Exhaustive Guide to Air Analysis: Atmospheric Composition and Pollutant Classification

Course Overview and Syllabus

• Course Code and Title: Air Analysis ($EMT325$).

• Credit Unit: $1$ Credit.

• Lecturers: Dr. A. F. Eghomwanre and Dr. M. O. Akharame.

• Syllabus Outline:

  • Air pollution and classification of air pollutants.

  • Criteria air pollutants.

  • Sampling and analysis of air pollutants.

  • Ambient air sampling guidelines.

  • Measurement and analysis of meteorological parameters.

  • Ambient weather parameters: wind speed, wind direction, relative humidity, temperature, and solar radiation.

Introduction to the Atmosphere and Air Pollution

• Atmospheric Composition: The Earth's atmosphere is primarily composed of four main gases:

  • Nitrogen ($N_2$): $78.08\%$

  • Oxygen ($O_2$): $20.95\%$

  • Argon ($Ar$): $0.93\%$

  • Carbon-dioxide ($CO_2$): $0.325\%$

• Trace Components: The remaining portion (less than $0.1\%$) includes gases such as helium, neon, xenon, ozone, and krypton. Additionally, the atmosphere contains water vapor, dust particles, smoke, and pollen.

• Impact on Human Health: Atmospheric pollution is a major factor responsible for:

  • Morbidity: The condition of suffering from a disease or medical condition.

  • Mortality: Death on a large scale.

Detailed Chemical Composition of Tropospheric Air

• Reactive Trace Gases:

  • Carbon-monoxide ($CO$): $0.1\,\text{ppm}$

  • Methane ($CH_4$): $1.4\,\text{ppm}$

  • Nitrogen-dioxide ($N_2O$): $0.5\,\text{ppm}$

  • Ammonia ($NH_2$): $6.0\,\text{ppm}$

  • Ozone ($O_3$): $0$ to $0.4\,\text{ppm}$

• Non-reactive Trace Gases:

  • Helium ($He$): $5.2\,\text{ppm}$

  • Neon ($Ne$): $18.0\,\text{ppm}$

  • Hydrogen ($H_2$): $0.5\,\text{ppm}$

  • Nitrous oxide ($NO$): $0.28\,\text{ppm}$

Definition and Classification of Air Pollution

• Definition: Air pollution is the introduction of any chemical, physical, or biological agent into the indoor or outdoor environment in harmful or excessive concentrations. These agents cause harm or discomfort to humans and other living organisms or damage the natural environment.

• Types of Harm:

  • Direct Harm: Effects on human health, reduction in crop yields, damage to rubber products (e.g., tires), and erosion of marble sculptures.

  • Indirect Harm: Large-scale environmental changes such as climate change.

• Classification Criteria: Air pollutants are classified in three ways:

  1. According to Origin.

  2. According to State of Matter.

  3. According to Sources.

Classification by Origin: Primary and Secondary Pollutants

• Primary Air Pollutants: These are emitted directly from identifiable sources or produced by natural events (e.g., dust storms and volcanic eruptions).

  • Examples: Smoke, dust, oxides of sulphur ($SO_x$), oxides of nitrogen ($NO_x$), hydrocarbons, and particulate matter.

• Secondary Air Pollutants: Formed in the atmosphere through chemical interactions between primary pollutants and other atmospheric constituents, often during photochemical reactions.

  • Characteristics: These often have short lifespans but are continuously formed and destroyed.

  • Reactive Radicals: Include hydroxyl radical, oxygen radical, and hydrogen radical (very short-lived and rarely measured).

  • Specific Examples:

    • Ground-level Ozone ($O_3$): Formed when $NO_x$ and volatile organic compounds ($VOCs$) react in sunlight.

    • Acid Rain: Created when sulphur dioxide ($SO_2$) and $NO_x$ react with water to produce sulfuric and nitric acids.

    • Photochemical Smog: A complex mixture involving ozone formed by $NO_x$, $VOCs$, and sunlight.

    • Peroxyacyl Nitrates ($PANs$): Formed from hydrocarbons, $NO_x$, and oxygen in the presence of light.

    • Others: Hydrogen peroxide, acids, and reactive radicals.

Classification by State of Matter and Sources

• By State of Matter:

  • Gaseous Air Pollutants: Exist as gas at normal temperature/pressure (e.g., $CO_2$, $NO_2$, $SO_2$).

  • Particulate Air Pollutants: Non-gaseous substances; including suspended droplets, solid particles, or mixtures of both.

• By Sources:

  • Natural Sources:

    • Volcanic Eruptions: Major source of $SO_2$ and particulates; releases complex chemical compositions and fluorine compounds.

    • Forest Fires: Produce $CO$, $CO_2$, $NO$, $NO_2$, $SO_2$, and particles through carbonation of wood.

