Soliftec - Smoke

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SMOKE
For information about which fuels smoke: Solid Fuels Page. How to burn wood with low smoke: Smoke Advice Leaflet

What smoke is, and how to spot it
Smoke is a suspension of tiny solid particles in a gas. It is important to differentiate between 'white' and 'dark' smoke. White 'smoke' is usually harmless tiny water droplets formed when steam condenses in cool air, it is more common in colder weather, easily visible against a dark background, but difficult to see against a light sky background. Dark smoke is mainly black carbon and often harmful, it is visible against a light sky but difficult to see at night or against a dark background.

How smoke is generated.
When solid fuels become hot, volatile matter - water or tars - inside the fuel element boils, giving rise to a myriad of sudden tiny explosions which shatter the solid material around them, throwing off tiny fast-moving particles which don't get time to burn properly. The smallest of these particles, below about 10 microns (micron = one thousandth of a millimetre), can get into the lungs. The bulk of smoke particles are pure soot - black elemental carbon - and are relatively harmless, the problem is the half-cooked residues which are left stuck to the particles, seen as a fuzzy coating in the photograph below. The residue from wood is almost all hydrocarbons, which if burned hot enough in a carefully designed stove fired with good fuel, can be broken down into harmless substances. Coal and oil smoke is more of a problem as it often contains sulphur and other compounds which simply cannot be destroyed.

Smoke in developing countries
In many countries a combination of poor combustion on indoor hearths leads to a very poisonous type of smoke, plus lack of chimneys and ventilation means it is inhaled directly, may contribute to around 1.6 million deaths each year, mostly of children under five. (see: World Health Organisation)

A domestic kitchen in rural Nepal, 2013
Image: Glyn Hughes/Soliftec

The variability of smoke
Smoke is hugely variable and very difficult to measure. Differentiating between different types or more- or less- harmful smoke is impossible without very advanced facilities. It is therefore extremely difficult to compare one smoke source with another different type. The table below gives 'official' emission figures for various vehicles and types of heating, from which it is perfectly possible to show that, in terms of smoke, 1 stove = 6 cars, or 6 cars = 1 stove.

Smoke is wildly variable and one poorly-used stove or one badly-tuned truck can have a huge impact. Net CO2 emissions are less uncertain, from which it is possible to present the following..

	AS DELIVERED mg					PER HOUR mg
	Net CO2	Exhaust dust		VOCs	NO2	CO2	VOCs	Dust Particles	NO2
SOLID HEAT	per kW.h					per 5kW.h output
BAT Stove (Cub)	15,630	71		10	623	93,780	60	357	3,738
Euro 2022 Stove	15,630	124		186	623	93,780	1,116	620	3,738
DEFRA Stove	15,630	465		300	623	93,780	1,800	2,325	3,738
Older Stove	15,630	775		300	623	93,780	1,800	3,875	3,738
Pellet Stove (Euro 2022)	15,630	60		111	623	93,780	666	300	3,738
Open fire, wood	15,630	1,600		500	623	93,780	3,000	8,000	3,738
Open fire, coal	362,880	4,700		500	4,610	2,177,280	3,000	23,500	27,660
Barbecue, chimenea, firepit	15,630	3,800		500	623	93,780	3,000	19,000	3,738

ROAD VEHICLES	per km	Exhaust dust	Road dust			at 30km/hr
'Good' petrol car (Euro 6 2020)	181,000	5	21	168	380	5,430,000	5,040	765	11,400
'Bad' petrol car (Euro 3 2000)	181,000	5	21	200	380	5,430,000	6,000	780	11,400
'Good' diesel car (Euro 6 2020)	173,000	5	23	252	1,840	5,190,000	7,560	825	55,200
'Bad' diesel car (Euro 3 2000)	173,000	50	23	300	1,840	5,190,000	9,000	2,190	55,200
Electric car	47,500	0	30	0	274	1,425,000	0	900	8,220
'Bad' truck (Euro I 1995)	867,000	120	84	255	12,770	26,010,000	7,650	6,120	383,100
'Good' Truck (Euro V (2012)	867,000	3	84	18	12,770	26,010,000	540	2,610	383,100

OIL HEATING	per kW.h					per 5kW.h output
Central heating	269,000				3,430	1,614,000			20,580

GAS HEATING	per kW.h					per 5kW.h output
Older FE Gas fire (30% efficient)	204,000	0			110	680,000			367
Gas Fire (2000 60%)	204,001	0			110	340,002			183
Gas CH 85%	204,002	0			110	240,002			129
Bottled gas heater (Propane) 90%	230,000	0			150	255,556			167

ELECTRIC HEATING	per kW.h					per 5kW.h output
Any type	256,000				1,370	1,250,000			12,500

Sources:
CO2 Emissions: https://www.gov.uk/..greenhouse-gas-reporting-conversion-factors-2019
Non-exhaust road dust: https://uk-air.defra.gov.uk/assets/ ..Non_Exhaust_Emissions_typeset_Final.pdf
Barbecues, etc. There is no data for these appliances - assumed to be c3g PM per kg based on analysis of 'three stone' fireplaces
Heating levels are limit levels in EN Standards
Electric car is based on Nissan Leaf
Dust emission from vehicles: https://en.wikipedia.org/wiki/European_emission_standards

EXAMPLE DATA: One way of trying to identify wood smoke is to look for traces of levoglucosan, a type of caramel formed when plant material is partly burned. However 'LG' is also produced from coal, cooking, bio-diesel and other sources.

This graph shows av. smoke; the blue line is levoglucosan from 'domestic' smoke from wood, but likely also from coal and cooking, the red line is other forms of smoke. (Measured at Kensington, London) https://kclpure.kcl.ac.uk/portal/files/12227807/Atmospheric_Environment.pdf