Air Pollutant Hazards

Daniel Vallero , in Fundamentals of Air Pollution (Fifth Edition), 2014

Abstract

Air pollutants may be "criteria pollutants" or "hazardous air pollutants". Criteria pollutants are used to determine whether a region is meeting air quality standards, i.e. is in "attainment" status. Hazardous air pollutants, known as "air toxics", are chemical compounds suspected of causing cancer and other chronic human health risks. Air pollutant hazard primarily focuses on the human toxicity of a chemical compound. The toxicity to other species is also of concern. For example, some species are sensitive to substances that may have low human toxicity. Other chemical hazards include fire hazard, explosiveness, corrosivity, and chemical reactivity. Hazards may also be biological and physical (e.g. radioactive).

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Respiratory Effects of Air Pollutants

Daniel Vallero , in Fundamentals of Air Pollution (Fifth Edition), 2014

9.5 Respiratory Health Effects

Air pollutants cause many respiratory diseases, both acute and chronic. Acute diseases include a range from mild irritations to inflammation to allergic reactions to impaired lung function to complete respiratory failure depending on the level of exposure. Chronic diseases include chronic obstructive pulmonary diseases (COPD), cardiovascular diseases, asthma, and lung and other cancers. Oxidative stress initiated by air pollutants appears to play a large role in such chronic diseases.

Principal vapor phase air pollutants that are associated with non-cancer effects of the respiratory system include ozone, sulfur oxides, carbon monoxide, nitrogen oxides, as well as PM. Numerous organic compounds, e.g. polycyclic aromatic hydrocarbons, have been linked to respiratory system cancers (e.g. lung cancer).

PM in various forms has been associated with cancer, including the organic fraction of the aerosol. Asbestos and other fibers have been linked to long-term effects, including mesothelioma, lung cancer, and asbestosis. Dust from coal has been associated with pneumoconiosis (so-called black lung disease). Dust from crushing silica-containing rocks has been linked to silicosis. Textile fiber exposures have led to byssinosis (so-called brown lung disease), which may result from bacteria in cotton (thus, a combined physical–chemical–biological air pollutant).

Exposure to elevated concentrations of tropospheric (ground-level) ozone is particularly harmful to people with asthma or lung disease and children who are more likely than adults to have asthma, which is aggravated by ozone. Chronic, continuous exposure to ozone for even short periods may cause children to have more breathing problems as adults. Older adults are more susceptible to lung disease. People engaged in heavy work or exercise are also at risk, since their ventilation rates and thus respiratory exposure doses are elevated. Infants are particularly vulnerable since their lungs continue to develop after birth and prolific tissue is more easily affected by air pollutants.

Tobacco smoke has been identified as a key factor in North America and Europe in the development and progression of COPD. Numerous air pollutants in the home and workplace can be synergistic with one another and with genetic factors and respiratory infections to increase the incidence and severity of COPD. In developing nations, indoor air quality plays a large role in the development and progression of COPD. 16

Both conventional pollutants and air toxins are associated with respiratory effects. In addition to effects in the respiratory system, the conveyance and distribution of air pollutants and their metabolites lead to problems in other parts of the body, especially cardiovascular problems. These are the subject of the next chapter.

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Air Pollution

Mike Ashmore , in Encyclopedia of Biodiversity (Second Edition), 2013

Sources, Distribution, and Effects of Major Air Pollutants

Air pollutant problems vary greatly in their spatial scales. Some are very local in character, with the environmental impact of the pollution restricted to the immediate vicinity of, for example, a road or a factory. Other problems are regional in character as a result of the long-range transport of pollutants such as acid deposition and tropospheric ozone. Similarly, pollutant impacts may vary on different temporal scales. Some impacts, for example, are the result of an accidental release of large pollutant concentrations, which may cause an immediate impact on biodiversity, and from which there may be a slow and gradual recovery, whereas others are the result of an accumulation of pollutant deposition over years or even decades.

This article provides an overview of the ways in which pollutants can affect ecological processes and biodiversity. Inevitably, it is not possible to provide a comprehensive account of the effects of the vast range of contaminants emitted into the atmosphere by human activity; therefore, this article will concentrate on those air pollutants for which the greatest evidence exists of impacts on biodiversity. Table 1 summarizes the major sources of these pollutants, their major ecological impacts, and the spatial scale of these impacts.

