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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 docs/api/instruments/chemical/IGAC.md for usage and docs/guide/reader-reference.md for the file layout, status codes and QC rules.

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 property 

MDL: dict

Method detection limits (µg/m³) for the species this instrument measures.

MR property 

MR: dict

Upper measurement range (µg/m³) per species.

Methods:

_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 and gas 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. Above MR : Concentration above the instrument's measurement range
  4. Ion Balance : Cation/Anion ratio outside valid range

Detection limits are reported per species in the log (how much of each sits below its MDL) rather than as a row-level flag. A below-MDL value is a valid measurement of a low concentration, not a broken row — and because a non-Valid flag NaNs the whole row downstream, flagging it would delete every other species measured in that same hour. Above-MR is different: it is outside what the instrument can report, so it is flagged.

Raw format

  • File pattern: *.csv
  • Native frequency: 1h
  • Encoding: utf-8-sig (a BOM is tolerated), undecodable bytes ignored
  • Header layout: a single header row; the first column is the timestamp and becomes the index (read_csv(parse_dates=True, index_col=0, na_values='-'))
  • Data structure:
    • Datetime index
    • Ion concentration columns (aerosol ions) and gas columns
    • PM2.5 mass concentration (used by Mass Closure when present)
    • Special values: - treated as NA

Parse recipe

  1. Column names are stripped of surrounding spaces.
  2. Every column is coerced to numeric (errors='coerce').
  3. Duplicate and NaT indices are removed.

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

The vendor specification lists PO43- (and the gas HF / ion F-) as not measured — their detection limit is None — so although PO43- is in the reader's ANION_COLUMNS, it is not among the species the reader keeps (see Output).

Status & error codes

None. The export carries no status register; see status modes for the readers that do evaluate one.

QC rules

Rule Condition Severity
Mass Closure Σ aerosol ions (Na+ NH4+ K+ Mg2+ Ca2+ Cl- NO2- NO3- SO42- present) > PM2.5, when a PM2.5 column exists — gases are not part of the PM budget; without PM2.5 the rule never fires error
Missing Main any of NH4+, SO42-, NO3- is NaN (only evaluated when all three columns exist) error
Above MR any species above its stated measurement range (reader.MR) error
Ion Balance cation/anion ratio (Σ cation µg/m³ ÷ Σ anion µg/m³, mass not equivalents) outside 1.5 × IQR (QualityControl.iqr on the ratio; an already-missing ratio also counts) error

Cation and anion sums use the columns of CATION_COLUMNS / ANION_COLUMNS that are present; a zero anion sum gives a NaN ratio.

Detection limits and measurement ranges

reader.MDL and reader.MR come from meta['IGAC'] in config/supported_instruments.py — the vendor specification, 17 species covering gases and aerosol ions. This is the single source of truth; the reader used to carry a second, disagreeing copy of the 9 aerosol ions. reader.MDL drops the three whose limit is None (HF, F⁻, PO₄³⁻ — not measured), and that 14-species list is what the reader keeps and checks; reader.MR is the spec's range table as-is (only PO₄³⁻ is None there).

Species MDL (μg/m³) MR (μg/m³)
HF None (not measured) 200
HCl 0.05 200
HNO2 0.01 200
HNO3 0.05 200
G-SO2 0.05 200
NH3 0.1 300
Na+ 0.05 300
NH4+ 0.08 300
K+ 0.08 300
Mg2+ 0.05 300
Ca2+ 0.05 300
F- None (not measured) 300
Cl- 0.05 300
NO2- 0.05 300
NO3- 0.01 300
PO43- None (not measured) None
SO42- 0.05 300

Below MDL is a diagnostic, not a flag

The log reports, per species, what fraction of it sits below its detection limit, worst first (log_below_mdl). With 17 species a per-column count says more than one row-level flag — and because a non-Valid flag NaNs the whole row at L3, a row-level Below MDL would delete every other species measured in that hour. A below-MDL value is a valid measurement of a low concentration; above-MR is different — it is outside what the instrument can report — so that one is flagged.

Output

L2 carries the 14 MDL species present in the file, gases included. Other columns of the export (including PM2.5, which is consulted for Mass Closure only) are not carried.

Column Unit Description
Na+, NH4+, K+, Mg2+, Ca2+ μg/m³ Cation concentrations
Cl-, NO2-, NO3-, SO42- μg/m³ Anion concentrations (PO43- is not measured and is dropped)
HCl, HNO2, HNO3, G-SO2, NH3 μg/m³ Gas-phase species

Files written per read are listed in RawDataReader Reference §1.

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