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Comment by samizdis | Hacker News Reader

Not just fossil fuels are problematic. An article in The Guardian last month [1] with the headline and sub-heading, Wood burning at home now biggest cause of UK particle pollution - Fires used by just 8% of population but cause triple the particle pollution of traffic, data shows is an eye-openeer.

[1] https://www.theguardian.com/environment/2021/feb/16/home-woo...

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In my country outside of the city center (where most homes have district heating or gas), wood burning stoves are the most common way people heat their homes. Coal never really caught on here, but there are abundant forests and not that many people, so there is always plenty of firewood that is easy to find.

That combined with low temperatures during winter (somehow it causes pollution to stay low to the ground?) means the government usually issue air quality warnings to stay inside a few times during the heating season.

There have been some attempts to improve the quality of the fuels used, e.g. funding to push upgrading to automatic pellet stoves which burn much cleaner, but most of the issue (which is also the case in the UK) is that older homes are simply poorly insulated and waste a lot of heat. The problem is by 'older homes' I mean anything more than 10 years ago, when the EU started pushing for lower energy use in housing. In the US that means today, for homes built to minimum building codes - which the majority of new housing is.

We are building a new 160m2 home - to modern insulation standards - and even the smallest 5kW wood burning stove would produce too much heat for the house. We probably won't even need to turn on the heating (electric heat pump) until it gets close to 0c outside.

The temperature effect on atmospheric circulation is called an inversion. Basically, air near the ground is normally warmer than that above it so rises buoyantly, mixing the atmosphere through convection. When the air near the ground is colder than the air above it (the gradient is "inverted") the air no longer rises, causing polluted air generated at the surface to linger. There are several circumstances that can lead to colder air at the surface than above it, including cold, cloud-free nights.

Thanks, that was really interesting! I never thought about it like that but it makes sense.

Wet wood is especially bad. The co2 released from burning is not much of an issue but it sends out huge amounts of unburned particles.

Is the particulate pollution universal for wood burning stoves? I was under the impression that modern designs burned quite efficiently.

I really don't know about the type of stove; things I've read about this refer to the type of fuel, and in this case specifically problems with burning wet wood rather than seasoned wood. (It's possible that some stoves or chimneys that vent them have some sort of particulate removal systems, but if they exist, they must be an absolute nightmare to unclog/clean etc. Having said that, I did find this site - https://woodstovefilter.co.uk/ - which seems to offer a solution ... but the product doesn't exist yet; it says "Expected to be ready for commercial sale early 2022". EDIT TO ADD: Actually, there seem to be a few companies selling "strap-on" systems to fit to chimneys that work on electrostatic removal of particles, such as Enervex [2], but again that's not to do with a stove type.)

The Guardian article points out that wet wood sales are to be banned from May this year: "The government is not planning a ban on wood burners but a ban on the retail sale of wet wood will come into force on 1 May, as will a ban on bags of house coal, the first such restrictions since the clean air acts of the 1950s. Wet wood has not been seasoned and produces higher levels of pollution."

The article also links to the UK Govt announcement [1] from last year, which as far as I can see has nothing to say about stove type, only fuel.

[1] https://www.gov.uk/government/news/government-takes-action-t...

[2] https://enervex.com/systems/particle-filter-system-for-stove...

Modern stoves do have a particulate removal system, either via a catalyst (just like the catalytic converted in your car), or via a secondary air system that causes the particulates to burn up before they exit the stove. You can't buy a new stove without one of these two systems due to emission standards.

Always good to test these things if possible. PM 2.5 detectors are pretty cheap.

For instance I used one to learn that fume hoods on stoves are basically inadequate. (Windows are more effective)

A good test “can you smell the thing you are cooking”. If so, your ventilation is not adequate.

I’d avoid using gas stoves at all unless it was inside a lab style fume hood.

Do you mean pm 2.5, or other stuff? I think a smell test is pretty good, but in my experience it is only a burning or dry cooking smell that sets off pm 2.5 meters.

So for example if I am frying chicken in a well oiled pan, and smell chicken, pm 2.5 does nothing. But if the chicken is browning and I smell....I dunno, the smell of browning chicken, that raises the meter.

Is this due to having a gas fueled stove or is it the food itself?

That is the food itself. Though it really depends on the method. Most cooking, including frying, won’t raise pm 2.5 levels.

But if something goes wrong and you can smell any kind of burning, then generally the levels will rise to between 150-500. I’m including small things, like a speck of food getting out of the fry pan and onto the burner. Or not enough oil in the pan, or anything producing a maillard reaction. The line between “nothing noxious” and “whoa that is dangerous” is very thing in my measuring experience. And the best way to deal it when it happens is opening windows. These should clear it out within 15 min or less in most cases.

Never had a gas stove so never tested for pm 2.5. Am guessing it is higher, and co2 as well.

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