Table 1. Summary of major sources and impacts of air pollutants of relevance to biodiversity

Pollutant Major sources Major impacts Scale of effects
Sulfur dioxide (SO2) Power generation: industry, domestic, and commercial heating Forest decline; elimination of lichens and bryophytes Local
Nitrogen oxides (NOx) and ammonia (NH3) Power generation and transport (NOx); intensive agriculture (NH3) Altered plant growth and enhanced stress sensitivity; soil acidification and eutrophication Local, regional
Acid deposition Secondary pollutant formed from SO2 and NOx Soil and freshwater acidification: forest decline Regional
Ozone (O3) Secondary pollutant formed from hydrocarbons and NOx Reduced plant growth: forest decline Regional
Toxic metals (e.g., lead and cadmium) Smelting industry; transport (lead) Reduced soil microbial activity; reduced soil invertebrate populations Local, regional
Persistent organic pollutants (POPs) Industry; fuel combustion; pesticide use Bioaccumulation in food chain Local, global

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Volume 1

D.G. Shendell , in Encyclopedia of Environmental Health (Second Edition), 2019

Cardiovascular and Respiratory Health

Outdoor air pollution has been associated, through basic science, clinical, epidemiological, toxicology, and environmental science and engineering research, over several decades with many different measurable indicators of adverse acute and chronic cardiovascular (heart-related) and respiratory (lung-related) health-related outcomes. Asthma, a chronic disease characterized by airway inflammation and bronchoconstriction after exposure to various airborne triggers and irritants, was briefly described at the beginning of this section. Other examples of adverse respiratory health outcomes associated with air pollution exposure include acute respiratory infections, bronchitis, chronic obstructive pulmonary disease, and lung cancer. Examples of adverse cardiovascular health outcomes of concern associated with air pollution exposure include data on measures of blood pressure of specific arteries and ventricles, hardening of the arteries or atherosclerosis, heart attacks, heart rate variability, ischemia, and myocardial infarctions.

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Air Pollutant Kinetics and Equilibrium

Daniel Vallero , in Fundamentals of Air Pollution (Fifth Edition), 2014

18.8 Dynamics within an Organism

Air pollutant transport and fate focus on the kinetics and equilibria of the processes leading to the release, behavior in environmental compartments, and movement among compartments. These same physical and chemical processes take place within an organism after uptake. The importance of the factors can be very different within the organism. For example, the degradation or activation of a pollutant may be much faster in the presence of organic catalysts, i.e. enzymes.

The reaction rates and equilibria differ, as do residence times and half-lives of chemical processes. However, the laws of thermodynamics and motion apply at every level of interest to air pollution, from cells to the planet.

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Volume 1

A. Fino , in Encyclopedia of Environmental Health (Second Edition), 2019

Air Pollutants

Air pollutants differ in a lot of features such as their chemical composition, their reactions, emissions, persistence in the environment, ability to be transported over long or short distances and their eventual impacts on human health and/or on the environment. However, they share some similarities and they can be grouped into different categories:

1.

Gaseous pollutants (e.g., SO2, NO2, CO, ozone, volatile organic compounds).

2.

Persistent organic pollutants (e.g., dioxins).

3.

Toxic heavy metals (e.g., lead, mercury).

4.

Particulate matter (including PM10 and PM2.5, respectively, known as coarse and fine particulate matter).

Gaseous pollutants contribute to a great extent in variations of the atmosphere composition and are mainly due to combustion of fossil fuels. Nitrogen oxides are mainly emitted as NO which rapidly reacts with ozone or radicals in the atmosphere forming NO2. The main anthropogenic sources are mobile and stationary combustion sources. Ground-level ozone (that differs from ozone present in upper layers of the atmosphere) is not emitted directly into the air, but is created by chemical reactions between nitrogen oxides (NO x ) and volatile organic compounds (VOCs) in the presence of sunlight. CO, on the other hand, is a product of incomplete combustion. Its major source is road transport. While the anthropogenic SO2 results from the combustion of sulfur-containing fossil fuels (principally coal and heavy oils), while volcanoes and oceans are its major natural sources. Many of the so-called classical pollutants belong to this category. They are: SO2, NO2, CO and O3. These pollutants have been subject to in depth investigation on their health effect and many air quality guideline values and standards have been defined over time for them.

