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.
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
Pat wrote:
Interesting side note, the reporter in NYC for NBC in discussing the current heat wave, noted that because of the asphalt and heat retention by concrete, the city would be up to 15 degrees warmer than ambient air. These are the same people that see AGW at every turn. It never occurred to them that the global temperature might not be as high if measured outside of UHE areas.
See, you shouldn’t be surprised; the favorite refrain of warmists is that “correlation is not causation”. Unless the correlation supports their cause, in which case it is 100% linked.
I don’t think this was really meant to be “climate science,” per se, although it sounds like the sort of thing Pielke, Sr is into. But look at who paid for this study:
“The research was funded by the U.S. Air Force Weather Agency, the U.S. Defense Threat Reduction Agency, and the National Science Foundation…”
In particular, according to DTRA:
“Each day, DTRA is working to predict, understand, and address the effects of nuclear and radiological weapons. Using innovative science and technology, DTRA works with federal agencies and foreign governments to improve global preparedness and response capabilities.”
A better understanding of how winds work around urban areas could be useful to someone interested in what happens with nuclear, chemical, biological or radiological weapons.
The neglect of focusing on UHI is intentional. Find someone from the left and I will show you someone that believes we should all be living in dense, tightly-packed cities.
The same could be said of black carbon, to a much lesser degree. Poor people (especially those outside of the Western world) rely the most on the burning of biomass to live. So, they routinely ignore the devestating effects of soot in favor of hyper-focusing on Co2. The rich man’s pollutant.
In what might be a coincidence (or might indicate the run up to a big “scientific conference” somewhere), the BBC’s Richard Black is back peddling alarm on urban air quality:-
http://www.bbc.co.uk/news/science-environment-13714931
Of course, I doubt that anyone on here will stick their chest out and say that air pollution is never a problem. And what Black reports and what Fei Chen and his co-authors say in their paper about Houston could be right. Or at least, more right than wrong.
But it does occur to me that it would be interesting to know what air quality was like in either Houston or London, 5, 10, 20 or 50 years ago?
How much “excess morbidity” was there then?
How do they compare with (say) Berlin, Rome, Moscow, Beijing, Mumbai, Cairo, Rio, Jakarta?
What “excess morbidity” is there in these cities?
And are any of the reported deaths genuine or are they all cyber-people predicted by a computer model?
It is inescapable that bad air quality gives people with asthma problems and may well increase the number of asthma sufferers.
But, cynic that I am, I just wonder if these guys are just shills for BigElectricCar?
Can’t be, surely…….
The phrase “Urban Heat Island” is conspicuously absent from the report. Is NCAR afraid of using terminology that has become associated with ‘deniers?”.
Like others, I have lived in the Houston area for many years, although closer to the coast (Clear Lake area). I would figure that the authors of this study would at least reference some historical data, such as this wind rose from the Texas Commission on Environmental Quality (this is for August, although the study did go from 8/30 through 9/9, one of the hottest times I remember here in Clear Lake)
http://www.tceq.texas.gov/assets/public/compliance/monops/air/windroses/iahaug.gif
Seems to me the predominate wind is from…the coast.
In short he suggests that Houston should stop being Houston and get with the program. Unless Houston went through a massive change, it was the largest city in the US that had no real zoning laws and the only way to achieve the level of change that is suggested is to change that which makes Houston great. Houston has expanded the way it has precisely because the government has very little to say on where a developer builds and what he builds. There are laws that prevent things such as bars being built within a certain distance of schools and what not, but zoning, nope. It is one of the last bastions of free market development, builders build where people want to be, not where the government says they are to be.
Maybe there is another way of looking at this. Not that the asphalt of a city heats but that the soils, lawns, and tree canopies of rural areas cool. Do leaves on a tree ever get as hot as concrete pavement or sand on a beach? I assume that the water necessary to keep a plant alive also somehow cools it.