ECOBROWNSTONE: The Art of Brownstone Greenovation -
Indoor Air Quality -- Identifying Sources and Making Renovation Choices that Eliminate Contamination
Noreen Adler
Founder and President, Ecobrownstone

Noreen is Founder and President of Ecobrownstone.  She has been a resident of brownstone Brooklyn (Park Slope, Brooklyn Heights and Carroll Gardens) for over two decades and has planned, designed and managed a wide range of renovation and real estate development projects in Brooklyn and elsewhere. As a developer she is a member of the NYC Committee evaluating the LEED for Homes Guidelines for application in New York.  She also has a personal passion for sculptural relief ceramic tiles and murals which she has designed and fabricated at her studio on the Gowanus Canal. 

By Noreen Adler
Published on 04/23/2008
Make the air inside your home cleaner than the air outside.  Identify the sources of indoor air pollution in the home, learn how to design your renovation project to eliminate them, and how to abate existing sources. 

Breathing fresh, healthy air is a basic human desire, and to achieve this goal our focus often lies with reducing or eliminating sources of outdoor pollution. However, the average person spends 90% of his or her time indoors, and EPA studies have shown that indoor air can be as much as 10-times more polluted than outside air in even the largest industrialized city.
Indoor air pollution is one of the top five environmental health risks, and improving your indoor air quality through the elimination of toxic, off-gassing substances and proper ventilation can have a significant, positive impact on your health.

According to the EPA, while pollutant levels from individual sources may not pose a significant health risk by themselves, the cumulative effects of indoor air contaminants can do so. Indoor air pollution is a significant contributor to asthma, headaches, nausea and dizziness, respiratory allergies, chronic fatigue, and more serious diseases like cancer and kidney and liver damage, and serious injury to children including brain, hearing and nervous system damage, and physical growth, developmental and behavioral problems and learning disabilities. Read on to learn how to identify and eliminate pollutants.

Most homes have more than one source that contributes to indoor air pollution. In addition, some of the products used in home construction, like standard paints and wood finishes and processed wood products such as cabinetry and flooring, give off volatile organic compounds (VOCs) that have a larger environmental impact because they create ground-level ozone pollution which is the primary component of smog. Below is a chart listing the most common chemicals and their sources, and health affects:

 gas boiler and furnaces  carbon monoxide, nitrogen dioxide and nitric oxide
 gas hot water heater  carbon monoxide, nitrogen dioxide and nitric oxide
 gas clothes dryer  carbon monoxide, nitrogen dioxide and nitric oxide
 gas stove and/or oven  carbon monoxide, nitrogen dioxide and nitric oxide
 unvented gas space heater/fireplace, kerosene heaters  carbon monoxide, nitrogen dioxide, nitric oxide and formaldehyde
 chimney flue (blocked, leaking, improperly sized or disconnected)  carbon monoxide
 gas powered equipment (i.e. generators)  carbon monoxide
 automobiles  carbon monoxide, benzene
 tobacco smoke  4,000 compounds including carbon monoxide, benzene, nitrogen dioxide (NO2) and nitric oxide (NO), formaldehyde, particulate matter
 wood burning fireplaces  particulate matter, carbon monoxide
 humidifiers, cooling coils or condensation pans  mold, mildew, bacteria
 unvented bathrooms  mold, mildew, bacteria
 Textiles: Draperies, bedding, carpeting, upholstery, permanent  dust and dust mites, animal dander, pest droppings and body parts, formaldehyde
 Textiles: permanent press clothing  formaldehyde
 paint (including painted furniture and old painted toys)  formaldehyde; benzene; old paint can contain lead
 paint strippers  methyl chloride, benzene, formaldehyde
 solvents, adhesive removers  methylene chloride
 aerosol sprays  methylene chloride
 household cleaners and disinfectants  click on "Resource Room" on the  CHEC’s (Children’s Health Environmental Coalition) HealtheHouse website
 herbicides  click on "Resource Room" on the CHEC’s (Children’s Health Environmental Coalition) HealtheHouse website
 rodenticides  click on "Resource Room" on the  CHEC’s (Children’s Health Environmental Coalition) HealtheHouse website
 moth balls  naphthalene, benzene
 hobby supplies  lead
 dry-cleaned clothing  perchloroethylene
 adhesive removers  methyl chloride
 insulation  asbestos, formaldehyde
 drop ceiling tiles  asbestos
 floor tiles  asbestos
 leaded crystal  lead
 soil, rock  radon
 plywood (softwoods)  formaldehyde
 composite wood particleboard furniture and cabinetry  formaldehyde
 flooring with particleboard backing  formaldehyde
 glues  formaldehyde
 adhesives  formaldehyde
 hardwood plywood paneling  formaldehyde
 medium density fiberboard (furniture)  formaldehyde
 bathrooms  biological pollutants
 kitchens  biological pollutants
 rodents  biological pollutants
 animals, pets  biological pollutants
 any poorly ventilated area with a source of water, moisture or steam  biological pollutants
 polyvinyl chloride (PVC) plastic, which is "vinyl". Plastics marked with a recycling symbol "3"  dioxins (in its production and incineration)
 fiberglass insulation  may contain formaldehyde; old insulation may contain asbestos
 composite or pressed-wood products; medium-density particle board  formadehyde
 softwood plywood and hardwood plywood paneling (used in decorative wall covering, cabinets and furniture)  formaldehyde
Copyright ©2008 Eden Industries, LLC d/b/a ECOBROWNSTONE™. All rights reserved.

