Air Pollution Kills

In recent years I have substantially increased my estimate of the deadly nature of air pollution. It’s not that I had a contrary opinion earlier but the number and range of studies showing surprisingly large effects has raised this issue in relative importance in my mind. I would not have guessed, for example, that the introduction of EZ Pass could reduce pollution near toll booths enough to reduce the number of premature and low birth weight babies. I also find the following result hard to believe yet also hard to dismiss given the the accumulating body of evidence. Diane Alexander and Hannes Schwandt find that Volkswagen’s cheating diesel cars increased the number of low birth weight babies and asthma rates. Here are some details:

In 2008, a new generation of supposedly clean diesel passenger cars was introduced to the U.S. market.These new diesel cars were marketed to environmentally conscious consumers, with advertising emphasizing the power and mileage typical for diesel engines in combination with unprecedented low emissions levels. Clean diesel cars won the Green Car of the Year Award in 2009 and 2010 and quickly gained market share. By 2015, over 600,000 cars with clean diesel technology were sold in the United States. In the fall of 2015, however, it was discovered that these cars covertly activated equipment during emissions tests that reduced emissions below official thresholds, and then reversed course after testing. In street use, a single “clean diesel” car could pollute as much nitrogen oxide as 150 equivalent gasoline cars.Hereafter, we refer to cars with “clean diesel” technology as cheating diesel cars.

We exploit the dispersion of these cheating diesel cars across the United States as a natural experiment to measure the effect of car pollution on infant and child health. This natural experiment provides several unique features. First, it is typically difficult to infer causal effects from observed correlations of health and car pollution, as wealthier individuals tend to sort into less-polluted areas and drive newer, less-polluting cars. The fast roll-out of cheating diesel cars provides us with plausibly exogenous variation in car pollution exposure across the entire socio-economic spectrum of the United States. Second, it is well established that people avoid known pollution, which can mute estimated impacts of air pollution on health (Neidell, 2009). Moderate pollution increases stemming from cheating diesel cars, a source unknown to the population, are less likely to induce avoidance behaviors, allowing us to cleanly estimate the full impact of pollution. Third, air pollution comes from a multitude of sources, making it difficult to identify contributions from cars, and it is measured coarsely with pollution monitors stationed only in a minority of U.S. counties. This implies low statistical power and potential attenuation bias for correlational studies of pollution (Lleras-Muney, 2010). We use the universe of car registrations to track how cheating diesel cars spread across the country and link these data to detailed information on each birth conceived between 2007 and 2015. This setting provides rich and spatially detailed variation in car pollution.

We find that counties with increasing shares of cheating diesel cars experienced large increases both in air pollution and in the share of infants born with poor birth outcomes. We show that for each additional cheating diesel car per 1,000 cars—approximately equivalent to a 10 percent cheating-induced increase in car exhaust—there is a 2.0 percent increase in air quality indices for fine particulate matter (PM2:5) and a 1.9 percent increase in the rate of low birth weight. We find similar effects on larger particulates (PM10; 2.2 percent) and ozone (1.3 percent), as well as reductions in average birth weight (-6.2 grams) and gestation length (-0.016 weeks). Effects are observed across the entire socio-economic spectrum, and are particularly pronounced among advantaged groups, such as non-Hispanic white mothers with a college degree. Effects on pollution and health outcomes are approximately linear and not affected by baseline pollution levels. Overall, we estimate that the 607,781 cheating diesel cars sold from 2008 to 2015 led to an additional 38,611 infants born with low birth weight. Finally, we also find an 8.0 percent increase in asthma emergency department (ED) visits among young children for each additional cheating diesel car per 1,000 cars in a subsample of five states.

Another surprising result is that on a global scale air pollution reduces life expectancy more than smoking. In part, because a single individual can’t quit air pollution.

Globally, the AQLI reveals that particulate pollution reduces average life expectancy by 1.8 years, making it the greatest global threat to human health. By comparison, first-hand cigarette smoke leads to a reduction in global average life expectancy of about 1.6 years. Other risks to human health have even smaller effects: alcohol and drugs reduce life expectancy by 11 months; unsafe water and sanitation take off 7 months; and HIV/AIDS, 4 months. Conflict and terrorism take off 22 days. So, the impact of particulate pollution on life expectancy is comparable to that of smoking, twice that of alcohol and drug use, three times that of unsafe water, five times that of HIV/AIDS, and more than 25 times that of conflict and terrorism.