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53-486: The six criteria air pollutants (CAP), or criteria pollutants , for which limits are set in the NAAQS are ozone (O 3 ), atmospheric particulate matter (PM 2.5 /PM 10 ), lead (Pb), carbon monoxide (CO), sulfur oxides (SO x ), and nitrogen oxides (NO x ). These are typically emitted from many sources in industry , mining , transportation , electricity generation and agriculture . In many cases they are

106-457: A planet 's atmosphere . Trace gases in Earth's atmosphere are gases other than nitrogen (78.1%), oxygen (20.9%), and argon (0.934%) which, in combination, make up 99.934% of its atmosphere (not including water vapor). The abundance of a trace gas can range from a few parts per trillion ( ppt ) by volume to several hundred parts per million by volume ( ppmv ). When a trace gas is added into

159-667: A sink is when a trace gas is removed from the atmosphere. Some of the sinks of trace gases are chemical reactions in the atmosphere, mainly with the OH radical , gas-to-particle conversion forming aerosols , wet deposition and dry deposition . Other sinks include microbiological activity in soils. Below is a chart of several trace gases including their abundances, atmospheric lifetimes, sources, and sinks.   Trace gases – taken at pressure 1 atm The Intergovernmental Panel on Climate Change (IPCC) states that "no single atmospheric lifetime can be given" for CO 2 . This

212-500: A VOC whose atmospheric concentration has increased tremendously during the last century, contributes to ozone formation but on a global scale rather than in local or regional photochemical smog episodes. In situations where this exclusion of methane from the VOC group of substances is not obvious, the term Non-Methane VOC (NMVOC) is often used. Indoors ozone is produced by certain high-voltage electric devices (such as air ionizers ), and as

265-531: A by-product of other types of pollution. Outdoor air used for ventilation may have sufficient ozone to react with common indoor pollutants as well as skin oils and other common indoor air chemicals or surfaces. Particular concern is warranted when using "green" cleaning products based on citrus or terpene extracts, because these chemicals react very quickly with ozone to form toxic and irritating chemicals as well as fine and ultrafine particles . The chemical reactions involved in tropospheric ozone formation are

318-444: A constituent of smog . Its levels have increased significantly since the industrial revolution, as NOx gasses and VOCs are some of the byproducts of combustion. With more heat and sunlight in the summer months, more ozone is formed which is why regions often experience higher levels of pollution in the summer months. Although the same molecule, ground-level ozone can be harmful to human health, unlike stratospheric ozone that protects

371-518: A given listed pollutant or class of pollutants." The standards are listed in 40 CFR 50 . Primary standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory diseases. Secondary standards are designed to protect public welfare, damage to property, transportation hazards, economic values, and personal comfort and well-being from any known or anticipated adverse effects of

424-484: A maximum concentration at the tropopause . About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere. Although tropospheric ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects . Ozone in the troposphere is considered a greenhouse gas , and as such contribute to global warming . as reported in IPCC reports. Actually, tropospheric ozone

477-453: A national level. The Clean Air Act requires the EPA to set US National Ambient Air Quality Standards (NAAQS) for the six CAPs. The NAAQS are health based and the EPA sets two types of standards: primary and secondary. The primary standards are designed to protect the health of 'sensitive' populations such as asthmatics, children, and the elderly. The secondary standards are concerned with protecting

530-508: A pollutant. A district meeting a given standard is known as an "attainment area" for that standard, and otherwise a "non-attainment area". Standards are required to "accurately reflect the latest scientific knowledge," and are reviewed every five years by a Clean Air Scientific Advisory Committee (CASAC), consisting of "seven members appointed by the EPA administrator ." EPA has set NAAQS for six major pollutants listed as below. These six are also

583-464: A repercussion on climate, as well. Also, since climate change is causing sea ice to melt, what occurs is the sea ice releases molecular chlorine , which reacts with UV radiation to produce chlorine radicals. Because chlorine radicals are highly reactive, they can expedite the degradation of methane and tropospheric ozone and the oxidation of mercury to more toxic forms. Ozone production rises during heat waves , because plants absorb less ozone. It

