)
3
High uncertainties for aerosol effects on global
radiation balance IPCC (2001)
4
Many aerosol effects are common for visibility
and climate change
5
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?

6
What is haze?
  • Haze is the visually perceived degradation of
    humanly appreciated views caused by polluting
    particles and gases.

7
What is Haze? Plume Blight Attribution to a
Single Source
8
Regional Haze (Not directly attributable to a
single source)
9
Poor and Natural Visibility at the Grand
Canyon WINHAZE (webcam.srs.fs.fed.us/winhaze.htm)
10
The human eye is more sensitive to sharp changes
in constrast
11
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.

12
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.

13
Particles and gases in the air scatter and absorb
light
14
How is haze quantified? Visibility Metrics
  • Perceived visual air quality What people think
    they see.
  • Light extinction (bext), I(x)/I(0) e-bextx
  • ContrastI(x)target/I(x)background
  • Visual range (VR4/bext or furthest observed
    distance)
  • Spatial frequency (Modulation Transfer Function)
  • ?bext4/x
  • Deciview (dv10ln(bext/10)
  • I(x)light intensity at distance x from
    target

15
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.

16
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

17
Nephelometers for particle light scattering
Radiance R903 with smart heater measures dry
particle scattering
Optec NGN-2 measures wet (total) particle
scattering
18
Temporal variability of particle scattering at
nearby sites
19
Chemical extinction Battery-powered minivol
PM2.5/PM10 sampler
AirMetrics impactors
PM10
PM2.5
Sampler Configuration in Tong Liang, China
20
PM2.5/scattering(dry) relationships
21
Chemical Extinction
bext (Mm-1) Sdry 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
dv10ln(bext/10)
22
Extinction efficiencies assume size distribution,
pure substances, and spherical particles
23
Scattering efficiency depends on RH, assuming an
initial size distribution. High RH measurements
are inaccurate
24
Chemical extinction equals measured extinction
25
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

26
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)

27
156 U.S. Mandatory Class I Areas
28
Reasonable Progress Glide Path
29
Chemical Contributions to Extinction Average of
Highest 20 bext, 1995-1999
30
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

31
Trends in 20 highest bext (Mm-1) 1988-1999
32
Comparison with Natural Conditions
33
Natural emitters (Asian dust and wildfires)
affect visibility as well as manmade sources
34
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
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