Over the past few years, I've been trying to learn about air quality, in a formal way.
I once tried learning about shampoo, in a detailed way,
and this was near-impossible to do.
Likewise, this has been a very tricky thing to learn about.
I thought I could share some of my thoughts on the matter:
I bought this guy for  150 bucks or so:
it ain't bad.

Suspicions about the Hidden Realities of the Air

Douglas coupland used to do this thing where he imagines himself talking to someone from the 12th Century.
He tries to describe the present time to them. People think they'll pull-out a iphone, and tap around on it, whooo! then that'll be it.
But really, the biggest-whopper may be communicating strange scientific realities that we've internalised, and now are bored-by.
One, for example:
THERE ARE LOTS OF THINGS IN THE AIR.
This is a really hostile concept.
Anybody from the past would accept a fancy little toy that can answer questions.
But I think it would be a tough-sell to tell people that all of the air is packed with things, and we discovered it, and simply ignore it.
The air is packed with things. We acknowledge it, and never think about it.
Here's my favourite examples of this:
Researchers boiled some water, then put it on the roof overnight.
There were millions of viruses in it in the morning. They fell right
from the sky. We pay no attention to any of this at all. We go on our day, as if the air is empty. Unfortunately, the ways we measure air quality (and weather) leave a lot to be desired:

PM2.5

This sounds cool, but is not that cool.
PM is just 'particulate matter', which means any stuff.
Maybe it's good stuff.
Sometimes it's perfume, incense, an air freshener.
A huge amount of money is spent reducing PM2.5, and also, a huge amount of money is spent increasing it.
Making a stir-fry can spike PM levels in your whole house for an hour.
I enjoyed reading this article where someone recorded their toaster PM output.
Sometimes at construction sites, they'll put on a sprinkler, which is comically effective at reducing particulate matter.
Boris Johnson got in trouble for doing something similar in London, before an air quality test. It's really not a strong thing to measure, or to minimize. I don't know, I want more.

Electric charge

I don't understand why this is left out of weather reports. You know how dust always collects on the tv screen? Or sometimes more than others?
The electric potential of the air changes, like weather, and varies dramatically from place-to-place.
Measurements of this happened in earnest during the 18th Century, but unfortunately, cheap sensors for atmospheric electricity are hard to find.
Sometimes 'woo-woo' circles a subject, like a vapour, and tarnishes any validity it deserves.
That's what's happened with negative ions, which are a favourite of health fraudsters.
I bought this to measure negative ions a while-back, and it is weird.
It can predictably measure negative ions from a generator I bought, but only within a few centimeters of it.
I bought an air filter that claims to generate negative ions and I detected nothing.
When I turn on the shower, it goes nuts, all the way to maximum.
This remains something I'd like to study (much) further.

Viruses in the air

Viruses are not only packed in the air, but they routinely travel
around the globe, and even at the height that airplanes fly.
We blame commercial airplanes for spreading infections, but viruses have been observed to cross the Pacific on their own.
Indoor air is an orgy of shared biological data, and we have no idea what this involves.
Much has been made of the gut biome, but nothing similar for the indoor air biome.
Some aspect of this may be involved in why dogs sniff eachother.
We lack the tools to replicate what a dog does in the dogpark.
There is no filter, or sensor for airborne viruses.
Viruses are measured in nanometers.
Chlorine works well in a pool, but the air is never, (and maybe has never been?) sterile, or biologically-empty. A gas chromatograph can detect chemical compounds from the air.
You've seen them used on CSI:
I tried buying one, they're very expensive. Transmission electron microscopes can see viruses, but only once they've been bred and prepared under meticulous conditions.
Like Apollo lacked the compute-power for non-manual spaceflight, we don't have the resources for interpreting a million unique viruses per exhale, in any real way.
There is some evidence that air-viruses contribute in a serious way to weather patterns, which is pretty-well unstudied.
We just simply do not understand anything.
It's nuts.
Apollo computer (no offence)
The study of virus cultures in the air is called:
It didn't exist a few years ago. Almost every air filter on the market will claim to remove viruses from the air. They don't. or maybe they do? Nobody know.

