Lentis/Cooking with Wood Fuel

Introduction

Cooking is the practice of preparing food by assembling ingredients then using heat to make it more fit for consumption. There are several reasons for cooking food including sterilization, preservation, increasing digestibility, and enhancing flavors. Cooking techniques vary widely, from grilling over an open flame, to frying over an electric stove, baking in an oven, or smoking and dehydrating. This activity is unique to humans, with archaeological evidence of cooking with fire suggesting the method originated at least a million years ago.

Sources of fuel, categorized as "clean" or "polluting". Noteː clean fuels which involve combustion are not fully clean due to byproducts.

Sources of Cooking Fuel

Solid fuels are the oldest and simplest source of cooking fuel, requiring ignition and maintenance of the solid fuel to release heat. Most solid fuels are composed of biomass and can be processed to increase burn efficiency. Examples of unprocessed fuels include wood and agricultural residues, whereas processed fuels include treated wood chips or charcoal briquettes. Since the 20th century, other sources of heat for cooking have become commonplace, such as electricity and natural gas used in stoves and ovens.

Reasons for Choosing Wood

Social/Cultural Factors

Family size and education strongly affect fuel choice, with family size influencing total fuel use and household education level determining perception of the fuel market and cooking trends. Food preference and aesthetics are also influential, as wood may introduce preferable flavors or induce a unique sear. Preestablished cooking customs and convenience are possibly the most significant factors. In developing countries, many households are already accustomed to cooking with wood, and likewise have developed recipes around its usage. Switching to another fuel source can involve redesigning these customs, which can make households hesitant.

Economic Factors

Finances are a major economic factor which can force a household to choose wood. Wood is one of the cheapest fuels in many locations, especially in those adjacent to forests which allow for harvest year-round. Because labor is the only cost of acquiring this wood, many low-income households are solely dependent upon it. On the other hand, many developing countries typically lack the required infrastructure (e.g., a well-developed electrical or natural-gas grid) to support alternative fuels as a household choice at all. In places where these choices are available, households take into account the cost of utility service, wiring/piping, and an appropriate stove.

Technical Factors

In many situations, wood is considered more useful than other cooking fuels because a wood-burning stove can be used for both cooking and heating a house. Although wood-burning stoves are usually less durable than other choices, they can be quickly and cheaply rebuilt.

Byproducts

When wood is combusted, it produces byproducts in the form of solid wood ash, and gaseous/aerosolized wood smoke. Their contents are as follows:

Wood Ash

Primary Components
Component	Chemical Symbol(s)	Household Usage
Calcium Carbonate	CaCO₃	Neutralizes acidic soil
Quicklime	CaO	Used in water purification
Potash	K₂O	Used in fertilizers
Phosphoric Acid	H₃PO₄	Used in fertilizers
Trace Components
Component	Chemical Symbol(s)	Household Usage
Iron	Fe	N/A
Silicon	Si	N/A
Aluminum	Al	N/A
Manganese	Mn	N/A

Wood Smoke

Primary Components
Component	Chemical Symbol(s)	Concerns
Water Vapor	H₂O	N/A
Carbon Dioxide	CO₂	Primary greenhouse gas
Carbon Monoxide	CO	Greenhouse gas, poisonous
Soot	(C₃H)ₙ	Toxic
Tar (Hydrocarbons)	CₙHₙ	Toxic, Carcinogenic
Trace Components
Component	Chemical Symbol(s)	Concerns
Formaldehyde	CH₂O	Toxic
Acetaldehyde	C₂H₄O	Toxic
Acrolein	C₃H₄O	Toxic

Impacts

Health Impacts

Although wood fires may emit a pleasant smell, wood smoke exposure poses a significant risk to human health. A typical inefficient wood stove can emit an equivalent amount of air pollution as five diesel trucks. Inhalation of the toxic particles in these emissions can lead to similar negative effects as those associated with smoking tobacco.

• Short-term exposure to wood smoke causes symptoms which range from unpleasant to life-threatening. Many will experience immediate irritation of the eyes, sinuses, and throat. When smoke reaches the lungs, it can cause difficulty breathing or trigger an asthmatic episode. Smoke may also displace oxygen by volume or chemically displace it in the bloodstream via carbon monoxide. This can lead to headache, fatigue, and possible loss of consciousness due to lack of oxygen.

• Long-term exposure to wood smoke may cause chronic health impacts may to emerge. The presence of carcinogenic byproduct particles in the body can lead to various forms of cancer, primarily in the lungs, neck, or head. In addition, constant strain on the respiratory and cardiovascular systems can lead to pneumonia, heart disease, arterial damage, and increased risk of stroke.