Persistent organic pollutants are a toxic group of chemicals. They persist in the environment for long periods of time and their effects are magnified as they move up through the food chain (bio-magnification). Bio-magnification or Bio-accumulation is an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment.

This group of pollutants include pesticides, as well as dioxins, furans and polychlorinated biphenyls PCBs.

Toxic Heavy metals include basic metal elements such as lead, mercury, cadmium, nickel, vanadium, chromium and manganese. They are natural components of the earth's crust; they cannot be degraded or destroyed, and can be transported by air, and enter water and food chain. In addition, they enter the environment through a wide variety of sources, including combustion, waste water discharges and manufacturing facilities. They enter human bodies where, at higher concentrations they can become toxic. Most heavy metals are dangerous because they tend to bio-accumulate in the human body and have adverse effects (this is the case of mercury and its compounds).

Particulate matter (PM) is the generic term used for a complex mixture of extremely small particles and liquid droplets that are suspended in the air, which vary in size and composition and are produced by a wide variety of natural and anthropogenic sources.

Major sources of particulate pollution are industries, power plants, incinerators, motor vehicles, construction activity, fires, and natural windblown dust. The size of the particles varies (PM2.5 and PM10 have an aerodynamic diameter smaller than 2.5 and 10   μm respectively) and different categories have been defined: Ultrafine particles—smaller than 0.1   μm in aerodynamic diameter, fine particles—smaller than 1   μm, and coarse particles—larger than 1   μm. In common ways of speaking, the PM10 and PM2.5 are respectively referred as coarse and fine PM. The size of the particles determines the respiratory tract where they will deposit: PM10 particles deposit mainly in the upper respiratory tract while fine and ultra fine particles are able to flow deeper reaching lung alveoli.

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Air pollution mitigation and global dimming: a challenge to agriculture under changing climate

Poonam Yadav , ... Bhupinder Singh , in Climate Change and Crop Stress, 2022

10.2 Ecological impact of pollution

Air pollutants impact and, in most cases, impair the functions of an ecosystem and the life it supports and vice versa. For instance, emission of gaseous pollutants such as SO 2 and NO2 results in effecting "acid rain," owing to the formation of sulfuric and nitric acids, respectively, as their reactive transformation products deposit on water bodies and soil to intensify acidity and affect adversely above- and underground vegetation and aquatic vegetation and microbial and aquatic life that the soil and water bodies support. All these attributes that are directly or indirectly impaired/manipulated in a polluted environment further restrict and impair the associated ecosystem services, which include mineral nutrients and carbon and water cycling, all of which together define the sustainability of life in an ecosystem. An increase in air pollutant load at the ground or near-ground level challenges plant growth and development depending upon the plant's ability and resultant response to the pollutants at the whole-plant, tissue, and/or cell level. These pollutants are known to limit key metabolic processes in crop plants to stimulate or limit growth and development (European Environment Agency, 2007) besides altering the resource use in the soil–plant environment (Fig. 10.1).

Figure 10.1. Air pollutants and its consequences on the soil–plant environment.

Trees and/or any other vegetation may act as a sieve to filter out the toxic air pollutants. Recently, Sharma et al. (2020) showed that foliage of Morus alba absorbed the heavy metals associated with the suspended particulate matter (SPM) and further provided radiochemical evidence involving the use of 65Zn-SPM to show that the SPM-associated 65Zn, absorbed via the foliar surface, travels through the vascular system to reveal both upward and downward transport respectively into the branches and the foliage above the point of 65Zn-SPM treatment and into the roots. Plants are, in fact, also capable of absorbing gaseous pollutants and mitigating ozone and its adverse effects to purify the air environment. It is thus important that we promote agroforestry to have sustainable food production and a sustainable environment. Any reduction in the tree or vegetation cover would reflect a reduced capacity to filter out the pollutants and to purify the air environment. Air pollutants may also cause eutrophication, where an increased accumulation of nutrients in the water bodies effectively destroys the aquatic ecosystem and its flora and fauna and the biodiversity by promoting algal bloom that dissipates oxygen to a level below the minimum that is required for supporting aquatic life (Ghosh & Mondal, 2012). The adverse effect of air pollutants/pollution may reach and impact even the humans and farm animals who depend on the water bodies for sufficing their drinking water requirements. Further, the air pollutants via the water bodies may seep into the deeper layers of the earth's crust to pollute groundwater and may revert back into the food chain via irrigation water use on agrifarms. So any threat or restriction of our green cover will not only affect the air quality but will also have a heightened effect on our water bodies to further limit the growth of farm crops and their economic productivity and produce quality, besides carbon sequestration.