 Crumbling, damaged, or disturbed insulation, fireproofing, acoustical materials such as drop ceilings, and floor tiles.  No immediate symptoms, but long-term risk of chest and abdominal cancers (mesothelioma) and lung diseases (asbestosis). Smokers are at higher risk of developing asbestos-induced lung cancer.
 carbon monoxide (CO)  combustion sources: gas stoves and ovens; gas furnaces and boilers; cracked chimney flues; wood stoves and fireplaces; gas water heaters and clothes dryers; unvented gas and kerosene heaters and "fireplaces"; gas powered equipment such as generators; automobile exhaust; tobacco smoke  reduces oxygen flow to the brain. In low concentrations causes fatigue, can cause chest pain in people with heart disease. At higher concentrations causes impaired vision and coordination; headaches; dizziness; confusion; nausea. Can cause flu-like symptoms that clear up after leaving the contaminated area. Fatal at very high concentrations. 
 benzene  tobacco smoke, stored fuels and paint supplies, and automobile emissions in attached garages, mothballs  a known carcinogen
 lead  deteriorating lead-based paint which can produce lead dust and further contaminate soil, drinking water, food; old painted toys and furniture; liquids stored in lead crystal vessels, hobbies such as leaded glazes for use in pottery and stained glass and refinishing furniture  Lead affects practically all systems within the body. At high levels (at or above 80 micrograms per deciliter of blood) can cause convulsions, coma, and even death. Lower levels adversely affect the central nervous system, kidney, and blood cells. Blood lead levels as low as 10 micrograms per deciliter can impair mental and physical development. In fetuses and young children can delay physical and mental development, lower IQ levels, lead to shortened attention spans, and increased behavioral problems.
 radon  uranium in soil and rock lung cancer
 formaldehyde (urea-formaldehyde resin)  building materials such as insulation and certain softwood plywoods; pressed or composite wood furniture using adhesives with urea-formaldehyde resins; tobacco smoke; the use of un-vented, fuel-burning appliances like gas stoves, gas fireplaces or kerosene space heaters; "permanent press" clothing, draperies and upholstery; glues and adhesives; paint; particleboard (used as sub-flooring and shelving and in cabinetry and furniture); hardwood plywood paneling (used for decorative wall covering and used in cabinets and furniture); medium density fiberboard (used for drawer fronts, cabinets, and furniture tops) which is the highest formaldehyde-emitting pressed wood product.  eye, nose, and throat irritation; wheezing and coughing; fatigue; skin rash; severe allergic reactions. May cause cancer.
 biological pollutants: mold, mildew, viruses, bacteria, animal dander, cat saliva, dust, mites, pest droppings and body parts (cockroaches, rat and mice urine), pollen  humid or wet/moist areas, plants, people, animals  hypersensitivity pneumonitis, allergic rhinitis, asthma. Can promote spread of infectious respiratory diseases. Molds and mildews release disease-causing toxins. Symptoms include sneezing, watery eyes, coughing, shortness of breath, dizziness, lethargy, fever, and digestive problems.
 tobacco smoke (Environmental Tobacco Smoke or Secondhand Smoke)  smoke from the burning end of a cigarette, cigar or pipe and smoke exhaled by a smoker  pneumonia and bronchitis, lung cancer, cough, excess phlegm, and wheezing, ear infections and reduced lung function, increased severity of asthma attacks, possible onset of chest pain
 particulate matter  Fireplaces, wood stoves, and kerosene heaters, and secondhand smoke  Eye, nose, and throat irritation; respiratory infections and bronchitis; lung cancer
 methylene chloride  paint strippers, adhesive removers, and aerosol spray paints  causes cancer in animals; is converted to carbon monoxide in the body
 naphthalene  moth balls  neurotoxin, may cause cancer
 Perchloroethylene  dry cleaning fluids  causes cancer in animals
 nitrogen dioxide (NO2) and nitric oxide (NO).  tobacco smoke, unvented combustion appliances, e.g. gas stoves, vented appliances with defective installations, welding  Eye, nose, and throat irritation, possible bronchitis and impaired lung function, increased respiratory infections in young children; extremely high-dose exposure (as in a building fire) may result in pulmonary edema and diffuse lung injury.
Copyright ©2008 Eden Industries, LLC d/b/a ECOBROWNSTONE™. All rights reserved.

