University of Chicago Air Quality-Life Index

By Andy May

The University of Chicago Energy Policy Institute has come up with a new measure of air pollution they call the Air Quality-Life Index or AQLI. It uses particulate pollution concentrations to compute an index that correlates well with expected life expectancy. Particulate concentrations <10 μm (PM10) and <2.5 μm (P2.5) are utilized in the study.

The results are supported by research on the health effects of Chinese domestic and industrial coal use (see PNAS, September 26, 2017, here). The study shows that the unregulated use of coal, i.e. without any pollution controls, to heat houses in China causes much of the Chinese population to be exposed to dangerous levels of PM10. They concluded that a 10 μg/m³ increase in PM10 reduces Chinese life expectancy by 0.64 years (95% confidence interval=0.21-1.07).

The abstract of this paper reads, in part:

“This estimate is derived from quasi-experimental variation in PM10 generated by China’s Huai River Policy, which provides free or heavily subsidized coal for indoor heating during the winter to cities north of the Huai River but not to those to the south. The findings are derived from a regression discontinuity design based on distance from the Huai River, and they are robust to using parametric and nonparametric estimation methods, different kernel types and bandwidth sizes, and adjustment for a rich set of demographic and behavioral covariates. Furthermore, the shorter lifespans are almost entirely caused by elevated rates of cardiorespiratory mortality, suggesting that PM10 is the causal factor. The estimates imply that bringing all of China into compliance with its Class I standards for PM10 would save 3.7 billion life-years.”

On the University of Chicago web site here, they explain that the new AQLI measure correlates well with life expectancy and prefer it to the EPA’s “Air Quality Index” or AQI. As explained here, the AQI is determined only by the pollutant with the highest index. Pollutants checked can include PM10, PM2.5, SO₂ (Sulfur Dioxide), O₃ (Ozone), CO (Carbon Monoxide), and NOx (nitrogen oxides, mainly NO₂). If the pollutants with a lower index are present, they are ignored. The AQI indices are computed separately, such that 100 or less meets the national ambient air quality standard and 500 is the level where significant harm to the population is expected.

The EPA describes the AQI here. They describe the details of the calculation here. The dangers of the various pollutants vary dramatically. High levels of ground level ozone are irritating to the part of the population that already has asthma or emphysema, but have not been linked to long term health problems for most people. Sulfur dioxide is an irritant, but not poisonous in small amounts.  But, carbon monoxide is a deadly poison. As the University of Chicago determined in China, PM10 concentrations are related to life expectancy. The different pollutants have different health effects, yet the AQI gives them equal weight, thus the AQI does not correlate with health risk.

Particulate pollution is strongly correlated to health risk and the University of Chicago study strongly suggests that particulate matter is the greatest current airborne environmental risk to human health. The University of Chicago provides maps of the particulate matter health risk. Figure 1 is for the world:

Figure 1: Health risk due to PM10 (source: University of Chicago)

The areas most affected burn wood and other biofuels or coal in their houses for cooking and heat. The United States, Western Europe, Canada and Australia produce much of their electricity from coal, but they use advanced pollution control equipment to remove most of the particulate matter and other pollutants from their smoke stacks, thus their air is mostly OK. Below is the University of Chicago map of the continental United States.

Figure 2: United States health risk due to particulates (source: University of Chicago)

The University of Chicago AQLI stands in stark contrast to the EPA’s AQI as can be seen from table 1. In table 1 the cities are listed in order by AQI, but the bars show the health risk from particulates. The only areas with an enhanced health risk due to particulate pollution in the U.S. are the Los Angeles and Chicago areas where the residents would live 0.5 years longer if the cities met the WHO air standards. San Diego and parts of New York City are also at some risk. The other major U.S. cities would realize no benefit.

Table 1 (source: University of Chicago)

Results and Discussion

The study, whether the conclusions are correct or not, is very useful. We are often told that all pollution is bad and the AQI makes the explicit assumption that various sources of air pollution are equally harmful. The University of Chicago attempts to measure the health effects of various pollutants and identifies particulate matter as the most harmful. I would like to see more studies of this type.

This sort of false equivalency is seen clearly in the media’s inane obsession with “carbon” pollution. They mean CO₂, which is not harmful to our health and is essential for life on Earth. I should note that if one smothers due to extraordinary levels of CO₂, it is the lack of sufficient oxygen that kills the person, not any CO₂ toxic effects. Plus, by using the term “carbon” they erroneously conflate carbon monoxide, carbon particulates and CO₂. Even the University of Chicago paper tried to conflate particulate pollution to climate change by noting that burning fossil fuels (supposedly) causes both. Yet, when we read their article a little more carefully we realize the health problem is not fossil fuel burning, but domestic coal and biofuel burning without pollution control equipment.

In the U.S., burning wood in fireplaces, dust, wild fires, effluent from diesel engines and coal-burning power plants all emit particulate matter. Wood-burning fireplaces can be particularly hazardous, since the burning takes place inside, when it is cold outside and the house is closed up, see the EPA discussion here. In cities like Chicago and Denver, many of the worst pollution days are in the winter and they are mostly due to a combination of temperature inversions and the use of wood-burning fireplaces (see the Chicago Tribune article here). Wood-burning fireplaces are wonderful on cold nights, but not very healthy, see figure 3 from the EPA.

Figure 3 (EPA)

Oddly, the climate change alarmist community, especially in Europe, has encouraged the burning of wood because they believe the CO₂ and other pollution from burning wood is somehow “safer” than fossil fuels (see the BBC report here). I note the BBC pages says biofuels “may not” produce particulate pollution, this does not apply to wood, charcoal or dung, which are 90% of the biofuels used and 63.7% of the world renewable energy supply (IEA). Figure 4 shows the breakdown of fuel use according the IEA.

Figure 4 (source IEA)

As can be seen in figure 4, the relatively particulate free biofuels, biodiesel and biogases, comprise a tiny fraction of the total biofuels used. The particulate emitting biofuels comprise 63.7% of the total renewables used and a whopping 90% of the total biofuels used. The only significant particulate-free fuels used, as a percentage of our energy supply, are natural gas (22%) and hydro (2.5%).

In summary, if the University of Chicago Energy Policy Institute is correct and particulate matter is the most dangerous air pollutant, biofuels are not helping. Natural gas is the healthiest abundant alternative. Further, the study suggests that we should rank pollutants by their health risk and not treat them all as equivalent as the EPA now does. This is a welcome study and I hope it is followed up with many more assessments of risk by pollutant. Artificially making all pollutants equivalent does not help our decision making.