Non methane VOC

Non-methane volatile organic compounds (NMVOCs) are organic compounds, which differ widely in their chemical composition. These organic compounds are often grouped under the NMVOC label as the majority display similar behaviour in the atmosphere. NMVOCs are emitted to air as combustion products, as vapour arising from petrol and solvent use and from numerous other sources. NMVOCs are involved in the photochemical production of ozone and secondary organic aerosols in the atmosphere over a large spatial scale.

Nitrogen Oxides

Studies have shown that oxides of nitrogen (NOx) can cause lung irritation as well as lowering people's resistance to pneumonia and bronchitis and other respiratory infections. In the presence of sunlight, NOx can react to produce a photochemical smog. If hydrocarbons are also present, ozone can be produced, which has a similar health effect to NOx. Although higher concentrations of NOx are found in city areas, resulting ozone concentrations tend to be higher in rural areas, where crop yields can be reduced as a result.

Hydrogen Fluoride

Hydrogen fluoride (HF) is, like hydrogen chloride (HCl), an acidic gas released to air from combustion of fuels that contain trace amounts of the related halogen element – in this case fluorine. Hydrogen fluoride is chemically very similar to HCl and emissions of HF display a similar source pattern to HCl, with 89% of emissions in 1990 and 64% of emissions in 2021 from the combustion of coal. As with HCl, UK emissions have decreased significantly (by 92%) since 1990 due to the declining use of coal across the UK economy.

Hydrogen Chloride

Hydrogen chloride (HCl) is an acidic gas which is primarily released to air from combustion of fuels which contain trace amounts of chlorine. Solid fuels, and particularly coal, do contain chlorine and, as a result, the combustion of coal is responsible for the majority of UK emissions: 96% in 1990 and 50% in 2021. Emissions have fallen by 98% since 1990 as a result of the decline in coal use throughout the UK economy, and the installation of emission controls at coal-fired power stations since 1993.

Hexachlorobenzene

Hexachlorobenzene (HCB) is an organochloride. It is formed as a by-product during the manufacture of other chemicals. It was widely used as a fungicide. Due to HCB's persistence in the environment, it has been banned globally under the Stockholm Convention on persistent organic pollutants. Very little information is available on the health effects of HCB via inhalation, however, the lungs may be affected by repeated or prolonged exposure. It is also considered to be a possible carcinogen.

Dioxins (PCDD/F)

Dioxins and furans (PCDD/F), often simply referred to as 'dioxins'. Emissions of dioxins have declined by 91% over the period 1990 to 2021. Dioxins can arise from any high temperature process where chlorine is present in any form. One of the largest sources of dioxins emissions in the past has been municipal solid waste (MSW) incineration; however, since the early 1990s, all MSW incineration must include energy recovery, as such emissions were recategorized, to be reported under energy generation rather than municipal waste incineration.

Carbon Monoxide

Carbon monoxide (CO) arises from incomplete fuel-combustion and is of concern mainly because of its effect on human health and its role in tropospheric ozone formation. It leads to a decreased uptake of oxygen by the lungs and can lead to a range of symptoms as the concentration increases. Road transport, in particular vehicles with petrol engines, was the largest source of carbon monoxide emissions.

Benzo[a]pyrene

Benzo[a]pyrene (BaP) is of concern because of its effect on human health. It is part of the group of Polycyclic Aromatic Hydrocarbons (PAHs) and is recognized as one of the most carcinogenic of the group. Emissions have decreased by 89% since 1990. Most of this reduction is due to improved control of emissions from aluminium production through the 1990s, this source contributed to 41% of emissions in 1990. Since 2000, UK emissions have decreased by 66%.

Ammonia

Ammonia (NH3) plays an important role in a number of different environmental issues including acidification, nitrification, and eutrophication. It also acts as a precursor to secondary particulate matter, therefore contributing to the related health impacts. The atmospheric chemistry of NH3 means that it can react with other chemicals to produce particles, which can be removed from the atmosphere by rain, or to produce other ammonia compounds, which can be transported long distances.

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