# Tag Info

## Hot answers tagged air-quality

61

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use ...

8

Silica gel is the standard for most purposes. It's the desiccant you find inside those paper sachets packed with new electronic equipment. It consists of tiny beads of silicon dioxide that are nanometres across (so that a little material has a lot of surface area), and although it's called a gel, the material itself is hard at room temperature and pressure....

5

Details have emerged in the German press that indicate this was known about in 2007 (from German newspaper Bild am Sonntag, as translated by Automotive News): According to the report, Bosch claims to have supplied diesel engine-management software to Volkswagen under the impression that it would be used only in vehicle testing. That software, which ...

5

Solid particle settling time in air depends mainly on the size of the particle. Different forces become significant depending on what size range you're talking about, so it's hard to give an answer that's both concise and accurate. I'll do my best to synthesize the important points rather than parrot a reference; that said, where practical applications in ...

5

The easy question Do any of the components above have higher costs to society than CO2 per same unit of measure (e.g. gram, kilogram, or ton)? Yes, absolutely. This should come as no surprise given the composition of the exhaust—it's mostly inert gases. Water vapor, CO2 and nitrogen gas are all products of the various reactions taking place in the vehicle'...

4

You are essentially asking, "can a cyclone be designed that works without, or against gravity?" and the answer is, of course, yes. Most practical industrial designs can use gravity to increase efficiency or reduce cost, and the equations you've seen need this simplification, but a cyclone doesn't depend on gravity. You just need to whip the air around fast ...

4

The short answer is that if the air in or around your home is not safe and breathable, you need to leave the area and possibly seek medical attention. You're extremely unlikely to be able to MacGyver your way out of a truly life-threatening air quality event caused by a wildfire (or any comparable industrial accident). Follow the advice laid out in the CDC ...

3

There are are three independent problems with air containing "smoke" from a fire: Particles Poisonous or unhealthy combustion gasses. Oxygen depletion. Unless you're really close to the fire, #1 is the biggest problem. As you already found, plain old mechanical filtration is the simplest way to address this. There are commercial air filters for HVAC ...

3

For an individual particle, you could use Stokes' law: $$v_{\text{terminal}}=\frac{2gR^2(\rho_{\text{particle}}-\rho_{\text{air}})}{9\mu}$$ where $\mu$ is the dynamic viscosity of the air, which is easy to calculate. Using Stokes' law assumes you know the initial height of a dust particle, and may not be convenient for large quantities because each particle ...

2

Once again, forced to answer because not enough reputation to comment. Several answers/comments have talked about requiring energy to reduce humidity. @Chuck specifically states you need energy to convert from vapor to liquid. In fact, the reverse is true. When vapor condenses to liquid it gives up energy. For water it's approximately 1000 BTU/pound ...

2

If the smokes are near and dense. You should disconnect the electricity and leave your house. You should not use any ventilation as it may cause soot and dangerous airborne pollutants recirculated. You should have an emergency evacuation plan with details as what needs to be done around the house and inside such as use of shutters and removing of the ...

1

Let us presume that the process being considered is vaporization of liquid water to a gas state in dry air. As long as the temperature and pressure of the liquid water is constant during the process, vaporization of the liquid to gas in dry air will not change the molar enthalpy of the remaining liquid. In those cases where for example the temperature of the ...

1

If there is smoke or toxic gas in the air outside your house do not use the exhaust fans. If possible cover the fans to prevent air entering the house via the holes occupied by the fans. An exhaust fan will remove air from the room where the fan is located and move it outside the house. The air displaced from the room by the fan will ultimately be replaced ...

1

There's nothing stopping you from doing a reverse air flow cleaning system. I think the type of particulate and filter media type would determine how well it would work. I would think the problem is where does the backflow material go? A big plenum you have to sweep out regularly maybe? If you are replacing the air handler entirely, pulse jet or ...

1

Ignoring the concept that "backwashing" a filter as exhaust effectively negates the value and purpose of having filters, consider instead of a constantly clogging filter system, one that separates the particulates from the primary air stream. I have a shop vac which has pleated filters. The filter is easily clogged by sawdust from a table saw, band saw, ...

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Air filters are made of fibrous material (paper typically) that is basically inert. There is no reason that storing it in a cool, dry place would cause it to expire. The HEPA designation has more to deal with how the air flows through it rather than the material that it is made from

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I don't think you're going to find an answer that meets the intention of your question as I read it. It takes energy to convert water from a vapor to a liquid. Some materials (minerals, sugar, etc.) can absorb water vapor from the air because they are hygroscopic, but it also means that there is a finite limit to the amount of water they can absorb before ...

1

How about this: You blow your humid air through the primary side of an air-air heat exchanger, here it is cooled a bit. Then this air passes through past a cold surface: either outside or underground, depending on oyour local climate. The air cools further and moisture condenses. The cool air passes through the secondary side of our air-air heat exchanger, ...

1

I'm betting that a big part of the discrepancy here lies in the duration of operation. Industrial separators are intended for long term continuous operation, while home cleaners can stand to shut down frequently to be emptied. The act of separating particles is accomplished centrifugally, neither gravity nor a secondary air stream are required. The issue ...

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