Do we really need cleaner air?

“Conservare” (Latin): ‘to keep, preserve, guard’.

Sometimes it is important to remember that the words ‘conservationist’ and ‘conservative’ come from the same root. How close conservatism and conservationism were in the past can be traced in the history of the US Environmental Protection Agency (EPA). It was founded by a Republican President (Richard Nixon) and championed by Republican lawmakers. Then came the Reagan Revolution and the shift towards deregulation (“The most terrifying words in the English language are: ‘I’m from the government and I’m here to help.’”). And ever since, conservatives in the US loved to hate the EPA.

But the original purpose of the EPA was to clean up the rivers (some of which were literally on fire) and the air, both of which were welcome by outdoorsmen, a natural constituency of the Republican Party. Today, some people argue that the air is already clean, and the EPA focuses on climate change and other doubtful regulations.

But is the air really clean? Or is it clean enough? And what are the economic costs of ‘dirty air’?

The air today is much cleaner than it was in 1973 when the EPA was created. But that doesn’t mean that it is that much healthier. Nolan Miller, David Molitor, and Eric Zou used wildfires in the US to provide not just correlational evidence but a causal link that air pollution well below the EPA guidelines causes economic costs that aren’t that much smaller than being trapped in smog. And it all is due to my favourite thing in nature: Nonlinear effects. They make everything scarier.

When it comes to wildfires and air quality in general the two variables of concern are PM10 and PM2.5. They describe the concentration of particulate matter in the air with a diameter of 10 microns or less (PM10) and 2.5 microns or less (PM2.5). For comparison, the width of a human hair is about 50 microns.

PM10 is mostly the ash created by a wildfire or the dust created by a construction site. When you breathe it in, you can feel it. PM2.5 is much more dangerous. These are aerosols that are created from burning wood, oil, gas, and many of these can create cancer. These particles are also so small that they are deposited deep in our lungs where they can create chronic lung diseases and some of these particulates can even cross into the blood stream and create havoc in other organs.

This is why the EPA has limits on how high the PM2.5 concentration in the air can be before it is considered a human health hazard. The annual average PM2.5 concentration in the US should be below 9 microgram per cubic meter and the maximum allowable 24-hour average is 35 microgram/cubic meter. In comparison, the WHO recommendation is to keep the annual average below 10 micrograms and the EU and UK limits are 25 micrograms and 20 micrograms, respectively.

With that information in mind, let’s have a look at the charts below. The top row shows how air pollution worsens in the days after a wildfire. On average, the PM2.5 concentration rises by 1 microgram/cubic meter on the day of a wildfire and stays there for a couple of days. This tiny increase in air pollution leads to an increase in emergency room visits of about 6 people per million inhabitants. Not a lot, but statistically significant.

What is more fascinating though is the second row of charts. The top row averages all incidents everywhere in the US. These are people who live right next to a wildfire and face massive air pollution up to people who live hundreds of miles away from the wildfire and presumably don’t notice anything. In the second row, the bottom left chart shows the change in air pollution depending on how far away from a wildfire you live. Note that even as far as 600km (400 miles) away from the wildfire, the increase in PM2.5 concentration is 3 to 5 micrograms per cubic meter.

Let’s keep that 3 to 5 microgram increase in mind when we look at the charts in the bottom centre and bottom right. These charts show that emergency room visits and excess deaths rise rapidly for PM2.5 concentrations as low as 2 to 5 micrograms per cubic meter and then level off. This is the opposite of what would naively expect. One would either expect a linear relationship (twice the air pollution leads to twice the number of ER visits) or an exponential relationship where emergency room visits and excess deaths are small for low levels of air pollution and then explode, once air pollution crosses a certain threshold.

Instead, even low levels of air pollution create a large increase in hospitalisations and excess death. Once we reach a certain level of air pollution (about 6 micrograms or one third below the legal limit) the economic and health damage levels off. In other words, from an economic perspective, the air needs to be much, much cleaner before the cost to the economy and human health is significantly reduced. And to get there we need stricter guidelines from the EPA.

Effects of wildfire smoke and health

Source: Miller et al. (2024)

PS: Before you start complaining that we cannot regulate wildfires. The point of using wildfires is that one can use them to prove causality. Regulation cannot reduce wildfires (it can make them less severe, though), but it can reduce emissions from burning other fossil fuels like oil and gas.