Carbon dioxide


Molar mass 44.01 g/mol
Lifetime in atmosphere No single lifetime can be given
Global Warming Potential over 100 years 1
Estimated emissions in 2008 51,762,916 Gg
Atmospheric concentration in September 2013 393,510,000 ppt

Nearly all of the carbon content in incinerated waste is emitted to the atmosphere as carbon dioxide. Municipal solid waste contains approximately the same mass fraction of carbon as does carbon dioxide itself (27%), so incineration of 1 tonne of waste is estimated to produce approximately 1 tonne of carbon dioxide.

Carbon dioxide emitted by human activity is of course the main cause of global warming leading to climate change. Under the Climate Change Act 2008, the UK is committed to reduce greenhouse gas emissions from 1990 levels by at least 80% by 2050. In 1990, emissions from energy consumption were 10.5 tonnes of carbon dioxide per capita, so the target is slightly over 2 tonnes per capita.

In 2011, UK emissions from energy consumption were 8 tonnes per capita, the reduction from 1990 largely due to the replacement of coal by gas in electricity generation. The Exeter Incinerator is designed to accept up to 60,000 tonnes per year of waste, from Exeter and the immediate surrounding area in Devon. With a population of about 120,000, that means 0.5 tonnes of carbon dioxide added to every person’s carbon budget. But suppose the Incinerator replaced some carbon emissions from other energy plant……

Incinerators have electricity generation efficiencies of 14-28%. The waste heat can be used in a district heating network, giving efficiencies higher than 80%. The Exeter Incinerator will initially provide electricity to the national grid, and has the potential to export heat but only if a district heating network is established on the Marsh Barton estate.

So the Incinerator will produce electricity at a substantially lower efficiency than the rest of the national grid, and displace lower carbon alternatives.

Nitrogen oxides


Nitric oxide (NO) and nitrogen dioxide (NO2) are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air. But removal of nitric oxide by incinerators is only about 60% effective and the remainder may be converted to nitrogen dioxide to form smog and acid rain.

Nitrogen dioxide has a variety of health impacts, such as higher incidence of respiratory symptoms in children, asthma, chronic obstructive pulmonary disease, lung cancer, heart disease in those over 65, and abnormally elevated immune and allergic responses. When nitrogen dioxide is combined with fine particulates and carcinogenic heavy metals (in particular cadmium), the effects on lung cancer are likely to be more potent.

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.