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636-428: A series of complex cycles in which carbon monoxide and VOCs are oxidised to water vapour and carbon dioxide. The reactions involved in this process are illustrated here with CO but similar reactions occur for VOC as well. The oxidation begins with the reaction of CO with the hydroxyl radical ( OH). The radical intermediate formed by this reacts rapidly with oxygen to give a peroxy radical HO 2 An outline of

689-457: A warming climate alters humidity and wind conditions in some parts of the world, resulting in a reduction in the frequency of surface cyclones. Changes in air temperature and water content affect the air's chemistry and the rates of chemical reactions that create and remove ozone. Many chemical reaction rates increase with temperature and lead to increased ozone production. Climate change projections show that rising temperatures and water vapour in

742-487: Is a trace gas in the troposphere (the lowest level of the Earth's atmosphere ), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere , where the ozone layer (2 to 8 parts per million ozone) exists which is located between 10 and 50 kilometers above the Earth's surface. The troposphere extends from

795-412: Is considered the third most important greenhouse gas after CO 2 and CH 4 , as indicated by estimates of its radiative forcing . Photochemical and chemical reactions involving ozone drive many of the chemical processes that occur in the troposphere by day and by night. At abnormally high concentrations (the largest source being emissions from combustion of fossil fuels ), it is a pollutant , and

848-507: Is estimated that curtailed ozone absorption by plants could be responsible for the loss of 460 lives in the UK in the hot summer of 2006. A similar investigation to assess the joint effects of ozone and heat during the European heat waves in 2003, concluded that these appear to be additive. Trace gas Trace gases are gases that are present in small amounts within an environment such as

901-650: Is known to have the following health effects at concentrations common in urban air: It was observed in the 1990s that ground-level ozone can advance death by a few days in predisposed and vulnerable populations. A statistical study of 95 large urban communities in the United States found significant association between ozone levels and premature death. The study estimated that a one-third reduction in urban ozone concentrations would save roughly 4000 lives per year (Bell et al., 2004). Tropospheric ozone causes approximately 22,000 premature deaths per year in 25 countries in

954-457: Is measured in a column from the surface to the top of the atmosphere, and is dominated by high concentrations of stratospheric ozone. Typical units of measure for this purpose include the Dobson unit and millimoles per square meter (mmol/m ). The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOCs), react in

1007-438: Is mostly due to the high rate of growth and large cumulative magnitude of the disturbances to Earth's carbon cycle by the geologic extraction and burning of fossil carbon. As of year 2014, fossil CO 2 emitted as a theoretical 10 to 100 GtC pulse on top of the existing atmospheric concentration was expected to be 50% removed by land vegetation and ocean sinks in less than about a century. A substantial fraction (20-35%)

1060-446: Is specifically for the troposphere. LIDAR is a common ground-based remote sensing technique that uses laser to measure ozone. The Tropospheric Ozone Lidar Network (TOLNet) is the network of ozone observing lidars across the United States. Ozonesondes are a form of in situ , or local ozone measuring instruments. An ozonesonde is attached to a meteorological balloon, so that the instrument can directly measure ozone concentration at

1113-461: Is the coefficient of variation , τ r is the residence time in years, and b is an empirical constant, which Junge originally gave as 0.14 years. As residence time increases, the concentration variability decreases. This implies that the most reactive gases have the most concentration variability because of their shorter lifetimes. In contrast, more inert gases are non-variable and have longer lifetimes. When measured far from their sources and sinks,

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1166-399: Is their molecular structure. For example, carbon dioxide has two basic modes of vibration that create a strong dipole moment , which causes its strong absorption of infrared radiation. In contrast, the most abundant gases ( N 2 , O 2 , and Ar ) in the atmosphere are not greenhouse gases. This is because they cannot absorb infrared radiation as they do not have vibrations with