Human beings, by virtue of their desire to propel development, perform several activities that over the years have caused an enormous rise in the quantum of gases such as CO2 in the atmosphere. Burning of fossil fuels, industrial explosion, deforestation, etc., are few such activities that have resulted in global warming mediated by a concomitant increase in the level of greenhouse gases (GHGs). The resultant change in climate will impact a number of social and development sectors, including agriculture. The projected climatic change is expected to impact crop yields, livestock management, and the location of production severely. Further, an increased frequency of extreme weather events under the climate change scenario is likely to aggravate the risk of crop failure considerably. An altered climate with an elevated CO2 and temperature will also alter the physicochemical and biological attributes of the soil, including its fertility and dynamics of nutrient availability for plant uptake. Apart from farm crops, an eminent change in climate is likely to alter the forest cover and the biodiversity they encompass. Change in the character of the forest is likely to come from the health of forest flora and fauna, productivity, carbon sequestration, and change in the altitudinal growing success of the tree species. Change in the climate will also restrict the fishery, marine, and coastal ecosystems. The latter is likely to see a higher rate of erosion, which thus may threaten the inland regions too (Kanawade, Hamigi, & Gaikwad, 2010).

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Air Quality Measurement and Effects of Pollution

Martin B. Hocking , in Handbook of Chemical Technology and Pollution Control (Third Edition), 2005

2.3 CLASSIFICATION OF AIR POLLUTANTS

Air pollutants can be classified into one of three main categories based on their physical characteristics. This enables potential emissions to be grouped so as to assess appropriate measures for avoidance of production, or emission control. On this basis, one or more types of emission control devices may be selected for use, based on their mode of action.

The first of these classes of air pollutants is called coarse particulate matter (PM), and comprises solid particles or liquid droplets which have an average diameter greater than about 10   μm(10‒3mm), (i.e., > PM10). Particles or droplets of this class of contaminants are large enough to fall more or less rapidly out of the air of their own accord.

The second group of air pollutants is the aerosol class. This can also comprise solid particles or liquid droplets, but they are limited to a size range generally less than about 10   μm average diameter (e.g., a median diameter of 2.5   μm, PM2 5). This class has particles or droplets small enough in size that there is a strong tendency for them to stay in suspension in air [6]. Powders of the denser solids, such as magnetite, would have to have a particle size of 2.5   μm or less to stay in suspension. This size range is also referred to as the Respirable Fraction, since these are not readily captured by ciliated mucous of the nasal passages and penetrate to the unciliated alveoli of the lungs [7]. A suspension of a finely divided solid in air is referred to as a "fume," and that of a finely divided liquid as a "fog."

The gases comprise the third major classification of air pollutants, which includes any contaminant in the gaseous or vapor state. This comprises the more ordinary "permanent" gases, such as sulfur dioxide, hydrogen sulfide, nitric oxide (NO), nitrogen dioxide (NO2), ozone, carbon monoxide, carbon dioxide (pollutant?), etc., as well as the less common ones such as hydrogen chloride, chlorine, tritium ( 3 1 H ) and the like. It also includes materials which are not ordinarily gases, such as hydrocarbon vapors, and volatile nonmetal or metal vapors (e.g., arsenic, mercury, zinc) when these are in the vapor state.

The dividing line between the particulate/aerosol classes, and the gaseous classes is clear enough because of the phase difference. However, the position of the dividing line between the particulate and the aerosol classes is less obvious, since it is based on whether or not a second phase stays in suspension in air. Consideration of the terminal velocities or speed of fallout of particles of differing diameters helps to clarify this dividing line. Table 2.1 illustrates that a significant terminal velocity in air begins to be observed at particle diameters of about 10   μm for a substance with a density of 1   g/cm3 and larger. This is the physical basis of the approximate dividing line between these two classes. Figure 2.1 gives examples of typical particle size ranges for some common industrial and domestic substances that may become airborne.