Humidity

Both bacteria and viruses love humid environments, so why is it that
flu-season is in the winter, when the air is the least humid?
our noses suffer from the dry air, and pathogens
get in the cracks
of our noses
one thing that's beautiful about humidity is that, like a thermometer, a hygrometer can work without batteries.
You can get a cheap one, put it on your shelf, and it will work all day without complaining.
Humidity changes like the weather changes, day-to-day, through the year.
In central Canada, we get really dried-out in the winter. I see 30% days in my apartment.
People wake-up with nosebleeds.
A small wal-mart humidifier won't move the needle even a few-percent.
I'll run the shower for a few minutes, or boil a pot of water, and I doesn't do enough either.
I think, in a regular apartment, the difference between a dry and normal day is probably a full bathtub of water, in the air.
People often blame an electric heater, but I'm told it has more to do with cold air carrying less water? Or when cold air meets warmed air?
I'm not sure.
In the summer, I've considered buying a 'swamp dehumidifier', thinking it will be a quiet, and less-costly alternative to a clunky A/C unit.
But dehumidifiers produce heat exhaust, which cancels-out any benefit they'd give someone in a 'stumid' summer climate.
I've looked for a while, and there are no lovely, easy humidity-control products.
People say houseplants help even-out the air, but I have a ton, and they don't.
Humidity a full type-of-weather, as important as the temperature, that we basically ignore, and can't control.

Carbon Monoxide

Holy, just get a detector.
You'll die in minutes.
It's 12 dollars.
People die every year.
Just get one.
They're on amazon.
You could die.

Radon

I had a geologist friend tell me once that during a earthquake, sometimes poison gasses are released from the ground.
They are heavier than the air, so the gasses hover close to the ground, and kill only livestock.
I remain terrified by this story -- that there are poison gases hovering at my feet -
I really wish he hadn't told me this.
Radon is the weirdest pollutant.
It comes from the ground.
It pools in basements.
It's invisible. It causes lung cancer.
It really causes lung cancer. It changes, like the weather every day. It's fully-scary.
We've made a HUGE effort, over decades, to remove asbestos from our buildings.
Radon may be a lot worse than asbestos.
A radon-tester is really cheap, and can be bought at some hardware stores.
If you have a basement, do this. This stuff is no joke.

Should you open a window?

Yes. Almost always yes.
I live next to a busy road.
I was concerned about the air pollution.
I bought an expensive air monitor and a couple of filters.
When I open a window the VOC's, CO2, and PM2 all drop precipitously, even when there is rush-hour traffic 2 metres from my window.
I was surprised by this.
Cars really don't seem to be as bad for air-pollution as I had imagined they are.
One thing that seems to be far-worse than I imagined is air traffic:
The predictable spikes on the 401 and the 427 are no surprise. That's some of the worst traffic in North America.
Nobody would live at the highway interchange, and not worry about their health.
The surprise in that image is spike in the top-left, home to some nice neighbourhoods with names like 'Richview' and 'Willowridge'.
That's in the flightpath of the Pearson International Airport.
If you could see the particulate matter, you would definitely care about it.
What I'm saying is, even in big cities, indoor air pollution is much worse than outdoor air pollution.
As we have improved the insulation of our homes, we have reduced the quality of the air.
If you can have a window open, especially at night, make it a habit.

Commercial Air Quality Sensors

There's been a number of startups offering air-quality measurement products lately, which is cool.
They all look like they've been designed by the same people, and probably use the same chips inside.
Note:
There are a bunch of cellphones that ship with a barometer, and are constantly recording in your pocket.
Double-check which sensors your phone has, before spending dough on one of these:
blueair- voc, pm, co2, humidity $200
atmotube - voc, pressure, humidity $100
netatmo - co2, pressure, humidity $200
awair - pm, humidity $200
plume flow - voc, pm, no2 $200