Heat Islands Evm

7/30/2019 Heat Islands Evm

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What Is an Urban Heat Island?

Buildings, roads, and other infrastructure replace open land and vegetation in urban areas.

Surfaces that were once permeable and moist become impermeable and dry. These changes

cause urban regions to become warmer than their rural surroundings, forming an "island" of

higher temperatures in the landscape.

Heat islands occur on the surface and in the atmosphere. On a hot, sunny summer day, the

sun can heat dry, exposed urban surfaces, such as roofs and pavement, to temperatures 50

90F (2750C) hotter than the air,while shaded or moist surfacesoften in more rural

surroundingsremain close to air temperatures. Surface urban heat islands are typically

present day and night, but tend to be strongest during the day when the sun is shining.

In contrast, atmospheric urban heat islands are often weak during the late morning and

throughout the day and become more pronounced after sunset due to the slow release of heat

from urban infrastructure. The annual mean air temperature of a city with 1 million people ormore can be 1.85.4F (13C) warmer than its surroundingscan be as much as 22F (12C).

Why Do We Care About Heat Islands?

Elevated temperature from urban heat islands, particularly during the summer, can affect a

community's environment and quality of life. While some heat island impacts seem positive,

such as lengthening the plant-growing season, most impacts are negative and include:

Increased energy consumption: Higher temperatures in summer increase energydemand for cooling and add pressure to the electricity grid during peak periods ofdemand. One study estimates that the heat island effect is responsible for 510% of

peak electricity demand for cooling buildings in cities.

Elevated emissions of air pollutants and greenhouse gases: Increasing energydemand generally results in greater emissions of air pollutants and greenhouse gas

emissions from power plants. Higher air temperatures also promote the formation

of ground-level ozone.

Compromised human health and comfort: Warmer days and nights, along withhigher air pollution levels, can contribute to general discomfort, respiratory

difficulties, heat cramps and exhaustion, non-fatal heat stroke, and heat-relatedmortality.

Impaired water quality: Hot pavement and rooftop surfaces transfer their excessheat to stormwater, which then drains into storm sewers and raises water

temperatures as it is released into streams, rivers, ponds, and lakes. Rapid

temperature changes can be stressful to aquatic ecosystems.

What Can Be Done?

Communities can take a number of steps to reduce the heat island effect, using four main

strategies:

increasingtree and vegetative cover;
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creatinggreen roofs(also called "rooftop gardens" or "eco-roofs"); installingcoolmainly reflectiveroofs; and usingcool pavements.

Typically heat island mitigation is part of a community's energy, air quality, water, or

sustainability effort. Activities to reduce heat islands range from voluntary initiatives, such as

cool pavement demonstration projects, to policy actions, such as requiring cool roofs viabuilding codes. Most mitigation activities have multiple benefits, including cleaner air,

improved human health and comfort, reduced energy costs, and lower greenhouse gas

emissions.

A brief definition of the main heat island types

Heat island: The presence of any area warmer than its surrounding landscape. They can be

developed on urban or rural areas. As it would be expected, there is a relatively minor

knowledge about non urban heat islands, since they usually do not represent a risk for the

human being or the environment. Meanwhile, urban heat islands have been profuselyaddressed during decades in urban areas with a wide range of climates and landscapes.

Urban heat island effect: The well-known phenomenon allusive to the atmospheric

temperature rise experienced by any urbanized area. The heat island phenomenon has been

commonly associated to cities, because their surfaces are characterized by low albedo, high

impermeability and favourable thermal properties for the energy storage and heat release.

Besides, many cities present narrow urban canyons with reduced sky view factors that tend to

absorb and reemit the radiated energy from their surfaces. These factors contribute to

urbanised areas increasing their temperatures in relation to their rural peripheries that are

usually more vegetated, and therefore moderate the temperatures mainly through the

evapotranspiration process, shades production and solar radiation interception.

Surface urban heat island: The remotely sensed urban heat island. It is observed by using

thermal infrared data that allow to retrieve land surface temperatures. Usually, close

relationships between the near surface air temperatures and land surface temperatures have

been found. Therefore, the surface urban heat island is a reliable indicator of the atmospheric

urban heat island.