Table 2.1. Gravitational Settling Velocity for Spheres of Unit Density in Air at 20   °C a

Examples Particle diameter (μm) Particles per microgram Micrograms per particle Terminal velocity b (mm/sec)
Carbon black   0.1 109 1   ×   10‒9   8.5×10‒4
Clay   0.5   1.0×10‒2
Clay   1.0 106 1   ×   10‒6   3.5×10‒2
Paint pigments   5.0   0.78
Silt, fog, flour   10 103 1   ×   10‒3   3.0
Fine sand, flour   20   12
Pollens   50 c   72
Medium sand, pollens 100 d 1 1 250
a
From Barrett [8], Spedding [9], and calculated results.
b
The final speed of a particle through are from the force of gravity, slowed by the drag imposed by air.
c
Roughly equivalent to a powder which would pass through a No. 325 sieve (325-mesh, 54   μm average opening size) and be retained on a No. 400 sieve (400-mesh, 45   μm average opening size).
d
Roughly equivalent to a powder which would pass through a No. 170 sieve (170-mesh, 103   μm average opening size) and be retained on a No. 200 sieve (200-mesh, 86   μm average opening size).

Figure 2.1. Typical particle size ranges of some types of precipitation, industrial and mineral processing streams and ambient air biologicals.

 (From Munger [10], with permission from McGraw-Hill.)

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Methods for Measuring Air Pollutants

Daniel Vallero , in Fundamentals of Air Pollution (Fifth Edition), 2014

25.2.1.1 Extractive Sampling

When bubbler systems are used for collection, the gaseous species generally undergoes hydration or reaction with water to form anions or cations. For example, when SO2 and NH3 are absorbed in bubblers they form HSO 3 − and NHO 4 + , and the analytical techniques for measurement actually detect these ions. Table 25.3 gives examples of gases which may be sampled with bubbler systems.

TABLE 25.3. Collection of Gases by Absorption

Gas Sampler Sorption Medium Airflow (l   m−1) Minimum Sample (l) Collection Efficiency Analysis Interferences
Ammonia Midget impinger 25   ml 0.1   N sulfuric acid 1–3 10 Nessler reagent –
Petri bubbler 10   ml of above 1–3 10 +95 Nessler reagent –
Benzene Glass bead column 5   ml Nitrating acid 0.25 3–5 +95 Butanone method Other aromatic hydrocarbons
Carbon dioxide Fritted bubbler 10   ml 0.1   N barium hydroxide 1 10–15 60–80 Titration with 0.05   N oxalic acid Other acids
Ethyl benzene Fritted bubbler or midget impinger 15   ml spectrograde isooctane 1 20 +90 Alcohol extraction, ultraviolet analysis Other aromatic hydrocarbons
Formaldehyde Fritted bubbler 10   ml 1% sodium bisulfite 1–3 25 +95 Liberated sulfite titrated, 0.01   N iodine Methyl ketones
Hydrochloric acid Fritted bubbler 0.005   N sodium hydroxide 10 100 +95 Titration with 0.01   N silver nitrate Other chlorides
Hydrogen sulfide Midget impinger 15   ml 5% cadmium sulfate 1–2 20 195 Add 0.05   N iodine, 6   N sulfuric acid, back-titrate 0.01   N sodium thiosulfate Mercaptans, carbon disulfide, and organic sulfur compounds
Lead, tetraethyl, and tetramethyl Dreschel-type scrubber 100   ml 0.1   M iodine monochloride in 0.3   N 1.8–2.9 50–75 100 Dithizone Bismuth, thallium, and stannous tin
Mercury, diethyl, and dimethyl Midget impinger 15   ml of above 1.9 50–75 91–95 Same as above Same as above
Midget impinger 10   ml 0.1   M iodine monochloride in 0.3   N hydrochloric acid 1–1.5 100 91–100 Dithizone Copper
Nickel carbonyl Midget impinger 15   ml 3% hydrochloric acid 2.8 50–90 190 Complex with alpha-furil-dioxime –
Nitrogen dioxide Fritted bubbler (60–70   μm pore size) 20–30   ml Saltzman reagent ∗ 0.4 Sample until color appears; probably 10   mL of air 94–99 Reacts with absorbing solution Ozone in fivefold excess peroxyacyl nitrate
Ozone Midget impinger 1% Potassium iodide in 1   N potassium hydroxide 1 25 +95 Measures color of iodine liberated Other oxidizing agents
Phosphine Fritted bubbler 15   ml 0.5% silver diethyl dithiocarbamate in pyridine 0.5 5 86 Complexes with absorbing solution Arsine, stibine, and hydrogen sulfide
Styrene Fritted midget impinger 15   ml Spectrograde isooctane 1 20 +90 Ultraviolet analysis Other aromatic hydrocarbons
Sulfur dioxide Midget impinger, fritted rubber 10   ml Sodium tetrachloromercurate 2–3 2 99 Reaction of dichlorosulfito-mercurate and formaldehyde-depararosaniline Nitrogen dioxide, § hydrogen sulfide
Toluene diisocyanate Midget impinger 15   ml Marcali solution 1 25 95 Diazotization and coupling reaction Materials containing reactive hydrogen attached to oxygen (phenol); certain other diamines
Vinyl acetate Fritted midget impinger and simple midget impinger in series Toluene 1.5 15 +99 (84 with fritted bubbler only) Gas chromatography Other substances with same retention time on column
∗
5   g sulfanilic; 140   ml glacial acetic acid; 20   ml 0.1% aqueous N-(1-naphthyl) ethylene diamine.
§
Add sulfamic acid after sampling.
Filter or centrifuge any precipitate.

