Saturday, 6 December 2014

Climate change: asphalt and urban heat islands

Asphalt is not necessarily the best material for building roads:
Futures Forum: Alternatives to asphalt for building roads ..... gravel, or ..... concrete, or ..... glass as solar panels

On the one hand, asphalt roads could be described as 'little more than coagulated oil slicks':

There is the ... usually overlooked question of the ‘demand side’ of the earth’s carbon cycle. All attention is focussed on the supply side - e.g. on exhaust fumes. Simply put, there is no acknowledgement of the fact that by physically covering the planet with roads, car parks, refineries, mines, etc, you erode its photosynthetic capacity, its ability to absorb the CO2 that is created. In England alone, “Since the war 705,000 hectares of countryside have gone - more than the combined area of Greater London, Hertfordshire, Berkshire and Oxfordshire ... 

At the present rate of loss, a fifth of England would be urban by the middle of the next century.” (2) These trends on a global level have meant that: “Before World War Two, photosynthesizers on dry land produced perhaps 150 billion tons of dry weight of organic matter each year. Now ... the annual production of organic matter in terrestrial ecosystems (both natural and human controlled) has fallen to only about 130 billion tons. Some of the reasons for the decline in productivity are fairly simple and obvious; photosynthesis cannot occur on or under buildings, parking lots, airports, streets or highways.” (3) 

‘Green’ cars will require an almost identical infrastructure, meaning that this assault on the earth’s photosynthetic capacity will continue unabated - indeed , might even step up a gear, as a perceived cleaning up of its act would buy more time for the continued existence of the car. 

(Tarmac, and other such substances used for paving,are, as the Mundi Club point out,little more than coagulated oil slicks. These substances are products of levels of the catalytic cracker process in the same way that oil is. They underwrite oil production - make it an economically viable enterprise when otherwise it would not be; for while “The oil industry is mainly interested in gasoline production and profits ... refineries must run at high utilisation of capacity to be efficient and profitable. Refineries must produce great quantities of asphalt and various chemicals which must go somewhere ... thus asphalt and herbicides are spread about the land making it possible for refineries to function...near full throttle.” (4) The advocates of a ‘fossil free energy strategy’ unfortunately do not accept an accompanying end to paving, one of the logical consequences of that strategy. 

The production of tarmac, etc, and the production of oil are interdependent parts of refinery operations, and of the petrochemical economy - without one, you cannot have the other. So how will they square this circle - do their proposals actually require a continuation of that petrochemical economy that we’ve come to know and love?)

Revolution Against The Megamachine - Oil Spills
Stopping The Industrial Hydra: Revolution Against The Megamachine

On the other hand, asphalt has a considerable effect on weather patterns. 
Sidmouth is not Houston, but as an urban area on the coast, one wonders what the effects of sea breezes, ozone production and summer traffic have...

Are Cities Changing Local And Global Climates?

From Mayans to Romans to people of today, some of the greatest achievements of Homo sapiens have been their ability to build fantastic cities. But newer, equally spectacular innovations, like the satellites and computer models created at NASA, are starting to show that humankind's ambitions regarding urban landscapes may be altering local and possibly global climates. That's because asphalt and cement absorb heat, buildings alter winds, and tiny airborne particles from pollution called aerosols change the way clouds form, all of which exerts unique forces on local climates.
More Summer Rain Near Cities? 

While cities might be cool and interesting places in a cultural sense, scientists are now learning that these Mecca's tend to be one to 10 degrees Fahrenheit [0.56 to 5.6' Celsius] warmer than surrounding suburbs and rural areas. Hard and dark city surfaces absorb heat and create urban heat islands. That heating creates rising warm air, which combined with the varied heights of buildings and other urban structures that alter winds, appear to alter rainfall in and around cities.
Animation of city in the summerLeft: Animation of How Pollution Increases Summer Precipitation: In summer, weaker winds move the clouds more slowly. Heat absorbed by the city and pollution's interference with raindrop formation interact to cause the clouds to intensify before producing precipitation. The onset of rainfall from a cloud leads eventually to its demise by cooling off the air near the ground. The air pollution delays the onset of precipitation, so that the intense storm clouds can build higher and larger before they start precipitating and subsequently dissipating. Therefore, these larger and more intense thunderstorm clouds produce eventually heavier rainfall on the city and the downwind areas. First is the unpolluted, then the polluted case. Credit: NASA 

