In-situ Gas and Aerosol Composition Monitor (IGAC)

The IGAC monitor provides real-time measurements of water-soluble inorganic ions in particulate matter.

Data Format

• File format: CSV file
• Sampling frequency: Variable
• File naming pattern: *.csv
• Data structure:
  • Datetime index
  • Ion concentration columns
  • PM2.5 mass concentration
  • Special values: '-' treated as NA

Measurement Parameters

The IGAC provides measurements of:

• Cations:
  • Sodium (Na+)
  • Ammonium (NH4+)
  • Potassium (K+)
  • Magnesium (Mg2+)
  • Calcium (Ca2+)
• Anions:
  • Chloride (Cl-)
  • Nitrite (NO2-)
  • Nitrate (NO3-)
  • Phosphate (PO43-)
  • Sulfate (SO42-)

Data Processing

Data Reading

• Processes CSV files with datetime index
• Handles special values as NA
• Standardizes column names
• Converts measurements to numeric format
• Removes duplicate timestamps

Quality Control

• Applies minimum detection limits (MDL):
  • Na+: 0.06 μg/m³
  • NH4+: 0.05 μg/m³
  • K+: 0.05 μg/m³
  • Mg2+: 0.12 μg/m³
  • Ca2+: 0.07 μg/m³
  • Cl-: 0.07 μg/m³
  • NO2-: 0.05 μg/m³
  • NO3-: 0.11 μg/m³
  • SO42-: 0.08 μg/m³
• Verifies total ion mass < PM2.5 mass
• Ensures presence of main ions (NH4+, SO42-, NO3-)
• Applies log-transformed IQR filtering
• Validates ion balance (cation/anion ratio)
• Applies lower exclusion thresholds

Output Data

The processed data contains:

• Time index: Data acquisition time
• Ion concentrations: All measured ions in μg/m³
• Quality-controlled measurements
• Validated ion balance

Notes

• Critical for secondary inorganic aerosol analysis
• Significant contributor to PM2.5 mass
• Comprehensive quality control procedures
• Ion balance validation
• Main ion species monitoring