Continuous Emissions Monitoring Systems (CEMS) are real-time stack monitoring installations that transmit emissions data directly to NCEC at defined intervals. Under RCER-2025, CEMS is mandatory for all major combustion sources, refineries, cement kilns, petrochemical units, and any facility flagged during EIA approval. The NCEC operates a central telemetry platform that compares your reported data to permit limits in near real-time — exceedances trigger automated violation notices.
Data availability
≥95% / quarter
RATA cadence
Annual
Record retention
≥5 years
Your key obligations
- Install CEMS on every regulated stack with permit-required analyte coverage
- Achieve ≥95% data availability per quarter — gaps must be reported and substituted per protocol
- Calibrate analyzers daily (zero/span) and conduct quarterly cylinder gas audits (CGA)
- Conduct annual Relative Accuracy Test Audits (RATA) by an accredited third party
- Stream 1-minute and 1-hour averages to the NCEC telemetry endpoint
- Maintain a calibration logbook, downtime log, and audit trail for ≥5 years
Mandatory Analytes
Typical RCER-2025 CEMS coverage includes NOx, SO2, CO, CO2, O2, PM (particulate matter), opacity, flow rate, temperature, and moisture. Refineries add H2S, total reduced sulfur, and VOC. Cement adds HCl, HF, and mercury.
Data Availability & Substitution
Missing or invalid data must be substituted using NCEC's published protocol — typically the 90th percentile of the previous 30 days for the first 24 hours of downtime, then permit limit thereafter. Persistent <95% availability triggers a Class 2 violation.
Acceptance & RATA Testing
New CEMS installations require a 30-day demonstration period, factory acceptance test, site acceptance test, and an initial RATA before NCEC certification. Annual RATAs must remain within ±10% relative accuracy for gaseous analytes and ±20% for PM.
Frequently asked questions
What happens if my CEMS goes down for 48 hours?＋
You must notify NCEC within 4 hours, apply the substitution protocol, document the root cause, and restore service ASAP. Repeated incidents within 12 months trigger escalation.