coastal cityRight: Animation of Urban Rainfall Effect in Coastal Cities: During the warmer months, the added heat creates wind circulations and rising air that produces new clouds or enhances existing ones. Under the right conditions, these clouds evolve into rain-producers or storms. Scientists suspect that converging air due to city surfaces of varying heights, like buildings, also promotes rising air needed to produce clouds and rainfall. Credit: NASACredit: NASA 

Animation of city in the winterLeft: Animation of How Pollution Reduces Winter Precipitation: In winter, moist air flows off the ocean and rises over the hills downwind of a coastal city, dropping its rain and snow mainly as it ascends the hills. As pollution from the city is pushed into the clouds by the hills downwind of the city, it interferes with droplet formation in the clouds and makes them smaller, as observed by NASA's satellites. The smaller cloud droplets convert more slowly into precipitation. Instead of precipitating, much of the water in the clouds evaporates, reducing the net rainfall downwind of the urban area by up to 15% to 25% on a seasonal basis. First is the unpolluted, then the polluted case. Credit: NASA 

Dr. J. Marshall Shepherd of NASA Goddard Space Flight Center and Steve Burian of the University of Utah used satellites and ground measurements to show higher rainfall rates during the summer months downwind of large cities like Houston and Atlanta. Burian and Shepherd also offered new evidence that rainfall patterns and daily precipitation trends have changed in regions downwind of Houston from a period of pre-urban growth in 1940-1958 to a post-urban growth period in 1984-1999. To obtain these findings the researchers used the world's first space-based rain radar aboard the Tropical Rainfall Measuring Mission (TRMM) satellite and dense rain gauge networks on the ground. The effects of urban heat islands, wind-altering buildings, and interactions with sea breezes are believed to be primary causes for the findings in a coastal city like Houston. 

In related work, Dr. Daniel Rosenfeld, an atmospheric scientist at Hebrew University, Jerusalem, Israel, reveals that tiny air particles from cars and industry called aerosols also change local rainfall rates around cities. Rosenfeld suggests that the particles provide many surfaces for water to collect on, preventing droplets from condensing into larger drops, and slowing conversion of cloud water into precipitation. In summer, rain and thunder increases downwind of big cities, as rising air from urban heat islands combines with dispersed water in aerosol laced clouds, creating bigger clouds and heavier rain. In contrast, Rosenfeld finds that in clouds that form in winter over hills downwind of coastal cities as in Israel and California, the pollution-induced slowing of precipitation results in loss of rainfall. 

NASA - Are Cities Changing Local And Global Climates?
Welcome to the Thunder Dome - NASA Science

One more reason to say asphalt affects local weather

Anthony Watts / June 9, 2011

Paved surfaces can foster build-up of polluted air

From the National Center for Atmospheric Research

BOULDER—New research focusing on the Houston area suggests that widespread urban development alters weather patterns in a way that can make it easier for pollutants to accumulate during warm summer weather instead of being blown out to sea.

The international study, led by the National Center for Atmospheric Research (NCAR), could have implications for the air quality of fast-growing coastal cities in the United States and other midlatitude regions overseas. The reason: the proliferation of strip malls, subdivisions, and other paved areas may interfere with breezes needed to clear away smog and other pollution.

Paved surfaces in the Houston area keep the city warmer than more natural surfaces. As a result, overnight temperatures are often similar between the city and nearby offshore areas, which weakens summertime breezes and enables air pollution to build up. The stagnant conditions also persist during the day because of larger-scale wind patterns. (©UCAR, Illustration by Lex Ivy. This image is freely available for media use. For more information, see Media & nonprofit use.*)

The research team combined extensive atmospheric measurements with computer simulations to examine the impact of pavement on breezes in Houston. They found that, because pavement soaks up heat and keeps land areas relatively warm overnight, the contrast between land and sea temperatures is reduced during the summer. This in turn causes a reduction in nighttime winds.

