Air Pollution, Heat Island Effect and Heat Waves

Air Pollution, Heat Island Effect Air Pollution, Heat Island Effect and Heat Wavesand Heat Waves

Effects of human activitiesEffects of human activitiesHuman beings are changing the global climate system in

three different ways:• Change land cover (deforestation and afforestation)• Release or cleanse pollutants (aerosols)• Release or cleanse greenhouse gases

Atmospheric PollutantsAtmospheric Pollutants

• 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.

Atmospheric PollutantsAtmospheric Pollutants• Introduction


• Particulates• Particulates (aerosols) are solid or liquid matter

suspended in the air (from 0.1 to 100 µm in size).

• Natural sources: natural fires, volcanic eruptions, salt spray from the oceans, pollen.

• Anthropogenic sources: burning of fossil fuels.

• Although particulates can remain in the air for some time due to their small size, rain removes them.

• PM10 (<10 µm) enters lungs (associated with asthma); PM2.5 even more dangerous (lung cancer).

Atmospheric PollutantsAtmospheric Pollutants• Carbon Oxides

• Carbon monoxide (CO) is a colorless, odorless gas from volcanic eruptions, forest fires and other processes.

• Extremely toxic and dangerous to humans and animals.

• Carbon dioxide (CO2) is an important greenhouse gas but is officially considered a pollutant by the US EPA.


• Carbon Oxides

Sulfur Compounds

• Sulfur compounds can occur as gaseous or aerosol forms.

• Natural sources: steam vents, volcanic eruptions, sea spray.

• Anthropogenic sources: burning sulfur containing fossil fuels (particularly coal and oil) and ore smelting.

• Sulfur dioxide (SO2) is a respiratory irritant.

• Sulfur trioxide (SO3) contributes to acid fog and acid rain.


• Sulfur Compounds


• Nitrogen Oxides (NOX)• Nitric oxide (NO) is a nontoxic,

colorless, and odorless gas.• Natural sources: biological

processes in soil and water.

• Nitrogen dioxide (NO2) is a toxic, yellow to reddish-brown gas that is pungent and corrosive.

• Provides polluted air with the yellow to reddish brown color.

• Anthropogenic sources: Vehicle traffic.

• Can cause pulmonary health problems.


• Volatile Organic Compounds (Hydrocarbons)• Volatile Organic Compounds (Hydrocarbons) are

made of carbon and hydrogen. Examples: methane, butane, propane, octane, etc.

• Natural sources: plant and animal emissions and decomposition of organic matter.

• Anthropogenic sources: primarily combustion from automobiles, trucks, buses, and other fossil fuel motors; also evaporation of gasoline and other chemicals.


• Photochemical Smog

• Ozone, NO2, formaldehyde and other gases combine with solar radiation to form Los Angeles-type photochemical smog.

• Ozone causes respiratory and heart problems.

• High levels of ozone result in environmental degradation.


• Air Quality Index• The EPA created an index for air pollution

monitoring called the Air Quality Index (AQI).

• A formula applies to ozone, particulates, carbon monoxide, sulfur dioxide, and nitrogen dioxide by expressing each pollutant on a scale that ranges from 0 to 500.

• The official AQI for any location at a particular time is the highest of the five individual pollutant values.


• Air Quality Index

Atmospheric Conditions and Air Atmospheric Conditions and Air PollutionPollution

• 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.

• Eddies can mix air vertically.


• Effect of Atmospheric Stability• Inversions can trap pollutants near the Earth’s

surface.


• Effect of Atmospheric Stability• Inversions can trap pollutants near the Earth’s

surface.

Local effect II: Dispersion of air pollutionLocal effect II: Dispersion of air pollution

• Dispersion depends on stability of BL

Unstable StableNeutral

• Dispersion also affected by inversions

Low level inversion Upper level inversion

Urban Heat IslandsUrban Heat Islands

• Introduction• Urban heat island refers to the increased local

temperatures that result from urbanization.

• Occurs due to modifications to the energy balance that result when natural surfaces are paved and built upon or when human activities release heat into the environment.

• Several variables influence the magnitude of the heat island: population density, radiation, changes in heat storage, sensible and latent heat transfer.


• Introduction


• Radiation Effects

• Increased particulates associated with urban activity absorbs and scatters incoming solar radiation.

• Buildings, often a part of urbanized areas, impact the radiation balance by albedo and energy transfer.


• Changes in Heat Storage

• Conduction and convection affect the energy balance to form urban heat island.

• The release of heat from buildings plays a major role in urban heat islands.


• Changes in Heat Storage


• Sensible and Latent Heat Transfer• Urbanization affects the routing of precipitation

in a way that favors increased sensible heat transfer.

• With more runoff, the reduction in available water increases the input of sensible heat to the atmosphere at the expense of latent heat and helps increase the temperature of the urban environment.


• Detection of Climate Change?• We must contend with the problem of enhanced urban

heat islands influencing the data, which means that records from large urban areas are not representative of the surrounding region.

• Atmospheric scientists are well aware of this source of bias in temperature records—which happens to be relatively small— and routinely account for its effect, either by discarding contaminated data or by adjusting values downward for affected stations.

Effects of different surface typesEffects of different surface types

Deeper heat reservoir (smaller T change) Deeper water reservoir (Wetter surface) Bowen ratio decreases (More LH contribution)

BL depth decreases Convective instability increases

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

Global distribution of different Global distribution of different vegetation typesvegetation types

(From Bonon et al. 2002)

Vegetation feedbackVegetation feedbackVegetation in turn is affected by environmental Vegetation in turn is affected by environmental

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

The heat island effectThe heat island effect

• Nighttime: City warmer than surrounding rural area• Daytime: City has same air temperature as rural area

Causes of the heat island effectCauses 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• Decrease sensible and latent heat

fluxes caused by canyon geometry (reduction of wind speed)

“Canyons” between buildings

Mitigation of heat island effectMitigation of heat island effect

• Greening the city (streets and roof top)

• Change construction materials

• Reduce anthropogenic heat sources

Global effect: Global effect: Anything released by human beings will be Anything released by human beings will be

transported globally by atmospheric circulations transported globally by atmospheric circulations and ocean circulationsand ocean circulations

The Global Carbon CycleThe Global Carbon Cycle

SummarySummary

• Effects of different surface types: desert, city, grassland, forest, sea. Deeper heat/water reservoir, decreased Bowen ratio, thinner BL and enhanced convective instability.

• Effects of vegetation: (1) makes heat/water reservoir deeper, (2) enhance evaporation, (3) grows and dies in response to environmental conditions

• Heat island effect. 7 causes• Dispersion of air pollution. Dependence on stability

(name of 3 types) and inversion (name of 2 types)• Global carbon cycle: linking the world together.

Therefore we need to protect the environment.

Documents

Air Pollution, Heat Island Effect and Heat Waves