**2. Upstream control strategies**

#### **2.1. Control transportation activities**

Strategies to control air pollutants emitted from transportation activities include regulations to control precursor pollutants in raw materials; the application of catalytic converters to reduce NOx, CO, and hydrocarbon emissions; the control of lubricant consumption; the reduction of motorized transportation demand; and the improvements to road quality and traffic flow.

### *2.1.1. Raw materials*

51

62

Air pollutants can be controlled based on regulations that control precursor pollutants in raw materials such as sulfur and lead. Sulfur oxides (SOx) in aerosol are formed during the combustion process of sulfur in fossil fuels such as gasoline and diesel. Therefore, the use of low-sulfur-content fuels can be considered as a control strategy to reduce SO2 emissions. Many regulations have been issued to reduce the sulfur content in all transportation fuels. For example, Figure 1 presents a selection of a few of the gasoline and diesel sulfur specifications in major countries and the regulatory timetable associated with the introduction of these specifications [7].

52 In the 1920s, refiners started adding lead compounds to gasoline in order to increase octane levels and improve engine 53 performance by reducing engine "knock" and allowing higher engine compression. However, the burning of leaded fuel **Figure 1.** Regulations and regulatory timetable for sulfur content in gasoline (A) and diesel (B) in several countries.

 introduced massive quantities of atmospheric lead leading to many adverse effects on human health. Therefore, regulations to eliminate lead from leaded fuel began to be issued worldwide from the 1970s. For example, the US EPA scheduled performance standards requiring refineries to decrease the average lead content of all fuels beginning in 1975, but these were postponed until 1979 through a series of regulatory adjustments. By the early 1980s, the lead content in fuels had declined by about 80% due to both the regulations and the fleet turnover [8]. In August 1984, the US EPA proposed a further reduction of lead to 0.1 grams per liter gallon (gplg) by January 1, 1986. However, several refineries were not able to achieve this time scale, so the US EPA postponed the deadline until January 1, 1988. Lead was banned as a fuel additive in the United States beginning in 1996. Figure 2

50 Figure 1: Regulations and regulatory timetable for sulfur content in gasoline (A) and diesel (B) in several countries.

61 shows the decline over time in the lead content of leaded fuel in the United States [9].

63 Figure 2: Temporal lead content in leaded fuel in the United States.

72 gasoline, both reformulated and conventional, nationwide, from 2011.

 Regulations concerning oxygenated gasoline and reformulated gasoline were also issued in the United States in 1990 to reduce the vehicular emissions of CO and VOCs. The oxygenated gasoline regulation required a higher oxygen content in gasoline in order to ensure more complete burning of the gasoline and thereby reduce harmful tailpipe emissions from motor vehicles. In this respect, oxygen dilutes or displaces the precursor pollutant components in gasoline such as aromatics (e.g., benzene) and sulfur and thus decreases their content in gasoline. The reformulated gasoline regulation is specially blended gasoline. Therefore, the gasoline can be burned more cleanly and can be prevented from evaporating as quickly as conventional gasoline, thereby reducing the emission of smog-forming and toxic pollutants. To reduce the emission of benzene (VOCs) into an aerosol, the US EPA required all refiners to meet an annual average gasoline benzene content standard of 0.62% by volume (vol %) in all their

73 In addition, the use of new-generation fuels such as biofuels and natural gas can be a valuable strategy to reduce air pollutant 74 emission. Feedstocks for biofuels, mostly plants, are much more environmental-friendly and evenly distributed around the world 75 than the feedstocks for traditional fuels such as oil and gas. Two of the most commonly used biofuels are ethanol and biodiesel.

2

In the 1920s, refiners started adding lead compounds to gasoline in order to increase octane levels and improve engine performance by reducing engine "knock" and allowing higher engine compression. However, the burning of leaded fuel introduced massive quantities of atmospheric lead leading to many adverse effects on human health. Therefore, regulations to eliminate lead from leaded fuel began to be issued worldwide from the 1970s. For example, the US EPA scheduled performance standards requiring refineries to decrease the average lead content of all fuels beginning in 1975, but these were postponed until 1979 through a series of regulatory adjustments. By the early 1980s, the lead content in fuels had declined by about 80% due to both the regulations and the fleet turnover [8]. In August 1984, the US EPA proposed a further reduction of lead to 0.1 grams per liter gallon (gplg) by January 1, 1986. However, several refineries were not able to achieve this time scale, so the US EPA postponed the deadline until January 1, 1988. Lead was banned as a fuel additive in the United States beginning in 1996. Figure 2 shows the decline over time in the lead content of leaded fuel in the United States [9].

