What is smoke?

According to an online dictionary (http://www.merriam-webster.com/dictionary/), smoke is “the gaseous products of burning materials especially of organic origin made visible by the presence of small particles of carbon” and steam is “a vapor arising from a heated substance”.

Steam is often resultant from wet feedstock, although wet biomass can also lead to other emissions.

A traditional stove. India 2010

In relation to cook stoves, emission measurements sometimes cover smoke, carbon monoxide and sulphur dioxide. These can be measured by a smoke density metre (i.e optical) and flue gas analyser (electrochemical or similar). Other harmful substances including PM2.5 (particles less than 2.5 micrometres) or 3.5 or 10 for example are also commonly measured by specialist devices (i.e electron microscope).
Other emissions from burning can include GHGs (methane, carbon dioxide, nitrous oxide), VOCs, NO/NO2, and other sulphates.

Gases chosen to be analysed are commonly those which are most harmful to health or are indicative of other harmful substances. There is not necessarily a link between emissions and efficiency (i.e thermal efficiency or fuel efficiency) – more on this later.

Analysis should be undertaken for the whole cooking cycle as emissions can change. Also lighter substances need to be taken into account (resin / rubber for example will produce high and noxious emissions), and also it should be noted that once pots are introduced into trials, the condensing smoke / steam can produce more visible emissions, although the actual emissions may not be changing.

Gasses can be ‘flared off’ from cook stoves, for example in a gasification stove. However more generally smoke and other emissions are produced with inefficient combustion, so increasing the efficiency of combustion (i.e by adding a grate to a traditional stove, which leads to increased oxygen supply) can be a simple way of reducing emissions from a stove.

Although it is outside the remit of this project we think that emissions measurements are critical to effectively analyse the potential for deployment of any stove type. A stove which has emissions higher than the baseline stove should never be considered.


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