Air Quality Standards and Pollution Monitoring

Air Quality

• Air quality is affected by pollution emitted from various sources
• The EPA classifies six principal pollutants: CO, O3, NOx, SOx, PM, and Pb
• The Clean Air Act established primary and secondary standards for air quality
  • Primary standards protect public health, including sensitive populations like asthmatics, children, and the elderly.
  • Secondary standards protect public welfare, including decreased visibility and environmental damage to animals, crops, vegetation, and buildings.

Ambient Air Quality Standards

• The US has set standards for various pollutants, such as Carbon Monoxide, Lead, Nitrogen Dioxide, and Particulate Matter (PM10 & PM2.5) with specific averaging times and primary/secondary classifications.

Purposes of Air Quality Monitoring

• Provide data for health risk assessments
• Provide data for dispersion modeling for industrial applications
• Evaluate air pollution control equipment
• Provide information for designing new process and control equipment
• Provide information on process operations

Stack Emission Monitoring Types

• Periodic Measurements: Measurements are taken at specific intervals (hourly, daily, weekly, etc.)
  • Samples are usually extracted from the stack (extractive sampling).
  • Spot or "grab" samples are collected over specific durations.
  • Samples may be analyzed on-site or in a laboratory.
• Continuous Emission Monitoring (CEM): Instruments permanently installed near the stack continuously monitor harmful air pollutants.

Representative Air Sampling in Stacks

• The goal is to collect a representative sample of the material being monitored.
• Achieving a representative sample depends on the homogeneity of the material.
  • If homogeneous, fewer samples are required.
  • If heterogeneous, more samples are needed.
• Factors to consider for choosing a sampling location:
  • Safe access
  • Entry for sampling equipment
  • Adequate space for equipment and personnel
  • Essential services (electricity)

Representative Air Sampling for Particulates and Gases

• Gases can become non-homogeneous due to variations in chemical composition, temperature, or velocity, leading to stratification.
• Special measures are needed for collecting representative samples from stacks when particles are present.
  • Inertial effects can lead to uneven distribution of particles.
  • Multiple sample points across the sampling plane are necessary.
  • Isokinetic sampling is used, following international standards like US EPA Method 5, to ensure representative samples.

Isokinetic Sampling

• For extractive methods of PM, sampling must be isokinetic, ensuring the velocity and direction of the gas/PM at the nozzle match the approaching gas stream in the stack.
• It is a complex, time-consuming process requiring specialized equipment.
• Used for determining PM concentrations in ducts or stacks.

Range of Stack Gas Measurements

• Measurements include:
  • Particulate Matter (PM)
  • Acid Gases
  • Metals
  • Dioxins and Furans
  • Amino acids and proteins
  • Combustion products
  • Full gas suite including: VOCs, CO, NOx, SO2, CO2, and O2

Ambient (Outdoor) Air Monitoring

• Ambient air quality monitoring stations gather data for various purposes:
  • Public dissemination of air pollution data
  • Compliance with national and international standards
  • Emission strategy development
  • Support for air pollution research, including exposure and health assessment and source identification.

Ambient Air Quality Monitoring Stations

• Stations are usually equipped with rack-mounted analyzers for measuring gases and PMs, as well as data logging systems with remote data retrieval capabilities.
• They also record meteorological information, including wind speed, wind direction, air temperature, atmospheric pressure, temperature, relative humidity, and rainfall.
• Windroses graphically present the frequency of wind direction and speed categories, aiding in data interpretation and modeling.

Mobile Analyzers / Laboratory Vans

• These units are used for mobile air quality monitoring and data collection.

Ambient Air Quality Monitoring Stations: Gas Analysis

• Various methods are used:
  • Colorimetric method
  • Chemical-sensing electrodes and electrochemical cells
  • Non-dispersive Infrared (NDIR)
  • Gas Chromatography (GC) with various detectors like Flame Ionization Detector (FID), Thermal Conductivity Detector (TCD), Chemiluminescence, and Mass Detector (MS).
• Specific gas analyzers are used for:
  • Sulphur dioxide (SO2) using UV/fluorescence analyzers
  • Hydrogen Sulfide (H2S) analyzer, utilizing catalytic conversion to SO2
  • Carbon monoxide (CO) using GFC-IR analyzer
  • Ozone by UV analyzer
  • Continuous Emission Monitoring (CEM) – Stack Monitoring

Measurements of Particulate Matter (PM)

• High-volume samplers (>1 m3/min)
• Medium-volume samplers (0.1 m3/min)
• Low-volume samplers