1219-432: Is then: The amount of ozone produced through these reactions in ambient air can be estimated using a modified Leighton relationship . The limit on these interrelated cycles producing ozone is the reaction of •OH with NO 2 to form nitric acid at high NOx levels. If nitrogen monoxide (NO) is instead present at very low levels in the atmosphere (less than 10 approximately ppt), the peroxy radicals (HO 2 • ) formed from

1272-471: Is thus not generally classified as a trace gas. Regionally, water vapor can trap up to 80 percent of outgoing IR radiation. Globally, water vapor is responsible for about half of Earth's total greenhouse effect . The second most important greenhouse gas, and the most important trace gas affected by man-made sources, is carbon dioxide. It contributes about 20% of Earth's total greenhouse effect. The reason that greenhouse gases can absorb infrared radiation

1325-513: The criteria air pollutants . The EPA National Exposure Research Laboratory can designate a measurement device using an established technological basis as a Federal Reference Method (FRM) to certify that the device has undergone a testing and analysis protocol, and can be used to monitor NAAQS compliance. Devices based on new technologies can be designated as a Federal Equivalent Method (FEM). FEMs are based on different sampling and/or analyzing technologies than FRMs, but are required to provide

1378-555: The Clean Air Act Amendments. In 2024, the Lung Association ranked Fort Collins 16th in the nation for high ozone days out of 228 metropolitan areas, 38 for 24-hour particle pollution out of 223 metropolitan areas, and 136 for annual particle pollution out of 204 metropolitan areas. In monitoring air quality, Boulder County , Colorado is classified by the EPA as part of a nine-county group that includes

1431-745: The Denver metro area and North Front Range region. This nine-county zone has recorded ozone levels that exceed the EPA's ozone standard since 2004. Attempts have been made under the Early Action Compact to bring the area's air quality up to the EPA's standards. However, since 2004 ozone pollution in Boulder County has regularly failed to meet federal standards set by the Environmental Protection Agency. The County of Boulder continues trying to alleviate some of

1484-492: The European Union. (WHO, 2008) The United States Environmental Protection Agency has developed an Air Quality index to help explain air pollution levels to the general public. 8-hour average ozone mole fractions of 76 to 95 nmol/mol are described as "Unhealthy for Sensitive Groups", 96 nmol/mol to 115 nmol/mol as unhealthy and 116 nmol/mol to 404 nmol/mol as very unhealthy. The EPA has designated over 300 counties of

1537-673: The United States, clustered around the most heavily populated areas (especially in California and the Northeast), as failing to comply with the National Ambient Air Quality Standards . In 2000, the Ozone Annex was added to the U.S.–Canada Air Quality Agreement . The Ozone Annex addresses transboundary air pollution that contributes to ground-level ozone, which contributes to smog. The main goal

1590-488: The atmosphere in the presence of sunlight, specifically the UV spectrum. NOx, CO, and VOCs are considered ozone precursors. Motor vehicle exhaust, industrial emissions, and chemical solvents are the major anthropogenic sources of these ozone precursors. Although the ozone precursors often originate in urban areas, winds can carry NOx hundreds of kilometers, causing ozone formation to occur in less populated regions as well. Methane,

1643-431: The atmosphere will likely increase surface ozone in polluted areas like the eastern United States. In particular, the degradation of the pollutant peroxyacetylnitrate (PAN), which is a significant reservoir species for long-range transport of ozone precursors, is accelerated by rising temperatures. As a result, as the temperature rises, the lifetime of PAN reduces, changing the long-range transport of ozone pollution. Second,

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1696-537: The atmosphere, that process is called a source . There are two possible types of sources - natural or anthropogenic. Natural sources are caused by processes that occur in nature. In contrast, anthropogenic sources are caused by human activity. Some sources of a trace gas are biogenic processes, outgassing from solid Earth, ocean emissions, industrial emissions, and in situ formation. A few examples of biogenic sources include photosynthesis , animal excrements , termites , rice paddies , and wetlands . Volcanoes are