    • Thunderstorms/Lightning: High energy splits molecules to form $NO_2$ via free radicals:

      • $N_2 \rightarrow 2N$

      • $O_2 \rightarrow 2O$

      • $N + O \rightarrow NO$

      • $NO + O \rightarrow NO_2$

    • Bacterial Action: Methane ($CH_4$) produced in swampy areas via bacterial mash.

    • Oceans: Release large amounts of $CO_2$ from marine organisms.

  • Anthropogenic Sources:

    • Point Sources: Stationary objects like factories, smoke stacks, power plants (thermal and nuclear), oil refineries, and metallurgical industries.

    • Non-point (Diffuse) Sources: Residential areas, hospitals, utility/waste units, and agricultural operations.

    • Mobile Sources (Sub-category of Non-point): Includes on-road (cars, trucks) and off-road (tractors, lawn mowers, boats, ships, locomotives, airplanes). Major emissions include hydrocarbons, $SO_x$, $NO_x$, $CO_x$, and smoke.

Criteria Air Pollutants (EPA Standards)

The Environmental Protection Agency (EPA) defines six major pollutants with set ambient standards to protect human health:

1. Carbon monoxide ($CO$).

2. Sulfur dioxide ($SO_2$).

3. Nitrogen oxides ($NO_x$).

4. Particulates ($PM_{10}$ and $PM_{2.5}$).

5. Ozone ($O_3$).

6. Lead ($Pb$).

Carbon Monoxide ($CO$): Characteristics and Health Impacts

• Properties: A poisonous, tasteless, odorless, and colorless gas.

• Formation: Result of incomplete combustion of fuels (biomass, coal, natural gas, kerosene, and Prime Motor Spirit ($PMS$)) due to poor mixing of air and fuel.

• Dominant Sources: On-road transportation (gasoline/diesel), off-road engines, biomass burning (cooking/heating in rural areas), and forest fires.

• Biological Mechanism:

  • Absorbed via lungs, crosses the alveolar-capillary membrane.

  • Enters red blood cells and binds to hemoglobin to form carboxyhemoglobin ($COHb$).

  • As an asphyxiant, it reduces the blood's capacity to carry oxygen.

• Health Effects: Tissue hypoxia (low oxygen levels), headaches, reduced mental alertness, heart attacks, cardiovascular diseases, and impaired fetal development.

Sulphur Dioxide ($SO_2$)

• Sources: Primarily fossil fuel combustion, refuse incineration, vehicular emissions, and decay of organic waste. Metal processing (roasting sulfide ores) is also a significant source.

• Regulation: While many developed countries have reduced sulfur in fuels, many others lack controls on mobile-source emissions.

• Environmental/Health Impacts: Associated with eye irritation, wheezing, shortness of breath, lung damage, acid rain formation, visibility impairment, and aesthetic damage to structures.

Nitrogen Oxides ($NO_x$)

• Forms: Nitrous oxide ($N_2O$), Nitric oxide ($NO$), and Nitrogen dioxide ($NO_2$).

• Origins: $N_2O$ comes from soil microbiological processes; $NO$ and $NO_2$ come from fossil fuel combustion, biomass burning, and lightning.

• Indoor Sources: Cigarette smoke, gas cookers, oil/kerosene/coal heaters, stoves, and electric water warmers.

• Properties: $NO_2$ is a reddish-brown, highly reactive gas and a precursor to secondary pollutants.

• Health Effects: Susceptibility to respiratory infections, lung irritation, coughing, chest pain, and difficulty breathing.

Particulate Matter (PM)

• Classification by Aerodynamic Diameter:

  • Coarse Particles ($PM_{10}$): Diameter $\le 10\,\mu \text{m}$. Deposited in extra-thoracic airways; causes pulmonary inflammation.

  • Fine Particles ($PM_{2.5}$): Diameter $\le 2.5\,\mu \text{m}$. Penetrates deeper into the alveoli through airflow and diffusion.

  • Ultrafine Particles ($PM_{0.1}$ or $UFP$): Diameter $\le 0.1\,\mu \text{m}$. Can pass through cell membranes and interact directly with cellular structures.

• Sources: Human activities (walking, cleaning), wood/fossil fuel combustion, and cooking (especially high-temperature preparation which emits water vapor and various particles). Other sources include incense, candles, and smoking.

• General Health Effects: Eye irritation, asthma, bronchitis, cancer, heavy metal poisoning, cardiovascular effects, and visibility impairment.

Ozone ($O_3$)

• Chemical Formation: Reactions between dioxygen ($O_2$) and singlet oxygen ($O$) in the presence of a third-body molecule to absorb reaction heat.

• Levels:

  • Stratospheric: Can move downward to increase background levels.

  • Tropospheric (Ground-level): High levels are caused by photochemical reactions between $VOCs$ and $NO_x$.

• Health Risks:

  • Respiratory distress (shortness of breath, pain during deep breaths, airway inflammation).

  • Increased risk of premature death, particularly from respiratory illness.

  • High risk for children due to higher dose-to-body-mass ratio and developing lungs.

  • Potential for skin cancer, eye diseases, and infectious diseases.