Bubblers are more often utilized for sampling programs that do not require a large number of samples or frequent sampling. The advantages of these types of sampling systems are low cost and portability. The disadvantages are the high degree of skill and careful handling needed to ensure quality results. Solid sorbents such as Tenax, XAD, and activated carbon (charcoal) are used to sample hydrocarbon gases by trapping the species on the active sites of the surface of the sorbent. Figure 25.6 illustrates the loading of active sites with increasing sample time. It is critical that the breakthrough sampling volume, the amount of air passing through the tube that saturates its absorptive capacity, not be exceeded. The breakthrough volume is dependent on the concentration of the gas being sampled and the absorptive capacity of the sorbent. This means that the user must have an estimate of the upper limit of concentration for the gas being sampled.

FIGURE 25.6. Solid sorbent collection tube.

(A) The tube is packed with a granular medium. (B) As the hydrocarbon-containing air is passed through the collection tube at t 1, t 2, and t 3, the collection medium becomes saturated at increasing lengths along the tube.

After the sample has been collected on the solid sorbent, the tube is sealed and transported to the analytical laboratory. To recover the sorbed gas, two techniques may be used. The tube may be heated while an inert gas is flowing through it. At a sufficiently high temperature, the absorbed molecules are desorbed and carried out of the tube with the inert gas stream. The gas stream may then be passed through a preconcentration trap for injection into a gas chromatograph for chemical analysis. The second technique is liquid extraction of the sorbent and subsequent liquid chromatography. Sometimes a derivatization step is necessary to convert the collected material chemically into compounds which will pass through the column more easily, e.g. conversion of carboxylic acids to methyl esters. Solid sorbents have increased our ability to measure hydrocarbon species under a variety of field conditions. However, this technique requires great skill and sophisticated equipment to obtain accurate results. Care must be taken to minimize problems of contamination of the collection medium, sample instability on the sorbent and incomplete recovery of the sorbed gases.

Special techniques are employed to sample for gases and particulate matter simultaneously. 12 Sampling systems have been developed which permit the removal of gas-phase molecules from a moving airstream by diffusion to a coated surface and permit the passage of particulate matter downstream for collection on a filter or other medium. These diffusion denuders are used to sample for SO2 or acid gases in the presence of particulate matter. This type of sampling has been developed to minimize the interference of gases in particulate sampling and vice versa.

The third technique, shown in Figure 25.3(C), involves collection of an aliquot of air in its gaseous state for transport back to the analytical laboratory. Use of a pre-evacuated flask permits the collection of a gas sample in a specially polished stainless steel container. By use of pressure–volume relationships, it is possible to remove a known volume from the tank for subsequent chemical analysis. Another means of collecting gaseous samples is the collapsible bag. Bags made of polymer films can be used for collection and transport of samples. The air may be pumped into the bag by an inert pump such as one using flexible metal bellows, or the air may be sucked into the bag by placing the bag in an airtight container which is then evacuated. This forces the bag to expand, drawing in the ambient air sample.

