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Carbon
Monoxide (CO) – Carbon monoxide air pollution is produced from the
partial oxidation of carbon-containing compounds, notably in internal-combustion
engines. Carbon monoxide forms in preference to the more usual carbon dioxide
when there is a reduced availability of oxygen present during the combustion
process. It is a colorless and
odorless, tasteless, yet highly toxic gas.
Both state and federal ambient air quality standards have been
established for carbon monoxide. These
standards pertain to one-hour and eight-hour.
The federal standards are 35 parts per million (ppm) for a one-hour
averaging time and 9 ppm for an eight-hour averaging time. The Hawaii standards
are more stringent and are set at 10 ppm for a one-hour averaging time and 5
ppm for an eight-hour averaging time.
The allowable one-hour and eight-hour concentrations may not be
exceeded more than once per year. The
West Oahu Air website shows the measured one-hour and eight-hour
concentrations of carbon monoxide in units of parts per million. Air Quality Index values are calculated and
displayed for one-hour and eight-hour averaging times.
Nitric Oxide (NO) – Nitric oxide is a toxic air
pollutant produced by cigarette smoke, automobile engines, fuel-fired power
plants (fossil and or bio fuels) and other industrial sources. When emitted into the atmosphere, it
generally rapidly converts to other chemical forms, especially in the
presence of ozone. Although nitric
oxide is measured at the West Oahu Air Monitoring Stations and the one-hour
averages are reported on the website, there is no specific state or federal
ambient air quality standard for NO.
Measurements of NO are primarily used to determine levels of nitrogen
dioxide (NO2), for which there are state and federal ambient air quality
standards. The West Oahu Air website
shows the measured one-hour average concentrations in units of parts per
billion (ppb). Because there is no
specific ambient air quality standard for nitric oxide, an Air Quality Index
value is not calculated for this parameter.
Nitrogen Dioxide (NO2) – Nitrogen dioxide is a reddish-brown
toxic gas that has a sharp, biting odor and is a prominent air
pollutant. It is generally not emitted
directly from industrial sources but forms in the atmosphere as a result of
emissions of nitric oxide that undergoes chemical transformations in the
presence of oxygen or ozone. Nitrogen
dioxide is not measured directly at the West Oahu Air Monitoring
Stations. Rather it is measured as the
difference between the measured concentrations of nitric oxide and oxides of nitrogen (NOx). There are both Hawaii and
federal standards for nitrogen dioxide.
The allowable concentration for an annual averaging period is set at a
concentration level of 37 parts per billion (ppb) by Hawaii, while the
federal annual standard is 53 ppb. Until recently, there were no
short-term standards for nitrogen dioxide. In January 2010, the
U.S. EPA published a new one-hour standard for nitrogen dioxide at a level of
100 ppb. Compliance is determined
based on a three-year average of the annual 98th-percentile value of the
daily one-hour maximum. Information shown on the West Oahu Air website
will reflect the new standard and the corresponding Air Quality Index
beginning in fall 2010.
Oxides of Nitrogen (NOx) – The term
oxides of nitrogen (NOx) is the term given to the total concentration of
nitric oxide (NO) plus nitrogen dioxide (NO2). The same instrument is used to measure
three related parameters: nitric oxide, nitrogen dioxide and oxides of
nitrogen, and the measured concentrations are reported in units of parts per
billion (ppb). There are no specific
ambient air quality standards for oxides of nitrogen, but it is used to
determine the nitrogen dioxide concentration (for which there are state and
federal standards). After the nitric
oxide concentration is subtracted from the
oxides of nitrogen concentration, the remainder is nitrogen
dioxide. Because there is no specific
ambient air quality standard for oxides of nitrogen, an Air Quality Index
value is not calculated for this parameter, but the West Oahu Air website
does report the one-hour average concentration of oxides of nitrogen in units of ppb.