**Figure 2.** Temporal lead content in leaded fuel in the United States.

2

precipitators, and fabric filter will be introduced in the chapter as methods to control partic‐ ulate matter pollutants. To control gaseous pollutants, the chapter will present methods such as adsorption, absorption, condensation, incineration, applications of biological system, and photocatalyst. Each technology will be presented in detail from definition to principle and applications. The advantages and disadvantages of each technology will be described and

Strategies to control air pollutants emitted from transportation activities include regulations to control precursor pollutants in raw materials; the application of catalytic converters to reduce NOx, CO, and hydrocarbon emissions; the control of lubricant consumption; the reduction of motorized transportation demand; and the improvements to road quality and

Air pollutants can be controlled based on regulations that control precursor pollutants in raw materials such as sulfur and lead. Sulfur oxides (SOx) in aerosol are formed during the combustion process of sulfur in fossil fuels such as gasoline and diesel. Therefore, the use of low-sulfur-content fuels can be considered as a control strategy to reduce SO2 emissions. Many regulations have been issued to reduce the sulfur content in all transportation fuels. For example, Figure 1 presents a selection of a few of the gasoline and diesel sulfur specifications in major countries and the regulatory timetable associated with the introduction of these

50 Figure 1: Regulations and regulatory timetable for sulfur content in gasoline (A) and diesel (B) in several countries.

61 shows the decline over time in the lead content of leaded fuel in the United States [9].

63 Figure 2: Temporal lead content in leaded fuel in the United States.

72 gasoline, both reformulated and conventional, nationwide, from 2011.

 Regulations concerning oxygenated gasoline and reformulated gasoline were also issued in the United States in 1990 to reduce the vehicular emissions of CO and VOCs. The oxygenated gasoline regulation required a higher oxygen content in gasoline in order to ensure more complete burning of the gasoline and thereby reduce harmful tailpipe emissions from motor vehicles. In this respect, oxygen dilutes or displaces the precursor pollutant components in gasoline such as aromatics (e.g., benzene) and sulfur and thus decreases their content in gasoline. The reformulated gasoline regulation is specially blended gasoline. Therefore, the gasoline can be burned more cleanly and can be prevented from evaporating as quickly as conventional gasoline, thereby reducing the emission of smog-forming and toxic pollutants. To reduce the emission of benzene (VOCs) into an aerosol, the US EPA required all refiners to meet an annual average gasoline benzene content standard of 0.62% by volume (vol %) in all their

73 In addition, the use of new-generation fuels such as biofuels and natural gas can be a valuable strategy to reduce air pollutant 74 emission. Feedstocks for biofuels, mostly plants, are much more environmental-friendly and evenly distributed around the world 75 than the feedstocks for traditional fuels such as oil and gas. Two of the most commonly used biofuels are ethanol and biodiesel.

 In the 1920s, refiners started adding lead compounds to gasoline in order to increase octane levels and improve engine performance by reducing engine "knock" and allowing higher engine compression. However, the burning of leaded fuel introduced massive quantities of atmospheric lead leading to many adverse effects on human health. Therefore, regulations to eliminate lead from leaded fuel began to be issued worldwide from the 1970s. For example, the US EPA scheduled performance standards requiring refineries to decrease the average lead content of all fuels beginning in 1975, but these were postponed until 1979 through a series of regulatory adjustments. By the early 1980s, the lead content in fuels had declined by about 80% due to both the regulations and the fleet turnover [8]. In August 1984, the US EPA proposed a further reduction of lead to 0.1 grams per liter gallon (gplg) by January 1, 1986. However, several refineries were not able to achieve this time scale, so the US EPA postponed the deadline until January 1, 1988. Lead was banned as a fuel additive in the United States beginning in 1996. Figure 2

**Figure 1.** Regulations and regulatory timetable for sulfur content in gasoline (A) and diesel (B) in several countries.

compared in the chapter.