Most air pollutants are sampled by obtaining a known amount of air in a container. For vapor-phase compounds, the containers are either a canister or bag. Depending on how long it takes to fill the container, this technique provides a prolonged snapshot of an air pollutant's concentration. That is, the sample is not a point, but is a time interval. For example, if a valve allows air to enter on a 6-l canister at a rate of 0.5  l   min−1, the canister will be full in 12   min. Thus, if the sample begins at 5:00 p.m. on Monday, it will be full at 5:12 p.m. that day. If the concentration of 1-3-butadiene is found to be 10   mg   m−3, that is the concentration at that location integrated over that 12   min period during rush hour. If only a few cans are available, but a longer time is needed, e.g. 1   h during the highest traffic, the valve may be adjusted to a lower flow rate, so that the canister fills 5 times more slowly, i.e. 0.1   l   min−1, and the concentration is integrated over the entire hour.

If the concentrations in the 12-min canister are 10   mg   m−3, but the 1-h canister is found to be 25   mg   m−3 for the same compound at the same location, this could indicate that traffic is higher after 5:12 p.m., or that a particular source (e.g. poorly maintained trucks) may appear later. Then again, this could be an anomalous event (one large source happened to pass by the sampler). For example, if three other similar sites find little difference between the 12-min and 1-h integration times, the site with the difference would probably need a few more comparisons. Finding the optimal sampling interval and the appropriate sampling locations depends on comparisons such as these.

Canisters and bags can be filled two ways. In the example above, the air in the canister had been removed and the empty canister's vacuum, pulled in the air, since fluids flow from higher to lower pressure. The canister or bag can then be returned to the laboratory whereupon the analyst removes small amounts of the contents into detectors.

Air pollution studies make wide use of evacuated stainless steel canisters with electropolished inner surfaces, 13 known as Summa canisters (Figure 25.7). The electropolishing and chemical deactivation yields an internal surface with very low chemical reactivity. These canisters are employed to sample for vapors, especially VOCs. 14 The VOCs sampled with Summa canisters consist of both aliphatic and aromatic hydrocarbons, including halogenated forms. 15 Several of these are shown in Table 25.4. This technique has also been applied to a variety of practical applications, such as indoor air quality problems. Canisters are cleaned and evacuated, so that the lower pressure inside the canister allows air to enter without the need for a sampling pump.

FIGURE 25.7. Six-liter summa canister. (For color version of this figure, the reader is referred to the online version of this book.)

 U.S. Environmental Protection Agency. http://www.epa.gov/region6/6pd/rcra_c/ca/canister.html; 2013 [accessed 13.08.13].

TABLE 25.4. Select Organic Compounds That Can Be Collected Using Summa Canisters and Tedlar Bags

Analyte CRQL (ppbv)
Acetone 5
Acetonitrile 5
Acetonitrile 5
Acrylonitrile 5
Benzene 2
Benzyl chloride 5
Bromodichloromethane 2
Bromomethane 5
1,3-Butadiene 5
2-Butanone 5
Chlorobenzene 2
Chlorodifluoromethane 2
Chloroethane 2
Chloroform 2
1,2-Dichlorobenzene
trans-1,2-Dichloroethene 2
1,2-Dichloropropane 2
Dichlorofluoromethane 2
t-1,2-Dichloropropene 2
cis-1,2-Dichloropropene 5
1,2-Dichloro-1,1,2,2-tetrafluoroethane 2
n-Pentane 2
Propylene 5
Styrene 5
1,2,4-Trichlorobenzene 2
1,1,1-Trichloroethane 5
1,1,2-Trichloroethane 5
1,1,2,2-Tetrachloroethane 2
Tetrachloroethene 5
Tetrachloromethane (carbon tetrachloride) 2
Toluene 5
Trichloroethene 2
Trichlorofluoromethane 2
1,1,2-Trichloro-1,2,2-trifluoroethane 2
Xylenes (m- and p-) 5
Xylene (o-) 5

CRQL   =   contract required quantitation limit; ppbv   =   parts per US billion by volume. The CRQL is the lowest concentration that must be detected by an EPA Superfund contract laboratory.

Source: U.S. Environmental Protection Agency. http://www.epa.gov/region9/qa/pdfs/aircrf.pdf; 2013 [accessed 13.08.13].