Micro urban heat islands: They refer to urban hot spots as poorly vegetated parking lots, non-

reflective roofs and asphalt roads. Micro urban heat islands are strongly affected by micro

climate factors, therefore remotely sensed data are more suitable than atmospheric data for

identifying heat spots.

Urban heat sink: Also called negative heat island. It is the expression of a city colder than

their countrysides. There are few references about this phenomenon. Heat sinks have been

observed in cities with temperate, tropical, semi-arid and arid climates, and mainly during the

mornings (more information about this topic can be found in Pea (2008) and Pea (2009).
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Heat Island Impacts

On a hot, sunny summer day, roof and pavement surface temperatures can be 5090F (27

50C) hotter than the air, while shaded or moist surfacesoften in more rural surroundingsremain close to air temperatures.These surface urban heat islands, particularly during the

summer, have multiple impacts and contribute to atmospheric urban heat islands. Air

temperatures in cities, particularly after sunset, can be as much as 22F (12C) warmer than

the air in neighboring, less developed regions.

Elevated temperatures from urban heat islands, particularly during the summer, can affect a

communitys environment and quality of life. While some impacts may be beneficial, such as

lengthening the plant-growing season, the majority of them are negative. These impacts

include:

increased energy consumption; elevated emissions of air pollutants and greenhouse gases; compromised human health and comfort; and impaired water quality.

Increased Energy Consumption

Elevated summertime temperatures in cities increase energy demand for cooling. Research

shows that electricity demand for cooling increases 1.52.0% for every 1F (0.6C) increasein air temperatures, starting from 68 to 77F (20 to 25C), suggesting that 510% of

community-wide demand for electricity is used to compensate for the heat island effect.2

Urban heat islands increase overall electricity demand, as well as peak demand, which

generally occurs on hot summer weekday afternoons, when offices and homes are running

cooling systems, lights, and appliances. During extreme heat events, which are exacerbated

by urban heat islands, the resulting demand for cooling can overload systems and require a

utility to institute controlled, rolling brownouts or blackouts to avoid power outages.

Elevated Emissions of Air Pollutants and Greenhouse Gases

As described above, urban heat islands raise demand for electrical energy in summer.Companies that supply electricity typically rely on fossil fuel power plants to meet much of

this demand, which in turn leads to an increase in air pollutant and greenhouse gas emissions.

The primary pollutants from power plants include sulfur dioxide (SO2), nitrogen oxides

(NOx), particulate matter (PM), carbon monoxide (CO), and mercury (Hg). These pollutants

are harmful to human health and also contribute to complex air quality problems such as the

formation ofground-level ozone (smog), fine particulate matter, and acid rain. Increased use

of fossil-fuel-powered plants also increases emissions of greenhouse gases, such as carbon

dioxide (CO2), which contribute to global climate change.
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In addition to their impact on energy-related emissions, elevated temperatures can directly

increase the rate of ground-level ozone formation. Ground-level ozone is formed when NOx

and volatile organic compounds (VOCs) react in the presence of sunlight and hot weather. If

all other variables are equal, such as the level of precursor emissions in the air and wind

speed and direction, more ground-level ozone will form as the environment becomes sunnier

and hotter.

Compromised Human Health and Comfort

Increased daytime temperatures, reduced nighttime cooling, and higher air pollution levels

associated with urban heat islands can affect human health by contributing to general

discomfort, respiratory difficulties, heat cramps and exhaustion, non-fatal heat stroke, and

heat-related mortality.

Heat islands can also exacerbate the impact of heat waves, which are periods of abnormally

hot, and often humid, weather. Sensitive populations, such as children, older adults, and those

with existing health conditions, are at particular risk from these events.

Excessive heat events, or abrupt and dramatic temperature increases, are particularly

dangerous and can result in above-average rates of mortality. The Centers for Disease Control

and Prevention estimates that from 19792003, excessive heat exposure contributed to more

than 8,000 premature deaths in the United States. This figure exceeds the number of

mortalities resulting from hurricanes, lightning, tornadoes, floods, and earthquakes combined.

Impaired Water Quality

High pavement and rooftop surface temperatures can heat stormwater runoff. Tests haveshown that pavements that are 100F (38C) can elevate initial rainwater temperature from

roughly 70F (21C) to over 95F (35C).This heated stormwater generally becomes runoff,

which drains into storm sewers and raises water temperatures as it is released into streams,

rivers, ponds, and lakes.