In addition, built structures interfere with local winds and contribute to relatively stagnant afternoon weather conditions. “The developed area of Houston has a major impact on local air pollution,” says NCAR scientist Fei Chen, lead author of the new study. “If the city continues to expand, it’s going to make the winds even weaker in the summertime, and that will make air pollution much worse.”

While cautioning that more work is needed to better understand the impact of urban development on wind patterns, Chen says the research can eventually help forecasters improve projections of major pollution events. Policymakers might also consider new approaches to development as cities work to clean up unhealthy air.

The article will be published this month in the Journal of Geophysical Research–Atmospheres, a publication of the American Geophysical Union. The research was funded by the U.S. Air Force Weather Agency, the U.S. Defense Threat Reduction Agency, and the National Science Foundation, NCAR’s sponsor. In addition to NCAR, the authors are affiliated with the China Meteorological Administration, the U.S. National Oceanic and Atmospheric Administration, and the University of Tsukuba in Japan. The research built on a number of previous studies into the influence of urban areas on air pollution.
Cleansing the air with more parks and lakes?

Houston, known for its mix of petrochemical facilities, sprawling suburbs, and traffic jams that stretch for miles, has some of the highest levels of ground-level ozone and other air pollutants in the United States. State and federal officials have long worked to regulate emissions from factories and motor vehicles in an effort to improve air quality.

The new study suggests that focusing on the city’s development patterns and adding to its already extensive park system could provide air quality benefits as well. “If you made the city greener and created lakes and ponds, then you probably would have less air pollution even if emissions stayed the same,” Chen explains. “The nighttime temperatures over the city would be lower and winds would become stronger, blowing the pollution out to the Gulf of Mexico.”

Chen adds that more research is needed to determine whether paved areas are having a similar effect in other cities in the midlatitudes, where sea breezes are strongest. Coastal cities from Los Angeles to Shanghai are striving to reduce air pollution levels. However, because each city’s topography and climatology is different, it remains uncertain whether expanses of pavement are significantly affecting wind patterns elsewhere.

Nine days of pollution

For the Houston study, Chen and his colleagues focused on the onset of a nine-day period of unusually hot weather, stagnant winds, and high pollution in the Houston-Galveston area that began on August 30, 2000. They chose that date partly because they could draw on extensive atmospheric measurements taken during that summer by researchers participating in a field project known as the Texas Air Quality Study 2000. That campaign was conducted by the National Oceanic and Atmospheric Administration, the U.S. Department of Energy, universities, and the Texas Natural Resource Conservation Commission.

In addition to the real-world measurements, the study team created a series of computer simulations with a cutting-edge software tool, NCAR’s Advanced Weather Research and Forecasting model.

Fei and his colleagues focused on wind patterns, which are driven by temperature contrasts between land and sea. If Houston were covered with cropland instead of pavement, as in one of the computer simulations, inland air would heat up more than marine air during summer days and cause a sea breeze to blow onshore in the afternoon. Conversely, as the inland air became cooler than marine air overnight, a land breeze would blow offshore—potentially blowing away pollution.

In contrast, the actual paved surfaces of Houston absorb more heat during the day and are warmer overnight. This results in stagnation for three reasons:
At night, the city’s temperatures are similar to those offshore. The lack of a sharp temperature gradient has the effect of reducing winds.
During the day, the hot paved urban areas tend to draw in air from offshore. However, this air is offset by prevailing wind patterns that blow toward the water, resulting in relatively little net movement in the atmosphere over the city.
Buildings and other structures break up local winds far more than does the relatively smooth surface of croplands or a natural surface like grasslands. This tends to further reduce breezes.

“The very existence of the Houston area favors stagnation,” the article states.

