1. Urban Heat Island and Pollution

2. 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.

3. 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)

4. Global urbanization map

5. Global urbanization prospects

6. The Heat Island Effect
Temperature distribution for Atlanta (from EPA)

7. Effects of vegetation
Makes water/heat reservoir deeper (transport deep water
out of soil)
Enhances evaporation (leafs increase evaporation area)
Dependent on vegetation type

8. Vegetation feedback Vegetation in turn is affected by environmental conditions (e.g. seasons, droughts, global warming)

9. Effects of different surface types
Convective instability increases
Deeper heat reservoir (smaller T change) Deeper water reservoir (Wetter surface) Enhanced latent heat flux

10. The heat island effect
Nighttime: City warmer than surrounding rural area
Daytime: City has same air temperature as rural area

11. Temperature distribution for Atlanta
(from EPA)

12. Dependence of heat island effect on population

13. 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

14. Mitigation of heat island effect
Greening the city (streets and roof top)
Change construction materials
Reduce anthropogenic heat sources

15. Air Pollution

16. Video: Science to Protect the Air We Breath (by EPA)

17. 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

18. Global distribution of PM2.5 (2001-2006)
Image from NASA
Credit: Dalhousie University, Aaron van Donkelaar

19. U.S distribution of PM2.5 (2001-2006)
Image from NASA
Credit: Dalhousie University, Aaron van Donkelaar

20. 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.

21. 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

22. 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)

23. The smog layer in Los Angeles
Base of inversions

24. Global effect: Anything released by human beings will be transported globally by atmospheric circulations and ocean circulations

25. 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

26. Works cited http://www.urbansciences.eu/Descipline.aspx?id=1