ISO 4220:1983

Overview

ISO 4220:1983 is an international standard established by the International Organization for Standardization (ISO) that specifies a titrimetric method with indicator or potentiometric end-point detection for determining a gaseous acid air pollution index in ambient air. This method is particularly applicable for measuring mass concentrations of sulfur dioxide (SO₂) higher than 30 µg/m³. The procedure evaluates the combined presence of acidic and alkaline gaseous pollutants in ambient air during a specified sampling and analysis period.

The standard guides environmental laboratories and air quality monitoring agencies in quantifying acidic air pollutants, allowing effective monitoring and control of air pollution that directly impacts human health and the environment.

Key Topics

• Scope and Application

  • Applicable to ambient air with sulfur dioxide concentrations greater than 30 µg/m³.
  • Measures an acid air pollution index accounting for water-soluble acidic gaseous pollutants.

• Principle

  • Acidic gaseous pollutants are absorbed and oxidized into sulfuric acid by hydrogen peroxide solution.
  • The formed sulfuric acid is then titrated to determine the pollution index using either a visual indicator or potentiometric pH measurement.

• Reagents and Solutions

  • Hydrogen peroxide solution (27–30% w/w) for absorption and oxidation.
  • Saturated potassium chloride solution for potentiometric titration.
  • Standardized sulfuric acid and sodium tetraborate solutions for titration.
  • pH 4.5 absorption solution and buffer solutions for calibration.

• Sampling and Analysis

  • Air sampling is done over 24 or 48 hours using specialized absorbers and filtering equipment compliant with ISO 4219.
  • Absorbed acid gas pollutants are chemically analyzed by titration to a pH endpoint of 4.5.
  • Titration can be detected via color change (using specific indicators) or by potentiometric pH meter for higher precision.

• Calculations

  • The acid pollution index is calculated based on titration volumes, sample air volume, and standard titrant concentrations, expressing results as micrograms per cubic meter (µg/m³) equivalent to sulfur dioxide.

• Equipment and Quality Control

  • Borosilicate glass absorbers, pH meters with temperature compensation, and magnetic stirrers are essential for accurate measurements.
  • Calibration and validation procedures ensure reliability and repeatability.

Applications

ISO 4220:1983 is highly valuable for:

• Environmental Monitoring

  • Continuous assessment of ambient air quality focused on acid gas pollutants, mainly sulfur dioxide.
  • Supports regulatory compliance and environmental protection agencies in pollution control programs.

• Air Pollution Research

  • Provides a standardized method for comparative air pollution studies globally.
  • Assists in understanding pollutant dispersion and acid rain precursors.

• Industrial Emission Monitoring

  • Enables monitoring of emissions from power plants, industrial facilities, and urban areas.
  • Helps in evaluating the effectiveness of pollution mitigation techniques.

• Public Health Protection

  • Quantification of acidic gas pollutants contributes to air quality indices that guide public warnings and health advisories.

Related Standards

• ISO 4219: Air Quality – Sampling of Sulfur Compounds

  • Specifies equipment and procedures for collecting sulfurous compounds from ambient air, complementing ISO 4220's analytical methodology.

• ISO 10396: Ambient Air – Determination of Sulfur Dioxide (SO₂) – Ultraviolet Fluorescence Method

  • An instrumental method offering continuous detection of SO₂, often used alongside titrimetric methods.

• ISO 10849: Ambient Air – Determination of Acidic Gases (NO₂ and SO₂)

  • Focuses on detection of other acid gases relevant for comprehensive acid pollution profiling.

Keywords: ISO 4220, acid air pollution index, sulfur dioxide measurement, titrimetric method, potentiometric titration, ambient air quality, gaseous acid pollutants, air pollution monitoring, sulfur dioxide analysis, environmental standard, ISO air quality standards.