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 feedbackVegetation in turn is affected by environmental

conditions (e.g. seasons, droughts, global warming)

Effects of different surface types

Deeper heat reservoir (smaller T change) Deeper water reservoir (Wetter surface) Enhanced latent heat flux

Convective instability increases

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 EPA)

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_3exwN-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 (2001-2006)

Image from NASA Credit: Dalhousie University, Aaron van Donkelaar

U.S distribution of PM2.5 (2001-2006)

Image from NASACredit: 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

Unstable StableNeutral

• There are many turbulent eddies in an unstable boundary layer, but few in a stable boundary layer

• Eddies can mix air vertically.

• 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)

Inversions

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