Maybe this will help better then anything.
C. Odor control
There are many common ways to reduce the fragrance of pungent cannabis flowers, including ionizers (negative ion generators), charcoal filters, air scrubbers, and chemical sprays. Unfortunately, reduce is the key word here. None of these methods will do much to eliminate any smells except from the smallest room or the least stinky garden. There are some strains of cannabis that are known for their lack of the trademark pot smell, and are perpetuated for that reason. I realize that you're more likely to find a charcoal filter than any particular clone, but I am trying to emphasize that basically, you should be prepared to deal with the beautiful smell of fragrant cannabis flowers.
Here is a brief overview of how these devices work. Ionizers work by generating negatively charged ions and dispersing them into the air. When these negative ions come in contact with positively charged particles floating in the air like dust or pollen, they change the particles' charge to negative, causing the particle to "precipitate", or to fall to the ground. This results in cleaner air, and dirtier floors and walls.
Another kind of ionizer is called a "collector ionizer". These incorporate some disposable filter and either a positively charged surface which attracts the ionized particles, or a small fan that moves the air through the filter (which usually also contains activated charcoal) and then injects the ions into the outgoing airstream. Charcoal filters are similar to these but use only the fan and activated charcoal, and are usually slightly more heavy duty, and seem to work about as well, as long as you keep the charcoal fresh by changing the filter regularly.
Air scrubbers consist of a large barrel of water with your exhaust piped into it, like a giant bong, and then to the outside. Pine cleaner and/or liquid smoke are added to the water to taint the smell. I have never personally built one of these but the theory makes sense, except that it seems awkward and I don't think it would work with high-powered exhaust blowers.
Chemical sprays are used in hospitals and kennels to deal with very harsh odors. They work, but I personally find the artificial, chemical odor overwhelming to the point of nausea. I do not recommend these sprays because they are impractical to use on a continuous basis, and frankly if its gonna stink, I'd rather have it stink like greenbud.
If you can't find or afford any of the above, a simple trick is to buy a box of urinal deodorizers from a janitorial supply store, or maybe car deodorizers, and put one or two next to your exhaust blowers' intake.
Now aside from the above described odor reduction devices there are two more things that I will recommend for this task. The first one is called an ozone generator. This mighty device generates ozone, an unstable oxygen molecule that actually changes the molecular structure of stinky particles that they come into contact with. This results in total odor elimination. The proper way to use an ozone generator is piped into your outgoing exhaust. (The generator has its own small blower built in.) Of course, like everything, there are trade-offs for this amazing performance. Ozone can be harmful to plants, animals or people in too high of a concentration. The only way to use it safely is by using it to treat the exhaust that is going outside. Also, ozone generators are quite expensive. The three models that I am familiar with run around $750., $1350., and on up to $2600., with this most expensive model being quite adequate to de-stinkify the 5000 C.F.M. exhaust of a large warehouse (25KW) full of stinkiness. (Yummy!) It seems to most people like a lot to spend, but in some situations, it can be your saving grace. I recommend ozone for all commercial growers. If you are interested in this device, try calling indoor grow supply stores with ads in the little nickel or yellow pages.
The second, most practical and most effective method of odor control is your exhaust system itself. You will learn later in this book that a good exhaust system is just as important to happy plants as light or water, and although this won't actually make the outgoing air less stinky, it allows you to control where the stinky air goes. For example, lets say you live in a third floor corner 2 bedroom apartment. One bedroom is your bedroom, the other is your grow room. A properly installed exhaust system can solve two odor problems at the same time. One, inside the living space of your apartment. By leaving your exhaust blower running 24 hours a day, there will always be "negative pressure" inside the grow room. This simply means that air will constantly be flowing into the grow room through every possible crack and opening, and when fresh air is constantly flowing in, no smell gets out. Two, outside your apartment. By cleverly routing the exhaust pipe into your unused chimney pipe, or out of the far back corner of your attic, the smelly air will end up where there are no noses to smell it- either 4 stories off the sidewalk or parking lot (and heading up) in the chimney pipe example, or on the backside of your building where there are no stairs and where nobody hangs out. (If a bud reeks in the city, but there are no noses to smell it, did it ever really smell at all?) Another thing to consider in apartment cultivation is that even if you can smell the weed out in the parking lot, there is no way to tell which apartment it is coming from. It sounds crazy, but 'round these parts it happens all the time. Smells pretty good, too.
source:
http://www.1stmarijuanagrowerspage.com/how-to-grow-marijuana-3.html#2c
