🌡️Environmental Monitoring and Control Unit 4 – Air Quality Monitoring & Control

Key Concepts in Air Quality

• Air quality refers to the condition of the air in terms of the presence or absence of pollutants and their concentrations
• Primary pollutants are emitted directly from sources (particulate matter, sulfur dioxide, nitrogen oxides)
• Secondary pollutants form in the atmosphere through chemical reactions (ozone, secondary particulate matter)
• Criteria air pollutants are common pollutants regulated by the EPA under the Clean Air Act (carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, sulfur dioxide)
• Air quality index (AQI) communicates the level of air pollution and associated health risks to the public
  • Ranges from 0 to 500, with higher values indicating greater health concerns
  • Calculated based on concentrations of criteria pollutants
• Meteorological factors influence air quality by affecting pollutant dispersion and chemical reactions (wind speed, temperature, humidity, atmospheric stability)
• Indoor air quality is affected by sources within buildings (volatile organic compounds from furniture and cleaning products, radon, mold)

Air Pollutants and Their Sources

• Particulate matter (PM) consists of solid and liquid particles suspended in the air
  • Primary sources include combustion, dust, and sea salt
  • Secondary sources form through chemical reactions (sulfates, nitrates, organic compounds)
  • Classified by size: PM10 (diameter ≤ 10 μm) and PM2.5 (diameter ≤ 2.5 μm)
• Sulfur dioxide (SO2) is emitted from the combustion of sulfur-containing fuels (coal, oil)
• Nitrogen oxides (NOx) are produced during high-temperature combustion processes (vehicles, power plants)
• Volatile organic compounds (VOCs) are emitted from various sources (solvents, paints, gasoline)
  • React with NOx in the presence of sunlight to form ground-level ozone
• Carbon monoxide (CO) is a product of incomplete combustion (vehicle exhaust, wood-burning stoves)
• Lead (Pb) emissions have decreased significantly due to the phase-out of leaded gasoline
  • Current sources include lead smelters, battery manufacturing, and aviation gasoline
• Greenhouse gases (carbon dioxide, methane, nitrous oxide) contribute to climate change

Measurement Techniques and Instrumentation

• Gravimetric methods determine PM mass by weighing filters before and after sampling
• Beta attenuation monitors measure PM mass by detecting the attenuation of beta radiation through a sample
• Tapered element oscillating microbalance (TEOM) measures PM mass by detecting changes in the oscillation frequency of a filter
• Chemiluminescence analyzers measure NO and NO2 concentrations based on the light emitted during the reaction of NO with ozone
• UV fluorescence analyzers measure SO2 concentrations by detecting the fluorescence of SO2 molecules excited by UV light
• Non-dispersive infrared (NDIR) analyzers measure CO and CO2 concentrations by detecting the absorption of infrared light
• Gas chromatography (GC) separates and quantifies individual VOCs based on their interaction with a stationary phase
• Passive samplers collect pollutants by diffusion onto a sorbent material without using a pump
  • Used for long-term monitoring of VOCs, NO2, and SO2
• Remote sensing techniques (satellite imagery, lidar) provide spatial coverage of air pollutants

Air Quality Standards and Regulations

• National Ambient Air Quality Standards (NAAQS) set by the EPA under the Clean Air Act
  • Primary standards protect public health, including sensitive populations (children, elderly, asthmatics)
  • Secondary standards protect public welfare (visibility, crops, vegetation, buildings)
• NAAQS exist for criteria pollutants: CO, Pb, NO2, O3, PM (PM10 and PM2.5), and SO2
  • Specify averaging times and concentration limits not to be exceeded
• State Implementation Plans (SIPs) outline how states will attain and maintain NAAQS
• New Source Performance Standards (NSPS) regulate emissions from new, modified, or reconstructed stationary sources
• National Emission Standards for Hazardous Air Pollutants (NESHAPs) control emissions of 187 toxic air pollutants
• Prevention of Significant Deterioration (PSD) program requires permits for major sources in attainment areas
• Regional haze regulations aim to improve visibility in national parks and wilderness areas

