Skip navigation

Many city dwellers have a special appreciation for a tree-lined street. The trees provide much-needed summertime shade to sidewalks and houses. Chirping birds make their homes in the branches. Dappled green light filters through the trees’ leaves. A new paper reports that properly arranged greenery can also cut air pollution on city streets by up to eight times more than was previously believed.


Thomas Pugh and colleagues explain that “urban canyons” formed by city buildings concentrate harmful pollutants. Burning fossil fuels in car engines and power plants produces pollutants — like nitrogen dioxide (NO2) and particulate matter (PM) – which may harm our lungs. The World Health Organization estimates that outdoor air pollution kills 1.3 million people each year. The authors report that levels of these two pollutants routinely reach unsafe levels on city streets and that the situation is only getting worse in many places.


Their Environmental Science & Technology paper describes three basic ways to reduce pollutant levels: curbing their emission, increasing their dispersion or getting them out of the air and onto something solid. The first two are tough in a city, where constant traffic is a given and tall buildings and right-angle intersections conspire to trap polluted air.


Both NO2 and PM will stick to hard surfaces like concrete and asphalt, but the authors say that plants do a better job of trapping pollutants, pointing to the “stickiness” of plant leaves, the way air moves around them and their large surface areas. That’s the key to their assertion that well-placed plants can reduce street-level concentrations of NO2 by as much as 40 percent and PM by 60 percent. The researchers say that more judicious placement of grasses, shrubs and trees could go much further than previous research suggested in making the air at street level cleaner.


The authors suggest that climbing plants like ivy, ground-covering grasses and shrubs and vertical gardens on the sides of buildings — which they liken to “green billboards” — might be the most effective way to combat pollution. They provide a lot of surface area for pollution deposition without blocking air movement.


On streets with light traffic, trees can still be effective because pollution is comparatively low. But where cabs, trucks, buses and cars are spewing out a lot of NO2 and PM, they caution against using trees, which can trap polluted air underneath their canopies. The authors even say that plants in urban spaces could make city air cleaner than in the surrounding areas.


Greening city streets has side benefits, too; the authors point out that more plants can lower temperatures, dampen loud noises and make a neighborhood more attractive.


What creative ways can you think of to bring more plants onto city streets?


“Effectiveness of Green Infrastructure for Improvement of Air Quality in Urban Street Canyons,” Environmental Science & Technology



Credit: iStock

Overeating has become a popular sport in the United States. And I’m not just talking about events like Nathan's Famous hot dog-eating contest in Coney Island, Brooklyn, N.Y., where Joey "Jaws" Chestnut last month won his sixth consecutive title. He downed 68 dogs with buns in 10 minutes.

Some of these eaters are very serious. A
350-pound man picketed an all-you-can eat fish-fry restaurant in Wisconsin this spring after they had the audacity to cut him off after a dozen pieces of fish. This overeating has, of course, had an effect on the population. During the past 20 years, there has been a dramatic increase in obesity in the United States and rates remain high. Today, one in three adults in the United States is obese and nearly one in four children and adolescents is significantly overweight, according to the Centers for Disease Control (CDC). Overeating is adding to obesity-related conditions including heart disease, stroke, type 2 diabetes and certain types of cancer.

And now there is a different problem related to the all-you-can-eat principle, and it’s in the laboratory, not the kitchen. The widespread practice of allowing lab rats and mice to eat as much as they want may be affecting the outcome of experiments in which scientists use them to test new drugs and other substances.

Laboratory mice and rats are understudies for people when research can’t be done on humans. Researchers Gale Carey and Lisa Merrill point out that the millions of lab rodents used in laboratory studies each year are fed differently from other test animals. While other test animals get regular meals, rodents can eat all they want whenever they want it. They take advantage of this choice and it shows: they put on more weight and more body fat than meal-fed rodents. And the two scientists also point to other research which has found that lab rodents with easy access to food often to develop abnormally high blood fat levels, high cholesterol, nerve and heart damage, cancer and other disorders, much as people do.

The scientists reported in the ACS Journal of Chemical Research in Toxicology that after analyzing 54 studies, they concluded that when rats and mice have free access to food, it likely affects the results of tests for harmful and cancer-causing effects of new drugs and other substances. This could explain why such study results have been so inconsistent recently. They suggest that scientists reconsider using the all-you-can eat approach for lab rodents.


“Meal-Feeding Rodents and Toxicology Research,” Journal of Chemical Research in Toxicology




mouse and food.jpg


Credit: iStock