Water temperature affects all aspects of aquatic life, especially the metabolism and

reproduction of many aquatic species. Rapid temperature changes in aquatic ecosystems

resulting from warm stormwater runoff can be particularly stressful, even fatal to aquatic life.

Causes of heat islands

The reason the city is warmer than the country comes down to a difference between the

energy gains and losses of each region. There are a number of factors that contribute to the

relative warmth of cities:
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1. During the day in rural areas, the solar energy absorbed near the ground evaporateswater from the vegetation and soil. Thus, while there is a net solar energy gain, this is

compensated to some degree by evaporative cooling. In cities, where there is less

vegetation, the buildings, streets and sidewalks absorb the majority of solar energy

input.

2. Because the city has less water, runoffis greater in the cities because the pavementsare largely nonporous (except by the pot holes). Thus, evaporative cooling is lesswhich contributes to the higher air temperatures.

3. Waste heat from city buildings, cars and trains is another factor contributing to thewarm cities. Heat generated by these objects eventually makes its way into the

atmosphere. This heat contribution can be as much as one-third of that received from

solar energy.

4. The thermal properties of buildings add heat to the air by conduction. Tar, asphalt,brick and concrete are better conductors of heat than the vegetation of the rural area.

5. The canyon structure that tall buildings create enhances the warming. During the day,solar energy is trapped by multiple reflections off the buildings while the infrared heat

losses are reduced by absorption.6. The urban heat island effects can also be reduced by weather phenomena. The

temperature difference between the city and surrounding areas is also a function of the

synoptic scale winds. Strong winds reduce the temperature contrast by mixing

together the city and rural air.

7. The urban heat island may also increase cloudiness and precipitation in the city, as athermal circulation sets up between the city and surrounding region.

Heat islands can occur year-round during the day or night. Urban-rural temperature

differences are often largest during calm, clear evenings. This is because rural areas cool off

faster at night than cities, which retain much of the heat stored in roads, buildings, and other

structures. As a result, the largest urban-rural temperature difference, or maximum heat island

effect, is often three to five hours after sunset.

Mitigation of heat island effects

There are a number of steps that communities can take to lessen the impacts of heat islands.

These heat island reduction strategies include:

1. Installing cool roofs or vegetated green roofs2. Installing green roofs3. Switching to cool paving materials.4. Planting trees and vegetation

The extent to which urban areas can benefit from heat island reduction strategies depends on

several factors. Some of these factors, like prevailing weather patterns, geography, and

pollution transported from upwind regions, are largely beyond the influence of local policy.

However, factors such as land-use patterns, materials used in road and building construction,and the coverage of urban trees and vegetation can be directly affected by decision makers.
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This is where policies and programs to reduce the impacts of heat islandsand achieve

related environmental and energy-savings goalscan be most effective.


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IMPACT OF VEHICLES ON POLLUTION

Road transport is one of the biggest sources of pollution in the UK, contributing to poor air quality,

climate change, congestion and noise disturbance. Of the 33 million vehicles on our roads, 27 million

are cars. Whilst travel by car is often the only practicable option, there are simple steps we can all

take to reduce the number of journeys we take and their impact on the environment.

Impacts of pollution from vehicles

Climate Change

Road transport accounts for 22% of total UK emissions of carbon dioxide (CO2)the major

contributor to climate change. The EU has agreements with motor manufacturers that aim to

reduce average CO2 emissions from new cars. Colour-coded labels, similar to those used onwashing machines and fridges, are now displayed in car showrooms showing how much CO2

new models emit per kilometre. However, as traffic levels are predicted to increase, road

transport will continue to be a significant contributor to greenhouse gas emissions.

Air Quality

Air pollutants from transport include nitrogen oxides, particles, carbon monoxide and

hydrocarbons. All have a damaging impact on the health of people, animals and vegetation

locally. Air quality in the UK is slowly improving, but many areas still fail to meet the health

based national air quality objectives and European limit valuesparticularly for particles and

nitrogen dioxide. In town centres and alongside busy roads, vehicles are responsible for mostlocal pollution. Vehicles tend to emit more pollution during the first few miles of journey

when their engines are warming up. Although new technology and cleaner fuel formulations

will continue to cut emissions of pollutants, the increasing number of vehicles on the road

and miles driven is eroding these benefits.

