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Acid Deposition |
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Total atmospheric deposition of acidity is determined using both wet
and dry deposition measurements. Wet deposition is the portion dissolved
in cloud droplets and is deposited during rain or other forms of
precipitation. Dry deposition is the portion deposited on dry surfaces
during periods of no precipitation as particles or in a gaseous form.
Although the term "acid rain" is widely recognized, the dry deposition
portion ranges from 20 to 60 percent of total deposition. |
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Acid Rain |
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When atmospheric pollutants such as sulphur dioxide and nitrogen
oxides mix with water vapour in the air, they are converted to sulphuric
and nitric acids. These acids make the rain acidic, hence the term "acid
rain". Acid rain is defined as any rainfall that has an acidity level
beyond what is expected in non-polluted rainfall. Acidity is measured
using a pH scale, with the number 7 being neutral. Consequently, a
substance with a pH value of less than 7 is acidic, while one of a
value greater than 7 is basic. Generally, the pH of 5.6 has been used
as the baseline in identifying acid rain. Thus any precipitation
that has a pH value of less than 5.6 is considered to be acid
precipitation. |
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Air Pollution Bandings |
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Four bands are used to describe
levels of pollution. The bands are low, moderate, high and very high.
Healthy people do not normally notice any effects from air pollution,
except occasionally when air pollution is 'very high'. |
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Air Pollution Index |
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A numerical index for air pollution from 1 to 10 related to the air
quality bands of ‘low’, ‘moderate’, ‘high’ or ‘very high’. |
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Air Pollution Information Service |
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The Air Pollution Information Service provides - free of charge -
detailed, easy-to-understand information on air pollution. This information
is particularly important to people with medical conditions which air
pollution may make worse. The latest information is available on this web site.
The Service gives summaries and detailed information on current pollution levels. |
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Air Quality Standards |
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Standards are the concentrations of 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. |
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Air Quality Objectives |
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Objectives are policy targets generally expressed as a maximum ambient
concentration to be achieved, either without exception or with a permitted
number of exceedences, within a specified timescale. |
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Ambient Air |
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The air occurring at a particular time and place outside of structures.
Often used interchangeably with "outdoor air." |
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Annual Mean |
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The average of the concentrations measured for each pollutant for one
year. Usually this is for a calendar year, but some species are reported for
the period April to March, known as a pollution year. This period avoids
splitting a winter season between two years, which is useful for
pollutants that have higher concentrations during the winter months. |
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Atmospheric Emissions Inventory (AEI) |
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AEI compiles estimates of
emissions to the atmosphere from Gibraltar sources such as
cars, trucks, power stations and industrial plant. These
emissions are estimated to help to find ways of reducing
the impact of human activities on the environment and
our health. |
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Automatic Monitoring |
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Monitoring is usually termed 'automatic' (or 'continuous') if it
produces real-time measurements of pollutant concentrations. Automatic
fixed point monitoring methods exist for a variety of different pollutants
and these can provide high resolution data averaged over very short time
periods. |
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Benzene (C6H6) |
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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. |
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Black Smoke |
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Black Smoke consists of fine particulates. These particles can be
hazardous to health especially in combination with other pollutants which
can adhere to the particulate surfaces. Black Smoke is emitted mainly from
fuel combustion. Following the large reductions in domestic coal use the
main source is diesel engined vehicles. Black smoke is measured by its
blackening effect on filters. It has been measured for many years in
the Gibraltar. Now interest is moving to the mass of small particles
regardless of this blackening effect. |
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1,3-Butadiene (C4H6) |
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1,3-butadiene, like benzene, is organic compound emitted into the
atmosphere principally from fuel combustion of petrol and diesel vehicles.
