Atmospheric CO₂
VC-MET-103 — the carbon-dioxide concentration of zone air in parts per million, the raw substrate of photosynthesis and a dual-purpose growth lever and personnel-safety gas.
Definition
Atmospheric CO₂ is the volumetric concentration of carbon dioxide in zone air, reported in parts per million. It is sensed directly by non-dispersive infrared (NDIR) analyzers on the PhytoSense Mesh, distributed at canopy height and at the zone return. CO₂ is both an input to be optimized — modest enrichment lifts photosynthetic rate — and a hazard to be bounded, since high concentrations threaten personnel and very low concentrations starve the canopy under bright light.
Why it matters
Carbon dioxide is the carbon source for every gram of biomass the facility produces. Under the bright PAR of the cultivation cells, an under-enriched zone becomes carbon-limited and net photosynthesis (and ultimately the Canopy Vitality Index, VC-MET-001) plateaus regardless of light. CHLORA meters CO₂ enrichment against PPFD and ventilation to hold the growth optimum without waste. The upper criticals are a life-safety bound: the same enrichment system that feeds the plants can, if a valve sticks, drive a zone toward occupational-exposure limits, so VC-MET-103 is interlocked with access control.
Formula
A directly measured signal. Zone CO₂ is the cluster trimmed mean with pressure and water-vapour compensation applied at the analyzer:
CO2_zone = trimmed_mean( { (raw_i − z_i) · s_i · k_P · k_H2O } )
raw_i NDIR absorbance reading, node i (ppm)
z_i zero baseline (N2 / scrubbed-air cal)
s_i span factor (certified 1000 ppm cal gas)
k_P pressure correction from VC-MET-112 (P/1013.25)
k_H2O water-vapour cross-sensitivity correction from RH
Baseline auto-zero:
ABC tracks the rolling 14-day minimum toward 415 ppm
outdoor reference; disabled in continuously enriched zones
to avoid false drift, where manual cal gas is used instead.
Inputs
| Channel | Sensor | Placement | Reference Band | Source |
|---|---|---|---|---|
| C1–C3 | NDIR CO₂ analyzer (±30 ppm) | Canopy plane, 3× per zone | 380 → 480 ppm | PhytoSense Mesh |
| C_ret | NDIR return-duct analyzer | HVAC return (mixing check) | 380 → 500 ppm | PhytoSense Mesh |
| P | Barometric pressure | Pressure compensation | VC-MET-112 | PhytoSense Mesh |
| PPFD | Canopy PAR | Carbon-limit context | VC-MET-104 | Spectral Canopy Array |
Units & Scale
Reported in parts per million to whole-ppm precision. Concentration is intensive and never summed; facility roll-up is the volume-weighted mean of zone values. Confidence degrades to DEGRADED when canopy and return analyzers diverge by > 80 ppm (poor mixing or a drifting node) or when an analyzer has not auto-zeroed within its calibration window. Enriched zones suppress auto-baseline correction and rely on scheduled cal-gas checks.
Sampling & Source
- Sampled every 1 minute from the PhytoSense Mesh NDIR cluster.
- Pressure-compensated against Barometric Pressure (VC-MET-112) and corrected for water-vapour cross-sensitivity.
- Stale handling: an analyzer silent > 3 min is dropped; loss of the canopy cluster fails over to the return analyzer with a DEGRADED flag.
- Calibration: monthly two-point check (scrubbed zero + 1000 ppm span); drift > 25 ppm raises a metrology work order.
Thresholds
OK
Ambient-to-light-enrichment band; carbon supply adequate. No action.
WARN
Carbon-starved draw-down (low) or over-enrichment (high); enrichment/ventilation review.
CRIT
Severe carbon limitation (low) or personnel-exposure hazard (high); auto-escalation.
Recent Trend
Zone-A canopy-plane CO₂, last 14 sampling roll-ups (ppm):
Interpretation Guidance
| Band | Reading | Likely Driver | Action |
|---|---|---|---|
| 380–480 ppm | Optimal | Ambient or light enrichment, balanced uptake | None; log as reference. |
| 320–379 ppm | Draw-down drift | Bright light, dense canopy, sealed zone | Open enrichment; check PPFD (VC-MET-104) coupling. |
| 481–900 ppm | Enriched / vent drift | Active enrichment or poor exchange | Trim enrichment to PPFD target; verify ventilation. |
| < 320 / > 900 ppm | WARN | Carbon limit or over-enrichment | Enrichment/ventilation review; CHLORA advisory. |
| < 280 / > 1500 ppm | CRIT | Starvation or exposure hazard | Auto-dispatch; valve interlock and air exchange. |
Related Metrics
PAR / PPFD
Sets the carbon demand CO₂ must supply.
VC-MET-112Barometric Pressure
Pressure correction for ppm.
VC-MET-111Canopy Airflow Velocity
Governs CO₂ delivery to the boundary layer.
VC-MET-100Air Temperature
Co-controls photosynthetic kinetics.
VC-MET-001Canopy Vitality Index
Reflects carbon-limited photosynthesis.
VC-MET-401Containment Integrity Index
Seal status enrichment depends on.
Related SOPs
- SOP Library — CO₂ enrichment & confined-space safety procedures.
- High-CO₂ personnel evacuation on CRIT — see Environment & Safety SOP set in the SOP Library.
- Enrichment-valve interlock & alarm escalation — Monitoring Systems.