Noise

Noise from road traffic affects 30% of people in the UK. Sources include engine noise, tyre

noise, car horns, car stereos, door slamming, and squeaking brakes. Vehicles have been

subject to noise standards for many years through EU legislation. The sound of engines is a

problem in towns and cities, while in more rural areas tyre noise on busy roads, which

increases with speed, is the main source. Low-noise road surfaces, effective noise barriers in

sensitive locations, and low noise tyres can all help reduce noise levels. Meanwhile,

encouraging people to close car windows when playing loud music, and discouraging the use

of 'boom box' car stereos would significantly reduce noise impact. (See our leaflet on Noise

Pollution for more)

Resource Use

Vehicles have a major impact on the environment through their construction, use and

eventual disposal. It is estimated that of the CO2 emissions produced over a car's lifespan10% come from its manufacture and 5% from its disposal, with the remaining 85% coming


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from fuel use and servicing operations. In addition to these emissions of carbon dioxide and

other air pollutants, the vehicle and related industries (e.g. fuels) consume large amounts of

raw materials, and produce significant quantities of waste.

Local Impacts

Vehicle use affects our whole quality of local life. Traffic can be dangerous and intimidating,

dividing communities and making street life unpleasant. Abandoned vehicles cause nuisance,

whilst air pollution and traffic noise can make urban living uncomfortable.

INGREDIENTS OF VEHICULAR POLLUTION

The following are the major pollutants associated with motor vehicles:

Ozone (O 3 ). The primary ingredient in urban smog, ozone is created when hydrocarbonsand nitrogen oxides (NO x )both of which are chemicals released by automobile fuel

combustionreact with sunlight. Though beneficial in the upper atmosphere, at the ground

level ozone can irritate the respiratory system, causing coughing, choking, and reduced lung

capacity.

Particulate matter (PM). These particles of soot, metals, and pollen give smog its murkycolor. Among vehicular pollution, fine particles (those less than one-tenth the diameter of a

human hair) pose the most serious threat to human health by penetrating deep into lungs.

In addition to direct emissions of fine particles, automobiles release nitrogen oxides,

hydrocarbons, and sulfur dioxide, which generate additional fine particles as secondary

pollution.

Nitrogen oxides (NO x ). These vehicular pollutants can cause lung irritation and weaken thebody's defenses against respiratory infections such as pneumonia and influenza. In addition,

they assist in the formation of ozone and particulate matter. In many cities, NO x pollution

accounts for one-third of the fine particulate pollution in the air.

Carbon monoxide (CO). This odorless, colorless gas is formed by the combustion of fossilfuels such as gasoline. Cars and trucks are the source of nearly two-thirds of this pollutant.

When inhaled, CO blocks the transport of oxygen to the brain, heart, and other vital organs

in the human body. Newborn children and people with chronic illnesses are especially

susceptible to the effects of CO.

Sulfur dioxide (SO 2 ). Motor vehicles create this pollutant by burning sulfur-containing fuels,especially diesel. It can react in the atmosphere to form fine particles and can pose a health

risk to young children and asthmatics.

Hazardous air pollutants (toxics). These chemical compounds, which are emitted by cars,trucks, refineries, gas pumps, and related sources, have been linked to birth defects, cancer,

and other serious illnesses. The EPA estimates that the air toxics emitted from cars and

trucks account for half of all cancers caused by air pollution.


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Curbing Vehicular Pollution

Vehicular emissions that contribute to air quality problems, smog, and global warming can be

reduced by putting better pollution-control technologies on cars and trucks, burning less fuel,

switching to cleaner fuels, using technologies that reduce or eliminate emissions, and

reducing the number of vehicle-miles traveled.