Unlike benzene, however, it is not a constituent of the fuel but is
produced by the combustion of olefins. 1,3-butadiene is also an important
chemical in certain industrial processes, particularly the manufacture
of synthetic rubber. The dominant source of 1,3-butadiene in the atmosphere is the motor
vehicle. 1,3-Butadiene is a known, potent, human carcinogen. |
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Carbon Monoxide (CO) |
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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. |
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COMEAP |
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The UK Committee on the Medical Effects of Air Pollutants COMEAP is an
Advisory Committee of independent experts that provides advice to the UK
Government Departments and Agencies on all matters concerning the
potential toxicity and effects upon health of air pollutants. |
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Data Capture |
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Gives the percentage of all the possible measurements for a given
period that were validly measured. |
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Days with Exceedences |
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The number of days in which at least one period has a concentration
greater than, or equal to, the relevant air quality standard (the averaging
period will be that defined by that standard). |
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Since air quality standards cover different time periods
(15 min average, 24 hour running mean etc.) this gives a useful way of
comparing data for different pollutants. |
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Diffusion Tube Samplers |
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Passive diffusion tube samplers collect nitrogen dioxide and other
pollutants by molecular diffusion along an inert tube to an efficient
chemical absorbent. After exposure for a known time, the absorbent
material is chemically analysed and the concentration calculated. |
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EMEP (Co-operative Programme for Monitoring and Evaluation of the Long-Range Transmission ofAir pollutants in Europe) |
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The EMEP programme consists on three main elements: (1) collection of
emission data, (2) measurements of air and precipitation quality and (3)
modelling of atmospheric transport and deposition of air pollution. EMEP
regularly reports on emissions, concentrations and/or depositions of air
pollutants, the quantity and significance of transboundary fluxes and
related exceedences to critical loads and threshold levels. The EMEP
programme is carried out in collaboration with a broad network of
scientists and national experts that contribute to the systematic
collection, analysis and reporting of emission data, measurement
data and integrated assessment results. |
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Emission Factor |
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The relationship between the amount of pollution produced and the
amount of raw material processed or burned. For mobile sources, the
relationship between the amount of pollution produced and the number of
vehicle miles travelled. By using the emission factor of a pollutant and
specific data regarding quantities of materials used by a given source,
it is possible to compute emissions for the source. This approach is
used in preparing an emissions inventory. |
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Emission Inventories |
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Emission inventories are estimates of the amount and the type of
pollutants that are emitted to the air each year from all sources. There
are many sources of air pollution, including traffic, household heating
and industrial processes. |
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EU Directives |
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The European Union has been legislating to control emissions of air
pollutants and to establish air quality objectives for the last two decades.
After many years of a somewhat piece-meal approach, ambient air quality
legislation is now being consolidated. Directive 96/62/EC on ambient
air quality assessment and management, the so called Air Quality
Framework Directive, sets a strategic framework for tackling air
quality consistently by setting European-wide limit values for twelve
air pollutants in a series of daughter directives. These supersede and extend existing European legislation. |
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Exceedence |
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A period of time where the concentration of a pollutant is greater
than, or equal to, the appropriate air quality criteria. For air quality
standards an exceedence is a concentration greater than the standard
value. For air quality bands an exceedence is a concentration greater
than, or equal to, the upper band threshold. |
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Global Warming |
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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. |
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Greenhouse Gases |
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Atmospheric gasses such as carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, ozone
and water vapor that slow the passage of re-radiated heat through the Earth's atmosphere. |
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Hydrocarbons |
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Compounds containing various combinations of hydrogen and carbon atoms. They may be emitted into
the air by natural sources (eg. trees) and as a result of fossil and vegetative fuel combustion, fuel
volatilization and solvent use. Hydrocarbons are a major contributor to smog. |
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Maximum hourly average |
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The highest hourly reading of air pollution obtained during the time period under study. |
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Microgrammes per cubic metre (µg/m3) |
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A measure of concentration in terms of mass per unit volume. A concentration of 1 µg/m3 means that one cubic metre of air contains one microgramme (millionth of a gramme) of pollutant. |
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Oxides of Nitrogen (NOx) |
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Combustion processes emit a mixture of oxides of nitrogen, primarily
nitric oxide (NO) and nitrogen dioxide (NO2), collectively termed NOx.
