Studies show that reduced resistance to disease is linked, among other things, to wood smoke exposure. Smoke produced by wood combustion harms the cellular membrane, slows down immune system activity, damages the inflammatory cells that protect and clean the respiratory tract, and also disrupts enzyme levels. (Lung Assn. Quebec).

I.R. Hill 1996. Department of Forensic Medicine, Guy's Hospital, London, UK.
Smoke is a mixture of particles and gaseous chemicals of varying physical and chemical properties. When inhaled these produce the characteristic features of smoke-inhalational injury. Although heat is produced in fires it is the chemical agents which cause the damage to the airways and the lungs. Mortality and morbidity are closely related to pulmonary injury and thus to the particulate and chemical nature of smoke. Moreover, there seems to be a potentiating effect, in that the particles worsen the toxicity of the chemicals present.

Enlarged wood smoke particle taken from a human lung:
Original picture size 3 7/8 " by 3 3/8" at 900x enlargement. Chest p.1232. Interstitial Lung Disease and Domestic Wood Burning, Ramage, Roggli, Bell and Piantadosi.
The wood smoke particle swells up inside the body.
It swells up inside the 99% humidity of the lung.
Growth is between 70% and 92%.
Higher loads of the combustion toxics are deposited directly into the lung.

Comparison of particle sizes:

The American Lung Association says:

MORE THAN 90% OF THE WOODSMOKE PARTICLE MASS

CONSISTS OF FINE PARTICLES, THE FRACTION OF PM
THAT MANY RESEARCHERS CONSIDER TO HAVE THE
GREATEST ASSOCIATION WITH ADVERSE HEALTH
OUTCOMES. IN ADDITION TO FINE PM, WOODSMOKE
EMISSIONS CONTAIN COMPONENTS SUCH AS CARBON
MONOXIDE (AN ASPHYXIANT), VARIOUS IRRITANT GASES
SUCH AS NITROGEN DIOXIDE, SULFUR DIOXIDE,
HYDROCHLORIC ACID, AND ALDEHYDES SUCH AS
FORMALDEHYDE AND ACROLEIN, AND CHEMICALS
KNOWN OR SUSPECTED TO BE CARCINOGENS, SUCH AS
POLYCYCLIC AROMATIC HYDROCARBONS (PAHs),
OXYGENATED PAHs, AND POLYCHLORINATED DIOXINS AND
FURANS.

FINDINGS FROM ANIMAL TOXICOLOGICAL STUDIES
DEMONSTRATE A REDUCTION IN PULMONARY ANTI-
BACTERIAL DEFENSE MECHANISMS ASSOCIATED WITH
WOODSMOKE EXPOSURE. WOODSMOKE EXPOSURE CAN
DISRUPT CELLULAR MEMBRANES, DEPRESS MACROPHAGE
ACTIVITY, DESTROY CILIATED AND SECRETORY
EPITHELIAL CELLS AND CAUSE ABERRATIONS IN
BIOCHEMICAL ENZYME LEVELS.

A LARGE BODY OF EVIDENCE LINKS PM WITH
ADVERSE HEALTH OUTCOMES, INCLUDING EXCESS
CARDIOPULMONARY ILLNESS

EPIDEMIOLOGICAL STUDIES SHOW A COHERENCE OF DATA
AMONG STUDIES OF HEALTH CONSEQUENCES FOR THOSE
EXPOSED TO WOODSMOKE. PERSONS AT HIGHER RISK
INCLUDE YOUNG CHILDREN, THE ELDERLY, AND PEOPLE
WITH PREEXISTING CARDIOPULMONARY DISEASE.
DEMONSTRATED EFFECTS INCLUDE INCREASED
PULMONARY SYMPTOMS, INCREASED HOSPITAL
ADMISSIONS FOR LOWER RESPIRATORY INFECTIONS,
EXACERBATION OF ASTHMA, AND DECREASED
PULMONARY FUNCTION IN SCHOOL-AGE CHILDREN.

Carcinogenic substances - some of the carcinogenic substances identified in wood smoke include aldehydes and polycyclic aromatic hydrocarbons and dioxins.

