Urban Heat Island and Pollution
Summary
• General circulation models: Grid size. Name of the basic set of
equations. 4 components of the climate system model.
• Mesoscale models: Grid size.
• Global climate models can reproduce the observed warming in the 20th
century. The warming is largely caused by human activities.
• Projected change in mean: temperature (largest warming over NH
continents), sea level, precipitation
• Projected change in extreme: temperature, precipitation
• Projected impacts: fresh water, ecosystems
• Mitigation: We can make a difference by reducing waste of energy, food
and other materials, and by purchasing environment-friendly products.
Future climate scenarios show that reducing greenhouse gas emissions
can substantially mitigate warming in the latter half of this century.
How do human activities change the
global climate?
• Release or cleanse greenhouse gases
• Change land cover (urbanization, deforestation
and afforestation)
• Release or cleanse pollutants (aerosols)
Global urbanization map
Global urbanization prospects
The Heat Island Effect
Temperature distribution for Atlanta (from EPA)
Effects of vegetation
• Makes water/heat reservoir deeper (transport deep water
out of soil)
• Enhances evaporation (leafs increase evaporation area)
• Dependent on vegetation type
Vegetation feedback
Vegetation in turn is affected by environmental
conditions (e.g. seasons, droughts, global warming)
Effects of different surface types
Convective instability increases
Deeper heat reservoir (smaller T change)
Deeper water reservoir (Wetter surface)
Enhanced latent heat flux
The heat island effect
• Nighttime: City warmer than surrounding rural area
• Daytime: City has same air temperature as rural area
Temperature distribution for Atlanta
(from
Dependence of heat island effect on
population
Causes of the heat island effect
• Increased SW absorption caused
by canyon geometry (increased
area and multiple reflection)
• Decreased LW loss caused by
canyon geometry
• Increased greenhouse effect
caused by air pollution
• Anthropogenic heat source
• Increased sensible heat storage
caused by construction materials
• Decreased latent heat flux caused
by change of surface type
• Decreased sensible and latent heat
fluxes caused by canyon geometry
(reduction of wind speed)
“Canyons” between buildings
Mitigation of heat island effect
• Greening the city
(streets and roof top)
• Change construction
materials
• Reduce anthropogenic
heat sources
Air Pollution
Video: Science to Protect the Air We
Breath (by EPA)
• http://www.youtube.com/watch?v=3PO_3e
xwN-I
Introduction
• Air pollutants are gases, liquids or solids in the air that
can adversely affect plant and/or animal life.
• Primary pollutants are pollutants that are emitted
directly by natural or anthropogenic (manmade)
processes.
• Secondary pollutants are pollutants that arise
from chemical reactions of atmospheric gases with
gases emitted by natural or anthropogenic
processes.
• There are six major pollutants: particulates (PM2.5 (<2.5
µm)), carbon oxides, sulfur dioxides, nitrogen oxides,
volatile organic compounds, ozone
Global distribution of PM2.5 (20012006)
Image from NASA
Credit: Dalhousie
University, Aaron
van Donkelaar
U.S distribution of PM2.5 (2001-2006)
Image from NASA
Credit: Dalhousie
University, Aaron
van Donkelaar
Atmospheric Conditions and Air Pollution
(1) Effect of Winds on Horizontal Transport
• High concentrations of
pollutants in a small area
(usually due to anthropogenic
sources) are the biggest air
pollution problems.
• The horizontal and vertical
transport of air pollutants by
winds help control the local
concentrations of pollutants.
• Concentrations are inversely
related to wind speed.
Atmospheric Conditions and Air Pollution
(2) Effect of Atmospheric Stability
• There are many turbulent eddies in an unstable boundary
layer, but few in a stable boundary layer
• Eddies can mix air vertically.
Unstable
Neutral
Stable
Inversions
• Inversions are absolutely stable and free of eddies
• Inversions can trap pollutants near the Earth’s surface.
Low level inversion
Upper level inversion
(most dangerous)
The smog layer in Los Angeles
Base of inversions
Global effect:
Anything released by human beings will be
transported globally by atmospheric circulations
and ocean circulations
Summary
• Effects of vegetation: (1) makes heat/water reservoir deeper, (2)
enhance evaporation, (3) grows and dies in response to
environmental conditions
• Effects of different surface types: desert, city, grassland, forest,
sea. Deeper heat/water reservoir and enhanced convective
instability.
• Heat island effect. 7 causes
• Air pollution. 2 categories. 6 types of major pollutants (particulates,
carbon oxides, sulfur dioxides, nitrogen oxides, volatile organic
compounds, ozone)
• Effect of wind and stability on pollution: Most dangerous is upper
level inversion
Works cited
• http://www.urbansciences.eu/Descipline.aspx?id=1
• http://www.un.org/esa/population/publications/WUP2005/
2005wup.htm