Nitrogen dioxide has a variety of environmental and health impacts. 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 dioxide emissions can also be further oxidised in
air to acid gases, which contribute to the production of acid
rain. |
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Ozone (O3) |
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Ozone (O3) is not emitted directly into the atmosphere, but is a
secondary pollutant produced by reaction between nitrogen dioxide (NO2),
hydrocarbons and sunlight. Whereas nitrogen dioxide (NO2) acts as a
source of ozone, nitrogen oxide (NO) destroys ozone acting as a local
sink. For this reason, ozone levels are not as high in urban areas
(where high levels of NO are emitted from vehicles) as in rural areas.
Ozone levels are usually highest in rural areas, particularly in hot,
still, sunny weather conditions giving rise to "summer smog". |
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PAHs |
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Polycyclic Aromatic Hydrocarbons (PAHs) belong to a large group of
organic compounds; several individual PAHs have been shown to be
carcinogenic. An EU Daughter Directive has recommended a standard for PAHs of 1 ng/m3
using benzo[a]pyrene as a marker compound. |
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Particulate matter (PM10) |
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Particulate matter consists of very small liquid and solid particles
floating in the air. Of greatest concern to public health are the
particles small enough to be inhaled into the deepest parts of the lung.
These particles are less than 10 microns in diameter - about 1/7th the
thickness of the a human hair - and are known as PM10 .Concern about
the potential health impacts of PM10 has increased very rapidly over
recent years. Increasingly, attention has been turning towards
monitoring of the smaller particle fraction (PM2.5) capable of
penetrating deepest into the lungs, or even to total particle
numbers. |
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Percentile |
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A value that is the rank at a particular point in a collection of
data. For instance, a 98th percentile of values for a year is the value
that 98% of all the data in the year fall below, or equal. |
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POPS |
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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) |
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ppb |
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parts per billion. The concentration of a pollutant in air in terms
of volume ratio. A concentration of 1 ppb means that for every billion
(109) units of air, there is one unit of pollutant present. |
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ppm |
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parts per million. The concentration of a pollutant in air in terms
of volume ratio. A concentration of 1 ppm means that for every million
(106) units of air, there is one unit of pollutant present. |
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Running mean |
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This is a mean - or series of means - calculated for overlapping time
periods, and is used in the calculation of several of the national air
quality standards.
For instance, an 8 hour running mean is calculated every hour, and
averages the values for eight hours. The period of averaging is stepped
forward by one hour for each value, so running mean values are given for
the periods 00:00 - 07:59, 01:00 - 08:59 etc. By contrast a
non-overlapping mean is calculated for consecutive time periods,
giving values for the periods 00:00 - 07:59, 08:00 - 15:59 and so on.
There are, therefore, 24 possible 8-hour means in a day (calculated
from hourly data) and 3 non-overlapping means. |
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Sulphur Dioxide (SO2) |
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Sulphur dioxide is a corrosive acid gas which combines with water
vapour in the atmosphere to produce acid rain. Both wet and dry deposition
have been implicated in the damage and destruction of vegetation and in
the degradation of soils, building materials and watercourses. SO2 in
ambient air is also associated with asthma and chronic bronchitis. |
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TOMPS |
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Toxic organic micro pollutants dioxins (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. |
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Volatile organic compounds (VOCs) |
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Carbon-containing compounds that evaporate into the air (with a few
exceptions). VOCs contribute to the formation of smog and/or may
themselves be toxic. VOCs often have an odour, and some examples include
gasoline, alcohol, and the solvents used in paints |
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Zones and Agglomerations |
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Gibraltar is considered as a single zone for the purposes of air
pollution monitoring, in accordance with EC Directive
96/62/EC. An Agglomeration is defined
as any urban area with a population greater than 250.000 |
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