OCEMS (OCEMS)

Online Continuous Emission Monitoring System (OCEMS) is CPCB's mandated regulatory framework requiring designated highly-polluting industries to install real-time emission sensors on their stacks and effluent outlets, transmitting pollutant data to SPCB and CPCB servers every 15 minutes. OCEMS was rolled out from 2014 onwards under CPCB's 17 categories of Highly Polluting Industries directive, replacing the earlier monthly third-party monitoring with continuous live-streamed data accessible to regulators 24/7.

Mandatory OCEMS parameters depend on industry category:

• Air emissions — SO₂, NOx, CO, PM (particulate matter), and where applicable HF, HCl, total VOC, mercury
• Water effluent — pH, TDS, COD, BOD (where measurable continuously), TSS, ammonia, flow rate
• Process parameters — stack temperature, oxygen percentage (for combustion correction), flue gas flow rate

Affected industries include thermal power plants, cement, iron and steel, refineries, fertilisers, oil and gas, large pulp and paper, large pesticide, large pharmaceuticals, large tyre and tube, large chlor-alkali, large dye and dye intermediates, large copper/zinc/aluminium smelters, common HW TSDFs, common biomedical waste incinerators, common ETPs, and large CETPs. Most CBG plants are below OCEMS thresholds, but large pyrolysis plants and integrated e-waste smelters increasingly fall under the requirement.

OCEMS hardware costs ₹25–60 lakh per stack/outlet point depending on parameter count and sensor technology. The data flows from the on-site analyser through a Data Acquisition System (DAS) to CPCB's central servers, where it appears on the public CARE Air and CARE Water dashboards. SPCBs run analytics on the data to flag exceedances and trigger inspection or Environmental Compensation.

The trade-offs are real for industry. OCEMS provides continuous compliance evidence (cheaper than periodic third-party sampling at ₹20,000–40,000 per visit), removes the inspector-driven harassment cycle, and signals environmental performance to lenders and customers. But sensor accuracy drift, communication failures, calibration intervals (typically quarterly with CPCB-empanelled labs), and the public visibility of any exceedance create ongoing operational burden. Most Indian OCEMS installations show 80–95% uptime, and unplanned downtime triggers SPCB show-cause notices even if actual emissions were within limits.