Pollution Control Technology

Federal and California regulations require the use of technologies that have dramatically

reduced the amount of smog-forming pollution and carbon monoxide coming from a vehicle's

tailpipe. For gasoline vehicles, "threeway" catalysts, precise engine and fuel controls, and

evaporative emission controls have been quite successful. More advanced versions of these

technologies are in some cars and can reduce smog-forming emissions from new vehicles bya factor of ten. For diesel vehicles, "two-way" catalysts and engine controls have been able to

reduce hydrocarbon and carbon monoxide emissions, but nitrogen oxide and toxic

particulate-matter emissions remain very high. More advanced diesel-control technologies are

under development, but it is unlikely that they will be able to clean up diesel to the degree

already achieved in the cleanest gasoline vehicles.

Added concerns surround the difference between new vehicle emissions and the emissions of

a car or truck over a lifetime of actual use. Vehicles with good emission-control technology

that is not properly maintained can become "gross polluters" that are responsible for a

significant amount of existing air-quality problems. New technologies have also been

developed to identify emission-equipment control failures, and can be used to help reduce the"gross polluter" problem.

Burning Less Fuel

The key to burning less fuel is making cars and trucks more efficient and putting that

efficiency to work in improving fuel economy. The U.S. federal government sets a fuel-

economy standard for all passenger vehicles. However, these standards have remained mostly

constant for the past decade. In addition, sales of lower-fuel-economy light trucks, such as

SUVs, pickups, and minivans, have increased dramatically. As a result, on average, the U.S.passenger-vehicle fleet actually travels less distance on a gallon of gas than it did twenty

years ago. This has led to an increase in heat-trapping gas emissions from cars and trucks and

to an increase in smog-forming and toxic emissions resulting from the production and

transportation of gasoline to the fuel pump.

This trend can be reversed through the use of existing technologies that help cars and trucks

go farther on a gallon of gasoline. These include more efficient engines and transmissions,

improved aerodynamics, better tires, and high strength steel and aluminum. More advanced

technologies, such as hybrid-electric vehicles that use a gasoline engine and an electric motor

plus a battery, can cut fuel use even further. These technologies carry with them additional

costs, but pay for themselves through savings at the gasoline pump.


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Zero-Emission Vehicles

As more cars and trucks are sold and total annual mileage increases, improving pollution-

control technology and burning less fuel continues to be vital, especially in rapidly growingurban areas. However, eliminating emissions from the tailpipe goes even further to cut down

on harmful air pollutants.

Hydrogen fuel-cell and electric vehicles move away from burning fuel and use

electrochemical processes instead to produce the needed energy to drive a car down the road.

Fuel-cell vehicles run on electricity that is produced directly from the reaction of hydrogen

and oxygen. The only byproduct is waterwhich is why fuel-cell cars and trucks are called

zero-emission vehicles. Electric vehicles store energy in an onboard battery, emitting nothing

from the tailpipe.

The hydrogen for the fuel cell and the electricity for the battery must still be produced

somewhere, so there will still be upstream emissions associated with these vehicles. These

stationary sources, however, are easier to control and can ultimately be converted to use

wind, solar, and other renewable energy sources to come as close as possible to true zero-

emission vehicles.

Cleaner Fuels

The gasoline and diesel fuel in use today contains significant amounts of sulfur and othercompounds that make it harder for existing control technology to keep vehicles clean.

Removing the sulfur from the fuel and cutting down on the amount of light hydrocarbons

helps pollution-control technology to work better and cuts down on evaporative and refueling

emissions.

Further large-scale reductions of other tailpipe pollution and CO 2 can be accomplished with a

shift away from conventional fuels. Alternative fuels such as natural gas, methanol, ethanol,

and hydrogen can deliver benefits to the environment while helping to move the United

States away from its dependence on oil. All of these fuels inherently burn cleaner than diesel

and gasoline, and they have a lower carbon contentresulting in less CO 2 . Most of these

fuels are also more easily made from renewable resources, and fuels such as natural gas andmethanol help provide a bridge to producing hydrogen for fuel-cell vehicles.

Reducing Driving

Because we are still dependent on fossil fuels and the number of cars on the road is expected

to double, a significant reduction in vehicular pollution requires more than gains in fuel

efficiency. Measures that encourage us to drive less can help curb vehicular pollution and

protect natural resources and public health.

Alternatives that can reduce the number of vehicle-miles traveled include


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providing transportation alternatives to cars, including mass transit, bicycle, and pedestrianroutes;

promoting transit-oriented, compact developments in and around cities and towns; andadopting policies to improve existing roads and infrastructure.

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