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Glossary of Environmental Terms

Achene – A dry fruit with one seed. Product of one carpel.

Acuminate – Leaf-tip tapering to a point – usually with concave sides.

Adventitious root – Any root that grows from an unusual plant tissue other than the central root tissues (e.g. from the outside of an old root, a stem or a leaf).

Air quality objective – Air quality policy targets generally expressed as a maximum ambient pollutant concentration to be achieved, either without exception or with a permitted number of exceedences, within a specified timescale.

Air quality standard –The concentrations of air pollutants in the atmosphere which can broadly be taken to achieve a certain level of environmental quality. The standards are based on assessment of the effects of each pollutant on human health including the effects on sensitive sub-groups.

Allelopathy – An effect whereby one plant chemically discourages growth of others in its environment, e.g. by toxins contained in fallen leaves or chemicals released by plant roots.

Alternate – Arrangement of leaves which arise singly on a stem, each one on the other side of the stem from the leaf below or above it.

Ambient air – The air occurring at a particular time and place outside of structures. Often used interchangeably with “outdoor air”.

Angiosperm – A flowering, seed-bearing plant in which the ovules are enclosed within the ovary.

Annual – Plants that complete their entire life-cycle, from seed to reproduction to death, within one year.

Anther – On a plant, the part of the stamen in which pollen is produced.

Apex – The tip of a plant root or shoot.

AQAP – Air Quality Action Plan. The document produced by a local authority to improve air quality in its area.

AQMA – Air Quality Management Area. An area designated by a local authority as requiring measures to reduce air pollution concentrations to acceptable levels.

AURN – Automatic Urban and Rural (air quality monitoring) Network, managed by contractors on behalf of DEFRA and the Devolved Administrations.

Axil – The point on a plant leaf where the upper side of the petiole joins the stem.

Below Ground Level (BGL) – A term used in topographical mapping to describe the distance below ground of a particular datum.

Benzene (C6H6) – Benzene is an aromatic organic compound which is a minor constituent of petrol (about 2% by volume). The main sources of benzene in the atmosphere in Europe are the distribution and combustion of petrol. Combustion by petrol vehicles is the largest component (70% of total emissions) whilst the refining, distribution and evaporation of petrol from vehicles accounts for approximately a further 10% of total emissions. Benzene is emitted in vehicle exhaust not only as unburnt fuel but also as a product of the decomposition of other aromatic compounds. Benzene is a known human carcinogen.

Biennial – When the lifecycle of a plant, from germination, flowering to death, occurs in two years.

Bioaccumulate – Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost. Thus, the longer the biological half-life of the substance the greater the risk of chronic poisoning, even if environmental levels of the toxin are very low.

Biological Control – Artificial control of pests and diseases by using other organisms (e.g. using the Myxomatosis virus to control rabbit populations and fungal diseases to control Japanese knotweed).

Blade – Either the whole plant leaf, excluding the petiole, or all parts of the leaf except the midrib, i.e. the lamina.

Blue billy – A soil contaminant often associated with gas works and spent oxides. Ferric and ferrous cyanides.

Bract – A modified plant leaf protecting the inflorescence.

BTEX – A common mixture of the hydrocarbon pollutants benzene, toluene, ethylbenzene and xylene.

Carbon Dioxide (CO2) – Carbon dioxide is produced by all animals, plants, fungi and microorganisms during respiration and is used by plants during photosynthesis to make sugars. It is also generated as a by-product of the combustion of fossil fuels and is an important greenhouse gas because it transmits visible light but absorbs strongly in the infrared.

Carbon monoxide (CO) – A colourless, odourless gas resulting from the incomplete combustion of hydrocarbon fuels. CO interferes with the blood’s ability to carry oxygen to the body’s tissues and results in adverse health effects.

Carpel – The female reproductive unit of a flower, consisting of the ovary with ovules.

Clone – Genetically identical, asexually derived offspring of a plant or animal.

Colloid – A fluid substance where minute particles of one substance are dispersed, without settling, in another.

COMEAP – Committee on the Medical Effects of Air Pollutants. COMEAP is an Advisory Committee of independent experts that provides advice to UK Government Departments and Agencies on all matters concerning the potential toxicity and effects upon health of air pollutants.

Cordate – Heart-shaped. Used to describe the shape of some plants’ leaves.

Corporate Social Responsibility (CSR) – Corporate Social Responsibility is a concept whereby organisations consider the interests of society by taking responsibility for the impact of their activities on customers, employees, shareholders, communities and the environment in all aspects of their operations.

Crown – The base of an herbaceous plant where roots or rhizomes and aerial stems or resting buds meet. Also used to describe the top of a tree, including the branches and leaves.

Cuspidate – Terminating abruptly into a sharp point. Often used to describe the shape of some plant leaf forms.

