Chapter 7 Air pollution-upload241112_360be5fc0f479d1ee9a1b0ffc151b9e7

Class and Exam Information

  • Course: CIVL1105 Environmental Engineering

  • Instructor: Lingyue Zhang (zly17@hku.hk)

  • Class Hours: 6 class hours from 15-26 Nov 2024

  • TA Session: Scheduled for 29 Nov 2024

Final Exam Details

  • Coverage: Chapters 7 and 8

  • Exam Format:

    • Multiple choice and open-ended questions

    • No calculations required

    • Focus on key slides and marked key points

Expected Learning Outcomes for Chapter 7

  • Understand major air pollutants including:

    • Sources

    • Effects on health and environment

    • Control measures

  • Analyze air pollution phenomena such as:

    • Photochemical smog

    • Meteorological effects

  • Grasp simple air pollution models

  • Discuss atmospheric stability

Types of Air Pollutants

  • Primary Air Pollutants: Emitted directly from sources (e.g., CO, NOx)

  • Secondary Air Pollutants: Formed from reactions between other pollutants (e.g., O3 from VOCs + NOx + sunlight)

  • Definition: Substances absent from natural atmosphere that are harmful to health/environment

Formation of Air Pollutants

From Combustion

  • Complete Combustion:

    • Example: CH4 + O2 -> CO2 + H2O

  • Incomplete Combustion Sources:

    • Low temperature, low oxygen, inadequate mixing

    • Results in CO and unburned hydrocarbons (HC)

  • Nitrogen Oxides Formation:

    • Thermal NOx formation occurs at high temperatures during combustion

Secondary Pollutant Formation

  • Photochemical Reactions:

    • VOCs + NOx + sunlight -> O3 (photochemical smog)

    • Major sources include mobile (transport) and stationary sources (industrial)

Effects of Air Pollution

Health Impacts

  • Historical event: London Smog (1952) resulted in ~4000 deaths

  • Chronic smog issues in southern California

Environmental Damage

  • Effects on vegetation, materials, and soil pH (Acid rain due to SOx, NOx)

  • Contribution to climate change and global warming (CO2)

Air Pollution in China

  • Significant smog incidents noted (e.g., Beijing, 25 days of smog in January 2013)

  • Major advancements in air quality detection and control measures

Air Pollution in Hong Kong

  • Sources: Motor vehicles, marine vessels, power plants

  • Main pollutants include CO, NO2, SO2, O3, PM2.5, and PM10

  • AQI and AQHI measures public air quality and health risk

Air Quality Index (AQI)

  • Purpose: Provides the public with an understanding of air pollution levels

  • Standard Pollutants: PM10, SO2, CO, NO2, O3

  • Health Effects Ratings:

    • Good (0-50): No health impact

    • Moderate (51-100): Sensitive individuals should reduce effort

    • Unhealthy (>100): General public may experience effects, more severe for sensitive individuals

Key Criteria Pollutants

  • Carbon Monoxide (CO):

    • Major source: vehicle emissions

    • Health effects include arterial oxygen transport disruption

  • Nitrogen Dioxide (NO2):

    • Health impacts begin at concentrations above ~0.7 ppm

    • Forms from combustion processes and leads to photochemical smog

  • Sulfur Dioxide (SO2):

    • Major source: coal-fired power plants

    • Health effects and contribution to acid rain

  • Lead (Pb):

    • Source: Historical usage of leaded gasoline

    • Neurological health risks particularly for children

  • Ozone (O3):

    • Secondary pollutant formed during photochemical reactions

    • Health effects include respiratory issues and damage to vegetation

Particulate Matter (PM)

  • Categories: PM10 and PM2.5

  • Source identification: Incomplete combustion, dust, mist, smoke

  • Health impacts linked to respiratory and cardiovascular systems

Control Measures for Air Pollution

Vehicle Emission Control

  • Alternative Fuels: Ethanol, methanol, CNG, etc.

  • Transportation Control: Promoting public transport

  • Emission Standards: Introduction of catalytic converters

Stationary Source Controls

  • Pre-combustion, combustion, and post-combustion controls aimed at reducing emissions

Atmospheric Stability and Air Quality Modelling

  • Stability: Influences dispersion of air pollutants dependent on thermal inversions and ambient conditions

  • Modeling Techniques: Used to assess pollutant concentration in urban settings

Indoor Air Quality

  • Sources of Indoor Pollution: Cooking, smoking, building materials

  • Greater health risks due to less dilution

Summary

  • Understanding air pollution involves identifying pollutants, their sources, health impacts, and control measures. It is crucial to study the interactions between pollutants and their effects on human health and the environment.