1749-494: The chain reaction that occurs in oxidation of CO, producing O 3 : The reaction begins with the oxidation of CO by the hydroxyl radical ( OH). The radical adduct (•HOCO) is unstable and reacts rapidly with oxygen to give a peroxy radical , HO 2 : Peroxy-radicals then go on to react with NO to produce NO 2 , which is photolysed by UV-A radiation to give a ground-state atomic oxygen, which then reacts with molecular oxygen to form ozone. The net reaction in this case

1802-443: The earth from excess UV radiation. Photolysis of ozone occurs at wavelengths below approximately 310–320 nanometres . This reaction initiates a chain of chemical reactions that remove carbon monoxide , methane , and other hydrocarbons from the atmosphere via oxidation . Therefore, the concentration of tropospheric ozone affects how long these compounds remain in the air. If the oxidation of carbon monoxide or methane occur in

1855-431: The environment. They are designed to address visibility, damage to crops, vegetation, buildings, and animals. The EPA established the NAAQS according to Sections 108 and 109 of the U.S. Clean Air Act, which was last amended in 1990. These sections require the EPA "(1) to list widespread air pollutants that reasonably may be expected to endanger public health or welfare; (2) to issue air quality criteria for them that assess

1908-422: The focus of the next cycle of scientific concern. In several parts of the northern hemisphere, tropospheric ozone levels have been rising. On various scales, this may have an impact on moisture levels, cloud volume and dispersion, precipitation, and atmospheric dynamics. A rising environment, on the other hand, favours ozone synthesis and accumulation in the atmosphere, owing to two physicochemical mechanisms. First,

1961-502: The ground up to a variable height of approximately 14 kilometers above sea level . Ozone is least concentrated in the ground layer (or planetary boundary layer ) of the troposphere. Ground-level or tropospheric ozone is created by chemical reactions between NOx gases (oxides of nitrogen produced by combustion) and volatile organic compounds (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, with

2014-410: The latest available scientific information on nature and effects of ambient exposure to them; (3) to set primary NAAQS to protect human health with adequate margin of safety and to set secondary NAAQS to protect against welfare effects (e.g., effects on vegetation, ecosystems, visibility, climate, manmade materials, etc); and (5) to periodically review and revise, as appropriate, the criteria and NAAQS for

2067-428: The main source for trace gases from solid earth. The global ocean is also a source of several trace gases, in particular sulfur-containing gases. In situ trace gas formation occurs through chemical reactions in the gas-phase. Anthropogenic sources are caused by human related activities such as fossil fuel combustion (e.g. in transportation ), fossil fuel mining, biomass burning , and industrial activity. In contrast,

2120-607: The oxidation will instead react with themselves to form peroxides , and not produce ozone. Health effects depend on ozone precursors, which is a group of pollutants, primarily generated during the combustion of fossil fuels. Ground-level ozone is created by nitrous oxides reacting with organic compounds in the presence of sunlight. There are many man-made sources of these organic compounds including vehicle and industrial emissions, along with several other sources. Reaction with daylight ultraviolet (UV) rays and these precursors create ground-level ozone pollution (tropospheric ozone). Ozone

2173-401: The ozone pollution through programming that encourages people to drive less, and stop ozone polluting activities during the heat of the day. Ground-level ozone is both naturally occurring and anthropogenically formed. It is the primary constituent of urban smog, forming naturally as a secondary pollutant through photochemical reactions involving nitrogen oxides and volatile organic compounds in

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2226-453: The presence of nitrogen monoxide (NO), this chain of reactions has a net product of ozone added to the system. Ozone in the atmosphere can be measured by remote sensing technology , or by in-situ monitoring technology. Because ozone absorbs light in the UV spectrum, the most common way to measure ozone is to measure how much of this light spectrum is absorbed in the atmosphere. Because