Defra – Department for Environment, Food and Rural Affairs. DEFRA (or Defra) is the UK Government department responsible for environmental protection, food production and standards, agriculture, fisheries and rural communities in England. Concordats set out agreed frameworks for co-operation between it and the other, devolved, administrations of the UK.

Dense non-aqueous phase liquids (DNAPL) – Dense non-aqueous phase liquids (DNAPL) are hydrocarbons that exist as a separate immiscible phase when in contact with water and/or air. DNAPL have a density greater than water e.g. solvents.

Department for Transport (DfT) – The DfT is the UK Government department responsible for the English transport network and transport matters in Scotland, Wales and Northern Ireland which are not devolved.

Design Manual for Roads and Bridges (DMRB) – The Design Manual for Roads and Bridges (DMRB) is a series of 15 volumes that provide official standards, advice notes and other documents relating to the design, assessment and operation of trunk roads, including motorways in the United Kingdom.

Dioecious – Bearing male or female flowers on different plants. This is a way of avoiding self-fertilisation (Japanese knotweed is an example of a dioecious plant species).

Dispersal – The movement of seeds away from the parent plant, e.g. by wind or birds.

Ecology – The study of organisms in relation to their environment.

Ecosystem – An ecological system in which organisms interact with each other and their non-living environment and in which there is a more or less closed cycle of nutrients.

Environmental Impact Assessment (EIA) – An Environmental Impact Assessment (EIA) is an assessment of the likely positive and/or negative influence a project may have on the environment. The purpose of the assessment is to ensure that decision-makers consider environmental impacts before deciding whether to proceed with new projects.

Environmental Management System (EMS) – Environmental Management System (EMS). An EMS is designed to enable an organisation to assess/manage and improve its environmental impacts through the develop an environmental policy, objectives, targets, procedures and auditing, taking into account environmental legal requirements and other requirements which the company subscribes. Two main EMS standards are ISO BS EN 14001 and Eco-Management and Audit Scheme (EMAS).

Eutrophic – Habitats with high levels of nutrients, sometimes due to human activity.

Evergreen – A plant (often tree) having green leaves throughout the year.

Expert Panel on Air Quality Standards (EPAQS) – The Expert Panel on Air Quality Standards (EPAQS) was set up by the UK Government in 1991 to provide independent advice on air quality issues, in particular the levels of pollution at which no or minimal health effects are likely to occur. Members of the Panel are primarily drawn from those eminent in the fields of health research, practice and teaching. The Panel’s recommendations were adopted as the benchmark standards in the National Air Quality Strategy.

Flood Risk Assessment (FRA) – Flood Risk Assessments are undertaken to ensure that flood risk is taken into account during the planning process, to prevent inappropriate development in high risk areas, and to direct development away from areas at highest risk of flooding.

Flora – The total of plant species in a particular region, country, continent etc.

Food Web – Food webs describe the feeding relationships between different organisms within an ecosystem.

Fruit – The fertilised and ripened plant ovary, with any attached structures. The function of the fruit is to protect the seeds as they develop and to help their dispersal.

Germination – The first stage in the growth of a plant seed into a seedling. Germination begins with the seed absorbing water and ends with the production of the first true leaves.

Gibberellic Acid – A growth stimulating and dormancy breaking plant growth regulator.

Glabrous – Smooth, hairless. Often used to describe the surface of plant leaves and stems.

Gland – A structure, whose function is to secrete or excrete substances, e.g. oils.

Global warming – An increase in the temperature of the Earth’s troposphere. Global warming has occurred in the past as a result of natural influences, but the term is most often used to refer to the warming predicted by computer models to occur as a result of increased emissions of greenhouse gases, such as CO2 and methane.

Greenhouse gases – Atmospheric gases such as carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, ozone, and water vapour that slow the passage of re-radiated heat through the Earth’s atmosphere.

Gymnosperm – Conifers, Cycads and Ginkgo; seed-bearing plants in which the ovules are not enclosed in an ovary.

Habitat – The place or kind of place in which an organism, or community is found.

Hybrid – A plant resulting from the cross-fertilisation of two different species, subspecies or varieties.

Hydrocarbon – Compounds containing various combinations of hydrogen and carbon atoms. They may be emitted into the air by natural sources (e.g. trees) and as a result of fossil and vegetative fuel combustion, fuel volatilization, and solvent use. Hydrocarbons are a major contributor to smog. Their historical storage and use in liquid form can cause contamination of the underlying soil, ground water and watercourses.

Indehiscent – A plant that does not have a natural mechanism for its fruit to open, on its own, in order to release its seed. e.g. many nuts and fleshy fruits.

Inflorescence – A plant shoot containing flowers and no leaves.

Internode – The space on a plant stem between two nodes.

