I came across Ian Cull on an indoor air quality social network—yes, such groups exist—providing authoritative information about just how many aerosol particles we exhaust each time we cough. I learned that the average person sick with influenza projects 75,400 aerosol particles per cough. Somehow this figure sounded significant and frightening, so I contacted Cull, who is the technical director of the Indoor Air Quality Association, to find out if any of the dozens of air cleaning devices advertised could mop up the air sufficiently to mollify this overwhelming viral onslaught.

“Most colds are not transmitted through the air,” he says. “It’s on the hands, hand to hand. To prevent colds, don’t buy an air cleaner, use hand sanitizer and be diligent not to touch your face. Having a well-ventilated home will reduce the transmission somewhat. Ultraviolet light can help in a clinical setting. But if I sneeze, the chances of this aerosol hitting you are much greater than likelihood of it getting into the HVAC system first and through the air sterilizing mechanism before you take your next breath.”

A building scientist and environmental engineer by training, Cull has become an educator and evangelist for healthy indoor air. He jokes about his given name, “Ian,” an accidental acronym for his handle in the indoor air quality blogosphere, IAN, the “Indoor Air Nerd.”

Beyond his duties with the Indoor Air Quality Association, Cull owns a small training and consulting company called Indoor Sciences, Inc. He describes his life’s passion as, “Helping people improve the quality of the air they breathe, and therefore improving their lives.” If you visit the IAQA University, you can select from 50 one-hour classes he teaches on a wide range of indoor air quality topics. And he has agreed to become a regular source for this column.

Cull tells me the first line of defense concerning indoor air quality comes with controlling moisture. “On the biological side, we’re concerned about a host of things, including mold, bacteria, viruses, and allergens that illicit an immune response, such as dust mites, pet dander, and insect droppings. But it’s not just one of those things, it’s the whole soup, and the recipe for this soup is a damp building. Wherever there are chronically damp areas, whether a damp foundation, a dripping window air-conditioning unit, or a steamy bathroom without adequate ventilation, you will find harmful health effects—it’s all in the potage of pathogens that prefer damp environments. Ventilation is part of the solution, but the more important aspect is to control moisture in the first place.”

The second line of concern comes with the range of chemical pollutants that concentrate inside the home. “The chemical nature of our modern environment includes building materials like paints and flooring, and also deodorants, hair sprays, cleaning supplies, and especially combustion by-products, like carbon monoxide and nitrogen. Even if you have a carbon monoxide detector installed—and you should—know it will not trigger until it detects high levels of carbon monoxide for several minutes. It’s a little like the idiot light on your dashboard that alerts you once you’re out of oil. It will not alert you to a chronically low level of carbon monoxide that might be making you sick because these devices are preset to limit potential false alarms and calls to the gas company and fire department. This is why I see a benefit to hiring an indoor air quality consultant to make an indoor air assessment, to test and commission a residence just as you would have an energy auditor do a blower door test and confirm the function of your HVAC system.”

Cull describes the roll of the indoor air quality consultant as a technician with the skills and testing equipment to pinpoint the solution to an indoor air quality problem—or better yet, to forestall it. The simple adage “Built tight; ventilate right” works in most circumstances, but Cull is often asked to identify the exact source of indoor environmental problems. These can be as simple as low levels of carbon monoxide, but more often entail hunting down the source of microbial spores or volatile organic compounds. “Rather than just add ventilation to dilute the pollution problem, I want to know what the pollutants are and where they come from,” says Cull. The highest priority is to stop the pollution at its source.

While ventilation usually works wonders, at times it can actually exacerbate a problem. “If we don’t know what the pollutant is, venting may make it worse—such as with outdoor pollen. Twenty percent of the population experiences seasonal allergies; if you have simple mechanical ventilation that adds outdoor air, but then the filter is in a return air duct installed inside a room, it won’t help, it will hurt. Less well known, but significant in some areas, especially in the southwestern United States, ventilation brings ozone indoors. A media filter will not remove the ozone, so now your indoor air pollution is made worse by bringing in outdoor air—ozone,” says Cull. In other words, like everything else, there are no simple solutions whereby you can close your eyes and do one thing to resolve all problems. You have to understand the problem and know the building science required to solve it. This is why Cull volunteers a lot of his time to education.

I ask Cull about the future of the indoor air quality industry and what developments we may see in the science. He tells me that Indoor airPLUS was a very good development because it brings awareness to indoor air quality concerns to builders and consumers, as well as a prescriptive path to improvement that works in the vast majority of cases. He would like to see more refinement on specifications based on local conditions.

“The ideal ventilation system is outdoor air brought in mechanically and filtered before it comes into the environment. Now this is where it can get complicated because filtration depends on the contaminants you’re concerned with in the outdoor air.” Cull pauses to explain to me that the typical dust you see in a ray of sun is composed of large particles that your nose and esophagus are equipped to filter, but there are smaller pollutants that neither your nose hairs nor a typical HVAC air filter will screen.

“If you’re in an area with high levels of PM-10, or particulate matter of 10 microns in diameter or less, these small particles can get into your lungs. In some areas, there are smaller pollutants, PM-2.5, that can burrow deep into your alveolar sacs. This is why you need to look at the outdoor air quality in your region. If there exists a local problem with particles of PM-10 or smaller, then you need a high-efficiency filter of at least 10 to 11 on the MERV scale,” says Cull. The MERV scale is a minimum efficiency reporting value set by ASHRAE, with MERV 1 providing the least filtering and MERV 20 the most. The standard furnace filter is a MERV 1-4 at best.

The EPA’s Indoor airPLUS requires MERV 8 filters or higher (Construction Specifications Section 4.7) with no visible bypass between the filter and filter rack. But presently Indoor airPLUS does not require outdoor air testing, which is something Cull would like to see added to the standard. Although the EPA does not presently require outdoor air testing, the agency provides information on outdoor air quality at www.epa.gov/ttn/naaqs/. There’s also a website that allows you to check regional air quality at http://www.airnow.gov/.

I ask Cull about emerging technologies, and he tells me about photocatalytic oxidation, a method of reducing VOCs. The process works by exposing ultraviolet light to a catalyst, such as titanium dioxide, producing primarily hydroxyl radicals, which are extremely reactive and can oxidize or “break down” typical VOCs in indoor environments, according to literature from the Lawrence Berkeley National Laboratory. However, when I ask Cull if he has one in his house, he tells me, “No, I would not put one in my house yet. It’s too new, and I’m always concerned about messing with the chemistry of indoor air quality. You often have unintended consequences.”

Cull says the best approach available to excellent indoor air is to start by engaging a building scientist early in the design process to work out an effective moisture transport system, work with an architect that specifies low-VOC products, and then hire a good HVAC technician that knows how to correctly size the equipment and ventilation. However, he cautions, “Even with the best green construction, if the homeowner brings in polluting chemicals, furnishings with formaldehyde, and they don’t control indoor humidity—then all bets are off. It’s not all on the architects and builders. The occupants play a huge roll, too.”