2279-418: The presence of bright sunshine with high temperatures. Regardless of whether it occurs naturally or is anthropogenically formed, the change in ozone concentrations in the upper troposphere will: As a result, photochemical smog pollution at the earth's surface, as well as stratospheric ozone depletion, have received a lot of attention in recent years. The disruptions in the "free troposphere" are likely to be

2332-514: The products of the combustion of fossil fuels or industrial processes. The National Emissions Standards for Hazardous Air Pollutants cover many other chemicals, and require the maximum achievable reduction that the EPA determines is feasible. The six criteria air pollutants were the first set of pollutants recognized by the United States Environmental Protection Agency as needing standards on

2385-469: The relationship can be used to estimate tropospheric residence times of gases. A few examples of the major greenhouse gases are water , carbon dioxide , methane , nitrous oxide , ozone , and CFCs . These gases can absorb infrared radiation from the Earth's surface as it passes through the atmosphere. The most influential greenhouse gas is water vapor . It frequently occurs in high concentrations, may transition to and from an aerosol (clouds), and

2438-459: The same CO 2 radiative forcing that causes global warming would chill the stratosphere. This cooling is projected to result in a relative rise in ozone (O 3 ) depletion in the polar region, as well as an increase in the frequency of ozone holes. Ozone depletion, on the other hand, is a radiative forcing of the climate system. Two opposite effects exist: Reduced ozone causes the stratosphere to absorb less solar radiation, cooling it while warming

2491-547: The same decision making quality when making NAAQS attainment determinations. Approved new methods are formally announced through publication in the Federal Register . A complete list of FRMs and FEMs is available. An air quality control region is an area, designated by the federal government, where communities share a common air pollution problem. Tropospheric ozone Ground-level ozone ( O 3 ), also known as surface-level ozone and tropospheric ozone ,

2544-439: The stratosphere has higher ozone concentration than the troposphere, it is important for remote sensing instruments to be able to determine altitude along with the concentration measurements. A total ozone mapping spectrometer-earth probe (TOMS-EP) aboard a satellite from NASA is an example of an ozone layer measuring satellite, and the tropospheric emission spectrometer (TES) is an example of an ozone measuring satellite that

2597-402: The troposphere; as a result, the stratosphere emits less long-wave radiation downward, cooling the troposphere. The IPCC believes that "measured stratospheric O3 losses over the past two decades have generated a negative forcing of the surface-troposphere system" of around 0.15 0.10 watts per square metre (W/m ). Furthermore, rising air temperatures often improve ozone-forming processes, which has

2650-550: The varying altitudes along the balloon's upward path. The information collected from the instrument attached to the balloon is transmitted back using radiosonde technology. NOAA has worked to create a global network of tropospheric ozone measurements using ozonesondes. Ozone is also measured in air quality environmental monitoring networks. In these networks, in-situ ozone monitors based on ozone's UV-absorption properties are used to measure ppb-levels in ambient air. Total atmospheric ozone (sometimes seen in weather reports)

2703-402: The world indicate that it typically takes 1–2 years for their concentrations to become well-mixed throughout the troposphere. The residence time of a trace gas depends on the abundance and rate of removal. The Junge (empirical) relationship describes the relationship between concentration fluctuations and residence time of a gas in the atmosphere. It can expressed as fc = b /τ r , where fc

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2756-439: Was also projected to remain in the atmosphere for centuries to millennia, where fractional persistence increases with pulse size. Thus CO 2 lifetime effectively increases as more fossil carbon is extracted by humans. The overall abundance of man-made trace gases in Earth's atmosphere is growing. Most originate from industrial activity in the more populated northern hemisphere. Time-series data from measurement stations around

2809-644: Was to attain proper ozone air quality standards in both countries. The North Front Range of Colorado has been out of compliance with the Federal Air Quality standards. The U.S. EPA designated Fort Collins as part of the ozone non-attainment area in November 2007. This means that the U.S.’s environmental law considers the air quality to be worse than the National Ambient Air Quality Standards, which are defined in

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