Lamina – The parts of a leaf on either side of the midrib.

Lanceolate – Lance-shaped, tapering to a spear-point. Often used to describe the shape of some plant leaves.

Leaf – A plant organ whose function is photosynthesis and transpiration. Leaves are produced from buds on the stem.

Light non-aqueous phase liquids (LNAPL) – Light non-aqueous phase liquids (LNAPL) are hydrocarbons which exist as a separate immiscible phase when in contact with water. LNAPL have a lighter density than water, e.g. oils and VOCs.

Local Air Quality Management (LAQM) – Local Air Quality Management (LAQM) requires local authorities to periodically review and assess the current and future quality of air in their areas. A local authority must designate an Air Quality Management Area (AQMA) if any of the air quality objectives are not likely to be met in its area in the relevant period.

Metabolism – The chemical reactions which occur in an organism or cell, to release energy for vital processes.

Microgrammes per cubic metre (µg.m‑3) – A measure of concentration in terms of mass per unit volume. A concentration of 1μg.m-3 means that one cubic metre of air contains one microgram (millionth of a gramm) of pollutant.

Midrib – The central vein of a leaf.

Monoecious – Bearing both male and female flowers separately on the same plant, or having individual flowers bearing both male and female parts.

National Air Quality Information Archive (NAQIA) – The National Air Quality Information Archive (NAQIA) is a UK website ( that is prepared and hosted by AEA Energy & Environment, on behalf of Defra and the Devolved Administrations. It holds a wide range of data, information and guidance on air quality across the UK.

Nitrogen dioxide (NO2) – Nitrogen dioxide (NO2) is an atmospheric pollutant that mainly forms from the oxidation of NO. It is also emitted, to a lesser extent, directly from the combustion of fossil fuels. NO2 has a variety of environmental and health effects. It is a respiratory irritant which may exacerbate asthma and possibly increase susceptibility to infections. In the presence of sunlight, it reacts with hydrocarbons to produce photochemical pollutants such as ozone.

Nitrogen monoxide (NO) – Nitrogen monoxide (NO), a.k.a. nitric oxide, is an odourless, colourless gas which is produced during high temperature burning of fossil fuels. Once it is mixed with air it quickly combines with oxygen, forming nitrogen dioxide (NO2).

nm – Nanometres. One billionth of a metre.

Node – The point on a plant stem from which a leaf grows.

Non aqueous phase liquids(NAPL) – Non aqueous phase liquids (NAPL) are hydrocarbons that exist as a separate immiscible phase when in contact with water and/or air. NAPL are made up of DNAPL and LNAPL.

Nut – A dry indehiscent fruit with a hard wall, containing one seed.

Obovate – Egg-shaped, with the small end towards the stem. Often used to describe the shape of some plant leaves.

Opposite – The arrangement of two leaves which arise at the same node, on either side of a plant stem.

Ovary – The interior of the carpel of a plant flower. The ovary has a thick wall, which develops into the fruit after the ovules inside have been fertilised.

Ovate – Rounded at both ends; broadest below the middle. Often used to describe the shape of some plant leaves.

Ovule – The unfertilised seed of a plant.

Oxides of Nitrogen(NOX) – Fossil fuel combustion processes emit a mixture of oxides of nitrogen, primarily nitric oxide (NO) and nitrogen dioxide (NO2), which are collectively termed NOX.

Ozone (O3) – Ozone (O3) is not emitted directly into the atmosphere, but is a secondary pollutant produced by the reaction between nitrogen dioxide (NO2), hydrocarbons and sunlight.

PAHs – Polycyclic Aromatic Hydrocarbons (PAHs) belong to a large group of organic compounds; several individual PAHs have been shown to be carcinogenic.

Panicle – A branched flowerhead.

Peak Particle Velocity (PPV) – Peak Particle Velocity (PPV) is used to measure vibration through a solid surface. When a vibration is measured, the point at which the measurement takes place can be considered to have a particle velocity. This particle vibration will take place in three dimensions (x, y and z) and will usually end up back where it started. The Peak Particle Velocity is the maximum velocity that is recorded during a particular event.

Peduncle – The stalk of a group of flowers.

Perennation – The survival of an individual plant, or of a dormant plant organ, over successive years or during unfavourable seasons.

Perennial – A plant lasting 3 or more seasonal cycles.

Persistent Organic Pollutants (POPs) – Persistent Organic Pollutants (POPs) are chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health and the environment. These include dioxins and furans (see TOMPS)

Petal – An often brightly-coloured modified plant leaf, to attract pollinators.

Petiole – The stalk of a leaf, which joins it to a node on the stem.

pH – A measure of the alkalinity or acidity of a medium. Neutral is represented by 7; with lower figures indicating increased acidity and higher figures, increased alkalinity.

