This Is My Research: Residential Noise Exposure and Health

This is Muzhe Yang's research published in the Journal of Environmental Economics and Management, Volume 103, September 2020. The paper is called: "Residential Noise Exposure and Health: Evidence from Aviation and Noise and Birth Outcomes" by Laura Argys (University of Colorado Denver), Susan Averett (Lafayette College), Muzhe Yang (Lehigh University).

Learn more about Muzhe Yang and his research.

What follows is a complete transcript of the video.

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MUZHE YANG: Noise pollution is not something new that has recently caught public health experts attention. In fact, noise pollution has been a subject of regulation under the Noise Control Act of 1972 in the United States. However, it has just not received adequate attention from policy makers. 

It was estimated that even in the year 2013 there were 104 million people at the risk of noise induced hearing loss and tens of millions more could suffer from noise related health effects. So, how does noise affect health. Well, it is through the activation of the human body's central stress response system. This activation will cause disruptive sleep, increased release of stress hormones, increased blood pressure and increased heart rate. What is also important to know is that this activation does not require the cognitive perception of the noise. 

So, what does this mean? It means that adverse health outcome can happen to a person whether or not that person feels annoyed by the noise or tries to adapt to the presence of noise. For this reason noise pollution is sometimes called a silent killer. Pregnant women are particularly vulnerable to noise because the central stress response system is more sensitive during pregnancy. Aircraft noise can be particularly damaging because of its loud and intermittent nature, but so far there have been very few studies focused on the fetal health impact of aircraft noise and if any the studies we found focus only on the correlation not causation between noise and health. Our study, arguably, is the first to successfully identify the causal effects of maternal exposure to noise during pregnancy on birth outcomes. 

So how do we get this done? The answer comes from a nationwide initiative called the Next Generation Air Transportation System or NEXTGEN. It provides a rare opportunity for researchers to identify the cause the effect of noise exposure. Let me now go over why. The most important feature of NEXTGEN is the use of precision satellite monitoring which replaced the old-fashioned radar-based monitoring. Compared with radars satellites are able to pinpoint the exact location of each aircraft. This means that more airplanes can fly closely together while being safely spaced so that airplanes can use the same route. These rules are also made to be more direct with the purpose of saving fuel and reducing flight time. Besides, under NEXTGEN aircraft now use a gradual descent approach which also save fuel but this will allow airplanes to land at a much lower altitude and therefore the noise will become louder to humans on the ground. 

In the end, whoever lives in an area that is covered by the satellite designed optimal rules has become the victim of an unexpected air show and there have been a lot of media reports on such cases. Here it is also important to point out that the implementation of NEXTGEN by the FAA was exempted by the Congress from normal environmental impact reviews and public hearings. While, this is unfortunate for the public, it is actually good for research. This means that the public were caught off guard and if they were caught off guard then the noise exposure could be viewed as exogenously imposed and this exogenous variation is what a researcher needs to identify the causal effect, Our study uses birth records collected by the New Jersey Department of Health. 

In the birthright records, we have information on each mother's home address. We focus on mothers living close to Newark airport one of the busiest airports in the country. We also combine birth data with noise data released by the U.S. department of transportation. We use this noise data to verify that indeed NEXTGEN has produced a narrow band covering the runways of Newark airport like a noise pollution corridor. We focus on those living within 5 miles of the airport. Conditional on choosing to live close to the airport, we argue that people probably do not have the knowledge about the exact landing and takeoff paths of airplanes, or they may think they will be exposed to similar levels of aviation noise since landing and takeoff paths, prior to NextGen, were less concentrated. This means that among those living close to the airport, whether or not they live inside the noise pollution corridor can be random, and therefore their noise exposure can be viewed as almost randomly assigned. Our focus on those living close to the airport also helps us disentangle the health effect of noise pollution from the health effects of air pollution. 

Here is why: in a small area around the airport, which is within 5 miles of the airport in our study, we present evidence showing that air pollution is likely to be evenly distributed within that small area, but in contrast, sharp changes in noise pollution exist. In the end, using the birth data from 2004 to 2016, we find an increase of 1.6 percentage points, or 22%, in the likelihood of having a low birth weight baby. Low birth weight is defined as birth weight below 2,500 grams (or 5.5 pounds). We find this increased fetal health risk among mothers who live within 5 miles of the airport, in the direction of the runway, exposed to noise levels that are above 55 decibels, which is the threshold used by the EPA and WHO, and during the period when NextGen was more actively implemented at the airport. 

So far there have been many, many efficiency benefits attributed to NEXTGEN, such as saving energy and reducing flight time. However, our study highlights the presence of a trade-off between NextGenís flight path optimization and human health, and we must recognize this trade-off, especially regarding compromised fetal health, because such a compromised health at birth will have long-term impact on many outcomes during adulthood, including health, educational attainment, work productivity and earnings.

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