222 Current Air Quality Issues

traffic flow.

*2.1.1. Raw materials*

specifications [7].

51

62

**2. Upstream control strategies**

**2.1. Control transportation activities**

Regulations concerning oxygenated gasoline and reformulated gasoline were also issued in the United States in 1990 to reduce the vehicular emissions of CO and VOCs. The oxygenated gasoline regulation required a higher oxygen content in gasoline in order to ensure more complete burning of the gasoline and thereby reduce harmful tailpipe emissions from motor vehicles. In this respect, oxygen dilutes or displaces the precursor pollutant components in gasoline such as aromatics (e.g., benzene) and sulfur and thus decreases their content in gasoline. The reformulated gasoline regulation is specially blended gasoline. Therefore, the gasoline can be burned more cleanly and can be prevented from evaporating as quickly as conventional gasoline, thereby reducing the emission of smog-forming and toxic pollutants. To reduce the emission of benzene (VOCs) into an aerosol, the US EPA required all refiners to meet an annual average gasoline benzene content standard of 0.62% by volume (vol %) in all their gasoline, both reformulated and conventional, nationwide, from 2011.

In addition, the use of new-generation fuels such as biofuels and natural gas can be a valuable strategy to reduce air pollutant emission. Feedstocks for biofuels, mostly plants, are much more environmental-friendly and evenly distributed around the world than the feedstocks for traditional fuels such as oil and gas. Two of the most commonly used biofuels are ethanol and biodiesel. Biodiesel fuels are oxygenated organic compounds of methyl or ethyl esters derived from a variety of renewable sources such as vegetable oil, animal fat, and cooking oil. There‐ fore, the use of biofuels for transportation activities can significantly reduce the atmospheric emissions of CO, hydrocarbon, and lead.

#### *2.1.2. Catalytic converters*

A catalytic converter is a vehicle emission control device that converts toxic pollutants in exhaust gas to less-toxic pollutants by catalyzing a redox reaction (oxidation or reduction). A catalytic converter comprised usually of the following three main parts is used in internal combustion engines: substrate, washcoat, and catalytic materials. The substrate material is usually a ceramic monolith with a honeycomb structure. A washcoat, usually aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina, is used as a carrier for the catalytic materials. The catalytic material is often a mix of precious metals such as platinum, palladium, and rhodium. The catalytic converter can reduce oxides of nitrogen (NOx) into nitrogen gas (N2), combine or oxidize carbon monoxide (CO) with/or unburned hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O). A schematic diagram illustrating the role of the catalytic converter in reducing air pollutants is shown in Figure 3.

**Figure 3.** A schematic diagram of a catalytic converter.

The relevant catalysts applied to reduce the pollutants emitted from specific engines are listed in Table 1 [10].

To reduce NOx, a controlled amount of the reactive chemical reductant such as anhydrous ammonia, aqueous ammonia, and urea is added to a stream of fuel or exhaust gas and adsorbed onto the catalyst. Due to the role of the catalysts, NOx can react with the reductant to produce nitrogen gas and water according to the following reactions:


**Table 1.** The relevant catalysts for specific engines

gasoline can be burned more cleanly and can be prevented from evaporating as quickly as conventional gasoline, thereby reducing the emission of smog-forming and toxic pollutants. To reduce the emission of benzene (VOCs) into an aerosol, the US EPA required all refiners to meet an annual average gasoline benzene content standard of 0.62% by volume (vol %) in all

In addition, the use of new-generation fuels such as biofuels and natural gas can be a valuable strategy to reduce air pollutant emission. Feedstocks for biofuels, mostly plants, are much more environmental-friendly and evenly distributed around the world than the feedstocks for traditional fuels such as oil and gas. Two of the most commonly used biofuels are ethanol and biodiesel. Biodiesel fuels are oxygenated organic compounds of methyl or ethyl esters derived from a variety of renewable sources such as vegetable oil, animal fat, and cooking oil. There‐ fore, the use of biofuels for transportation activities can significantly reduce the atmospheric