Phloem – Complex vascular tissue involved in the-transport of nutrients throughout a plant.

Photosynthesis – The manufacture, fuelled by solar energy, of complex organic molecules within the green tissues of plants, from the raw materials, carbon dioxide and water.

PM10Airborne particulate matter with an aerodynamic diameter of less than 10 micrometres (i.e. <100th of a millimetre). These suspended particles are small enough to be inhaled into the deepest parts of the lung. Concern about the potential health impacts of PM10 has increased very rapidly over recent years.

PM2.5Airborne particulate matter with an aerodynamic diameter of less than 2.5 micrometres (i.e. <400th of a millimetre). In recent years attention has been turning towards monitoring the PM2.5 particle fraction, which is smaller than the more commonly quoted PM10 fraction. It is believed that these smaller particles can penetrate deeper into the lung and cause more damage than PM10 particles.

ppb parts per billion – The concentration of a pollutant in terms of volume ratio. A concentration of 1 ppb means that for every billion (109) units of air/soil/water, there is one unit of pollutant present.

ppm parts per million – The concentration of a pollutant in terms of volume ratio. A concentration of 1 ppm means that for every billion (106) units of air/soil/water, there is one unit of pollutant present.

Primordium – A tissue or plant organ in its earliest distinct state.

Pubescent – Covered with short, fine, soft hairs. Often used to describe the surface of plant stems and leaves.

Raceme – A group of flowers arranged along a single peduncle.

Rhizomatous – Bearing specialised stems, rooting and shooting from the nodes.

Rhizome – A stem that extends by growing underground, bearing buds that produce aerial shoots and adventitious roots. This is a way of vegetative reproduction and perennation, whereby the extending rhizome eventually develops into groups of new plants.

Riparian – Of or inhabiting a riverbank.

Rosette – Leaves radiating from a single crown, at ground level.

Ruderal – Applied to plants which inhabit old fields, waysides or waste land.

Samara – A dry fruit with wing-like outgrowths to aid in its dispersal by wind.

Sepal – A part of the outer flower-protecting structure.

Serrate – Bearing a saw-toothed edge. Often used to describe the form of a leaf on some types of plant.

Sessile – Stalkless or apparently so. Often used to describe how a leaf or fruit is attached to a plant stem.

Stamen – The male pollen-producing organ in a flower.

Stigma – The pollen accepting organ in a flower.

Strategic Environmental Assessment (SEA) – Strategic Environmental Assessment (SEA) is a system of incorporating environmental considerations into policies, plans and programmes. It is sometimes referred to as Strategic Environmental Impact Assessment. An SEA is usually conducted before a corresponding EIA is undertaken. This should mean that information on the environmental impact of a plan will be able to cascade down through the tiers of decision making and be used in an EIA at a later stage.

Style – The elongated narrow structure supporting the pollen receptor in a flower.

Sustainable Urban Drainage Systems (SUDS) – Sustainable Urban Drainage Systems (SUDS) are designed to reduce the potential of flooding on new and existing urban developments. Unlike traditional urban stormwater drainage systems, they also help to protect and enhance ground water quality. Sustainable Drainage System (SuDS) are the same as SUDS.

TOMPs – Toxic organic micro pollutants (TOMPs) are produced by the incomplete combustion of fuels. They comprise a complex range of chemicals some of which, although they are emitted in very small quantities, are highly toxic or carcinogenic. Compounds in this category include: PAHs (Polycyclic Aromatic Hydrocarbons); PCBs (PolyChlorinated Biphenyls); dioxins; and furans.

Troposphere – The troposphere is the lowest portion of the Earth’s atmosphere, which includes the portion where air pollutants are emitted, mixed, react with each other and where people are exposed to their effects.

UKAQS – The Air Quality Strategy for England, Scotland, Wales and Northern Ireland. This describes the plans drawn up by the Government and the devolved administrations to improve and protect ambient air quality in the UK in the medium-term. The Strategy sets objectives for the main air pollutants to protect health.

Vein – One of the many lines which can be seen on the surface of a leaf, marketing the position of the vascular bundle.

Vibration Dose Value (VDV) – Vibration Dose Value (VDV) is a metric used in vibration monitoring. It is calculated by taking the fourth root of the integral of the fourth power of acceleration after it has been frequency-weighted. The frequency-weighted acceleration is measured in m.s-2 and the time period over which the VDV is measured is in seconds. This yields VDVs in m.s-1.75.

Volatile Organic Compounds (VOC) – Volatile Organic Compounds. Carbon-containing compounds that are volatile (i.e. evaporate with relative ease). VOCs contribute to the formation of smog and can be toxic. VOCs often have an odour and some examples include petrol, alcohol, and the solvents used many in paints and glues.

Whorl – Where three or more plant organs are arranged around a node.