Let’s look further at some of the biggest offenders. Due to the important nature of this topic, we have not limited ourselves to construction- and renovation-related substances.

Environmental tobacco smoke (ETS), or Secondhand Smoke is the mixture of smoke that comes from the burning end of a cigarette, pipe, or cigar, and smoke exhaled by the smoker. According to the EPA, it is a complex mixture of over 4,000 compounds, more than 40 of which are known to cause cancer in humans or animals and many of which are strong eye, nose and throat irritants. In a study conducted in the early 1990s the EPA concluded that ETS is responsible for approximately 3,000 lung cancer deaths each year in nonsmoking adults and impairs the respiratory health of hundreds of thousands of children. For more information visit the EPA website.  

Radon The American Lung Association, the American Medical Association and the Center for Disease Control agree that radon causes, on average, 14,000 deaths from lung cancer every year. Radon gas enters homes through dirt floors, cracks in concrete walls and floors, floor drains, and sumps, and can be a problem in any home, however some areas of the countgry are more at risk than others. Consult the EPA’s Radon Zone Map , to find out if your home is in a risk area -- New York City and Boston are in a low potential zone, Chicago is in a moderate potential zone. In addition, for an in depth discussion of radon we recommend you refer to the EPA website “A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon”.
You can test for radon by obtaining an inexpensive, do-it-yourself radon test kit through the mail and in hardware stores. Look for kits that are state certified or have met the requirements of some national radon proficiency program. Alternatively you can hire a contractor to do the testing for you, and you can obtain a list of state certified radon contractors from your state’s radon office, state radon office (in New York state can be contacted at 1-800-458-1158 ext. 27556 or 518-402-7556 or email, and see also the New York State Departmentof Health Radon information resources, or you can also contact either the National Environmental Health Association's (NEHA) National Radon Proficiency Program (NRPP)  or the National Radon Safety Board (NRSB) for a list of proficient radon measurement and/or mitigation contractors.

Formaldehyde – Due to its prevalence in the manufacturing of building materials, furniture, cabinetry and fabrics and its nature as a byproduct of certain combustion processes, formaldehyde has become ubiquitous. The rate at which products like pressed wood or textiles release formaldehyde can change over time and will generally decrease as products age. When the products are new, high indoor temperatures or humidity can cause increased emissions.

Lead The EPA and other federal agencies initiated policies starting in the 1980’s to phase out lead in gasoline, to ban or limit lead used in consumer products, including residential paint, to reduce lead in drinking water and in industrial air pollution. Lead is equally dangerous whether it is inhaled or ingested, and lead dust, from sources like deteriorating lead paint for example, can be ingested in both those manners.

Children are more prone to ingesting lead due to dust settling on toys and floors where they crawl and play, and childrens’ proclivity for putting objects and hands into their mouths. Children's growing bodies absorb more lead, and their brains and nervous systems are more sensitive to the damaging effects of lead. If not detected early, children with high levels of lead in their bodies can suffer from damage to the brain and nervous system, behavior and learning problems (such as hyperactivity), slowed growth, hearing problems and headaches. 

Adults who are exposed to lead can suffer from difficulties during pregnancy, reproductive problems in both men and women, high blood pressure, digestive problems, nerve disorders, memory and concentration problems, and muscle and joint pain.

