I’m old enough to recall when America stood tall, and produced its own air pollution. Instead of having to import it from Canada.
To cut to the chase: Air pollution in the DC area is at an extreme level today. This, owing to Canadian forest fires. But the level of particulates in the air — currently a PM 10 reading of around 300 (micrograms per cubic meter) — would not have been hugely unusual in the 1960s. Back then, each year, about 10% of U.S. cities would have seen at least one day with particulates roughly at that level.
It just takes a bit of work to find the data, and translate the obsolete measure (total suspended particulates) to the modern data (PM 10).
And so, as with our recent “extreme” winter weather, the long-term trend obscures the fact that things were much different in the recent past. Cold weather that triggers alarms today would have been a yearly occurrence three decades ago (Post #1664). And particulate levels that result in cancellation of outdoor activities today, would, in the 1960s, have been — not common, exactly — but frequent enough that all of us of that generation recognize the term “smog alert” as shorthand for a day with bad air pollution.
Back when I was a kid …
I had an funny interaction at my bank this morning. Had to get a document notarized, and ended up chit-chatting with the Notary Public.
Talk turned to the unhealthful air today, the result of smoke from Canadian forest fires. Said smoke now blanketing much of the U.S. Northeast.
In all innocence, I said something like “this reminds me of my youth.” My assertion being that, back in the 1960s, in the Washington DC area, we routinely had summertime air that looked about like the air we have today. Visibility was a mile or two. Beyond that, everything sort of faded to a gray-white. The summer sky was always a uniform fish-belly white, from the combination of humidity and particulates in the air.
That opaque air, in turn, was due to the routinely high levels of air pollution. That era predates pretty much every form of air pollution control. Power plants burned coal, and nobody had heard of smokestack scrubbers. Catalytic converters for cars didn’t come in until 1974, so unburnt hydrocarbons ruled the suburban air. And car fuel systems were open to the air — you simply dumped gas vapors every time you filled up. Worse, carburetor bowls were vented directly to the atmosphere, leading to continuous dumping of gasoline vapors as you drove or parked.
In this area, the result was massive amounts of photochemical and other types of smog. Or “haze”. In the summertime, the most common weather report was hot, humid, and hazy.
But the notary was a young guy, and he frankly did not believe what I was saying. Having grown up well after the mid-1960s passage of the Clean Air Act, he could not conceive of a world where the current level of air pollution was considered — well, not normal, exactly — but not uncommon, either.
So that’s the task for today. Was the air in this area routinely hazier back in the day, or is it merely my memories that have become hazy?
Historical Air Pollution Levels
For sure, the U.S. had some dramatic, short-lived air pollution events in that era. Today, newspapers are recalling the Great New York Smog of 1966. Such extreme but short-lived smog events were common in New York city, in that era. Pollution levels during those smogs equaled or exceeded current levels.
And, of course, Los Angeles famously had a unique problem owing to geography. Air trapped in the Los Angeles basin would more-or-less accumulate everything emitted into it, leading to chronic visible smog.
But I’m looking for information on day-to-day air pollution and visibility levels, going back to the 1960s, ideally in the summertime, in the Washington DC area.
The problem is that, at the very best, I can find modern-format going back as far as 1980. That appears to be the year when U.S. EPA put into place the National Air Quality System (reference), which is an arrangement for gathering and storing air quality data from monitoring stations all around the U.S.
Worse, older EPA air quality data use an outdated measure of particulates. Currently, we track PM 2.5 and PM 10, the numbers referring to the maximum size of the particles (in microns?) By contrast, EPA data from the 1960s uses Total Suspended Particulate, which apparently corresponds to something like PM 50, and is routinely several times higher than the current PM 2.5 or PM 10 measures. That said, when the annual 90th percentile of maximum daily total suspended particulates was around 400 (micrograms per cubic meter), it’s clear that there was a lot of stuff in the air back then. 
Source: 1973 national air quality report, downloaded from this EPA page on historical air quality reports. Number EPA-450/1-73-001-a.
By contrast, today’s air quality crisis is due to PM 2.5 concentrations around 200 (micrograms per cubic meter), and PM 10 concentrations around 300 (same units).
Source: Accuweather, data for the DC area, 2 PM 6/8/2023
Luckily, the EPA reports themselves provide a rough crosswalk between the older total particular matter and newer PM 10 measures. Based on a comparison of the 1990 (left) and 1991 (right) reports, PM 10 appears to run about 2/3rds the value of total suspended particulates, as measured by the EPA.
Source: 1990 and 1991 EPA air quality trends reports, from this page at the EPA.
The upshot.
Today’s PM 10 concentration of 300 (micrograms per cubic meter) is equivalent to a reading of about 450 (same units) for total suspended particulates. Which is just slightly higher than the 90th percentile figure from the 1960s, from the graph above.
In other words, back in the 1960s, every year, 10% of U.S. cities would have seen an air pollution day that was nearly as bad as what DC is experiencing today.
That doesn’t mean that the average was that bad. It really means that “smog alerts” were not unheard-of, when I was a kid. And that, thankfully, that’s no longer true, so the current generation no longer has to treat them as just another fact of life.
I still have not found the data to address the main question of visibility. Was the air routinely as opaque as it is today, back when I was a kid?
Currently, Dulles Airport is reporting visibility of 2 miles. But apparently, visibility is only kept in the raw hourly observations, and so far, I have not been able to find 1960s visibility data for my area, from any source. If I find it, I’ll post it.