The study also found that drought conditions can worsen air pollution. This is because dry soil tends to heat up more quickly than wet soil during the day. It releases more of that heat overnight, reducing the temperature contrast between land and water and thereby reducing nighttime breezes. By comparing observations taken in 2000 with computer simulations of Houston-area winds and temperatures, the researchers were able to confirm that the Advanced Weather Research and Forecasting model was accurately capturing local meteorological conditions.

About the article

Title: A numerical study of interactions between surface forcing and sea-breeze circulations and their effects on stagnation in the greater Houston area

Authors: Fei Chen, Shiguang Miao, Mukul Tewari, Jian-Wen Bao, and Hiroyuki Kusaka

Publication: Journal of Geophysical Research–Atmospheres

One more reason to say asphalt affects local weather | Watts Up With That?
Air quality worsened by paved surfaces: Widespread urban development alters weather patterns -- ScienceDaily

See also:

What to do about it?

Green roof of City Hall in Chicago,Illinois.
The temperature difference between urban areas and the surrounding suburban or rural areas can be as much as 5 °C (9.0 °F). Nearly 40 percent of that increase is due to the prevalence of dark roofs, with the remainder coming from dark-colored pavement and the declining presence of vegetation. The heat island effect can be counteracted slightly by using white or reflective materials to build houses, roofs, pavements, and roads, thus increasing the overall albedo of the city. Relative to remedying the other sources of the problem, replacing dark roofing requires the least amount of investment for the most immediate return. A cool roof made from a reflective material such as vinyl reflects at least 75 percent of the sun’s rays, and emit at least 70 percent of the solar radiation absorbed by the building envelope. Asphalt built-up roofs (BUR), by comparison, reflect 6 percent to 26 percent of solar radiation.[65]
Using light-colored concrete has proven effective in reflecting up to 50% more light than asphalt and reducing ambient temperature.[62] A low albedo value, characteristic of black asphalt, absorbs a large percentage of solar heat creating warmer near-surface temperatures. Paving with light-colored concrete, in addition to replacing asphalt with light-colored concrete, communities may be able to lower average temperatures.[66] However, research into the interaction between reflective pavements and buildings has found that, unless the nearby buildings are fitted with reflective glass, solar radiation reflected off light-colored pavements can increase building temperatures, increasing air conditioning demands.[67][68]
A second option is to increase the amount of well-watered vegetation. These two options can be combined with the implementation of green roofs. Green roofs are excellent insulators during the warm weather months and the plants cool the surrounding environment. Air quality is improved as the plants absorb carbon dioxide with concomitant production of oxygen.[69] The city of New York determined that the cooling potential per area was highest for street trees, followed by living roofs, light covered surface, and open space planting. From the standpoint of cost effectiveness, light surfaces, light roofs, and curbside planting have lower costs per temperature reduction.[70]
A hypothetical "cool communities" program in Los Angeles has projected that urban temperatures could be reduced by approximately 3 °C (5 °F) after planting ten million trees, reroofing five million homes, and painting one-quarter of the roads at an estimated cost of US$1 billion, giving estimated annual benefits of US$170 million from reduced air-conditioning costs and US$360 million in smog related health savings.[71]

Urban heat island - Wikipedia, the free encyclopedia


Bao‐Liang Chen, Sankha Bhowmick, and Rajib B. Mallick (rajib@wpi.edu)
November, 2008

This white paper presents the concept of using a piping network below the surface of asphalt pavements to flow an appropriate fluid, to reduce the temperature of the asphalt pavement, reduce Urban Heat Island Effect, and use the heated fluid for different end applications such as heating, power generation or refrigeration.  The reduced temperature will extend the life of the pavement, while the reduced temperature of the near surface air will lead to savings in energy consumption of adjacent buildings and improvement in air quality (such as by reducing ozone concentration).  


See also:
Futures Forum: What to do about car emissions: from Paris to London... 
Futures Forum: What to do about car emissions: Exeter 
Futures Forum: What to do about car emissions: the West Country 

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