For more information visit the EPA website

VOC's - Decreasing Your Risk
Steps to Reduce Exposure

General Steps.
In a nutshell, the best way to reduce or eliminate exposure to VOCs is to eliminate the source of the contaminant. When renovating it is possible to choose materials, finishes and furnishings that do not emit VOCs -- simply ask a few questions about the presence of VOC emitting substances before you make decisions about materials and products, and choose alternatives that do not emit VOCs. It is now possible to buy non-toxic grout and caulk, paint, wallpaper adhesives, and floor and wood finishes. See our PROVIDER DIRECTORY for sources of no-VOC and low-VOC materials. Make it a priority to avoid products (paint strippers, adhesive removers, and aerosol spray paints) that contain methylene chloride and benzene. Never mix household cleaning products.

Apart from completely avoiding products that emit VOCs, ventilation is the name of the game. If a substance you are using contains VOCs, meet or exceed the manufacturer’s instructions and label precautions regardng handling and ventilation. Do not store opened containers of unused paints and similar materials, don’t buy larger quantities than you need and, because VOCs can escape from sealed containers, safely dispose of any unused substances but be sure to do so when your garbage collection service deals with toxic substances. Eliminate, by removal or sealing, existing sources of formaldehyde and don’t introduce new ones.

Secondhand Smoke
Simple: Don't smoke at home or permit others to do so. Ask smokers to smoke outdoors.
If smoking indoors cannot be avoided, increase ventilation in the area where smoking takes place by opening windows or using exhaust fans – this will have an adverse affect on your energy consumption.
Do not smoke around children, particularly infants and toddlers.

In addition to the measures noted above, keep in mind that “exterior-grade" pressed wood products emit lower levels of formaldehyde because they contain phenol resins, not urea resins. Also, the amount of formaldehyde that is released can depend on heat and humidity, so controlling the indoor climate to moderate heat and humidity levels can cut down on emissions from pre-existing sources; be sure to regularly empty and clean humidifier collection pans to prevent them from becoming a breeding ground for biological contaminants. Sealing surfaces with a non-formaldehyde-emitting sealant may also help for a period of time but be sure to seal every surface and edge.

Lead and Dust Particulate Matter Reduction During Construction

Many houses and apartments built before 1978 have paint that contains lead. Removing lead-based paint improperly can increase the danger to your family. If your project involves removing paint, sanding, patching, scraping, or tearing down walls or any other job that may require you to break through a painted surface (like replacing windows or doors, moldings, plumbing fixtures, heating and ventilation duct work, or electrical systems) then you may risk releasing lead dust or fumes.

First, determine if you have any lead paint. Areas that get a lot of wear and tear, such as windows and doors, pose the greatest risk because the paint will deteriorate faster due to the friction of surfaces rubbing against each other, and the lead can become airborne each time the painted surface is moved. A “paint inspection” will tell you the lead content of every different type of painted surface in your home, but won’t analyze whether it poses a risk. A “risk assessment” will tell you if you are currently subject to any sources of lead exposure and what to do to mitigate the risk. Lead inspectors trained and certified by the EPA or the state conduct visual inspections, use an x-ray fluorescence machine that measures the amount of lead in paint, and send paint samples to a lab for testing and test dust. Home test kits may not be reliable and the EPA recommends that homeowners not rely on them before doing renovations. To find a certified lead professional see The New York City Department of Health and Mental Hygiene website which has a comprehensive list of information resources on lead. The Environmental Network website  has listings for lead contractors in New York City and nationwide. Or call the EPA at 1-(888) LEADLIST.

One basic rule is to never dry sand, dry scrape or use a heat gun or propane torch to remove leaded paint because these activities can release lead dust and fumes that can remain in the house long after the renovation is completed. If possible, the EPA recommends that you move out while demolition work is being done, particularly if you have children under 6 or are pregnant, and that you don’t return until the area has been thoroughly cleaned, however cleaning itself may not be enough unless you have thoroughly sealed all airducts, vents etc. before the work was done. Lead dust can come to rest out of your reach.

Eliminating the risk of lead exposure during renovation is thoroughly dealt with in the EPA booklet entitled "Reducing Lead Hazards When Remodeling Your Home". This brochure explains what to do before, during, and after renovations and includes very clear instructions about the precautions summarized below. Most are very easy to implement, common sense precautions and make sense when doing a renovation whether or not there is a lead hazard because they are extremely effective in reducing the level of dust that gets into the non-work areas of the house. The procedures involve the use of relatively inexpensive materials (plastic, tape, respirators that are readily accessible at hardware stores, overalls, buckets, cleaning products) and a bit of extra time setting up the work area, but the result in protecting the rest of your home from dust can be tremendous.
Also refer to the EPA’s guidelines “Lead Paint Safety, A Field Guide for Painting, Home Maintenance, and Renovation Work“ for excellent step-by-step work procedures.

