One study on formaldehyde and VOC levels utilizing air monitoring found that "the levels of volatile organic compounds (VOCs) in new homes decreased markedly after 1 year". This is due primarily to the off-gassing process which diminishes over time. If you don't happen to have expensive air monitoring equipment lying around, you could always use your sense of smell. Just remember that not all VOCs are detectable with the human nose.
Preventing Exposure to VOCs
Identify, and if possible, remove the source. If it’s not possible to remove, reduce exposure by using a low or no VOC sealant on surfaces and other furnishings emitting chemicals. You should always increase ventilation during the period of VOC off gassing and consider using an air purifier.
Potentially hazardous products often have warnings aimed at reducing exposure to the user. Many people, however, don't bother to read the label before every use (guilty as charged). If a label states to use the product in a well-ventilated area, go outdoors, open the windows or work in areas equipped with an exhaust fan. You should always provide the maximum amount of clean air flow possible. This rule applies when you are using petroleum-based products, fuels, hydraulic fluids, paint, thinners, cleaning agents and the like. This also applies to your new carpet, new car, air fresheners and a variety of other surprising sources.
Other preventative measures
Safely disposing of empty containers or those with very little product remaining. - Using products according to the manufacturer’s directions. - Buying in quantities that you may consume quickly to prevent additional exposure from seepage or vapors, like paint VOCs, that may escape from poorly sealed containers. - Keeping products out of the reach of children and pets. - Making every effort to utilize integrated pest management techniques when using pesticides. - Never mixing products unless directed on the label. - Choosing low VOC or VOC free products.