Ozone (O3) – Ozone is
generally not emitted directly by air pollution sources but instead is
produced by chemical transformations that occur in the atmosphere between
oxides of nitrogen and oxygen in the presence of sunlight. Ground-level ozone is an air pollutant with
harmful effects on the respiratory systems of humans and animals. However, the ozone layer in the upper
atmosphere filters potentially damaging ultraviolet light from reaching the
earth's surface. Thus, ground-level
ozone can be detrimental to health, whereas upper-level ozone is essential
for protection from the sun’s harmful radiation. Ozone is present in low concentrations
throughout the Earth's atmosphere. Hawaii has
relatively high natural background levels of ozone due to the abundance of
sun and because it is surrounded by water (which reduces natural ozone
destruction). Both state and federal
ambient air quality standards have been established for ground-level ozone. Presently, both the Hawaii standard
and the federal standard limit the eight-hour average ozone concentration to
75 parts per billion (ppb). The
eight-hour average is computed as a moving average; the fourth highest value
in the year may not exceed the level of the standard. The West Oahu Air website shows the measured
one-hour and eight-hour concentrations of ozone in units of parts per
billion. Air Quality Index values are
calculated and displayed for the eight-hour averaging time.
Particulate
Matter (PM10) – Particulate matter air pollution is produced by both natural
sources (such as wind blown dust, sea salt, pollen, etc.) and anthropogenic
sources (such as fuel combustion, rock quarrying/crushing and agriculture). High levels of particulate matter in the
atmosphere are associated with increased respiratory symptoms and disease,
difficulty in breathing, and premature death.
Larger particle sizes are generally considered to be mostly a
nuisance. It is the smaller particle
sizes, generally less than 10 microns, that are considered the most damaging
to health. Both state and federal
ambient air quality standards have been established for particulate
matter. These standards pertain to
24-hour and annual averaging times and to two different size fractions: less
than 10 microns and less than 2.5 microns.
The 10-micron size fraction (PM10) is measured at the West Oahu Air
stations. Both the Hawaii and
the federal standards are set at the same concentration levels: 150
micrograms per cubic meter for a 24-hour average and 50 micrograms per cubic
meter for an annual average. The
allowable 24-hour concentration may not be exceeded more than once per
year. The West Oahu Air website shows
the measured one-hour and 24-hour concentrations of PM10 in units of
micrograms per cubic meter. Air
Quality Index values are calculated and displayed for the 24-hour averaging
time.
Precipitation – Precipitation is
measured at the West Oahu Air stations by a tipping bucket rain gauge mounted
on the roof of the station at a height of about 10 feet above ground. The precipitation reported on the West Oahu
Air website pertains to the hourly total and is reported in units of
inches. The 24-hour total is also
indicated and reported in units of inches.
Sulfur Dioxide (SO2) – Sulfur dioxide
is produced by volcanoes and in various industrial
processes. Since coal and petroleum
often contain sulfur compounds, their combustion generates sulfur
dioxide. Further oxidation of SO2,
usually in the presence of a catalyst such as NO2, forms H2SO4, which results
in acid rain. Sulfur dioxide is an
allergen to which some people are sensitive.
SO2 is associated with increased respiratory symptoms and disease,
difficulty in breathing, and premature death.
Both state and federal ambient air quality standards have been
established for sulfur dioxide. In
June 2010, the U.S. EPA published a new primary one-hour standard for SO2 and
revoked the 24-hour and annual primary standards. The new federal one-hour standard for SO2
is set at 75 ppb. Compliance is
determined based on a three-year average of the annual 99th-percentile value
of the daily one-hour maximum. This revises
the previous standards of 140 ppb over 24 hours (second-highest annual value)
and 30 ppb evaluated over one year. To
date, Hawaii standards remain set at the previous federal levels. Beginning in fall 2010, the West Oahu Air
website will display Air Quality Index values corresponding to the new
one-hour federal standard. Three-hour
and 24-hour average concentrations will also be reported (but AQI values for
these averaging periods will not be calculated).
Temperature – Temperature is measured
at the West Oahu Air stations at a height of approximately 30 feet above
ground. The temperature reported on the West Oahu
Air website pertains to the hourly average and is reported in units of
degrees Fahrenheit (deg F).
Wind Direction – Wind direction is
measured at the West Oahu Air stations at the standard height of 33 feet
above ground by a wind vane mounted on a tower. The wind direction reported on the West
Oahu Air website pertains to the hourly average and is reported in terms of
the direction sector from which the wind is blowing. A blowing wind from the north is indicated
as “N”, a wind from the northeast is indicated at “NE”, etc.
Wind Speed – Wind speed is measured at
the West Oahu Air stations at the standard height of 33 feet above ground by
a propeller anemometer mounted on a tower. The wind
speed reported on the West Oahu Air website pertains to the hourly average
and is reported in units of miles per hour (mph).
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