Before you start the work:
• Remove furniture, area rugs, curtains, food and clothing.

• Cover the floor and furnishings that can’t be removed (counters, shelving etc.) with a layer of 6 mils or higher polyethylene plastic sheeting. Cover all openings, air ducts and gaps around pipes, with plastic and duct tape.

• Create an air seal with plastic over the doorway in and out of which workers will travel to the work area.

• Turn off forced-air heating and air conditioning systems during renovation and remodeling and seal all vents with plastic and duct tape. Keep windows closed unless you are using volatile chemicals and need ventilation – eliminate this complication by choosing no-VOC options.

Refer to the pamphlets for detailed instructions on what to do during the work, which includes taking the following precautions:
• Clean dust with a HEPA-filter vacuum cleaner
• Use NIOSH certified respirators equipped with HEPA filters (always purple)
• Wear, and isolate from other household laundry, protective clothing. Leave contaminated shoes in the work area or wash them including the soles (a pan of water for dipping your feet and a towel can work), before leaving the area, and remove contaminated clothing and keep it sealed until it can be washed separately
• Use wet sanding equipment and spray bottles to minimize dust and prevent it from spreading.
• Work on small, contained areas at a time and completely clean up before moving on.
• Use all-purpose cleaners or those designed to clean up lead dust, for washing surfaces and equipment etc., and dispose of all contaminated waste water down they toilet.
• Refrain from eating, drinking and smoking in the work area, and implement the personal clean-up precautions of showering and washing your hair as soon as possible.

The booklet also describes procedures for working outdoors, for preparing walls for wallpapering, removing carpeting, floor refinishing, replacing windows and cleaning up lead waste.

In addition, it is possible to buy dust wall kits for building a kind of vestibule around doorways for creating a dust barrier. The kits consist of spring-loaded poles that hold themselves up between wall and ceiling, to which plastic can be attached in order to build plastic walls. Also, by installing a fan in a window to direct air to the outside, preferably with a HEPA filter to remove particulate matter and potential hazardous substances like lead dust from the outgoing air stream, you can remove dust from the work area and create a negative pressure in the work area that also helps keep the dust from traveling to other parts of the house.

Designing to Reduce Exposure to Respirable Particles
When designing your renovation, design to reduce indoor particulate pollution. Vent all combustion sources, such as furnaces and boilers and gas clothes dryers, to the outdoors. The EPA recommends that you keep interior doors to the rest of house open when using unvented space heaters. Properly size woodstoves and make sure they meet EPA emission standards. Last, have a trained professional inspect, clean, and tune-up your central heating system (furnace, flues, and chimneys) annually, including changing filters and repair any leaks properly. This will also have a favorable effect on your energy consumption.

After the Renovation - Home Air Cleaners
If it is not possible or practical to remove all sources of indoor air pollutants, and if ventilation proves inadequate, it is possible to further clean the air with home air cleaners. Indoor air cleaners are designed to clean the air of either particulate matter, such as dust, smoke, pollen, animal dander, rodent droppings, tobacco smoke, particles generated from combustion appliances such as cooking stoves, and particles associated with tiny organisms such as dust mites, molds, bacteria, and viruses; or gaseous pollutants, VOCs, from the sources we discussed above (gas cooking stoves, vehicle exhaust, and tobacco smoke, building materials, furnishings, adhesives, paints, varnishes, cleaning products, and pesticides).

Air cleaners can either be installed within the duct work of a central HVAC (heating, ventilating, and air-conditioning) system or be portable.

Particle Removal can be accomplished by two types of air cleaning devices -- mechanical air filters and electronic air cleaners. Mechanical air filters remove particles by capturing them on filter materials such as a high efficiency particulate air (HEPA) filters. Electronic air cleaners employ the use of charged ions (ion generators, or ionizers) that attach to pollutant particles and such devices may either include the presence of an oppositely charged collection plate that attracts the charged particle and pulls it out of the air (electrostatic precipitators), or may not use a collector plate but rather rely on the property of charged particles to settle faster or to attach to surfaces such as walls and furniture.