A catalytic converter is a vehicle emission control device that converts toxic pollutants in exhaust gas to less-toxic pollutants by catalyzing a redox reaction (oxidation or reduction). A catalytic converter comprised usually of the following three main parts is used in internal combustion engines: substrate, washcoat, and catalytic materials. The substrate material is usually a ceramic monolith with a honeycomb structure. A washcoat, usually aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina, is used as a carrier for the catalytic materials. The catalytic material is often a mix of precious metals such as platinum, palladium, and rhodium. The catalytic converter can reduce oxides of nitrogen (NOx) into nitrogen gas (N2), combine or oxidize carbon monoxide (CO) with/or unburned hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O). A schematic diagram illustrating the

The relevant catalysts applied to reduce the pollutants emitted from specific engines are listed

To reduce NOx, a controlled amount of the reactive chemical reductant such as anhydrous ammonia, aqueous ammonia, and urea is added to a stream of fuel or exhaust gas and adsorbed onto the catalyst. Due to the role of the catalysts, NOx can react with the reductant to produce

role of the catalytic converter in reducing air pollutants is shown in Figure 3.

their gasoline, both reformulated and conventional, nationwide, from 2011.

emissions of CO, hydrocarbon, and lead.

**Figure 3.** A schematic diagram of a catalytic converter.

nitrogen gas and water according to the following reactions:

in Table 1 [10].

*2.1.2. Catalytic converters*

224 Current Air Quality Issues

$$\begin{aligned} 4NO + 4NH\_3 + O\_2 &\rightarrow 4N\_2 + 6H\_2O \\ 2NO\_2 + 4NH\_3 + O\_2 &\rightarrow 3N\_2 + 6H\_2O \\ NO + NO\_2 + 2NH\_3 &\rightarrow 2N\_2 + 3H\_2O \end{aligned}$$

The reaction typically takes places at an optimal temperature range between 630 and 720 K, but can operate from 500 to 720 K with longer residence times. To operate an effective process, the engine requires an external urea tank and dosing system. The specific NOx/ammonia and ammonia/catalyst ratios can be designed to optimize a specific application. At optimal conditions, the application of a catalyst in the downstream of engine can reduce NOx emissions from vehicles by 70–90%.

The reactions to oxidize carbon monoxide and unburned hydrocarbon are described by the following reactions:

$$\begin{aligned} \text{2CO} + \text{O}\_2 &\rightarrow \text{2CO}\_2\\ \text{C}\_xH\_{2\times 2} + [(3\text{x} + 1)/2] \text{O}\_2 &\rightarrow \text{xCO}\_2 + (\text{x} + 1)H\_2\text{O} \end{aligned}$$

#### *2.1.3. Lubricant consumption*

Lubricants are composed of a base fluid and additives. The base fluid is the major part of the lubricant formulation and is mainly made from petroleum-based oils. The additives are used to obtain desirable properties. Lubricants are very important substances for reducing the wear and tear of machine parts. Lubricants also reduce friction, which in turn reduces heat loss. The worldwide consumption of lubricants is more than 41 million tones [11]. They have a soluble organic fraction of 60%, which contributed between 20% and 90% of the total particulates in air that were generated from engine lubricant consumption. Therefore, the particulate emission rate can be significantly reduced by controlling engine lubricant consumption. The strategies to control engine lubricant consumption include changing the piston-ring design and manipulating the operation conditions of the engine such as intake air pressure. The use of biolubricants is also a valuable strategy to reduce the adverse effects of traditional lubricants to the atmospheric emissions of particulate matter. Biolubricants are described in many ways such as eco-friendly lubricants, green lubricants, biodegradable lubricants, recyclable, nontoxic, and reusable.

