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In-situ Gas and Aerosol Composition Monitor (IGAC)

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

AeroViz.rawDataReader.script.IGAC.Reader 

Reader(path: Path | str, reset: bool | str = False, qc: bool | str = True, **kwargs)

Bases: AbstractReader

IGAC (In-situ Gas and Aerosol Composition) Monitor Data Reader

This class handles the reading and parsing of IGAC monitor data files, which provide real-time measurements of water-soluble inorganic ions in particulate matter.

See full documentation at docs/source/instruments/IGAC.md for detailed information on supported formats and QC procedures.

Attributes

nam class-attribute instance-attribute 

nam = 'IGAC'

CATION_COLUMNS class-attribute instance-attribute 

CATION_COLUMNS = ['Na+', 'NH4+', 'K+', 'Mg2+', 'Ca2+']

ANION_COLUMNS class-attribute instance-attribute 

ANION_COLUMNS = ['Cl-', 'NO2-', 'NO3-', 'PO43-', 'SO42-']

MAIN_IONS class-attribute instance-attribute 

MAIN_IONS = ['SO42-', 'NO3-', 'NH4+']

MDL class-attribute instance-attribute 

MDL = {'Na+': 0.06, 'NH4+': 0.05, 'K+': 0.05, 'Mg2+': 0.12, 'Ca2+': 0.07, 'Cl-': 0.07, 'NO2-': 0.05, 'NO3-': 0.11, 'SO42-': 0.08}

Functions

_raw_reader 

_raw_reader(file)

Read and parse raw IGAC monitor data files.

Parameters:

Name Type Description Default
file Path or str

Path to the IGAC data file.

 required

Returns:

Type Description
DataFrame

Processed IGAC data with datetime index and ion concentration columns.

_QC 

_QC(_df)

Perform quality control on IGAC ion composition data.

QC Rules Applied
  1. Mass Closure : Total ion mass > PM2.5 mass
  2. Missing Main : Main ions (NH4+, SO42-, NO3-) not present
  3. Below MDL : Ion concentration below detection limit
  4. Ion Balance : Cation/Anion ratio outside valid range

Data Format

  • File format: CSV file
  • Sampling frequency: 1 hour
  • 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 water-soluble ions:

Cations

Ion Unit Description
Na+ μg/m³ Sodium
NH4+ μg/m³ Ammonium
K+ μg/m³ Potassium
Mg2+ μg/m³ Magnesium
Ca2+ μg/m³ Calcium

Anions

Ion Unit Description
Cl- μg/m³ Chloride
NO2- μg/m³ Nitrite
NO3- μg/m³ Nitrate
PO43- μg/m³ Phosphate
SO42- μg/m³ Sulfate

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

The IGAC reader uses the declarative QCFlagBuilder system with the following rules:

+-----------------------------------------------------------------------+
|                         QC Thresholds                                 |
+-----------------------------------------------------------------------+
| MDL (Minimum Detection Limits):                                       |
|   Cations: Na+ 0.06, NH4+ 0.05, K+ 0.05, Mg2+ 0.12, Ca2+ 0.07 μg/m³   |
|   Anions:  Cl- 0.07, NO2- 0.05, NO3- 0.11, SO42- 0.08 μg/m³           |
| Main Ions: NH4+, SO42-, NO3- (must be present)                        |
| Ion Balance: 0.8 < cation/anion ratio < 1.2                           |
+-----------------------------------------------------------------------+

+-----------------------------------------------------------------------+
|                            _QC() Pipeline                             |
+-----------------------------------------------------------------------+
|                                                                       |
|  [Pre-process] Calculate ion sum, cation/anion equivalents            |
|       |                                                               |
|       v                                                               |
|  +---------------------------+    +---------------------------+       |
|  | Rule: Mass Closure        |    | Rule: Missing Main        |       |
|  +---------------------------+    +---------------------------+       |
|  | Ion sum > PM2.5 mass      |    | NH4+, SO42-, or NO3-      |       |
|  | (physically impossible)   |    | is missing                |       |
|  +---------------------------+    +---------------------------+       |
|           |                                |                          |
|           v                                v                          |
|  +---------------------------+    +---------------------------+       |
|  | Rule: Below MDL           |    | Rule: Ion Balance         |       |
|  +---------------------------+    +---------------------------+       |
|  | Any ion below its         |    | Cation/Anion ratio        |       |
|  | detection limit           |    | outside 0.8-1.2 range     |       |
|  +---------------------------+    +---------------------------+       |
|                                                                       |
+-----------------------------------------------------------------------+

QC Rules Applied

Rule Condition Description
Mass Closure Ion sum > PM2.5 Total ion mass exceeds PM2.5 (physically impossible)
Missing Main NH4+, SO42-, or NO3- is NaN Primary ion species are missing
Below MDL Value < MDL Measurement below minimum detection limit
Ion Balance Ratio < 0.8 OR > 1.2 Cation/Anion equivalent ratio imbalance

Minimum Detection Limits

Ion MDL (μg/m³)
Na+ 0.06
NH4+ 0.05
K+ 0.05
Mg2+ 0.12
Ca2+ 0.07
Cl- 0.07
NO2- 0.05
NO3- 0.11
SO42- 0.08

Ion Balance Check

    Cation/Anion Ratio
         ^
     1.2 +-------------------------------- Upper limit
         |   +-----------------------+
         |   |    VALID RANGE        |
     1.0 +---|       (balanced)      |
         |   +-----------------------+
     0.8 +-------------------------------- Lower limit
         +----------------------------> Sample

Output Data

The processed data contains:

Column Unit Description
Na+, NH4+, K+, Mg2+, Ca2+ μg/m³ Cation concentrations
Cl-, NO2-, NO3-, PO43-, SO42- μg/m³ Anion concentrations

QC_Flag Handling

  • The intermediate file (_read_igac_qc.pkl/csv) contains the QC_Flag column
  • The final output has invalid data set to NaN and QC_Flag column removed

Notes

  • Critical for secondary inorganic aerosol analysis
  • Significant contributor to PM2.5 mass
  • Comprehensive quality control procedures
  • Ion balance validation ensures data integrity
  • Main ion species (NH4+, SO42-, NO3-) typically dominate