The effectiveness of mechanical in-duct particulate filters is measured by the minimum efficiency reporting value (MERV) developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and filters are rated on a scale of a low 1 to a high of 20. As a reference, LEED for Homes requires a minimum MERV value of 8 or higher, meaning that the filter will remove 20-35% of particles that are 3 to 10 microns in size (mold spores, for example vary from 4 to 40 microns, most being less than 10).

There is no standard measurement for the effectiveness of electronic air cleaners. They may remove small particles but are not effective at removing large particles becasue most settle out of the air before reaching the filter, and some units produce ozone which has adverse health effects associated with it as described below.

VOCs/Gaseous Pollutant Removal is attempted through a gas-phase filter which employs the use of an absorbent material, such as activated carbon, designed to remove VOCs from the air that passes through the filter. However, gas-phase filters are of limited utility because they are designed to remove only certain gases and won’t remove others, and do not have the capacity to remove all the gaseous pollutants found in a typical home. There is no standard measurement for the effectiveness of gas-phase air filters. These filters often have short useful lives become they can quickly become clogged and may re-release pollutants back into the air. Under current technology a filter large enough to be effective would likely not fit into a typical home HVAC system.  Also, the useful life of these filters may be short.

Pollutant Destruction air cleaners use ultraviolet (UV) light technology to destroy biological pollutants, such as viruses, bacteria, allergens, and molds. These air cleaners are called ultraviolet germicidal irradiation (UVGI) cleaners and photocatalytic oxidation (PCO) cleaners. Ozone generators that are sold as air cleaners intentionally produce ozone gas, a lung irritant, to destroy pollutants. These all have their limitations and draw backs.

UVGI filters are designed to prevent build-up of biological polutants on the HVAC equipment and are not meant to clean the air for an entire house. There is no standard measurement for the effectiveness of UVGI cleaners. The UV light produced by these filters is not strong enough to kill all bacteria and mold because they tend to be resistant to UV radiation and require more light or longer time of exposure, or both, to be killed, and in any event dead mold spores can still trigger allergic reactions.

PCO cleaners are designed to convert VOCs into harmless gases but they do not remove particulate matter. There is no standard measurement for the effectiveness of PCO cleaners, and they are generally considered ineffective because the catalysts currently used are not capable of destroying all VOCs and indeed can create new ones.

Ozone is a lung irritant that can cause adverse health effects, and at safe concentrations ozone has little effect in removing most indoor air contaminants. Ozone also can react to chemcials found in household cleaning products and produce ultrafine particulate pollutants. Thus, ozone generators are not always safe and effective in controlling indoor air pollutants.

Portable Air Cleaners
Portable air cleaners may employ a combination of filter types discussed above and are usually small units that can be moved from room to room. The effectiveness of portable air cleaners is measured by the clean air delivery rate (CADR) which was developed by the Association of Home Appliance Manufacturers (AHAM) and measures the volume, in cubic feet, of filtered air that the filter delivers per minute. The CADR rating lists three numbers -- one for tobacco smoke, one for pollen and one for dust. The higher the tobacco smoke, pollen and dust numbers, the faster the unit filters the air. AHAM recommends that consumers apply a 2/3 rule: look for a unit with a tobacco smoke CADR at least 2/3 of the size of your room’s area (cubic square footage), and if the ceilings are higher than 8 feet (typical in brownstones) choose a unit rated for a larger room. The EPA notes that most portable air cleaners currently on the market do not have high enough CADR values to effectively remove large particles such as pollen, dust mite, and cockroach allergens. Some portable air cleaners using electronic air cleaners might produce ozone, which is a lung irritant as described above.

Cleaning air the natural way: PLANTS In the book How to Grow Fresh Air  the NASA scientist B.C. Wolverton described his research into creating a healthy, breathable environment for a space station and his resultant discoveries that house plants, including those as humble and easy to grow as the tulip and Boston fern, are excellent air filters and remove some of the most ubiquitous offenders found in households today, including ammonia, formaldehyde, and benzene. He also rates each plant for its effectiveness in removing various pollutants, and its ease of growth and maintenance.

Stop germs and chemicals at the front door. Adopting the simple custom of removing street shoes upon entering the home in fact eliminates the introduction of hundreds of chemicals and biological pollutants into your home environment. It follows that wiping down Rover’s paws after a jaunt around the block (not to mention other body parts if your pooch shares the furniture with you) has the same effect.