What is PEMS?

PEMS (Predictive Emission Monitoring Systems) estimate emissions like NOx, SO2, CO from regulated combustion sources. They use mathematical models to correlate inputs with emissions, offering cost-effective alternatives to conventional CEMS. PEMS comply with regulations, reducing capital costs and serving as backup for CEMS downtime. US EPA Performance Specification 16 (PS-16) outlines compliance and excess emission PEMS, ensuring emissions are within limits.

Initial Certification

PS-16 mandates a Relative Accuracy Test Audit (RATA) to certify PEMS accuracy. Unlike CEMS RATA, PEMS RATA compares audit data with algorithm predictions. PEMS RATA covers various process conditions, while CEMS RATA typically has nine runs at a single condition. Continuous compliance PEMS need nine runs at each level, while excess emission PEMS require three runs. Compliance PEMS undergo additional statistical tests (bias, variance, correlation coefficient) for certification.

Periodic RATA & RAA

Following initial certification, a PEMS must undergo ongoing compliance tests: an annual Relative Accuracy Test Audit (RATA) and quarterly Relative Accuracy Audits (RAAs) as per PS-16. HGI performs annual RATAs using Auto-CEMS, which can immediately collect reference method data if a PEMS issue arises during RATA. This avoids downtime without extra costs. Quarterly RAAs use portable analyzers and ASTM D6522-00. After initial certification, three successive quarterly RAAs and one annual RATA, only one RAA per year is needed. Compliance testing restarts if PEMS model changes are required based on audit results.