#### *2.1.4. Reduce motorized transportation demand*

Strategies applied to encourage the use of nonmotorized transport, discourage nonessential trips, shorten trip lengths, and restrain the use of private cars can reduce the overall demand for motorized transport and thus minimize the emission of air pollutants from transportation activities. The strategies could be instigated based on the following regulations:


#### *2.1.5. Road quality and traffic flow*

Road quality also directly affects the air pollutants emitted from transportation activities. For example, the operation of vehicles on unpaved roads can introduce a significant amount of atmospheric particulate matter. Therefore, road qualities need to be improved to reduce air pollutant emission. The strategies to improve road quality include:


Strategies to improve traffic flow and thereby minimize unnecessary braking and reduce congestion can result in high efficiency of vehicle operation and reduce undesired pollutant emissions. These strategies can be obtained based on the following methods:


#### **2.2. Control agricultural activities**

Air pollutants emitted from the agricultural sector are mainly methane (CH4), nitrous oxide (N2O), and ammonia (NH3). Agriculture is also a major source of PM, both primary and secondary in origin [12]. Agricultural pollutants are mainly generated from livestock produc‐ tion and the application of fertilizers and pesticides. Therefore, strategies to control air pollutants emitted from agriculture activities are strongly linked to the activities including strategies to control livestock feeding, animal housing systems, manure storage systems, application of manure for crops, and application of fertilizers and pesticides.

#### *2.2.1. Livestock feeding*

to the atmospheric emissions of particulate matter. Biolubricants are described in many ways such as eco-friendly lubricants, green lubricants, biodegradable lubricants, recyclable,

Strategies applied to encourage the use of nonmotorized transport, discourage nonessential trips, shorten trip lengths, and restrain the use of private cars can reduce the overall demand for motorized transport and thus minimize the emission of air pollutants from transportation

**•** Provide safe and comfortable conditions for walking and other forms of nonmotorized transport

Road quality also directly affects the air pollutants emitted from transportation activities. For example, the operation of vehicles on unpaved roads can introduce a significant amount of atmospheric particulate matter. Therefore, road qualities need to be improved to reduce air

**•** Investigate new types of asphalt and concrete, which are cheap and environmental-friendly

Strategies to improve traffic flow and thereby minimize unnecessary braking and reduce congestion can result in high efficiency of vehicle operation and reduce undesired pollutant

**•** Reduce vehicle speeds because fast moving vehicles stir up dust (a reduction in speed from 40

activities. The strategies could be instigated based on the following regulations:

**•** Compact design of retail and entertainment centers with workers and public transport

**•** Limit use of private vehicles both by pricing and by administrative regulation

pollutant emission. The strategies to improve road quality include:

**•** Sweep roads frequently (can reduce concentrations of PM up to 20%)

emissions. These strategies can be obtained based on the following methods:

nontoxic, and reusable.

226 Current Air Quality Issues

**•** Increase fuel taxes

**•** Increase parking charges **•** Increase road pricing

*2.1.5. Road quality and traffic flow*

**•** Try to pave unpaved roads

**•** Cover operating trucks

**•** Control traffic signals

**•** Increase infrastructure capacity

**•** Reduce congestion by congestion charging

**•** Flush roads with water in the dry season

**•** Design road systems by use of ring roads and bypasses

miles per hour (m/h) to 20 (m/h) reduces dust emissions by 65%)

*2.1.4. Reduce motorized transportation demand*

**•** Improve public transportation quality and efficiency

Because the quantity of nitro compounds, such as ammonia and nitrous oxide excreted from animal feces and urine, is linearly dependent on the intake of nitrogen in food (protein), the strategies to reduce the oversupply of protein in animal feedstock can reduce nitrogen excretions and thus decrease the emissions of nitrogen-containing compounds [13]. Such strategies involve adapting the amount of proteins in the food to the needs of the animals. For instance, young animals and high-productive animals require more protein than older and less-productive animals. On average, this measure leads to a NH3 emission reduction of 10% for a 1% reduction in the mean protein content in the diet, but efficiencies depend strongly on the animal categories. It has no implications on animal health as long as the requirements for all amino acids are ensured. It is most applicable to housed animals while the practical applicability of feeding strategies to grazing animals is limited.

#### *2.2.2. Animal housing systems*

The available strategies to reduce NH3 emissions from animal housing systems have been well known for decades and apply one or more of the following principles [13]:


#### *2.2.3. Manure storage*

The strategies to eliminate air pollutants emitted from manure storage can be based on the following principles:


#### *2.2.4. Manure used for crops*

The application of manure for crops can emit a significant amount of atmospheric pollutants. The strategies or application techniques to control the emissions can be based on the following principles:


#### *2.2.5. Fertilizer application*

The strategies to reduce emissions of pollutants from the application of fertilizers are based on one or more principles including:


For example, the techniques for the application of urea and ammonium-based fertilizers can reduce levels of ammonia emission as follows [13]:


#### **2.3. Control construction fields**

The strategies to control air pollutants emitted from construction fields can be classified into four categories: control of site planning, construction traffic, demolition works, and site activities [14].

