Transcript Proxy Climate Data - University of Texas at Austin

Lecture 33: Air Pollution & The Ozone Hole
Air Pollution and The Ozone Hole
We will discuss:
1. Air pollution types, sources, and trends
2. Tropospheric and stratospheric ozone
3. Pollution in the urban environment
Types & Sources of Air Pollution
Primary air
pollutants enter
the atmosphere
directly, while
secondary
pollutants form
by chemical
reaction.
Pollutant
sources are both
natural, such as
volcanoes and
forest fires, and
human caused,
such as cars and
industry.
Emission inventories
Area
sources
Point
sources
On-road and
non-road
mobile
sources
Biogenic emissions
Principal Air Pollutants
VOC
SOX
NOX
Carbon monoxide,
sulfur oxides,
nitrogen oxides,
volatile organic
compounds, and
particulate matter
are the most
prevalent primary
pollutants, and
transportation
and power
generation are the
primary sources
for these
pollutants.
Definitions:
NOx oxides of nitrogen (NO + NO2)
NO colorless, odorless, nonflammable
NO2 orange, toxic, corrosive, sharp
odor
Emitted by combustion processes
National emission inventory (18,690
tons N/day)
Definitions:
Volatile Organic Compounds, VOCs
VOCs are a group of compounds,
characterized by their ability to
evaporate and their reactivity in the
atmosphere
National emission inventory (133,200
tons C/day)
Emitted by combustion processes
(especially vehicles), fuel and
solvent evaporation
Particulate Matter Pollution
Particulates (particles or droplets) are classified as having
diameters less than 10 μm (PM10) and less than 2.5 μm (PM2.5).
1 inch = 25,000 microns (μm). One larger PM2.5 particle width=30 times smaller than that of a human hair.
PM10 pollutants settle out of the atmosphere relatively quickly
compared with the lingering PM2.5.
Both can adversely affect human health and reduce visibility.
Visible & Invisible Pollutants
Suspended hygroscopic particles may scatter light and create a
white wet-haze, while carbon monoxide and sulfur dioxide are not
visible.
The reaction of nitrogen dioxide and hydrocarbons in the presence
of sunlight may generate unsightly photochemical smog.
Ozone in the Troposphere
OZONE = Volatile
Organic
Compounds *
Oxides of
Nitrogen *
Sunlight *
Stagnant Air
Human health is compromised by exposure to ozone and
photochemical smog, which is formed when on a daily cycle when
sunlight dissociates NO2.
The product O reacts with atmospheric O2 to create O3.
Usually, the product NO would then react with and destroy the O3.
Excessive hydrocarbons, often from automobile exhaust, react with
the product NO and O3 concentrations increase to harmful levels.
Ozone in the Stratosphere
UV radiation has enough energy to
adversely impact the health of
plants and animals, including
humans.
Naturally occurring O3 in the
stratosphere can block the most
harmful UV radiation from
entering the troposphere.
Stratospheric Ozone Destruction
Naturally destructive
agents of ozone include
NO and NO2, or oxides of
nitrogen, which largely
originate from bacterial
activity at the earth's
surface.
Human released
chlorofluorocarbons
(CFCs) have upset the
balance of O3 production
and destruction, and have
caused formation of
ozone holes and an
increase in human UV
exposure.
CFCs and Ozone Depletion
90% of ozone in atmosphere occurs
in a ‘layer’ between 19 and 48 km
altitude in stratosphere.
Natural production and destruction
O2 + O + UV  O3
O3
+ UV  O2 + O
CFC’s destroy ozone:
CFC’s + UV  Cl
O3 + Cl  ClO + O2
No loose O to make O3
One Cl atom in a CFC molecule can
destroy thousands of O3 molecules
Stratospheric ozone protects
life on Earth from harmful
UV radiation
Evidence of Ozone Depletion
Short history of discovery of ozone problem
1970: P. Crutzen showed that nitrogen oxides are involved in reactions
that destroy ozone.
NO + O3  NO2 + O2
1976: M. Molina and F. Rowland theorized that chlorine in
chlorofluorocarbons (CFCs: e.g., CH3Cl) also help destroy the
ozone layer.
Cl + O3  ClO + O2
1985: Ozone "hole" above
Antarctica discovered
1987: Montreal Protocol signed
to restrict CFCs emissions
1995: Crutzen, Molina and
Rowland share Nobel Prize.
Ozone depletion is a global problem!
Ozone depletion is not just confined to the stratospheric Arctic and Antarctic.
Over the United States in March, 1994, ozone levels fell between 8 and 16%
below the values observed during March, 1979.
Decline of CFCs
1987: Montreal Protocol signed to restrict CFCs emissions
1992: more than half the world’s nations called for a quicker-phase out
1996: NOAA reported a 1% decline around the world from ground stations
1997: stratospheric chlorine concentrations peaked about 1997
Air Pollution Patterns & Trends
Air quality in the U.S. may
have been at its worst in the
1970s, but programs
implemented by the Clean Air
Act have helped the U.S. move
toward primary ambient air
quality standards.
Regional Air Quality Indices
may identify certain nonattainment areas, which are
then targeted by the
Environmental Protection
Agency for improvement.
Trends in Tropospheric Ozone
Yearly ozone trends are
influenced by hot sunny
weather and light surface
winds, but many cities have
demonstrated an overall
decline in harmful ozone
levels during the 1980s.
Air pollutants of concern in Texas
PM10 and PM2.5 - Fine particulate matter suspended
in the atmosphere degrades visibility and has been
associated with increased rates of mortality
O3 - Ozone at ground level is an irritant, and is
associated with increased incidence of respiratory
disease and decreased respiratory function
Hazardous air pollutants – A variety of health
impacts associated with exposure to HAPs
Air Quality in Texas cities
•
Houston, Dallas/Fort Worth Beaumont/Port
Arthur and El Paso violate the current ozone
standard and Austin, San Antonio and
Longview would violate the new ozone
standard.
•
El Paso violates the current particulate matter
standard. Houston and possibly DFW would
likely violate the new particulate matter
standard.
32-Hour back trajectories for days with peak 8-hour
ozone levels over 75 ppb in Austin (1993-1999)