Environmental Impacts

During a wood fire, the wood smoke that is released contains particles which are less dense than the surrounding air, causing them to rise into the atmosphere. As it rises, wood smoke also diffuses into the surrounding air, increasing its overall volume and the area it covers. Within this affected area, the same toxic particles associated with many health risks are present in elevated levels. Additionally, there is typically a strong smell and a noticeable discoloration of air.

When rain clouds form in the surrounding area, raindrops may begin by condensing around toxic smoke particles. Likewise, as precipitation begins, these particles are deposited into the surrounding ground or water supply. Toxic smoke particles may also cool down or lose velocity due to environmental conditions. When they do so, they begin to settle on adjacent surfaces. These surfaces may accumulate high particle concentrations which may be directly contacted or which precipitation may weather and carry into the ground or water supply.

In developing countries that lack proper forestry management, over-reliance on wood fuels has lead to the destruction of forest habitats and the reversal of greenhouse gas capture. As trees are burned, the carbon dioxide which they have captured through photosynthesis is released back into the atmosphere, negating its positive effect without proper replacement.

Mitigation

Methods exist to manage direct exposure and capture particles before they are released into the environment. The most basic form of emission management is ensuring proper ventilation. Fires kept outdoors or in shelters with openings in the ceiling can allow for the natural release of wood smoke. For more effective smoke redirection, a chimney can be built around and above a fire to guide smoke away from people or outside of a building. Chimneys can also be equipped with filtration systems that pull toxic particles out of wood smoke, but this technology is often not cost-effective and does not mitigate the release of carbon dioxide.

The creation of toxic smoke particles can also be minimized by ensuring a more-proper combustion, breaking down more of smoke's byproducts into pure carbon dioxide and water with trace elements left in ash. This can be achieved by using dry wood (<20% moisture content), maintaining high heat (>1100°F), and ensuring proper oxygenation.

Transition away from Wood

Over the last century, wood has seen a steady decline in use as a fuel source for cooking in favor of natural gas and electricity. These alternative sources of energy are more reliable and have a smaller carbon footprint. This transition has been dependent upon the needs of households and the actions of key social groups.

Social Groups

Nearly 2.5 billion people still utilize wood as a fuel source for cooking, with most of those people residing in low- and middle-income countries. Almost 100% of rural populations in developing nations depend on wood fuel. These populations are impacted the most by the negative health and environmental effects of burning wood. An estimated 1 billion people still live without electricity or natural gas access at all, and hundreds of millions more live with unreliable and expensive electricity coverage.

In countries where electric or natural gas infrastructure is not widespread, governmental bodies typically leverage their growing energy demands to raise funds and allocate them in expanding their utility grid. These bodies are not typically invested directly in replacing wood as a cooking fuel, but rather see it as a supplemental benefit of grid expansion. Often these countries rely upon external utility companies for construction and maintenance as it is more cost-effective to hire established companies than to develop new ones.

There are several multinational organizations whose focus is developing low-income countries, including The World Bank Group and several subsections of the United Nations. These organizations aid developing countries by providing capital and labor with the explicit goal of expanding infrastructure. The World Bank in specific believes that "access to electricity is key to the development of a country" and as such has donated over $5 billion for energy access. Incentives, such as these, are crucial for helping electric companies develop infrastructure in otherwise expensive, rural areas. In more developed countries, advocacy groups like the Families for Clean Air lobby for regulations on wood smoke pollution.

Projections

As the issue of availability is solved, wood will continue to be replaced by cooking fuels such as natural gas and electricity. Once a household converts away from wood, it is rare for it to convert back. Likewise, the household reliance upon wood has been declining by roughly 1% of total households per year.

Conclusion

Humans have been reliant upon wood as a primary fuel source for cooking for millions of years. Although many choose it for its low-cost and high-availability, it comes with the side-effect of releasing toxic particles into the air which pose a significant risk to humans and the environment. As nations continue to develop, households can afford to avoid these side-effects and transition from wood to natural gas and electricity. Unfortunately, many rural areas still lack the proper infrastructure to make these alternative fuel sources affordable and reliable. Thus, a concentrated effort must be made by governments and multinational organizations to expand access.

In the future, it would be worthwhile to explore the history of wood as a cooking fuel and the beginning of its replacement. Additionally, because wood may not end up fully replaced, more exploration into mitigation techniques including wood stove technology and particle capture is warranted.