Particulate matter


Incinerators may emit fine particles, and the EU Waste Incineration Directive puts limits on emissions to air of heavy metals, dust, and total organic carbon, among other pollutants. Therefore, incinerators operate a filtration system to control particulate emissions.

Emissions of particulate matter from an incinerator typical of those currently operating in the UK (230,000 tonnes per year) are approximately equivalent to emissions from a 5 km stretch of typical motorway. That is, emissions from the Exeter Incinerator will be approximately equivalent to the emissions from the M5 between junctions 29 and 30.

PM10 is defined as the mass of particles of less than about 10 microns (or one-hundredth of a mm) in diameter per cubic metre of air. PM2.5 is the mass of particles of less than about 2.5 microns in diameter per cubic metre of air. PM10 and PM2.5 samples from around the world can vary substantially in their chemical composition and size distribution, and it is possible that associated metals and ultrafine particles are important. Yet international and national regulations are currently framed in terms of mass concentrations instead of, say, the chemical (metallic) composition, the number of particles and total surface area of particles per unit volume of air, or the capacity of particles to generate free radicals.

Long term exposure to particles affects the risk of mortality, especially from cardiovascular disease and from lung cancer. Short-term increases in concentrations cause increases in deaths from and hospital admissions for heart attacks and respiratory disease, and related symptoms.

Mercury and other metals


Of the heavy metals, mercury is a major concern due to its toxicity and high volatility. It is subject to the European Waste Incineration Directive, which puts limits on emissions to air, so the flue gas is treated post-combustion. The resulting toxic fly ash must be handled as hazardous waste.

Acute exposure to mercury vapour can lead to irritation of the lungs, coughing, chest pain and shortness of breath, and central nervous system (CNS) effects such as tremors and mood changes. Chronic exposure also leads to CNS effects such as increased excitability, excessive shyness and irritability.

Cadmium emissions from an incinerator the size of the Exeter plant are approximately equivalent to one-eightieth of the emissions from a medium sized UK coal-fired power station.

Acute inhalation exposure to cadmium can lead to irritation of the lungs. Chronic exposure can cause a build-up of cadmium in the kidneys that can lead to kidney disease.

Although zinc poses no documented health risks, if its physical state is altered during use then health risks can be created. Inhalation of metallic oxide fumes can lead to metal fume fever.

Non-ferrous and/or ferrous metals are recovered (separated from Municipal Solid Waste or Incinerator Bottom Ash) and recycled from most incinerators in the UK.

Hydrogen halides


Hydrogen fluoride and hydrogen chloride, but not hydrogen bromide, are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air.

They are acidic gases primarily released to air from combustion of fuels which contain trace amounts of fluoride, chloride or bromide. They are highly corrosive, and inhalation of air containing low levels of hydrogen chloride can cause throat irritation or asthma. Exposure to higher levels may result in effects including rapid breathing, blue colouring of the skin, fluid accumulation in the lungs and in extreme cases severe swelling of the throat, suffocation and death. Inhalation of air containing hydrogen fluoride can cause irritation of the eyes, nose and throat. Exposure to high levels may cause muscle spasms and can damage the lungs and heart and in extreme cases can result in death. 

Pattern – Bonds


Download this pattern as a pdf

See also the patterns for the atoms and the number and colours of atoms and bonds needed for each particle.

Double knit
3.75mm DPNS

Pattern – joining two atoms of the same colour

Cast on 4 sts, leaving a 20 cm tail
Knit i-cord for 16 rows
Cast off i-cord, leaving a 20 cm tail

Pattern – joining two different colour atoms

Cast on 4 sts, leaving a 20 cm tail
Knit i-cord for 8 rows
Knit 1 stitch i-cord, join the second colour and knit the rest of the row
Knit i-cord for 7 rows
Cast off i-cord, leaving a 20 cm tail

Knot the tails of the two colours at the join.
Thread each tail in turn onto a needle, pass through the cord of the same colour, cut so ends stay inside.
Work the knot inside the cord, and the stitches so they even out.


Thread each 20cm tail onto a needle and sew the bond onto the atom.
Pass remaining tail through atom, cut so ends stay inside.

Pattern – Atom


Download this pattern as a pdf

See also the patterns for the bonds between atoms and the number and colours of atoms and bonds needed for each particle.

Our prototypes were made with bog-standard acrylic wool, and the atoms stuffed with a slightly shredded half of a plastic charity collection bag. These are the sorts of materials that will be burnt in the Incinerator. But really, anything that is weatherproof will be suitable.

If you are new to knitting, some of the codes below may be a mystery. But the internet is full of
marvels such as tutorials and knitting videos. It’s how we learnt i-cord.

knit into the front an back of the stitch
repeat stitches in between
knit two together
slip stitch, knit next stitch, pass slip stitch over the knitted stitch
Double knit
26 stitches to 10cm

The atom will be approx 20 cm in circumference.


Cast on 12 sts

kfb into each st (24 sts)
purl all
*k1, kfb* across row (36 sts)
cast on 1 st, purl across row, cast on 1 st at end (38 sts)
continue in stocking stitch for 12 rows starting with a knit row
k2tog, *k1, skpo* (25 sts)
k2tog, *skpo* to last 3 sts, k1, k2tog (13 sts)
p1, *p3tog*

Cut yarn leaving a 20 cm tail.
Thread onto needle, thread through remaining stitches and pull tight.
Sew edges together, stuff atom, thread through casting on stitches and pull tight.
Knot tails together, thread onto needle and pass through atom, and cut so ends stay inside.