#### *2.3.1. Site planning*

**•** Decreasing the surface area where emissions can take place, i.e., by covering the storage,

The application of manure for crops can emit a significant amount of atmospheric pollutants. The strategies or application techniques to control the emissions can be based on the following

**•** Decrease the exposed surface area of slurries applied to surface soil through band application,

**•** Decrease the time that emissions can take place, i.e., bury the slurry or solid manures through

**•** Decrease the source strength of the emitting surface, i.e., through lowering the pH and NH4

The strategies to reduce emissions of pollutants from the application of fertilizers are based

**•** Decrease emission sites by decreasing the surface area via band application, injection, and

**•** Decrease the emission periods of pollutant via rapid incorporation of fertilizers into the soil or

For example, the techniques for the application of urea and ammonium-based fertilizers can

**Fertilizer type Application techniques Emission reduction %**

Incorporation following surface application

Incorporation following surface application

>80 >30 >50 >40 ~100 >80

>50 >40

Surface spreading with irrigation

Surface spreading with irrigation

**•** Decrease the emitting source surface strength via urea inhibitors and blending

**•** Ban use of pollutant precursors such as ammonium (bi) carbonate

Urea inhibitors

Ban Injection

reduce levels of ammonia emission as follows [13]:

encouraging crusting, and increasing the storage depth

**•** Reducing the pH and temperature of the manure

**•** Minimizing disturbances such as aeration

*2.2.4. Manure used for crops*

injection, and incorporation

*2.2.5. Fertilizer application*

incorporation

via irrigation

Ammonium carbonate Ammonium-based fertilizers

injection or incorporation into the soil

on one or more principles including:

Urea Injection

concentration of the manure (through dilution)

principles:

228 Current Air Quality Issues

Regulations applied to control air pollutants emitted from site planning include:


#### *2.3.2. Construction traffic*

Regulations applied to control air pollutants emitted from construction traffic activities include:


#### *2.3.3. Demolition works*

Regulations applied to control air pollutants emitted from demolition works include:


#### *2.3.4. Site activities*

Regulations applied to control air pollutants emitted from site activities include:


#### **2.4. Miscellaneous**

Coal, the most abundant solid fuel and widely used for power plant and other industrial activities, is the largest source of air pollutant emissions. Coal combustion produces a signif‐ icant amount of air pollutants such as SOx, heavy metals, and PM. For example, sulfur in coal occurs both as inorganic minerals (mainly pyrite and marcassite) and organic compounds incorporated in the combustible part of coal. The sulfur content can be converted into SOx during the coal combustion. Therefore, reducing the sulfur content in coal before the combus‐ tion processes is a great strategy to reduce SOx emissions from the upstream coal combustion process. Inorganic sulfur in coal can be removed by coal washing and the organic sulfur by using chemical hydrogenation and gasification processes.

Mining activities can produce significant air pollutants such as heavy metals (in PM form), SOx and NOx. Strategies to reduce air pollutants emitted from mining activities from the upstream process include enclosure or cover mine, mining area, and transfer areas; water spraying mining area; and stabilizing unpaved traffic areas.

Indoor activities can also be a significant source of air pollution. Strategies to reduce air pollutants emitted from indoor activities include improvement of cooking devices, use of alternative fuels for cooking and reducing the need for fire. Strategies to improve cooking devices include stabilization of stove materials and improvement of stove chimneys, in particular, biomass stoves. Uses of alternative fuels for cooking including charcoal, biogas, liquid petroleum gas, and electricity can significantly reduce air pollutant emissions. For example, the transition from wood to charcoal for cooking can reduce PM10 emissions by more than 80% (although the wider environmental impacts of charcoal production must be consid‐ ered). The need for fire can be reduced based on the use of solar heating or electric devices.

The change of building materials from high-polluting materials such as paint, linoleum, and gypsum to low-polluting materials such as PVC and polyolefin can also control air pollutants from upstream emissions.