The following information is from a link
published on the Tasmanian Government Environment Division website:

Harmful Substances in Woodsmoke

• Types of Air Pollutants
• What is Concentration?
• Carbon Dioxide
• Carbon Monoxide
• Nitrogen Oxides
• Particulate Matter
• Volatile Organic Compounds
• Aldehydes
• Benzene, Toluene and Xylenes BTX
• Polynuclear Aromatic Hydrocarbons
• Further Information

If wood is burned properly, the only products that will be formed are a gas called carbon dioxide, some water which comes off as steam and a small amount of ash, which cannot burn. However, often the wood does not burn completely and it can make a lot of smoke with hundreds of different chemicals, called "products of incomplete combustion".

Types of Air Pollutants

We can put these many different chemicals into groups of similarity called classes. Scientists know that some of these chemicals can cause problems for people, like causing disease in their lungs or heart, or making their illness worse if they are already sick. However, there are a number of chemicals Scientists still hardly know anything about their affect on human health and research is being done to try and find out. Some of the chemicals are gases, some are liquids and others are solids. When there is more of a chemical mixed into the air than is good for us, we call it a pollutant.

What is Concentration?

Concentration is the word we use to describe how much of a pollutant is mixed with the air. There are two main ways, called "units", that we use to describe concentration.

For particles, we use "micrograms per cubic metre", written as "1 µg/ m3". If you read further down, you will see a description of particles, or particulate matter.

• If you imagine a large cardboard box that is one metre high, one metre wide and one metre deep, it will contain one cubic metre of air. It is written as "m3". This is called the "volume" of air.
• One microgram is one millionth of a gram. This is very tiny amount, but still large enough for us to measure. We shorten this to "1 µg", where the Greek letter "µ" means "millionths of", and "g" means "gram".
• So a concentration of one microgram of smoke per cubic metre means that there is one millionth of a gram of smoke in each cubic metre of air, and we write it as "1 µg/ m3".

For gases, we use another unit, called "parts-per-million", written as "ppm". This is a little harder to explain. There are several gases described lower down on this page. For example, carbon monoxide is a gas that often occurs in air.

• Imagine the same large cardboard box that you did before, containing a volume of one cubic metre of air.
• If we take a tiny box that has a volume of one cubic centimetre of carbon monoxide and add it to the air in our box, we make a concentration of 1 part-per-million of carbon monoxide in air, which is shortened to "1 ppm".

Chemicals from Wood Burning

Some types of chemicals that come from burning wood are:

Carbon Dioxide (CO2)

Carbon dioxide is a gas that we cannot see or smell. It is given off whenever anything that contains carbon in its chemical structure is burned completely, along with water. It is not dangerous to us in open air but it can asphyxiate us if there is too much of it in a small space. In other words, it prevents us from getting enough oxygen from the air to keep us alive. It is also what we call a greenhouse gas, which may be causing the earth to warm up.

Carbon Monoxide (CO)

Carbon monoxide is a gas that we cannot see, smell or taste. At very high concentrations, it is very poisonous, because it makes it very difficult for our blood to take oxygen from our lungs around to all the different parts of our bodies. However, luckily it is very unusual to get much carbon monoxide in the outside air, except where there are many cars and trucks on busy roads, especially if they are stuck in a traffic jam. Even then, people need to be exposed for some time at the kinds of levels found in city streets, because it takes time for carbon monoxide to build up in our bloodstream. So At lower concentrations in air, carbon monoxide can affect people with heart disease, because it makes their heart work harder to transport oxygen around their bodies. It has an Air Quality Standard of 9 ppm over 8 hours.

Nitrogen Oxides (NOx)

Nitrogen oxides can be made by fire, either because the fuels used contain chemicals with nitrogen in them, or because the fire is so hot that a small amount of nitrogen from the air combines with oxygen to form them. For example, a gas flame will often make nitrogen oxides because it is very hot. Nitrogen oxides are also made by burning fuels like petrol and diesel in the engines of cars and trucks. There are two main types made by burning: nitric oxide (NO) and nitrogen dioxide (NO2), although there are some others that may be made in smaller amounts. Nitrogen dioxide may also come from some industrial factories that make a powerful acid called nitric acid, factories that galvanise steel (coat it with zinc) and others that make glass or power stations that generate electricity.

Nitrogen dioxide has more effects on our health than nitric oxide. It can irritate our lungs and cause bronchitis and other lung diseases. Over a long time, it can cause scarring of the very delicate air spaces in our lungs and reduce the amount of oxygen that they can absorb into the blood. Because of its health effects, there is an air quality standard of 0.16 ppm for an hour.

Particulate Matter