Many air pollutants are chemically reactive and may combine with chemicals on the surfaces inside of collection systems. Thus, stainless steel canisters are now often coated with relatively inert substances, especially fused silica, which allows them to be stored longer prior to chemical analysis. a When the canister is delivered to the laboratory, it is pressurized with nitrogen, and the contents are analyzed by gas chromatography/mass spectrometry (GC/MS).

Several canisters can be used to provide a map of air pollution. The number of canisters per unit area is known as the sampling density. Highly reactive contaminants with short half-lives may require greater sampling density than less reactive pollutants, since the former may breakdown in relatively short distances from their sources.

The amount of time that a sample can be stored in a container varies by the type of compounds and the container. For example, the U.S. EPA recommends that VOCs not be held in a Summa canister for more than 14   days from collection and 12   days from the receipt at the laboratory. In tedlar bags, the holding times are much shorter, i.e. 40   h form collection and 36   h from receipt by the laboratory. Also, the conditions of storage are usually specified. For VOCs, both bags and canisters can be preserved at ambient temperatures and near atmospheric pressure. However, for some highly reactive compounds, refrigeration, and other preservation techniques will be required.

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Fuels

E. Lois , ... A.K. Gupta , in Encyclopedia of Physical Science and Technology (Third Edition), 2003

III.C Air Quality Standards

Air pollutants are natural and artificial airborne substances that are introduced into the environment in a concentration sufficient to have a measurable effect on humans, animals, vegetation, or building materials. From a regulatory standpoint of EPA these substances become air pollutants. As part of the regulatory process, the Clean Air Act requires the EPA to issue a criteria document for each pollutant documenting its adverse effects. Regulated pollutants are therefore referred to as criteria pollutants. The EPA uses the information in the criteria documents to set National Ambient Air Quality Standards (NAAQS) at levels that protect public health and welfare. Table X lists the criteria pollutants and the federal and California standards. In most cases, the California standards are more stringent. Some of the criteria pollutants, like carbon monoxide, are primary pollutants, which are emitted directly by identifiable sources. Others, like ozone, are secondary pollutants, which are formed by reactions in the atmosphere. And others, like particulates, are of mixed origin.

TABLE X. Ambient Air Quality Standards

Criteria pollutant Maximum average concentration
Averaging time Federal standard California standard
Ozone (O3), ppm 1-hr 0.12 0.09
8-hr 0.08 —
Carbon monoxide (CO), ppm 1-hr 35 20
8-hr 9 9.0
Nitrogen dioxide (NO2), ppm 1-hr — 0.025
annual 0.053 —
Sulfur dioxide (SO2), ppm 1-hr — 0.25
24-hr 0.14 0.05
Annual 0.03 —
Suspended particulate 24-hr 150 50
Matter (PM10), μg/m3 Annual 50 30
Suspended particulate 24-hr 65 —
Matter (PM2.5), μg/m3 Annual 15 —
Lead, μg/m3 30-day — 1.5
Quarterly 1.5 —
Sulfates, μg/m3 24-hr — 25

Table XI lists the EPA standards for heavy-duty highway engines. The EPA also has engine emission standards for diesel buses, off-road diesels, marine diesels, and railroad diesels. California sets its own limits on diesel emissions, which are generally the same as the federal standards, although sometimes slightly more restrictive. The European standards for heavy trucks are listed inTable XII.

TABLE XI. Federal Heavy-Duty Highway Diesel Engine Emission Standards

Year CO (g/bhp-hr) HC (g/bhp-hr) NO x (g/bhp-hr) PM (g/bhp-hr)
1990 15.5 1.3 6.0 0.60
1991–1993 15.5 1.3 5.0 0.25
1994–1997 15.5 1.3 5.0 0.10
1998+ 15.5 1.3 4.0 a 0.10 b
a
This standard had to be met by 1996 in California.
b
Urban buses must meet a 0.05   g/bhp-hr PM standard.

TABLE XII. European Heavy Diesel Trucks Emission Standards

Year CO (g/kWh) HC (g/kWh) NO x (g/kWh) PM (g/kWh)
1983 14.0 3.5 18.0 —
1990 11.2 2.4 14.4 —
1992 4.5 1.1 8.0 >85 kW 0.36 ≤85 kW 0.63
1996 4.0 1.1 7.0 0.15 0.30

Exhaust emissions are very dependent on how a vehicle is operated. To standardize the test conditions, specific test cycles have been established and each engine is tested according to a specified speed-time cycle on an engine dynamometer.

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