Wednesday, February 6, 2013

Your Box of Air during Inversions

We are all aware that during inversions most of our emissions are trapped in the Salt Lake Valley.  It can be difficult, however, to recognize the impact of our individual emissions, so here's an attempt to bring it down to a personal level.

The Salt Lake Valley is roughly 40 km long and 25 km wide between the benches.  The depth of the pollution varies from event to event, but let's assume it extends to 0.3 km above the valley floor, which is roughly bench level.  This means that the volume of the valley atmosphere is 25x40x0.3 = 300 cubic kilometers.  That's 300,000,000,000 cubic meters, which seems like an awful lot of air.  The problem is that there are 1,000,000 people (the 2010 US Census put the population of Salt Lake County at just over 1 million), so your personal allotment is only 300,000 cubic meters.  That still seems pretty big right?

Actually, 300,000 cubic meters is the equivalent of a cube that is only 67 meters (about 75 yards) on a side.  That is about half the length of a block in the Avenues.  Imagine now that during an inversion each of us gets a cube that is about half an Avenues block on a side.  Our personal emissions go into this box.  Chemical reactions, aerosol processes, and atmospheric turbulence and transport can perhaps remove some of the emissions and resulting pollution and bring in cleaner air, but for the most part your emissions are accumulating in this small box.

Of course not all 1,000,000 Salt Lake County residents own a home or drive a car (although they all contribute emissions, but to varying degrees).  Maybe that helps.  On the other hand, there are also emissions from long-haul trucks, trains, planes, industry, and other sources.

Now here's the thing.  Your box is getting smaller.  In 1984, when the population of Salt Lake County was about 600,000, each citizen got a box that was 79 meters (about 86 yards) on a side (500,000 cubic meters).  Today it is 67 meters on a side.  Tomorrow?

Source: Google
If we want cleaner boxes, we either need better meteorology, so that the air in your box is replaced more frequently, or a reduction in per capita emissions.

Feel free to review my math and assumptions as maybe I've made an error and our personal boxes are bigger than I've estimated.  It is early in the morning and I haven't had any caffeine yet.

1 comment:

  1. Great thought experiment. Another point is that industry also gets to put stuff into that volume. So probably we should account for that by correcting the volume of our personal boxes, or by setting a baseline industrial pollution level in our box.