Monitoring Networks and Data Analysis

• State and Local Air Monitoring Stations (SLAMS) are the primary network for compliance with NAAQS
  • Measure criteria pollutants and meteorological parameters
  • Sited to represent population exposure, source impacts, and background levels
• National Air Toxics Trends Stations (NATTS) monitor hazardous air pollutants to assess trends and evaluate regulations
• Interagency Monitoring of Protected Visual Environments (IMPROVE) network measures visibility-impairing pollutants in national parks and wilderness areas
• Chemical Speciation Network (CSN) characterizes the composition of PM2.5 for source apportionment and health studies
• Air Quality System (AQS) database stores and manages air quality data collected by monitoring networks
• Data validation and quality assurance procedures ensure the accuracy and reliability of monitoring data
  • Calibration, audits, and data completeness requirements
• Statistical analyses (trend analysis, spatial interpolation) and air quality modeling provide insights into pollutant behavior and source contributions

Control Technologies and Strategies

• Electrostatic precipitators (ESPs) remove particulate matter from industrial exhaust gases using electrostatic attraction
• Baghouses filter particulate matter from gas streams using fabric filters
• Wet scrubbers remove pollutants by contact with a liquid (usually water) in a spray tower or packed bed
  • Used for controlling PM, SO2, and other soluble pollutants
• Selective catalytic reduction (SCR) reduces NOx emissions by reacting NOx with ammonia over a catalyst
• Flue gas desulfurization (FGD) removes SO2 from power plant exhaust gases using a sorbent (limestone, lime)
• Vapor recovery systems capture and control VOC emissions during fuel storage and transfer
• Transportation control measures reduce emissions from mobile sources (vehicle inspection and maintenance programs, fuel reformulation, congestion pricing)
• Energy efficiency and renewable energy reduce emissions by decreasing fossil fuel consumption
• Urban planning strategies (mixed-use development, public transit) reduce vehicle miles traveled and associated emissions

Health and Environmental Impacts

• Particulate matter exposure is linked to respiratory and cardiovascular diseases, premature mortality, and reduced lung function
  • PM2.5 can penetrate deep into the lungs and enter the bloodstream
• Ozone exposure can cause respiratory irritation, reduced lung function, and aggravate asthma
  • Damages vegetation and reduces crop yields
• Nitrogen dioxide exposure can aggravate respiratory diseases and increase susceptibility to infections
  • Contributes to the formation of ozone and particulate matter
• Sulfur dioxide exposure can cause respiratory irritation and aggravate asthma
  • Contributes to the formation of acid rain, which damages ecosystems and buildings
• Carbon monoxide exposure reduces the blood's oxygen-carrying capacity and can be fatal at high concentrations
• Lead exposure can cause neurological damage, especially in children
  • Accumulates in the environment and bioconcentrates in the food chain
• Air pollution contributes to climate change through the emission of greenhouse gases and the formation of short-lived climate pollutants (black carbon, ozone)

Future Trends and Challenges

• Population growth and urbanization will increase the demand for energy and transportation, potentially leading to higher emissions
• Climate change may exacerbate air quality problems by affecting meteorological conditions and pollutant formation
  • Higher temperatures can increase ozone formation and the frequency of wildfires
• Emerging pollutants, such as ultrafine particles and engineered nanomaterials, may pose new health risks
• Transboundary air pollution requires international cooperation and agreements to address effectively
• Environmental justice concerns arise when disadvantaged communities are disproportionately affected by air pollution
• Balancing economic development with air quality improvements is a challenge, particularly in developing countries
• Technological advancements (electric vehicles, renewable energy, low-emission industrial processes) offer opportunities for reducing emissions
• Integrated approaches that consider the interactions between air quality, climate change, and other environmental issues are needed for sustainable solutions