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September 22, 2015 10:52 AM   Subscribe

As I now know, my TDI is emitting 40x more NOx than the EPA allows. NOx is a major contributor to smog and asthma exacerbation. How much of this stuff hangs around my house?

I'm horrified to be contributing to this environmental mess, in general.

I have asthma, so I'm particularly* interested in how the NOx affects me, the driver and owner. Is NOx dense, and I'm polluting my own environment? How fast does it dissipate? Does it hang around my house for hours, or diffuse away in minutes?

*sorry about that.
posted by Dashy to Science & Nature (8 answers total) 1 user marked this as a favorite
 
Your car is irrelevant since you probably rarely drive it in your house.

What's more important is your proximity to major traffic sources. Here's some data from NYC on fine particles (smog) and traffic density.

(i am not your environmental epidemiologist, in fact, i am not even an environmental epidemiologist, but i work with several)
posted by entropone at 11:13 AM on September 22, 2015


Response by poster: Please consider the question asked -- about my house. I drive my car up to or away from my house (and into my garage, though yes, I know the garage does not exchange air with the house) 4-6x a day. My house's main air source is the air around it. I understand the general smog picture, but I'm asking about the physics of a very specific one, my own microenvironment.

If proximity to a highway is in fact more important than my own car and house, I'd like to know specifically how and why, based on things like density and diffusion constants.
posted by Dashy at 12:01 PM on September 22, 2015


I don't have info on NOx in your house and its effects, but apropos of the last note, these are a few links with more information regarding studies that have been done that linked specific health effects to proximity to auto pollution.

The Hidden Toll of Traffic Jams

How the Street You Live on May Harm Your Health

Is Exercising in Pollution Bad for You?
posted by limeonaire at 12:11 PM on September 22, 2015 [1 favorite]


Even the tightest of houses experience a complete change of air every couple of hours. Most houses experience more changes than that and a typical 60s house might experience a complete change as often as every 20 minutes. So your car isn't polluting your house to any long lasting lingering degree besides it's impact on the local microclime. The closer you are to arterials, the wind patterns at your house and how they interact with those arterials are a much bigger factor in most cases. Without taking measurements and comparing with car and without at your location no one is going to be able to give you specifics.

For example if you live next to a truck stop in a relatively calm (wind wise) area the impact of your car is going to be completely swamped by the several orders of magnitude greater emissions from the commercial traffic. If you lived next to the ocean with a constant on shore wind again you wouldn't see a measurable difference from your car because the emmission are constantly being swept away. If your house is tucked into a box canyon way out in the country or some other geographical set of features that inhibits air exchange than all the NOx from your car might hang around for hours and result in levels dozens of times higher than the base. No real way of telling without extensive measurements.

But even then, if your neighbour has an old diesel tractor or a generator or welder or something your car's emissions might be completely swamped by the several orders of magnitude greater emissions from that equipment.
posted by Mitheral at 12:20 PM on September 22, 2015 [2 favorites]


Does it hang around my house for hours, or diffuse away in minutes?

Minutes. This is the nature of gases in general, barring any special circumstances. Unless you live somewhere like a narrow canyon or similar, this is not something specifically to worry about.
posted by ssg at 12:25 PM on September 22, 2015 [2 favorites]


I don’t know enough to comment on the health effects, but I can try to answer this chemistry question:
Is NOx dense, and I'm polluting my own environment?
NOx refers to two different compounds, NO and NO2. These are not highly-dense gases like radon. Their molecular weights are about the same as the gases that make up most of the Earth's atmosphere, like N2, O2, and CO2.
posted by mbrubeck at 12:52 PM on September 22, 2015 [1 favorite]


Best answer: Entropone's opening line is really the most pertinent here. Even aside from the fact that there is air exchange as Mitheral points out, any gas is going to tend to disperse into its container, which in this case is the outside world.

Consider how we remediate a gas we consider to be cancer causing, radon. The solution is simply to pull it away from the area under your home via a sealant on the floor and a pump and discharge it into the open air outside your home. Since it's a heavier than "air" gas it's done at a bit of a height to allow it to better dissipate, but the presumption is that it will simply spread out into the world.

N2O is different from radon but the question of it being everywhere versus being collected into your environment is identical. Vehicles constitute 5% of the N2O being pumped into the air (though obvs locales will be different) and your vehicle is just one of many. You may create a localized hotspot but even at 40x more than every other car you're the tiniest drop in the bucket.

So if you're concerned perhaps avoid parking that car in the garage where you create an open-ended container. But out in your driveway? I think you could visualize this by blowing out a match there and watching how quickly the smoke dissipates. By the time you're a few feet away the total level has spread out so much that you've barely changed the baseline even with that 40x number.

By the time the N2O has spread out into a sphere large enough to go from your tailpipe to the other side of your home you're talking about what, 30 feet away at minimum? That's (4*pi*30^3)/3, or 113,076 cubic feet. Spread out that far your point source isn't going to make much of an impact compared to the quantity of other sources in your area.
posted by phearlez at 12:55 PM on September 22, 2015


Does it hang around my house for hours, or diffuse away in minutes?

Let's assume you have an acre lot, so it's about 200 ft long, and assume a light breeze of 5 MPH. At that speed it takes 27 seconds for air to flush across your yard, evicting the bulk of the air that was present. Turbulent mixing and diffusion will of course mean that not all of the air is swept out, some will be removed faster and some slower, but the basic timescale we are talking about is on the order of minute(s).
posted by kiltedtaco at 4:00 PM on September 22, 2015 [1 favorite]


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