Thursday, December 21, 2006

What distance is a "safe" distance from a highway?

Question:
I have read, with great interest some of your statements and a presentation of yours on indoor air pollution resulting from close proximity to highways. My wife and I are considering a relocation, in order to decrease my commute time. However, almost every property we look at is within 1.5 miles of a major highway, which is often congested with trucks, etc. I have read over 10 studies documenting increased risk for childhood leukemia and asthma. What is considered a"safe distance" from a major highway? These studies don't state the exact distance at which they measured. Also, I have read of the ability of plants such as bamboo and areca palm in removing 80% of benzene in the air. Have you read those claims and do they seem to be valid?

Response:
You are right that many recent studies have shown that pollution from traffic, especially diesel-powered traffic (such as trucks) is bad for health. Traffic pollution has been linked to increased death and hospital admissions for heart and lung disease, increased asthma attacks, and early indicators of cardiac disease. Consistent with these findings, several studies have also shown that living near a major highway or road presents greater health risks. While there have been some differences among studies, there seems to be a general consensus that the critical distance from a busy road or highway is within 100 meters (or about 300 feet). After this distance, you generally no longer see a dramatic increase in traffic-related pollution above urban background. In a city, however, it is difficult to get away from all traffic-related pollution as it can travel relatively long distances.

It is not clear what pollutant or pollutants emitted from motor vehicles are responsible for the observed health problems. It is possible that plants (such as bamboo) under certain conditions can be used to remove certain gaseous pollutants from motor vehicles, such as benzene, carbon monoxide and nitrogen dioxide. I haven't heard of any plants that remove particles from motor vehicles. l think that most of the studies examining pollutant removal by plants have been conducted in closed environments. The effectiveness of using plants to clean your air in your yard will probably be much lower, as outdoor air moves pretty freely.

3 comments:

Mairaj said...

this is a great blog. looking forward to frequently visiting. a follow-up question:
you mention pollutants emitted from motor vehicles versus motor-vehicle related gaseous pollutants - what's the difference?
can you elaborate on what these pollutants are?

also are there inexpensive monitors available?

and lastly what is the scientific communities opinion on HEPA and carbon filter air "purifiers"?

many thanks.

Prof. Helen said...

Motor vehicles are associated with many air pollutants. These air pollutants are generally classified in several different ways. One of the most common ways is to label them as either a gas or a particle, based on their typical form in the environment.

Gaseous air pollutants related to motor vehicles include carbon monoxide, nitrogen dioxide, and benzene. Elemental carbon, very small or ultra-fine particles, and PAHs are examples of motor vehicle-related particulate air pollution. Practically, whether the pollutant is a gas or a particle may mean little, but can provide some information about how far the pollutant may travel, whether it can come indoors, how to measure it, and potential health risks.

For traffic-related air pollutants, measurements are generally performed by the government or by scientists. I am not aware of any "off-the-shelf" kits. It is possible to measure some of the traffic-related pollutants with relatively inexpensive methods; however, these monitors tend to be not that accurate and not so easy to use or analyze.

I was recently asked a question about air cleaners. I am going to post the question and answer in a later posting - hopefully tomorrow or over the weekend.

Hope that this helps!

jenny said...

I was wondering if there were any more current information about what a safe distance is to live from a highway. I was reading somewhere that 1500 ft is the goal, and was wondering how comfortable you are with the 300ft number. I have a 3 yr old, and am asthmatic, and they are building a 6 lane parkway 500 ft from my house. We are naturally concerned regarding the health consequences, but this is a really bad real estate market to attempt a move. If you still feel its relatively safe, we may stay put. Thanks!